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Butyrylcholinesterase (BChE) is associated with many neurodegenerative diseases, especially Alzheimer's disease (AD). Developing specific imaging tools for BChE is now highly pursued because BChE has substantially similar biochemical properties to acetylcholinesterase (AChE) but distinct roles in AD. Inspired by the BChE-catalyzed hydrolysis of specific substrates (benzoylcholine, tetracaine, and cocaine) containing benzoyl group in physiological condition, a bioinspired probe PM1 with high specificity towards BChE was designed. The docking models indicated that PM1 could easily access the active center of BChE rather than AChE, showing the significance of benzoyl group in specific recognition of BChE. The control probes PM2–5 with smaller recognition groups displayed lower specificity to BChE than PM1 , showing the high efficiency of the bioinspired design strategy. The living cells experiments showed that PM1 signals were weakened by BChE inhibitor but not influenced by AChE inhibitor, which was in contrast to the performance of probe PM2–5 , showing the specific recognition of PM1 for BChE in biological system. Moreover, PM1 has been used to study the positive correlation between BChE level and cell apoptosis for the first time, and the further study showed that Aβ deposition could induce the increase in BChE level and accompany the occurrence of cell apoptosis. Notably, PM1 was successfully traced the enhancement of BChE activity in the brain slice of AD mouse model. Such a rational approach may provide a solid basis for designing specific probes with different properties to study BChE in biosystems. [Display omitted] • Inspired by the BChE-catalyzed hydrolysis of specific substrates, a bioinspired probe towards BChE was designed. • Screening probes with different recognition groups and the docking models showed rationality of our probe. • Probe PM1 has been used to study the positive correlation between BChE level and cell apoptosis for the first time. • The study showed that Aβ could induce the increase in BChE level and accompany the occurrence of cell apoptosis. • PM1 was successfully traced the enhancement of BChE activity in the brain slice of AD mouse model. [ABSTRACT FROM AUTHOR]

A fluorescent probe (probe 1) with selectivity and sensitivity for H 2 S and N 2 H 4 has been developed. Probe 1 exhibits dual-excitation and dual-emission fluorescence response to H 2 S and fluorescence enhancement toward N 2 H 4 with distinct naked-eye color changes. Moreover, probe 1 displayed low detection limits for H 2 S and N 2 H 4 of 0.90 nM and 23.6 nM, respectively. The reaction mechanism of probe 1 toward H 2 S and N 2 H 4 was established using 1H NMR and HR-MS spectroscopy. Additionally, probe 1 was used for monitoring and differentiating H 2 S and N 2 H 4 in HeLa cells and displays good biocompatibility and low cytotoxicity. • Probe 1 exhibits dual-emission fluorescence-enhanced detection of H 2 S in mitochondria. • Probe 1 exhibits a turn-on response for the detection of N 2 H 4 in mitochondria. • Probe 1 exhibits rapid response, good optical performance, high selectivity, and high sensitivity in solution. • Probe 1 displays multi species detection in the mitochondria of HeLa cells and zebrafish. • Detection using Probe 1 can be achieved using a smartphone with a chromaticity APP. [ABSTRACT FROM AUTHOR]

Emerging studies demonstrates that mitochondrial G-quadruplex (G4) may be a prospective diagnostic and therapeutic target for cancer. Fluorescent probes targeting mitochondrial G4 are crucial for in-depth research on G4 function and mechanism and developing new diagnostic techniques. Here, we report a benzothiazole derivative named ThT-E, which can be prepared with high yield through only one step of reaction. ThT-E exhibits superior detection sensitivity compared to existing probes, and also demonstrates reliable performance for in situ characterization of mitochondrial G4 in living cells. Interestingly, ThT-E has been used to differentiate tumor cells from normal cells by quantifying the formation of mitochondrial G4s, implicating that ThT-E may have wide applications in tumor diagnosis. • A benzothiazole derivative for monitoring mitochondrial G-quadruplexes. • More pronounced fluorescence enhancement in tumor cells than normal cells. • More G-quadruplex formation in tumor mitochondria. • Mitochondrial G-quadruplex as a potential cancer biomarker. • New probe tool for tumor diagnosis. [ABSTRACT FROM AUTHOR]

Mitophagy is a critical cellular self-protective mechanism involving the degradation and recycling of damaged or excessive mitochondria, which has been implicated in various diseases. In our study, we designed and synthesized two phenothiazine-based fluorescent probes, DPTZ and CMDP , specifically targeting mitochondria and lysosomes, respectively, to investigate mitophagy. H 2 S, a cell-protective agent, was chosen as the target molecule for both probes. Our findings demonstrate the selective localization of DPTZ to mitochondria and CMDP to lysosomes. Both probes exhibited rapid, selective, and highly sensitive recognition of H 2 S, enabling imaging of exogenous and endogenous H 2 S. By employing split-targeting and simultaneous detection, we were able to monitor changes in H 2 S levels in mitochondria and lysosomes, providing dynamic and visual imaging of the mitophagy processes. Upregulation of mitochondrial and lysosomal H 2 S was observed during mitochondrial autophagy. This work introduces valuable research methods and tools for investigating mitophagy, thereby enhancing our understanding of the molecular mechanisms underlying this process. [Display omitted] • Phenothiazine-based probes DPTZ and CMDP detect hydrogen sulfide. • DPTZ and CMDP target mitochondria and lysosomes for imaging in A549 cells. • Split-targeting and detection strategy reveals hydrogen sulfide fluctuations in autophagy. [ABSTRACT FROM AUTHOR]

Despite the impressive success of metal halide perovskite nanocrystals (NCs) in diverse fields, such as solar cells, light-emitting diodes, photodetectors, and so forth, their intrinsic sensitivity to water limits the extending applications in aqueous systems. Herein, enhanced water stability is achieved for NH 2 -PEG-COOH capped Mn2+-doped CsPbCl 3 /CsPb 2 Cl 5 core/shell NCs through the synergistic effect of ion doping, core/shell construction and polymer encapsulation. The NH 2 -PEG-COOH encapsulation is validated crucial for the formation of CsPbCl 3 /CsPb 2 Cl 5 core/shell structure, since it retains contact for CsPbCl 3 NCs with trace water, and guarantees a slow water-etching process, triggering the CsPbCl 3 to CsPb 2 Cl 5 transformation. Thanks to the high formation energy induced by Mn2+ doping, CsPbCl 3 /CsPb 2 Cl 5 hetero core/shell construction and NH 2 -PEG-COOH protective barrier, the obtained NCs exhibit unattenuated photoluminescence quantum yield after dipped in water for 15 days. Based on the robust water stability, the NH 2 -PEG-COOH capped Mn2+-doped CsPbCl 3 /CsPb 2 Cl 5 NCs work well in cell nucleus imaging and acid phosphatase detection. This work not only produces a novel perovskite fluorescence probe in aqueous systems but also provides a general and effective combination strategy to enhance the water stability of perovskite materials. [Display omitted] • Water-resistant NH 2 -PEG-COOH capped Mn2+-doped CsPbCl 3 /CsPb 2 Cl 5 core/shell perovskite nanocrystals are synthesized. • The perovskite nanocrystals exhibit unattenuated photoluminescence quantum yield after dipped in water for 15 days. • The perovskite nanocrystals are successfully employed as fluorescent probes for cell imaging and acid phosphatase detection. [ABSTRACT FROM AUTHOR]

Quantitative assays and the structural monitoring of human serum albumin (HSA) are essential for disease diagnosis, drug development, and physiological studies. Commonly used methods for quantifying HSA are based on the dye-HSA binding mechanism, which involves determining the absorption or fluorescence signal when the dye binds non-covalently to HSA. However, these methods generally suffer from poor selectivity and susceptibility to interference from co-existing species. Herein, an ultrasensitive and selective fluorescent probe, 2-(2-morpholinoethyl)-1,3-dioxo-2,3-dihydro-1 H-benzo[de]isoquinolin-6-yl cyclopropanecarboxylate (MDDH), was designed based on the pseudoesterase activity of HSA and used to monitor the acetylation modification, configuration transformation, and biological levels of HSA. Upon catalysis by HSA, the cyclopropanecarbonyl ester bound to MDDH undergoes hydrolysis, yielding a strong fluorescent signal. In contrast to conventional HSA-binding dyes, MDDH demonstrates superior sensitivity (with a 302-fold fluorescence enhancement), high selectivity for distinguishing between HSA and bovine serum albumin, and strong anti-interference against various coexisting species. By sensing HSA pseudoesterase activity, MDDH allows for the sensitive monitoring of structural changes in HSA, including aspirin-induced acetylation, guanidine hydrochloride-induced defolding and trypsin-induced cleavage. Moreover, MDDH exhibits strong stability, low cytotoxicity and good cell membrane permeability. It is suitable for the quantitative determination of HSA in the serum and urine, as well as for the fluorescence imaging of HSA in cells. Our work provides an efficient tool for monitoring the acetylation modifications, configuration changes, and biological content of HSA. • A novel fluorescent probe, MDDH, was designed based on HSA pseudoesterase activity. • MDDH is ultrasensitive and selective for HSA with minimal interference from co-existing species. • MDDH can monitor structural changes in HSA such as acetylation, defolding and cleavage. • MDDH is suitable for HSA quantification in serum and urine and HSA imaging in cells. [ABSTRACT FROM AUTHOR]

High signal-to-background ratio (SBR) monitoring of formaldehyde (FA) delivery in living systems is of great significance for the precise study of the physiological and pathological functions of FA. However, traditional FA donors mainly use fluorescent signals to monitor FA release, which hampers the high-performance bioimaging due to the undesirable background autofluorescence, leading to poor SBR and compromised imaging sensitivity. Herein, we present the first bioluminogenic donor B-FAD for esterase-activated FA release with high contrast bioluminescence imaging. By protecting the hydroxyl group of D-luciferin with acetoxymethyl ether group, B-FAD cannot be catalyzed by luciferase to emit light. In the presence of esterase, the ester bond of B-FAD breaks, producing FA and D-luciferin. B-FAD selectively and sensitively releases FA in the presence of esterase, accompanied by 34-fold bioluminescence enhancement. In addition, B-FAD has been successfully applied for FA delivery and bioluminescence imaging in living cells, with a SBR about 50 times higher than those obtained by fluorescence imaging. Therefore, in addition to providing an effective tool for imaging FA delivery in living cells, this work establishes a general approach for high contrast monitoring other reactive biological species release by easily changing the responsive unit on D-luciferin. [Display omitted] • A bioluminogenic donor B-FAD is synthesized for activated formaldehyde release. • B-FAD selectively and sensitively releases formaldehyde in the presence of esterase. • B-FAD displays high signal-to-background ratio monitoring of formaldehyde release in living cells. • The donor system can expand to high contrast monitoring of other reactive biological species release. [ABSTRACT FROM AUTHOR]

ONOO- and SO 2 are important microenvironment parameters in organisms, the intracellular levels of ONOO- and SO 2 are abnormal in rheumatoid arthritis (RA) mice. Mitophagy plays a key role in maintaining mitochondrial quality and quantity, and viscosity monitoring is a crucial aspect of real-time visualization of mitophagy. Therefore, a mitochondria-targeting three-channel fluorescent probe HCPVP was first developed for the detection of ONOO-/SO 2 and viscosity. HCPVP can sensitively detect ONOO- (514 nm) and SO 2 (674 nm) change with different channels, meanwhile display turn-on fluorescence at 678 nm as the amount of glycerol increased. The fluorescence imaging of cells showed that HCPVP was able to better target mitochondria, monitor ONOO-/SO 2 changes, and visualize the mitophagy process. HCPVP has been successfully used for monitoring ONOO- and SO 2 in RA mice model, providing the early image of RA with the aid of the potential biomarkers ONOO- and SO 2. More importantly, HCPVP could evaluate the response of the RA treatment with impressive results, which held the potential for assessing treatment and drug screening for RA. A mitochondria-targeting NIR fluorescent probe was firstly developed for the detection of ONOO-/SO 2 and viscosity, which can track and detect mitophagy through the change of mitochondrial viscosity, and the early image and therapeutic assessment of RA through change in ONOO-/SO 2 levels. [Display omitted] • A mitochondria-targeting NIR fluorescent probe was firstly developed for the detection of ONOO-/SO 2 and viscosity. • The fluorescent probe was able to target mitochondria, monitor ONOO-/SO 2 changes, and visualize the mitophagy process. • The mitochondrial targeted ONOO-/SO 2 fluorescent probe was used for early imaging and drug treatment evaluation of RA. [ABSTRACT FROM AUTHOR]

Copper is an essential micronutrient that play indispensable roles in living systems. Small-molecule based fluorescence probes for imaging cuprous (Cu+) dynamics are essential to elucidate its biology. Nonetheless, the availability of near infrared (NIR) fluorogenic probes for Cu+ imaging in vivo is still limited. Here we develop a new NIR fluorogenic probe that allows imaging of Cu+ dynamics and assessing its ionophores in live cells and in vivo. The probe is comprised of a xanthene-based fluorophore as a reporter and a thioether rich unit as a Cu+ binding and reporter-quenching moiety. We demonstrate that the fluorescence probe using xanthene-conjugated with 1-methylindole-3-carboxaldehyde exhibits fluorogenic NIR fluorescence with excitation/emission wavelengths of 640 nm/704 nm, high sensitivity with a limit of detection of 28.4 ± 0.3 nM from three replicates, high selectivity and desirable reversibility in response to Cu+. The probe is further employed to image Cu+ dynamics under different conditions and assess the efficacy of Cu+ ionophores in different cancer cell lines. Its ability to image Cu+ fluctuation and evaluate the efficacy of Cu+ ionophores in vivo is demonstrated in a 4T1 tumor-bearing mice model using bovine serum albumin as a probe carrier. Our probe could afford a valuable tool for elucidating copper biology and assessing Cu+ ionophores for treating related diseases in living systems. • A new near-infrared fluorogenic probe for Cu+ imaging in live cells and in vivo. • Cu+ can be detected based on the fluorescence signals of the probe. • Useful for evaluating Cu+ ionophores in live cells and in vivo. [ABSTRACT FROM AUTHOR]

Precise imaging identification of tumor tissues from normal tissues is still challenging. In this study, a new dual-locked near-infrared fluorescent probe BBQ650-SS-BTZHC-E was developed for the discrimination between cancer cells and normal cells. The probe consists of a hemicyanine fluorophore conjugated to an esterase substrate and a quencher connected via a disulfide bond. The esterase substrate blocks the excited state intramolecular proton transfer (ESIPT) process, while the quenching agent forms a Förster resonance energy transfer (FRET) pair with the fluorophore. The fluorescence activation is dependent on the presence of both esterase and glutathione (GSH), resulting in the "ESIPT on" and "FRET off" states, which represent an "AND" logic. The characterizations showed that the kinetics of fluorescence activation are dependent on the concentrations of the two activators with a high specificity. Fluorescent imaging experiments using BBQ650-SS-BTZHC-E successfully distinguished cancer cells (HeLa, 4T1, RAW264.7) from normal cells (HFL1) with high contrast and specificity, and imaged 4T1 tumor on live mice. This study provides a simple platform for the development of dual-locked fluorescent probes for bio-imaging applications. [Display omitted] • A new hemicyanine-derived NIR "AND" logical dual-locked fluorescent probe. • The activation of the fluorescence is based on ESIPT and FRET processes. • The probe distinguished cancer cells from normal cells with high imaging contrast and specificity. • This work represents a platform for dual-locked NIR probes that is easy to synthesize and modify. [ABSTRACT FROM AUTHOR]

The investigation of cell membrane polarity is critical to determining cell physiological states and related disease for diagnosis and treatment. Herein, a ratiometric NIR cell membrane-targeted fluorescent probe, Cy-C 12 -MpN , was designed and synthesized to assess cell membrane polarity, which has an amphiphilic structure consisting of a dodecyl unit and a quaternary ammonium unit. It exhibited changes in emission wavelength and fluorescence intensity with the changes in polarity of the solution. It can use the ratio signal of the two peaks to report the polarity difference in its environment. The self-tuning of the probe internal system ensures the reliability of the test results and can be a semi-quantitative detection method. Indeed, in vitro polarity test, the ratio signal reported by Cy-C 12 -MpN had an optimal linear range with respect to polarity. Cell imaging illustrated the excellent cell membrane-targeted ability of Cy-C 12 -MpN , as it can rapidly target the cell membrane within 30 s and still anchor at it well after 1 hr. Moreover, Cy-C 12 -MpN showed that cell membrane polarity decreases after cells become cancerous, and observed the changes in cell membrane polarity caused by homeostatic membrane response stimulated by polyunsaturated fatty acids firstly. Imaging in vivo demonstrated the ability of Cy-C 12 -MpN to distinguish between tumor cells and normal cells, and further demonstrated that tumor cells have lower cell membrane polarity. In summary, the accuracy of the ratio detection of the probe Cy-C 12 -MpN and its excellent cell membrane targeting ability reveal reliable results that can provide very useful insights for cancer research. [Display omitted] • A novel NIR fluorescent probe for ratiometric detection of cell membrane polarity. • The degree of electron-hole transfer of the probe is calculated by Multiwfn to evaluate its polarity sensitivity. • The changes of cell membrane polarity in cell membrane homeostasis response stimulated by DHA were revealed. [ABSTRACT FROM AUTHOR]

The development of bifunctional AIEgens for direct delivering and visualizing bioactive species together remains a great challenge to date. Herein, we fabricated a novel photoactivatable nitric oxide (NO) donor with a built-in AIE fluorophore, which can rapidly release NO and AIEgen upon light irradiation. The ultrafast NO generation can be obtained in 2.1 ps, with the yielding of a greatly drastic fluorescence turn-on AIEgen probe (300,000-fold intensity enhanced). Using this NO donor, real-time cell images of NO-releasing through the emission of AIEgen were successfully achieved through direct excitation of the donor in cells in situ. [Display omitted] • The first AIE-caged photoactive NO donor was developed. • Ultra-fast NO release (2.1 ps) was achieved by photoexcitation. • An extremely high fluorescence intensity was obtained (300,000-fold). • The NO release was visualized by fluorescent technology. • Cell imaging was successfully performed using this NO donor. [ABSTRACT FROM AUTHOR]

Designing functionalized MOFs with specific reactivity and NIR photoelectrochemical and fluorescent response is critical for developing biosensing systems. Herein, SCy7, a conjugate macrocycle ligand with a specific fluorescence responsive group to HClO, was designed and synthesized. Responsive Nd-MOF nanorods were successfully prepared by using SCy7 as the organic ligand and Nd3+ as the metal central ion. Nd-MOF nanorods show good absorption characteristics in the wavelength range of 200–1200 nm with a band gap of 0.89 eV. Nd-MOF nanorods were employed as a photoactive material to construct a near-infrared photoelectrochemical cytosensor for MCF-7 cells by integrated with an aptamer. The photocurrent variation exhibits a good linear response to MCF-7 cells in the concentration range of 50–1.0 × 107 cells mL−1, and a comparatively low detection limit of 18 cells mL−1 (S/N = 3). The NIR PEC cytosensor was also employed for monitoring endogenous HClO released from MCF-7 cells as being stimulated by PMA. HClO is an electron acceptor that can convert the anodic photocurrent into cathodic photocurrent, thus achieving monitoring HClO through the conversion of photocurrent polarity. Furthermore, Nd-MOF was coated with F127 to improve its hydrophilicity and biocompatibility, and to provide a Nd-MOF@F127 with a fluorescence emission peak at 830 nm. Nd-MOF@F127 show specific fluorescence response to HClO, and thus was successfully used in imaging HClO variation in cells and breast cancer bearing mice. [Display omitted] • Nd-MOF nanorods with specific response to HClO were successfully synthesized. • A NIR PEC cytosensor based on Nd-MOF was developed for MCF-7 cells assaying. • Real-time monitoring HClO was achieved by photocurrent polarity conversion. • Fluorescence imaging HClO in cells and mice was performed by using Nd-MOF@F127. [ABSTRACT FROM AUTHOR]

In this work, arginine functionalized niobium carbide MXene quantum dots (arginine-Nb 2 C MQDs) were synthesized using Nb 2 AlC, NaOH and arginine as reagents. The as-synthesized probe showed bluish-green fluorescence under UV light at 365 nm. The structural and morphological changes of as-synthesized arginine-Nb 2 C MQDs were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy and high-resolution transmittance electron microscopy (HR-TEM). The synthesized fluorescent arginine-Nb 2 C MQDs were stable, with an average size of 1.92 ± 0.52 nm. As-synthesized arginine-Nb 2 C MQDs act as a sensor for detecting superoxide anion (O 2 •−) via a fluorescence "turn-off" mechanism with the detection limit of 31.89 nM. The fluorescence of arginine-Nb 2 C MQDs is quenched by O 2 •− via dynamic fluorescence quenching mechanism. Fascinatingly, the synthesized arginine-Nb 2 C MQDs showed negligible cytotoxicity on HeLa cells and acted as promising candidates for sensing of O 2 •− in Saccharomyces cerevisiae cells. [Display omitted] • HF-free synthetic strategy was used for the fabrication of arginine-Nb 2 C MQDs. • Arginine-Nb 2 C MQDs act as a fluorescent sensor for selective detection of O 2 •−. • The developed approach exhibited an impressive detection limit of 31.89 nM for O 2 •−. • Arginine-Nb 2 C MQDs served as probe for cell imaging with minimal cytotoxicity. • The developed technique was used to determine O 2 •− in environmental samples. [ABSTRACT FROM AUTHOR]

The design of optical nanosensors based on carbon nanozymes has gained considerable interest in analyte detection. In this study, a simple and rapid fluorescence/colorimetry probe, NH 2 GQDs/o-phenylenediamine (OPD), was constructed by combining amino-functionalized graphene quantum dots (NH 2 GQDs) and o-phenylenediamine. In the presence of NH 2 GQDs/H 2 O 2 , OPD was oxidized to 2,3-diaminophenazine (DAP), giving fluorescent and colorimetric signals, which can be used to quantitatively measure H 2 O 2. Furthermore, NH 2 GQDs/OPD/ H 2 O 2 exhibited high selectivity and sensitivity for detecting ascorbic acid (AA) with a detection limit of 0.062 μM using the fluorescent method. Its selectivity for AA was ascribed to the formation of the condensation compound of DAP with dehydroascorbic acid rather than the quinoxaline path for dopamine and glucose. The colorimetric sensing system NH 2 GQDs/OPD displayed yellow in the presence of H 2 O 2 , while it changed to green upon adding AA. This sensing system was successfully applied for imaging H 2 O 2 and AA in human cervical cancer cells and onion tissues. Additionally, the flexible sensing system can be used to fabricate the logic gate "AND." The results provide a valuable method for its potential application in the biosensing, clinical medicine, and food industries. [Display omitted] • A dual optical sensing system was constructed by combining amino-functionalized graphene quantum dots and o-phenylenediamine. • The amino-functionalized graphene quantum dots exhibit high peroxidase activities. • The sensing system was used to cascade detection of H 2 O 2 and ascorbic acid in living cells. • The fluorescent mechanism is based on IFE and the formation of new fluorescent species. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) plays important roles in both physiology and therapeutics. Nonetheless, the in-situ monitoring of NO release from most existing donors is challenging, inhibiting advanced research in both chemistry and biology. In this study, we introduce an innovative photochemotherapeutic agent that incorporates a nitroaniline NO moiety with an integrated pyrene fluorophore. This design enables controlled NO release upon light irradiation, allowing for precise quantification through a dramatic fluorescence enhancement (with a 3000-fold increase in intensity). Ultrafast spectroscopy data revealed that the NO release process is exceptionally rapid, completing within 13.3 ps. Additionally, the donor's fluorescence was successfully utilized for in situ cell imaging upon direct photoexcitation. Consequently, using this fluorescent probe enables the accurate visualization of NO release kinetics, dosage, and localization in real-time. The unique advantages of this NO donor are anticipated to significantly advance research in NO chemistry and biology. [Display omitted] • The first pyrene-based photoactivated NO donor was fabricated. • Photoactive ultrafast NO release (13.3 ps) was obtained. • Real-time NO-releasing was monitored by a strong fluorescent probe (3000-fold). • Cellular imaging was performed to demonstrate NO-releasing in situ. [ABSTRACT FROM AUTHOR]

Designing a multifunctional nucleic acid platform with the ability to identify multiple biomarkers is crucial for accurate molecular diagnostics. Here we reported a dual-target branch-shaped nucleic acid probing (DBNP) system and its targeted delivery for simultaneous analysis of intracellular microRNAs (miRNAs). The system consisted of a cross-shaped DNA scaffold equipped with four hairpin strands and an aptamer strand. The four hairpin strands constituted two catalytic hairpin assembly (CHA) reactions, enabling the system to simultaneously recognize and amplify two kinds of miRNAs. We demonstrated that the cross-shaped DNA scaffold structurally offered a spatial-confinement effect, well-known in increasing the intramolecular collision of the probes and accelerating the CHA reactions, which allows us to resolve multiplex miRNAs profiling with high efficiency by using DBNP system. In addition, because of the inherent character of aptamer capable of specifically binding with cell-membrane receptor, targeted delivery of DBNP system into the unique receptor-positive cells can be realized to detect intracellular miRNAs. The dual miRNA-mediated stimuli-response, operating in parallel with a receptor-specific recognition of target cells, synergistically enhances the accuracy of cell discrimination and cancer diagnosis. This innovative approach holds great promise for advancing the development of cutting-edge signal amplification technologies and biosensors utilized in cancer diagnostics. • The DBNP system was designed to detect multiplex miRNAs with high efficiency. • The DNA scaffold offered a spatial-confinement effect for accelerating CHA reactions. • DBNP system displays an excellent specificity and LOD can be down to 10 fM. • The cell-specific and dual-target response provided an accurate diagnosis. [ABSTRACT FROM AUTHOR]

Achieving specific and sensitive imaging of mRNA in living cells plays a key role in cancer diagnosis and treatment. Catalytic hairpin assembly (CHA) has been widely used for mRNA imaging. However, it has been significantly constrained by limited in-depth amplifications. Herein, a novel feedback catalytic hairpin assembly (FCHA) with exponential amplification efficiency was proposed for mRNA imaging in living cells. The FCHA system consisted of with two hairpin DNAs (H 1 , H 2) and a double stranded DNA (H 3 L). After the probes enter the cell by using β-FeOOH nanoparticles (NPs) as delivery vector, the intracellular target Tk1 mRNA acted as catalyst to trigger the FCHA between H 1 , H 2 and H 3 L, which achieved the exponential growth of CHA product. This FCHA system has demonstrated improved reaction kinetics and sensitivity compared to traditional CHA, which was 106 times more sensitive than conventional CHA. This strategy can be used for real-time imaging and indication of changes in the mRNA expression. This strategy slao can distinguish the expression difference of mRNA in normal and tumor cells, and can evaluate the anti-tumor drug's efficacy. Benefiting from these outstanding advantages, we believe that this FCHA will become a powerful tool for early cancer diagnosis. [Display omitted] • A novel feedback catalytic hairpin assembly with exponential amplification efficiency is developed. • The FCHA system had improved reaction kinetics compared to traditional CHA. • FCHA system allows accurate differentiation of mRNA expression of cancer cells and normal cells. • The method had the potential for antitumor drug efficacy evaluation and adjuvant new drug screening. [ABSTRACT FROM AUTHOR]

The filamentous protein 'actin' plays an essential role in maintaining a proper cellular health and any disruption in its structure and dynamics may induce the growth and metastasis of cancerous cells. Recent studies have shown that, actin can serve as a potential therapeutic target and an indicator to examine the efficacy of modern chemotherapeutic agents. In this regard, the microscopy imaging of actin using fluorescent dyes can pave the way toward development of efficient drugs for cancer treatment. Herein, we report the synthesis of an organic fluorescent dye (BCH) which shows good selectivity toward F-actin at physiological pH. The dye displays a large Stokes shift (∼232 nm), strong emission intensity, good photostability and great sustainability over a wide pH range of 2–10. The dye can directly bind and localize in the actin-rich region of gut, testes and eye of a model organism, Drosophila melanogaster in both living and fixed cells and enable their confocal microscopy imaging without using any actin binding domain. Interestingly, the BCH dye is proved to be nontoxic in the tested organism and has been successfully employed as a potential tool to visualize cellular actin in living tissues of larva and pupa of the organism. [Display omitted] • A benzil biscoumarinyl hydrazone based fluorescent dye has been synthesized. • The dye can bind and image cellular filamentous actin directly without any binding domain. • The dye is proved to be nontoxic in model organism Drosophila melanogaster. • The dye has been successfully employed to visualize cellular actin in living tissues of larva and pupa of the organism. [ABSTRACT FROM AUTHOR]

Multiplexed fluorescence imaging is mainly applied to cellular imaging. However, the application of an analogous technique to mammals remains challenging due to the presence of substantial scattering and autofluorescence in biological tissues in the visible (350–700 nm) and near-infrared I region (NIR-I, 700–900 nm). Herein, we report multiplexing excitation and single-channel detection in the near-infrared II region (NIR-II) with two fluorescent probes for dual-color imaging in vivo. The first one, FNIR-1090 was constructed on Pr-1099 derivative by attaching with 1-Ethylpiperazine through the SRN1 displacement reaction. The second one, IR-765 was synthesized by a one-step reaction between the Vilsmeier–Haack reagent with 2-(3,5,5-trimethylcyclohex-2-enylidene) malononitrile (TEMO). It is noteworthy that the absorption spectrum of FNIR-1090 is almost completely separated from that of IR-765, which facilitates dual-color in vivo imaging. The two dyes can be used for high-contrast dual-channel vivo imaging of different tissues. All these prominent performances show the great promise of FNIR-1090 and IR-765 in non-invasive, real-time, and dual-color NIR-II imaging (>900 nm) in vivo. [Display omitted] • Multiplexed fluorescence imaging in NIR-II region. • Design and synthesis of two NIR fluorescent probes for dual-color in vivo imaging. • Superior NIR-II imaging capability of two probe (FNIR-1090 and IR-765) without spectral cross-interference. • Real-time analysis of biological processes at high resolution through different channels. [ABSTRACT FROM AUTHOR]

Long-wavelength emission with high contrast toward species of interest is highly desired for fluorescence imaging in living objects. Herein, we proposed an exquisite enzyme-regulated "aggregation-induced emission (AIE) and intramolecular charge transfer (ICT)" strategy to optimize the signal-to-noise ratio for highly sensitive detection of enzymes. Benefiting from the synergistic effect, probes ABT-Gal-1 and ABT-Gal-2 exhibited faint background signals but dramatically enhanced near-infrared fluorescence upon exposure toward β-galactosidase (β-gal). Notably, both probes could be accessible in aqueous media. Preferably, the fluorescence intensity of ABT-Gal-1 exhibited a satisfactory linear relationship in the wide concentration range of 0.5–30 U/L with a very low detection limit to 0.24 U/L. Further, by monitoring endogenous β-gal in ovarian cancer cells, a precious merit of resistance to multiple washes was identified, which was facilitated by the nanoaggregate formation in situ upon activation. This work proposes a guiding strategy for manipulating various lighting mechanisms to develop attractive probes and, equally importantly, it provides an ideal practical tool for elucidating the biological role of β-gal in biological scenarios. [Display omitted] • Comprehensive insights into the ICT and AIE characteristic of amino-type ESIPT-based fluorophore are proposed. • An exquisite enzyme-regulated "AIE and ICT" strategy to optimize the signal-to-noise ratio is reported for the first time. • Debut of activatable AIE probe for β-gal with emission in near-infrared window is well presented. • Probe ABT-Gal-1 was allowed in aqueous media with the lowest detection limit (0.24 U/L) compared with reported probes. • The nanoaggregation-allowed probe was firstly disclosed with resistance to multiple washes during cell imaging. [ABSTRACT FROM AUTHOR]

Esterase serves as a crucial biomarker for the diagnosis of tumors due to its overexpression in cancer cells. Ratiometric fluorescent probe has the advantage of having two distinct emission wavelengths, which allows for the elimination of the effects of light intensity and optical path length by using the fluorescence intensity ratio between the two emission wavelengths. In this work, a novel near-infrared (NIR) fluorescent probe P 1 for ratiometric monitor esterase activity was developed. Compared with ordinary ratiometric probes, both emission wavelengths of this probe are in the NIR region, which can effectively eliminate various fluctuations and blurriness in image contrast and achieve precise quantitative analysis. P 1 itself shows a fluorescence emission at 717 nm. After incubated with esterase, a new emission peak at 822 nm emerged due to esterase's catalysis, and the fluorescence intensity at 717 nm steadily decreased, which achieved the highly sensitive detection of esterase with a detection limit calculated as 0.25 mU/mL. What's more, P 1 showed high selectivity for esterase and was successfully applied for biological imaging in living cells and in vivo. [Display omitted] • A ratiometric fluorescent probe for the determination of esterase was developed. • Both of the two emissions before and after incubation with esterase were located in NIR region. • The probe shows fast response, high selectivity and high sensitivity for esterase. • The probe showed a linear relationship for esterase in 0–100 mU/mL with a LOD of 0.25 mU/mL. • The probe was successfully applied for biological imaging in living cells and in vivo. [ABSTRACT FROM AUTHOR]

Stress granules (SGs) are a fascinating type of membrane-less organelle that form through liquid-liquid phase separation in eukaryotic cells. Our previous investigations have been instrumental in the development of the first small-molecule fluorescent probe, named TASG , which can selectively identify SGs. However, the practical utility of TASG for monitoring SG dynamics in live cells has been hindered by the difficulty in visualizing small nascent SGs. To overcome this obstacle, the present study systematically modified the structure of TASG , with the aim of discovering fluorescent chemical probes that exhibit superior performance. Among the evaluated candidates, TASG-8 exhibited the most promising ability to image SGs. Importantly, TASG-8 possessed a critical advantage over TASG , in that it could effectively label small nascent SGs. The structure-activity relationship of the candidates was analyzed. Additionally, the underlying mechanism responsible for this enhancement was extensively explored. Collectively, our research presents a rational strategy for the development of innovative fluorescent probes that selectively target SGs, and introduces a powerful new tool, TASG-8 , which has the potential to facilitate more comprehensive and efficient investigations into the functions of SGs in cells. • The structure-activity relationship of benzothiazoles that target SGs is clarified. • TASG-8 is the first fluorescent probe capable of visualizing small nascent SGs. • Our study presents a novel concept for developing probes that are specific to SGs. [ABSTRACT FROM AUTHOR]

The misfolding and aggregation of specific proteins induced by endogenous oxidation are closely related to some incurable diseases including cancers, diabetes and neurodegenerative diseases. Reactive oxygen species (ROS), as a common oxidizing substance in vivo would induce the oxidation of endogenous biomacromolecules like proteins. However, it remains a challenge to detect protein aggregation induced by specific ROS. Herein, we demonstrate that the developed probe (P2) with a dual function that can simultaneously detect hydrogen peroxide (H 2 O 2) levels and protein aggregates formed by oxidative stress. In this probe, the boronic acid pinacol ester group was conjugated to fluorescent molecular rotor 4-hydroxybenzylidene-imidazolinone (HBI) and served as the H 2 O 2 detection group. Experimental results show that the fluorescence of P2 can be activated by H 2 O 2 and exhibited a positive correlation with the degree of protein aggregation. Moreover, combined with AggTag method P2 was successfully applied to dual-channel imaging of protein aggregation that is stressed by H 2 O 2 in cellular. In general, this work not only provides a potential method to study protein aggregation that associates with oxidation in live cells but also can be generally applied to study other biological processes. • A dual-functional probe activated by hydrogen peroxide (H 2 O 2) and viscosity was designed and synthesized. • The probe responds to H 2 O 2 with high selectivity. • The probe exhibits a cascade response to H 2 O 2 and protein aggregation. • Revealing the process of protein aggregation under H 2 O 2 stress in live cells. [ABSTRACT FROM AUTHOR]

Construction of artificial DNA molecular reaction networks (DMRNs) represents an effective approach in biosensing. Here we developed a reaction network consisting of a dual catalytic hairpin assembly-mediated tandem molecular circuit combined with strand displacement reaction (DCHA-SDR) for proteinase-free and highly specific mRNA imaging in living cells. The strand displacement reaction (SDR) was designed to be orthogonally activated in exact order by two fuel strands that separately split into inactive species and grafted into the dual catalytic hairpin assembly-mediated molecular tandem circuit (DCHA). The fuel strands can be activated only when the specific mRNA is introduced, and DCHA is initiated by using two different pieces of mRNA sequences as target. In this way, the target mRNA can be automatically matched twice to obtain an accurate and amplified recognition. Comparative analysis indicates that this orthogonal strategy for target identification is superior to the strategy consisting of single CHA-mediated molecular circuit and strand displacement reaction (SCHA-SDR). Moreover, we demonstrate that the DCHA-SDR system comes with the benefit of proteinase-free progress, which makes the approach suitable for operation in living cells. Final application in various cancer cells and normal cells reveals its enormous potential for highly specific mRNA imaging in biological systems. • Orthogonal activation strategy provided an accurate identification of target interest. • Reliable imaging of mRNA in complex cellular environments can be achieved. • LOD can be down to 50 fM by using dual CHA-mediated tandem molecular circuit. • Final applications show the great potential for highly specific mRNA imaging in biological systems. [ABSTRACT FROM AUTHOR]

A new fluorescent sensor for imaging cancer cells was designed by bioconjugation of holo-transferrin (hTf) with a nitro-pyrazinotriazapentalene moiety (PyTAP-NO 2) as a bioreductive fluorescent unit. hTf was chosen to increase its selective delivery to cancer cells through transferrin receptor (TfR) mediated endocytosis. PyTAP-NO 2 was applied to enhance the fluorescent signal in oxygen-deprived cells due to the increased expression of nitroreductases under such conditions. A protein-dye bioconjugate had an average of 8 fluorophore molecules per protein that effectively amplifying the fluorescence signal. The designed hTf- PyTAP-NO 2 was non-toxic and its efficient accumulation through TfR, as well as its high stability and sustained intracellular retention, was proven. hTf-PyTAP-NO 2 bioconjugate allows selective accumulation in cancer cells containing increased levels of TfRs with simultaneous slight enhancement of signal in hypoxic cells due to increased expression of nitroreductases. [Display omitted] • Bioconjugation of holo-transferrin with a nitro-pyrazinotriazapentalene for cell imaging. • Fast and efficient cellular uptake exclusively via transferrin receptor endocytosis. • A high fluorescent signal in cells additionally amplified under hypoxic conditions. • Resistant to degradation and sustained intracellular retention. [ABSTRACT FROM AUTHOR]

Fluorescent nanoprobes for carbon monoxide (CO) imaging emerged as an excellent tool for cancer diagnosis, but they are activated by single-biomarker. Herein, we developed a dual-locking fluorescent nanoprobe (HA-DMC) for HAase-triggered carbon monoxide imaging in the mitochondrion of the cancer cells. The fluorescent nanoprobes have "double locks" structures made of acetyl hyaluronic acid chains (hyaluronidase-triggered, first lock) as a barrier to form nanoparticles and the nitro group (CO-triggered, second lock) as intramolecular charge transfer (ICT) groups to quench the fluorescence of coumarin-pyridine derivative dyes. When the "locks" were only unlocked in sequence (from hyaluronidase to CO), a strong green fluorescence appeared for achieving cancer imaging. Meanwhile, the HA-DMC exhibited some satisfactory properties, such as mitochondria-targeting properties, excellent selectivity and sensitivity (24-fold), good water dispersibility, low detection limit (225 nM), and low cytotoxicity. Such features ensured that the HA-DMC could be successfully utilized for fluorescently imaging exogenous CO in the mitochondrion of living cells. In addition, the HA-DMC was successfully used to monitor exogenous and endogenous CO in vivo. We thus envision that HA-DMC is a promising platform for CO imaging in the mitochondrion of cancer cells and would promote the progress of fluorescent nanoprobes. [Display omitted] • A dual-locking fluorescent nanoprobe (HA-DMC) for CO imaging was well developed. • HA-DMC was used for HAase-triggered mitochondrial CO imaging in cancer cells. • This work provides the first dual-locking probe for HAase and CO in tumor cells. [ABSTRACT FROM AUTHOR]

Hypochlorous acid (HClO) is a vital bioactive molecule. Abnormal levels of HClO can affect the body's immune system and pathological processes, leading to many diseases such as kidney disease and neurodegenerative diseases. Therefore, it is very important and necessary to develop a rapid and sensitive HClO detection method. In this work, we propose a novel phenothiazine-xanthene fluorophore, which has flexible adjustability and outstanding responsiveness to HClO. Using phenothiazine-xanthene fluorophore, a "turn-on" probe 7-ethyl-1,2,3,7-tetrahydrochromeno[2,3- b ]phenothiazine-4-carbaldehyde (PTZ-CHO) was designed and synthesized for the trace analysis of HClO. In the presence of HClO, the sulfur atom on phenothiazine is rapidly oxidized to the sulfoxide, and a significant fluorescence enhancement (about 100-fold) was observed. Moreover, the advantages including fast response (<10 s), ultra-high sensitivity (limit of detection = 6 nM), strong specificity, and splendid light stability can all be achieved by PTZ-CHO. Benefitting from these advantages, this unique HClO-responding probe has been successfully applied to the detection of HClO in Hela cells, RAW 264.7 cells, and environmental water samples. [Display omitted] • A novel phenothiazine-xanthene fluorophore PTZ-CHO was first synthesized. • PTZ-CHO has fast response time (<10 s) and high sensitivity (LOD = 6 nM) to HClO. • PTZ-CHO shows 100-fold fluorescence enhancement after responding to HClO. • PTZ-CHO was employed for imaging of exogenous and endogenous HClO in living cells. • PTZ-CHO was applied to the detection of HClO in real water samples. [ABSTRACT FROM AUTHOR]

• A green fluorescent probe for low-cost, efficient, precise, and universal live/dead cell imaging is developed. • An accurate quantification method for live/dead cells is proposed. • Real-time dynamic visualization of in vivo drug toxicity/efficacy is realized. Rapid and quantitative discrimination between live and dead cells is highly desirable yet remains a challenging task. Here, we report the use of the ultrabright green-emitting organosilica nanodots (OSiNDs, photoluminescence quantum yield: ˜100%) for fast (1 min in vitro and 5 min in vivo), wash-free, and universal labeling of the dead bacterial, fungal, and mammalian cells, which meets the demand of the green fluorescent probes that can specifically image the dead cells. The photostability of OSiNDs surpasses that of the commercial dyes, such as propidium iodide (PI) and SYTOX Green nucleic acid stain (SYTOX), making OSiNDs more suitable for long-term and stable monitoring of the cell viability. With the assistance of a commercial red fluorescent dye SYTO 60, we develop an in situ method for rapid and accurate quantification of live/dead cells. Motivated by the unique optical advantages and high sensitivity of OSiNDs to the cell viability, the OSiNDs are employed to observe the in vivo cellular changes induced by doxorubicin using zebrafish as a model, demonstrating their great potential for evaluating the toxicity/efficacy of the therapeutic agents in real time. Owing to the excellent biocompatibility and low cost, the OSiNDs can be a universal probe for efficient and accurate differentiation and quantification of the live and dead cells, which may find wide applications in the biomedical field. [ABSTRACT FROM AUTHOR]

• A novel fluorescence strategy based on MPA-AgInZnS QDs for sensitive and effective detection of protamine and trypsin. • This assay we investigated was simple, cost-effective, convenient and does not need any complicated pretreatment. • We successfully applied the AgInZnS QDs to intracellular imaging and lysosomes localization. In this study, a fluorescence strategy based on MPA-AgInZnS quantum dots (AIZS QDs) for the sensitive, effective detection of protamine and trypsin was developed. Protamine as a cationic peptide exhibited electrostatic interactions with AIZS QDs, leading to the aggregation of QDs and subsequent enhancement of the fluorescence intensity. The added trypsin catalyzed the hydrolysis of protamine and led to less formation of AIZS QDs/protamine complex, thereby decreasing the fluorescence intensity. Thus, a method for direct determination of protamine and indirect measurement of trypsin using protamine as a tool was developed. The protamine and trypsin concentrations were determined by the detection of the change in fluorescence intensity. Under the optimized conditions, the fluorescence intensity exhibited a good linear response to the protamine concentration, with a limit of detection (LOD) of 0.13 μg mL−1, and trypsin exhibited a linear relationship, with an LOD of 0.04 μg mL−1. The probe exhibited good biocompatibility and low cytotoxicity according to the MTT assay. Moreover, the application of this probe for intracellular imaging and lysosome localization demonstrates potential development in the biomedical and clinical fields. [ABSTRACT FROM AUTHOR]

• A mitochondria-targeted ratiometric fluorescent probe for cyanide was developed. • Mito-CP can detect endogenous cyanide in plant tissues and rat PC12 cells. • Mito-CP can recognize cyanide with dual-channel mode fluorescence imaging. • Mito-CP could detect cyanide in real water samples with quantitative detection. Various fluorescence probes for cyanide anions in water solution have been reported, but the investigation for endogenous cyanide recognition in plant tissues and mammalian cells is still limited. Here, a mitochondria-targeted cyanide fluorescent probe Mito-CP with colorimetric and ratiometric response was developed. The detection for cyanide was performed via the nucleophilic addition of cyanide to carbon-carbon double bond between coumarin moiety and pyridine moiety of the probe, which resulted in a color change from red to colorless and fluorescence change from red to blue. The probe showed high sensitivity (0.17 nM) and selectivity for cyanide over other common anion species and biothiols and could detect cyanide in real water samples with quantitative detection. Probe Mito-CP was successfully applied to detect endogenous cyanide in cassava root plant tissues. In addition, colocalization experiment showed that the probe has the property of targeting mitochondria with overlap coefficient being 0.93. A549 and HeLa living cells imaging experiment demonstrated the practical value of the probe in tracing CN− in biological systems. The probe also can detect endogenous cyanide change in mitochondria of rat pheochromocytoma (PC12) cells. [ABSTRACT FROM AUTHOR]

• A dicyanoisophorone-based fluorescent probe was developed for sensing H 2 S with a large Stokes shift (155 nm). • The probe showed faster time response and high sensitivity for H 2 S. • The probe can be used to detect exdogenous and endogenous H 2 S in living HeLa cells. Due to the importance of hydrogen sulfide (H 2 S) in physiology and pathology, the development of fluorescence probes for the detection of H 2 S has attracted extensive attention of researchers. We developed a H 2 S fluorescence probe (DCN-S) based on dicyanoisopentanone using dithioether and ester groups as the reaction sites. Under the nucleophilic substitution of H 2 S, disulfide bond of DCN-S was broken. Then the probe changed into dicyanoisophorone derivative and emitted an orange fluorescence band from 530 nm to 700 nm (centred 580 nm). Upon response for H 2 S, DCN-S exhibited high sensitivity (88 nM detection limit) and large stokes shift (155 nm). Importantly, the probe also was successfully used for endogenous and exogenous imaging of living cells. [ABSTRACT FROM AUTHOR]

• The synthetic route of the probe is very simple. • The probe has good reversibility in physiological environment. • The probe Cu-1 shows excellent selectivity toward Cys. • This assay has high sensitivity and exhibits short response time. • This probe is AIE-active leading to high luminous efficiency in cell imaging. In this work, an effective and simple aggregation-induced emission (AIE) active fluorescent probe based on ESIPT luminescence principle, 2-hydroxy-1-naphthal-4-aminoantipyrine (1), was synthesized via a simple chemical reaction. It displayed strong fluorescence enhancement in water. The AIE mechanism of 1 was explored by electron microscopy and computational analysis. We demonstrate the combination effect of intramolecular hydrogen bonds and π-π stacking to endow 1 with such a property. Importantly, the ensemble of 1 with copper ions (Cu-1) as a fluorescent probe enables highly selective and sensitive turn-on fluorescence detection of cysteine (Cys) over other interfering substances. Under optimal detection conditions, this probe has a good linear relationship in the concentration range of Cys between 0 and 8 μM, and the detection limit of Cys was estimated as 84 nM. Furthermore, this assay exhibits good reversibility of 1 to Cu2+ and Cys. Due to its good biocompatibility evaluated by CCK-assay, the probe Cu-1 was finally applied in imaging of Cys within Min6 cells successfully. [ABSTRACT FROM AUTHOR]

• A fluorescence strategy was proposed for detection and imaging of multiple microRNAs. • A pH-responsive ZnO nanoprobe was designed. • The strategy showed good sensitivity and specificity for multiple microRNAs. • Different levels of miR-21 expression in three types of cells were differentiated. • Simultaneous imaging of miR-21 and miR-373 in same living cells was achieved. Here, a pH-responsive ZnO nanoprobe mediated DNAzyme signal amplification strategy was proposed for sensitive detection and live cell imaging of multiple microRNAs. The nanoprobe including ZnO nanoparticles (ZnO NPs) core as carrier and cofactor provider and polydopamine shell for adsorption the functional hairpin DNAs was designed. When nanoprobe entered the cell through endocytosis, the acidic environment of the cell could decompose the ZnO NPs core to release the functional hairpin DNAs and Zn2+. The Zn2+ could act as cofactor for the DNAzyme cleavage amplification reaction, avoiding additional cell delivery processes. The recognition hairpin DNAs (H1 and H3) recognized microRNA and exposed the DNAzyme. The DNAzyme cleaved cyclically the reporter hairpin DNAs (H2 and H4), producing enhanced fluorescent signal for miR-21 and miR-373 detection with the detection limit of 54 pM and 38 pM, respectively. Expression levels of miR-21 in Hela, HepG-2 and L02 cells were differentiated. Furthermore, simultaneous imaging of miR-21 and miR-373 in same living cells was achieved. These results indicated this strategy could have a potential application in microRNAs assays for the accurate diagnosis and therapy of cancer. [ABSTRACT FROM AUTHOR]

• A cystamine based an organic-inorganic nanohybrid [ L1-ONP-Co(II) ] probe has been synthesized. • The photophysical detection of NADH by L1-ONP-Co(II) with a real time imaging of cancer cells. • The probe has a detection limit as low as 83.89 nM for NADH. • The higher level of NADH in cancer cells 'Turn On' the green colored fluorescence of L1- ONP-Co(II). The pronounced demand of sensing of biological analytes which play a significant role in progress of cancer cells encouraged us to develop a novel chemosensor having high selectivity and sensitivity for NADH. Therefore, imine linked dipodal receptor (L1) was synthesized and its organic nanoparticles (L1-ONP) were prepared using reprecipitation method to enhance their water solubility. These ONPs form a metal complex with Co(II) which was characterized by UV–vis absorption and Fluorescence Spectroscopy. The ONPs show highly sensitive affinity having a low detection limit (LOD) of 16.95 nM for the cobalt ions. The prepared ONPs metal complex exhibits high selectivity and sensitivity to sense the NADH with a very low LOD of 83.89 nM without any interference from other potentially interfering biological molecules. Fluorescence response from NADH was also not affected by pH and UV irradiation. The sensor was also employed for detection of NADH in MCF-7 cells. [ABSTRACT FROM AUTHOR]

• A new near infrared fluorescent probe was reported to detect ATP and target lysosomes in cells. • Probe 1 was used in selective lysosome staining and for real-time ATP level monitoring. • Probe 1 exhibits excellent photostability, low cytotoxicity, and good cell membrane permeability. A new near infrared fluorescent probe was designed and prepared to detect ATP and target lysosomes in cells. The non-fluorescent probe was turned on during the interaction with ATP, affording a 115-fold increase in fluorescence intensity. The colorless probe turned purple upon interaction with ATP. The probe displayed high sensitivity and selectivity toward ATP compared with other biomolecules, such as AMP, ADP, GMP, and CMP. Such significant spectroscopic changes derive from a structural change of the probe's spirocyclic moiety to its ring-opened form. This occurs through electrostatic and π,π-stacking interactions between the probe and ATP. This probe was also used in selective lysosome staining and for real-time ATP level monitoring. It exhibits great advantages in cell imaging studies, such as excellent photostability, low cytotoxicity, and good cell membrane permeability. [ABSTRACT FROM AUTHOR]

Herein, we report a simple green platform based on a novel type of polymer dots (Pdots) as a sensitive and rapid "off-on" fluorescent probe for ratiometric Fe3+ and Cu2+ detection. The ratiometric probe has been designed using green-emitting PIM-1 Pdots and red-emitting PFTBT Pdots as detecting probes and internal stable standard probes, respectively. The dual-emission characteristics of PIM-1/PFTBT Pdots allowed us to apply ratiometric ion determination based on aggregation-caused quenching (ACQ) of PIM-1 Pdots at 490 nm, while the red emission intensity kept highly stable. The role of porosity and surface carboxylic groups of PIM-1 to achieve high sensitivity and selectivity using quantum-mechanical calculation and cellular imaging was successfully demonstrated so that the detection limit of 7.4 nM for Fe3+ and 14.8 nM for Cu2+ was obtained. The "on" process with excellent selectivity was realized by the introducing of glutathione (GSH) into PIM-1/PFTBT/Cu2+ and Cytochrome c (Cyt c) into PIM-1/PFTBT/Fe3+ with fluorescence recoveries of the blank sample 92 % and 91 %, respectively. The proposed strategy detects GSH and Cyt c with a good linearity ranging from 300 nM to 1800 nM and 10 nM to 120 nM by the limit of detection of 85.3 nM and 0.6 nM, respectively. This combinational off-on strategy provides a promising nanosensing platform for monitoring Fe3+ and Cu2+ in the environmental samples and introduces a sensitive probe with high biocompatibility for intracellular target imaging. [Display omitted] • Synthesized novel polymer dots (Pdots) from porous organic polymers. • Design a novel ratiometric fluorescent probe based on porous Pdots. • Harnessing the ability of modified Pdots toward turn-off-on sensing strategy. • Newly fluorescent Pdots have found promising applications in fluorescence imaging. [ABSTRACT FROM AUTHOR]

Exploring base mismatching-fueled catalytic hairpin assembly (mf CHA) is intriguing to regulate the fluorescence of DNA-scaffolded red Ag nanoclusters (r AgNC) for rapid and amplifiable biosensing of miRNA-155 (miR-155). Herein, we report the first design of a miR-155-responsive mf CHA route with rapid reaction kinetics and high conversion efficiency to light-up the fluorescence of r AgNC. The mf CHA was operated by a signaling hairpin (SH) programmed with the r AgNC template sequence and miR-155-discernible segment, and a G-rich (G12) enhancing hairpin (EH*). To implement faster and more efficient mf CHA amplification as a big challenge in traditional CHA, the locked stem of SH and the loop of EH* were encoded with single mismatched base in different sites, endowing mf CHA with more negative reaction standard free energy as driving force. Note that the originally synthesized r AgNC in SH was non-emissive. However, the presence of miR-155 initiated hairpin assembly between SH and EH* , leading to the displacement of miR-155 for repeated recycling and progressive mf CHA. Rationally, the red fluorescence of r AgNC was remarkably lighted-up due to the proximity to G12 enhancer in the shared dsDNA duplex products. Thus, this mf CHA-based assay platform displayed good simplicity, cost-effectiveness, rapidness, high sensitivity, and potential application for cell imaging. [Display omitted] • A sensitive fluorescence biosensor is developed by using red AgNC (r AgNC) as signaling reporter. • Base mismatching of reactive hairpin stem is designed to fuel catalytic hairpin assembly (mf CHA). • The mf CHA route owns faster reaction kinetics and higher conversion efficacy than traditional CHA. • The r AgNC fluorescence emission is remarkably lighted-up when placing close to a G12 enhancer. • The targeting input is repeatedly displaced and recycled for amplifiable assay and cell imaging. [ABSTRACT FROM AUTHOR]

The development of a DNA-based logic device capable of simultaneously detecting two microRNAs (miRNAs) has the potential to enhance the accuracy of cancer diagnosis. However, existing approaches are hindered by slow response times, limited sensitivity, and inadequate cellular delivery. In this study, we integrated logic operations with 3D catalytic hairpin assembly (3D-CHA) to devise a sensing system for the AND-gated analysis of miR-21 and miR-155 in living cells and tissues. We utilized two DNA nanospheres, designated AN1 and AN2, which, upon the presence of both miRNA inputs, release an initiator via strand displacement, consequently triggering 3D-CHA between AN1 and AN2 and generating an amplified output. Our findings demonstrate that the AN nanoprobe facilitates the logical analysis of dual miRNAs in buffers, living cells, and tissues, offering effective cellular delivery, nuclease resistance, heightened sensitivity, and rapid response time. The AN nanoprobe represents a promising diagnostic tool for the accurate detection of breast cancer and exhibits considerable potential for clinical applications. • A strategy based on AND-gated operation and 3D catalytic hairpin assembly was firstly employed for dual miRNA detection. • The sensing system improves cancer diagnosis accuracy through simultaneous detection of miR-21 and miR-155. • The system provides accurate and efficient breast cancer detection in living cells and clinical tissue samples. • The detection limit at the picomolar level was achieved in buffers and serum solutions. • Fast response time could be realized through the spatial-confinement effect. [ABSTRACT FROM AUTHOR]

Lipid droplets (LDs) have attracted much attention due to their unique structure and key connections with various organelles in cells. Here, we constructed a reactive oxygen species (ROS) -generating system by carefully designing photosensitizers (TT2CN) with proper lipophilicity, excellent light stability and cell imaging ability. In detail, TT2CN can selectively accumulate into LDs (as carriers for TT2CN) and then a subcellular photo-inducible ROS-generating system was formed. Confocal fluorescence imaging revealed the contact behavior of dynamic LDs with other organelles in the cells and the photo-produced ROS can induce multiple organelle damages. Flow cytometry, AM / PI and 3D multicellular tumor spheres (3D MCTs) experiments further verified and demonstrated its promising biological application. This work not only uncovers the communication behavior between LDs and other organelles, but also provides a new anticancer strategy of LDs-mediated photodynamic therapy. [Display omitted] • TT2CN has excellent photostability and cell imaging ability. • Constructing ROS-generating system, viz, TT2CN -loaded LDs. • Confocal fluorescence imaging revealed the contact behavior of this ROS-generating system with other organelles. • ROS-generating system outstanding capability to mediate multiple subcellular organelle damage. [ABSTRACT FROM AUTHOR]

Hypochlorous acid (HOCl) is a crucial reactive oxygen species in biological systems, and its abnormal metabolism is associated with various diseases. Therefore, it is essential to accurately detect HOCl to understand its biological function and develop related therapeutic strategies for diseases. In this work, we developed a novel fluorescence probe, BCy-S , based on the twisted intramolecular charge transfer (TICT) mechanism for rapid and sensitive detection of HOCl in an aqueous solution. The probe exhibited a significant turn-on fluorescence response to HOCl, with high selectivity, rapid kinetics (less than 40 s), large Stokes shift (about 170 nm), and low detection limit (35.2 nM), based on the specific oxidation reaction of HOCl with sulfur atoms. Additionally, the outcomes of the bioimaging experiment showed that BCy-S was capable of real-time fluorescence visualization of HOCl in living HeLa cells and zebrafish. The development of BCy-S presents a new tool for investigating the physiological function of HOCl and its pathological role in diseases. [Display omitted] • A new TICT-based HOCl fluorescent probe has been designed and developed. • The probe exhibits an excellent sensitivity, large Stokes Shift and low detection limit to HOCl. • The probe could be applied for real-time fluorescence imaging of HOCl in live HeLa cells and zebrafish. [ABSTRACT FROM AUTHOR]

The abnormal changes of intracellular potassium ion (K+) concentration are usually associated with various diseases, therefore, real-time monitoring of intracellular K+ dynamic balance is crucial for disease research. Herein, we present a design strategy based on conjugated polymers (CPs) as potassium ion fluorescence probes. Six novel CP-based K+ sensors (P1 , P2 , P3 , PP1 , PP2 and PP3) were synthesized. These probes have different conjugated length backbones composing of stilbenzene, fluorene, thiophene, and/or benzothiadiazole units and different numbers of K+ selective ligands of triazacryptand (TAC), so as to study their spectral characteristics and response to K+. Among them, PP3 exhibits exceptional responsiveness and selectivity to K+. With a longer conjugated backbone, it shows a longer emission at 628 nm compared to other probes. Especially, the fluorescence intensities of PP3 showed a linear relationship with the concentrations of K+ in the range of 0–250 mM. PP3 has been successfully applied to detect the dynamic equilibrium of potassium ion concentration in living cells. This study proposes and validates the feasibility of the CP-based K+ fluorescence probe design strategy and expands the range of K+ probes, providing a new tool for understanding disease pathogenesis. [Display omitted] • A new design strategy of K+ sensor based on cross-conjugated CPs was proposed. • Six new cross-conjugated CPs K+ sensors were designed and synthesized. • PP3 is the first CPs probe that can detect the dynamic equilibrium of K+ in cells. • The design strategy based on cross-CPs K+ sensor has been proved to be feasible. [ABSTRACT FROM AUTHOR]

Monoamine oxidase A (MAO-A) is involved in various diseases such as heart failure (HF), prostate cancer (PCa), psychiatric disorders, etc. The precise sensing of MAO-A is important to elucidate its function in various biological processes, as well the diagnosis and treatment of related diseases. In this research, we created a brand-new fluorescence probe ANET for the specific detection of MAO-A. Propylamine moiety of ANET was specifically recognized for MAO-A and then the product EHBT was released. A well-calculated p K a value of 8.01 ± 0.02 was achieved for EHBT by pH-dependent spectra. The fluorescence at 700 nm of EHBT was observed at pH 8.0 due to the enhanced intramolecular charge transfer (ICT). The fluorescence intensity of EHBT at 559/700 nm was in a linear relationship with MAO-A concentration in the 0.375–1.50 μg/mL range. The detection limit was 19.8 ng/mL. It is well known that the environment of mitochondria is microalkaline (pH 8.0), however, other organelles are neutral or acidic. So the fluorescence at 700 nm of ANET could be notably turned on by MAO-A in mitochondria. In addition, ANET can selectively accumulate in the mitochondria through powerful electrostatic attractions. Finally, ANET was applied for specific imaging of MAO-A in mitochondria of SH-SY5Y, PC-3, and glucose-deprived (GD) H9c2 cells. [Display omitted] • A probe was developed for Monoamine Oxidases A (MAO-A) based on ICT. • ANET can selectively accumulate in the mitochondria through strong electrostatic interactions. • Since the p K a of EHBT matches the pH in mitochondria, fluorescence of EHBT can be specifically turned on at 700 nm. • ANET was capable of differentiating MAO-A overexpressing cells from other cells. [ABSTRACT FROM AUTHOR]

• A FRET-based probe presented showed selective and rapid detection of nitric oxide (NO) with LOD ∼1 nM. • The nitric oxide detection is assisted by Cu2+ ion, which in turn provide more specific detection. • The detection of NO with Cu2+ ion assistance constructs a molecular level security device. • High efficiency for NO detection in HeLa cells by dual channel (green/red), low cytotoxicity and high brightness. • The probe has dual fluorophores, FRET mechanism, smart device application and useful for NO detection in HeLa cells. A rhodamine-dansyl conjugate (RPD) has been synthesized for rapid FRET-based ratiometric detection of nitric oxide (NO) up to nM level mediated by the Cu2+ ions. The emission band of dansyl centered at 481 nm showed quenching upon addition of Cu2+ and further addition of NO, showed a decrease at dansyl emission band and ratiometrically generate a new band at 580 nm corresponding to the open spirolactam derivative of rhodamine. Subsequent chemical inputs of Cu2+ and NO generate a smart molecular level security device with a unique set of inputs to unlock the device. The rapid detection of NO is devoid of false signalling, as the detection is dependent on sequence-based two input correct combination. The [ RPD -Cu2+] solution was also highly efficient to detect NO in solution by a visual change in colour: i.e. colourless to pink and pale green to orange under naked eye and UV-light respectively. The probe-Cu2+ solution exhibits excellent NO imaging in HeLa cells with low cytotoxicity and the lower level of emission in the presence of probe-Cu2+ which is advantageous to see the initial incubation of probe inside the live cells. The applicability of [ RPD +Cu2+] has been proven by efficient detection of NO in HeLa cells by dual enhanced emissions in green /red channels. [ABSTRACT FROM AUTHOR]

" Vigna radiata " based green c-dots for photo dynamic therapy (PDT), multicolor imaging and sensing of Fe3+. • Nitrogen doped C-dots were prepared using " Vigna radiata " as a sole carbon precursor. • The as synthesized N@VRCD exhibits excellent quantum yield of ∼58%. • N@VRCD selectively sense Fe3+ with LOD of 140 nM. • N@VRCD acts as photosensitizer upon irradiation by generating photo-induced singlet oxygen. Fluorescent C-dots have drawn increasing attention due to their superior properties such as high aqueous solubility, optical absorptivity, favorable biocompatibility and appreciable photoluminescence. Nature offers various precursors for the synthesis of green C-dots like fruits, vegetables, flowers, animal derivatives and many more. Herein, nitrogen doped C-dots (N@VRCD) were developed by economical, one step hydrothermal method using " Vigna radiata " sprouts as sole carbon precursor and ethylenediamine as the nitrogen source, which was optimized for enhanced optical properties. To the best of our knowledge, N@VRCD shows excellent quantum yield ∼58%. Importantly, N@VRCD also exhibits significant light induced phototoxicity to cancerous cells which enable the possibility of using it as a potential theranostics agent. Further, the N@VRCD displays highly sensitive and selective sensing behaviour towards Fe3+ ions by getting fluorescence "turn-off" with the limit of detection as low as 140 nM. Moreover, N@VRCD shows biocompatible and hemocompatible nature with a potential of multicolor live cell imaging and intracellular Fe3+ detection which was validated by confocal microscopy and flow cytometry. [ABSTRACT FROM AUTHOR]

• Preparation of cationic polyfluorene based fluorescent nanoparticle (CPF). • pH dependent reversible "turn off/turn on" emission of CPF with folic acid (FA). • CPF is highly sensitive to FA at biological pH of 7.4 to turn off 91% fluorescence. • FA pre-treated folate receptor positive cancer cell imaging by CPF nanoprobe. Herein, we have developed an efficient approach for folate receptor (FR) over expressed cancer cell targeting and imaging through non-covalent conjugation between folic acid (FA) and a polyfluorene based amphiphilic, fluorescent polymer nanoprobes (CPF) by fluorescence "turn off" mechanism. The pH dependent supramolecular complexation/decomplexation tendency of CPF nanoprobes with FA provides the effective reversible fluorescence "turn off/turn on" of CPF fluorescence. The complete pH dependent complexation/decomplexation phenomena is characterized by photophysical and morphological characterization. The FESEM image study reveals the alteration of nanosphere structure of CPF to interconnected network after complexation with FA at pH 9 and consequently restoration of nanosphere morphology by decomplexation at pH 2. Again, the CPF nanoprobes exhibit 91% fluorescence quenching even in physiological pH 7.4 to reveal that the nanoprobes can be a suitable candidate for FA targeted turn-off fluorescent nanoprobes for FA pre-treated FR-positive cancer cells in vivo study. The fluorescence of CPF nanoprobes is significantly quenched in FA pre-treated FR-positive B16F10 cancer cell whereas it remains unchanged in FR-non overexpressed normal human corneal cell (HCE cells) even after FA pre-treatment. Furthermore, the present study can provide a dissimilar protocol to use a "turn off" fluorescent nanoprobe for FR-positive cancer cell imaging using free FA and fluorescent polymer nanoparticle rather than the conventional direct FA-fluorescent conjugated polymer complex. [ABSTRACT FROM AUTHOR]

• Development of a novel red-emitting fluorescent probe (HSA) for the detection of Cys. • The probe can high sensitivity detect Cys with a low LOD. • Successfully verified the experimental results by the theoretical calculation study. • The probe can be used for exogenous Cys monitoring and endogenous Cys cell imaging experiments. Herein, we synthesized a red-emitting fluorescence turn-on probe (HSA) for specific detection of cysteine (Cys) over other biothiols (glutathione (GSH) and homocysteine (Hcy)). The acrylate group was chosen as the recognition site for specific discrimination of Cys. Absorption and emission spectra display a high selectivity towards Cys over GSH/Hcy, organic small-molecule interfering substances and anions, with a high sensitivity towards Cys (0.12 μM) in 1% ethanol-containing PBS buffer solution (25 mM, pH = 7.4). Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were conducted to clarify the luminescence mechanism of the probe. Furthermore, the probe was successfully applied to the determination of free Cys in human serum and the fluorescence imaging of endogenous Cys in living cells. [ABSTRACT FROM AUTHOR]

Highlights • Complex 1 is the first long-lived probe to detect IO 4 − in living cells. • Complex 1 has a detection limit of 0.077 μM for IO4− in aqueous buffer, more sensitive than reported fluorescence probes. • The long lifetime of Complex 1 enables its luminescence response to IO4− to be detected in the presence of organic dyes. Abstract Periodate (IO 4 −) is a widely used reagent in organic synthesis and for biomolecular modification. However, highly sensitive fluorescence detection methods for IO 4 − are lacking. In this work, we designed and synthesized iridium(III) complexes for the detection of IO 4 − by the incorporation of a methylthio group to serve as a luminescence trigger. The results showed that complex 1 could detect IO 4 − in a sensitive and selective manner with a detection limit of 0.077 μM, rendering it more sensitive than reported fluorescence methods. Meanwhile, its inherently long emission lifetime enables its luminescence response to IO 4 − to be detected even in the presence of organic dyes by the use of time-resolved emission spectroscopy (TRES). This probe was further demonstrated to detect IO 4 − in living cells. To our knowledge, complex 1 is first long-lived iridium(III)-based probe for the sensitive detection of IO 4 −, and is also one of few existing imaging probes for IO 4 −. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new N-oxide based and turn on fluorescent probe for Fe2+ was developed. • The probe possessed a high selectivity for Fe2+ among various biologically relevant species and fast rapid response. • Monitoring Fe2+ with TPM fluorescence imaging for the first time. Abstract Iron is an essential element for human body, involved in important biochemical processes in the body, especially in biological oxidation. Misregulation of iron levels in the cell is concerned with serious diseases. Here, a novel two photon and turn on NIR-fluorescent probe based ICT for detection of Fe2+ is first reported. The probe exhibited brilliant selectivity and excellent sensitivity (DL = 4.5 μM), rapid response (15 min) and "naked-eye colorimetric sensor" for monitoring of Fe2+. More importantly, the probe was successfully applied to real-time monitor Fe2+ in living cell through two-photon microscopy fluorescence imaging with excitation 680 nm. [ABSTRACT FROM AUTHOR]

Highlights • The method with photocaged probes for imaging was efficient and spatiotemporal. • The two probes NDPPI and NNDPPI could be applied in cells and human tissues with satisfactory results. • This strategy can be used in other modified reagents for controlling biological function with light. Abstract Two compounds with nitrobenzene-derived caging groups were designed and synthesized for cells and tissues imaging. After 350 nm irradiation, the two reagents can realize highly efficient fluorescence turn on with large Stokes shift. As for the two probes can bare out a common functional group of aldehyde group under UV irradiation, it may be used for detection of cysteine, DNA methylation in a spatiotemporal method with selectivity. The idea of design and synthesis might be used in other modified reagents for controlling biological function with light. [ABSTRACT FROM AUTHOR]