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PEGylated 2-(2-(6-(dimethylamino)benzooxazol-2-yl)vinyl)quinolin-8-ol (BQ-mPEG) was synthesized, which exhibited strong fluorescence at 610 nm (φf = 0.11) and a large Stoke's shift (Δλ = 202 nm) in the aqueous solution. The fluorophore displayed a two-photon absorption characteristic and a strong red emission (λem = 625 nm) was observed with NIR (950 nm) irradiation. The feasibility of using BQ-mPEG as a fluorescent imaging reagent suggested that the fluorophore targets mitochondria, and with 950 nm excitation, bright fluorescence images in HeLa live cells were observed. Furthermore, the fluorophore exhibited some advantages of high photostability and pH stability, as well as low cytotoxicity. [ABSTRACT FROM AUTHOR]

In this paper, nitrogen-doped carbon dots (NCDs) were synthesized via a facile hydrothermal method using gum arabic (GA) and tris(hydroxymethyl)methyl aminomethane (tris) as precursors. The resultant NCDs show uniform size distribution and stable optical performance. Then a fluorescent signal quenching probe based on NCDs was proposed for the quantitative detection of mercury ions (Hg2+). The developed fluorescent nanoprobe based on NCDs demonstrated a good linear relationship in the range of 10 to 120 μM (R² = 0.99265) for toxic mercury(II), with a detection limit of 4.87 μM. Additionally, the present assay system could be efficiently used for the detection of Hg2+ in real water samples with a satisfactory recovery rate (96.11-104.04%). The metal-free NCDs, which exhibited little cytotoxicity, were successfully applied to in vitro fluorescence imaging of human triple negative breast cancer (TNBC) cells, achieving visualization of Hg2+ in cells. With good water solubility and biocompatibility, the nitrogen-doped carbon dots synthesized by this economical and ecologically friendly process are suitable for use in analytical testing and biological research. [ABSTRACT FROM AUTHOR]

Aza-BODIPY biotin-based nano-self-assembly has been designed with a biotin receptor for selective NIR turn-on fluorescence activity against cancer cells. The nanostructured aza-BODIPY assemblies exhibit distinctive fluorescence characteristics via an avidin-induced partial disintegration process. The in vitro studies for nanoprobes NSA-DPR1a and NSA-DPR1b showed effective recognition and can discriminate biotin receptor-positive cancer cells (MDA-MB-231 and MCF7) compared to non-cancerous cells (MCF10A). [ABSTRACT FROM AUTHOR]

Water-soluble [3]pseudorotaxane with enhanced fluorescence emission was successfully constructed and applied in cell imaging and photodynamic cancer therapy. [ABSTRACT FROM AUTHOR]

In vivo selective fluorescence imaging of carboxylesterase 2 (CES2) remains a great challenge because existing fluorescence probes can potentially suffer from interference by other hydrolases. In addition, some fluorescent probes that have been separately reported for measuring CES2 activity in vitro are affected by autofluorescence and absorption of the biological matrix due to their limited emission wavelength or short Stokes shift. Herein, based on the substrate preference and catalytic performance of CES2, a novel and NIR fluorescent probe was developed, in which a hemi-cyanine dye ester derivative was used as the basic fluorescent group. In the presence of CES2, the probe was hydrolyzed to expose the fluorophore CZX-OH (λabs ∼ 675 nm, λem ∼ 850 nm), which led to a notable red-shift in the fluorescence (∼175 nm) spectrum. Confocal imaging of cells and live mice demonstrated that the fluorescent signal of this probe was related to the real activities of CES2 in cancer cells. All these results will powerfully promote the screening of CES2 regulators and the analysis of CES2-related physiological and pathological processes. [ABSTRACT FROM AUTHOR]

The current study shows that Schiff base HL, (Z)-2,4-dibromo-6-(((piperidin-2-ylmethyl)imino)methyl)phenol, can be used successfully as a selective chemosensor for Zn(II) and Ni(II) among several competing cations in purely aqueous and semi-aqueous media. Under UV light in methanol–water (9 : 1) HEPES buffer, the receptor gives its response by changing its color to cyan color in the presence of Zn(II) and to bluish cyan color in the presence of Ni(II). Surprisingly, the chemosensor can only reliably identify Zn(II) in a hundred percent aqueous medium by changing its color to light yellow. UV and fluorescence studies in both aqueous and semi-aqueous media are used to further investigate this Zn(II) and Ni(II) recognition phenomenon. The high values of the host–guest binding constants, obtained by electronic and fluorescence titration, ensure that a strong bond exists between HL and Ni(II)/Zn(II). As anticipated, two highly luminescent mononuclear, crystalline compounds, complexes 1 and 2, have been developed by a separate reaction of HL and Zn(II)/Ni(II), and the high luminous properties are due to the occurrence of Chelation Enhanced Fluorescence (CHEF). According to the single crystal structure, the asymmetric units of both complexes consist of two deprotonated chemosensor units and one Zn(II)/Ni(II), leading to the formation of an octahedral complex. For Ni(II) and Zn(II) sensing, the predicted LOD is in the nanomolar range. Both complexes 1 and 2 are fluorescence active and studies to check their ATP detection ability, but intriguingly, only complex 2 is capable of detecting ATP in a fully aqueous solution. Finally, the live cell imaging study validates the two sensors' biosensing functionality. [ABSTRACT FROM AUTHOR]

In the present study, we synthesized a novel near-infrared turn-on BODIPY probe and a new norbornene-modified glucosamine derivative. The probe exhibits a significant NIR fluorescence emission with a turn-on response and can perform tumour-specific imaging in tumour-bearing mice. The non-natural glucosamine provides metabolic glycoengineering labelling. It can be expressed on cells as chemical tags and further reacted with fluorescence dyes for cell labelling. The combination of the two derivatives enables quick and sensitive cell imaging in vitro and in vivo using the iEDDA reaction. [ABSTRACT FROM AUTHOR]

Selenite (SeO32−), as the most toxic form of selenium in water, is a great threat to water quality and human health, which also has been closely associated with various physiological and pathological processes. The sensitive detection and quantification of SeO32− are imperative for the early diagnosis and prevention of selenite-associated disease. Herein, we constructed novel o-phenylenediamine functionalized carbon quantum dots (OPD-CQDs) by a one-step hydrothermal method. The OPD-CQDs exhibited good water solubility, high quantum yield, strong photostability, excellent biocompatibility and cell imaging capabilities, and also displayed high selectivity and sensitivity to SeO32− with an excellent linear relationship and a low limit of detection (86 nM). Moreover, the OPD-CQDs were successfully employed for the quantitative determination of SeO32− in tap water and human serum with high accuracy and recovery rate. In particular, the designed OPD-CQDs were successfully applied for intracellular SeO32− detection with excellent biocompatibility and cellular imaging capability. The present research demonstrated that OPD-CQDs provided a novel approach for imaging and detecting SeO32− in live cells and in vivo. Based on these excellent properties and comprehensive applications, OPD-CQDs illustrated great potential to offer a scientific and effective method for SeO32− detection in complex environments and clinical early diagnosis of SeO32− related diseases. [ABSTRACT FROM AUTHOR]

Interlinked aggregation induced emissive (AIE) fluorophores (triphenylamine (TPA) donor (D) and indanedione acceptor (A)) via non-conjugated spacers (1–3) showed concentration-dependent tunable fluorescence from blue to deep red/NIR in solution and deep red emission in the solid-state. 1–3 exhibited weak broad solid-state fluorescence covering the blue to deep red region (433 to 706 nm, ΦF = 2.3 to 5.3%). It is noted that the non-interlinked TPA-indanedione fluorophore was non-emissive in solution but showed strong solid-state fluorescence at 611 nm (ΦF = 17.7%). In contrast, 1–3 showed strong fluorescence in the solution state (ΦF = 0.001 to 0.09 compared to fluorescein). Importantly, 1–3 exhibited concentration-dependent tunable fluorescence from blue (457 nm) to deep red/NIR (720 nm) in CHCl3 due to varied aggregation of fluorophores. Dynamic light scattering (DLS) studies confirmed the molecular aggregation even at very low concentrations (10−7 M). The increasing concentration lowered the solubility and produced bigger aggregates with wide size distribution that caused tunable fluorescence. The deep red fluorescence of 1 was utilized for live-cell imaging applications using E. coli cells. Fluorescence microscopic images revealed clear red fluorescent E. coli cells with a rod morphology. Furthermore, the non-toxic nature of 1 was confirmed by in vitro as well as in vivo studies. Thus, deep red/NIR emissive fluorophores were achieved by interlinking two AIEgens using a non-conjugated spacer and utilized for live cell imaging. [ABSTRACT FROM AUTHOR]

Oxidative stress is a hallmark of a range of diseases including cancer, HIV-AIDS and cardiovascular disorders. Blood plasma cysteine (Cys) is an established biomarker for oxidative stress, rendering the development of sensitive and technically straightforward approaches for its estimation extremely desirable. Herein, we achieve this goal by developing a series of Michael addition–elimination–cyclization based turn-on fluorescence (MADELCY TOF) probes that selectively detect Cys over other amino acids and biothiols such as homocysteine (Hcy) and glutathione (GSH). Cysteine detection by these compounds involves cascaded fluorophore release via the Michael addition of the cysteinyl thiol followed by the elimination of a leaving group and lactamization via the cysteinyl amine. Conveniently, the Cys-reactivity of these probes can be tuned via both inductive and mesomeric effects imparted by their β′ position-substituents. One of our probes that contains the p-nitrophenyl group at its β′ position demonstrated rapid kinetics (t1/2 = 2.9 min) with excellent sensitivity (detection limit = 8.2 nM) towards Cys. This probe also enabled the sensitive (detection limit = 9.5 pM) estimation of the blood plasma levels of the cancer and liver cirrhosis biomarker, the aminoacylase-1 (ACY-1) enzyme. Furthermore, another probe of our library enabled live cell imaging of cellular Cys allowing us to develop an imaging-based assay to monitor hydrogen peroxide-induced oxidative stress in mammalian cells. [ABSTRACT FROM AUTHOR]

Hypochlorite plays a vital role in biological systems and our daily life. The rapid and convenient detection of hypochlorite is imperative and significant for disease treatment and human health. In this work, EY/UiO-66-NH2 (EY = eosin Y) was prepared through a hydrothermal process and could be applied to the detection and bioimaging of hypochlorite as a self-calibrating sensing nanoprobe. EY/UiO-66-NH2 features two emissions at 432 nm and 533 nm, and the emission intensity of 533 nm is enhanced with increasing ClO− concentration. EY/UiO-66-NH2 could be utilized as a ratiometric fluorescence sensor of ClO−. The linear range of EY/UiO-66-NH2 towards ClO− is 0.1–200 μM and its detection limit is 46.4 nM. In comparison with previously reported probes for ClO−, EY/UiO-66-NH2 has the advantages of a wide linear range, low detection limit, turn-on fluorescence and ratiometric response. This work provides a new method for ClO− detection in living cells. [ABSTRACT FROM AUTHOR]

Lipid droplets (LDs) have emerged as a hot target for cancer therapeutics in recent years owing to findings that have shown them to be key organelles involved in maintaining cellular stability and regulating inter-organelle communication through molecular trafficking. LDs emerge from the endoplasmic reticulum (ER) as a form of cellular homeostasis control. We herein report the study of a library of asymmetric squaraines as superior fluorescence probes to track and image LDs in their native state and environment within cancer cells. The probes are highly selective towards LDs and displayed prominent bright fluorescence with just 1 μM probe concentration. They also possess bimodal LD and ER staining capability via the simple diffusion of small lipophilic molecules. The probes almost instantly stained LDs, while the ER staining rate is dependent on the probe's lipophilicity and the incubation duration. These "on-demand" organelle-selective probes are highly desirable tools for revealing the role of LDs in governing many cellular processes, especially in malignant cells. [ABSTRACT FROM AUTHOR]

The dysregulation of lipid droplets (LDs) is closely related to certain metabolic diseases, while the role of LDs during pathological processes remains mysterious. It would be of great value to monitor the dynamic changes of LDs in a visible way so as to study their biological functions. In this study, we report a LD-specific fluorescence probe TBI for precise LD-targeting imaging in cells and atherosclerotic tissues. TBI exhibited great biocompatibility, remarkable oil-enhanced fluorescence emission, good photostability and impressive intracellular and tissular LD-specific imaging performance. Importantly, TBI could efficiently stain the LDs at a low concentration of 50 nM, and the motion tracking of LDs could be observed via fluorescence imaging. Moreover, TBI could efficiently light up the LD distribution in mouse atherosclerotic plaques with high resolution, which revealed the ultra-structure of atherosclerotic plaques. In conclusion, these results imply that TBI could be a potential tool for investigating the physiological and pathological role of LDs. [ABSTRACT FROM AUTHOR]

Analysis of single-cell microRNA is essential to reveal cell heterogeneity at the genetic level. It raises a high demand for single-cell analytical methods because single-cell microRNA sequences are highly similar and small in size and feature low-level expression. Herein, SERS and fluorescence imaging technology were introduced into a microfluidic droplet platform to realize direct in situ, nondestructive, and highly sensitive detection of a small number of microRNA-21 (miR-21) in a single intact living cell. A multifunctional plasmonic nanoprobe was designed by decorating a gold nanoparticle with fluorescent dye (ROX)-labeled probe DNA and capture DNA strands. The dual-signal switching of fluorescence turn-off and SERS turn-on of ROX in response to miR-21 achieves highly sensitive and reliable detection of miR-21 in a single cell. The turn-on of SERS signal with a zero background guarantees the sensitivity of the detection. The fluorescence-SERS simultaneous response strategy was able to mutually corroborate the test results, improving the reliability of determining low-level expression of miR-21. SERS combined with encapsulation of microdroplets provides a feasible way to conduct in situ, nondestructive determination of miR-21 secreted by single cells, avoiding cell lysis and tedious time-consuming steps of miR-21 isolation. As a result, the miR-21 expressed by various types of single cells was investigated by fluorescence imaging and the cellular heterogeneity in miR-21 expression was evaluated accurately and quantitatively by SERS. This research would provide important reference information for understanding the effects of miRNAs on cancer diseases at the single-cell level. [ABSTRACT FROM AUTHOR]

As a specific biological marker for the occurrence and progression of tumor cells, detection of telomerase activity is of great importance for the physiological research of tumors. However, in situ measurement of telomerase activity in living cells still remains a challenge. Herein, we report a precisely designed oligonucleotide-functionalized gold nanoparticle probe that has realized high-efficiency detection of telomerase activity for cellular imaging toward the identification of tumors. Our method has achieved intracellular imaging of telomerase activity and shows good performance towards the distinction of tumor cells from normal ones. Moreover, the method reported here for tracking tumor cells in blood has wide applications in cancer diagnosis. This strategy offers an opportunity for cancer diagnosis, guiding therapy and evaluating prognosis. [ABSTRACT FROM AUTHOR]

The accurate and effective imaging of tumor-related miRNA in living cells has been playing an increasingly important role in cancer imaging. However, due to the low miRNA content and complex intracellular microenvironment, the current imaging methods of miRNAs in living cells still have some limitations. In this work, we developed a designer nanoprobe of tetrahedral DNA framework (TDF) combined with MB (termed TDFM nanoprobe) for the efficient fluorescence imaging of tumor-related miRNA-214 in living cells. In cell-free experiments, we demonstrated that the TDFM nanoprobe has sensitive detection and good specificity by fluorescence measurements. Before the TDFM nanoprobe was used for intracellular miRNA-214 fluorescence imaging, we confirmed its intracellular stability and negligible cytotoxicity by a standard MTT assay. In intracellular imaging experiments, we observed the strong fluorescence signal exhibited by the cells incubated with the TDFM nanoprobe using confocal fluorescence microscopy, which indicated that the TDFM nanoprobe was suitable for detecting and imaging tumor-related miRNA-214 in living cells. Furthermore, under the optimal incubation conditions, we employed the TDFM nanoprobe to study differences in the expression levels of tumor-related miRNA-214 in human breast cancer cells (MCF-7) and human umbilical vein endothelial cells (HUVEC). The TDFM nanoprobe we designed shows great potential to be applied in the development of DNA nanodevices, providing an improved strategy for the fluorescence imaging of miRNAs in living cells. [ABSTRACT FROM AUTHOR]

We developed a dual-responsive fluorescent probe MC-V-P for the simultaneous detection of ONOO− and viscosity by different imaging channels. MC-V-P has high sensitivity and selectivity, and shows good stability at different pH levels. Notably, the probe has two independent fluorescence signals toward ONOO− and viscosity changes at 580 nm and 740 nm, respectively. Cell imaging experiment results demonstrated that MC-V-P exhibits low cytotoxicity and could be used to monitor viscosity and ONOO− in living HepG2 cells simultaneously. [ABSTRACT FROM AUTHOR]

A series of naphthalimide – tetrazines were developed as bioorthogonal fluorogenic probes, which could produce significant fluorescence enhancement, notable aggregation-induced emission (AIE) characters and multicolor emissions after bioorthogonal reaction with strained dienophiles. Manipulating the π-bridge in the fluorophore skeleton allows fine-tuning of the emission wavelength and influences the AIE-active properties. With these probes, we succeeded in no-wash fluorogenic protein labeling and mitochondria-selective bioorthogonal imaging in live cells. [ABSTRACT FROM AUTHOR]

A small-sized chromophore, BTTA-2OH, manifesting favorable solubility, large two-photon excitation efficiency, and good fluorescence photostability was synthesized to label the membrane of living cells for visualizing the dynamic movement of membrane-related vesicles via a two-photon fluorescence imaging technique based on wavelength-tunable temporal-focusing multiphoton excitation microscopy. [ABSTRACT FROM AUTHOR]

Mesoporous silica nanocarriers with dual/multifunctionalities are thought to be good candidates for dual/multimodal applications such as combined drug delivery and bioimaging. In this study, new red fluorescent organosilica materials were conveniently produced with diurea-ethidium bromide (DU-EB) functional units integrated in the pore wall framework for simultaneous diagnosis and therapy. We found that the prepared mesoporous silica hybrid nanocarrier system exhibited strong red fluorescence under UV-light (365 nm) while retaining excellent photo- and chemical-stability. The integrated ethidium bromide functional units in the mesopore walls cause the red fluorescence. By loading/releasing doxorubicin (Dox)/5-fluorouracil (5-FU) as a model cargo, the synthesized DU-EB@MSH materials were tested at various pH levels (pH 5.0, 6.2 and 7.4), and the cytocompatibility of the red-fluorescent DU-EB@MSH nanocarrier system was assessed using human breast cancer (MCF-7) cells. The experimental results revealed that the drug release behavior is primarily determined by the pH of the intracellular medium, and red-fluorescence was induced by a UV-light (365 nm) trigger. All the study results suggested that the DU-EB@MSH drug carrier system could be useful for red-fluorescence bioimaging and chemotherapeutic applications in cancer therapy. [ABSTRACT FROM AUTHOR]

In this work, by installing a free-rotating benzene ring to suppress the intermolecular π–π stacking effect in the aggregated state, a naphthalimide-derived hypochlorite (ClO−) fluorescent probe, Probe A, with the aggregation-caused quenching (ACQ) effect was successfully transformed into Probe B possessing typical aggregation-induced emission (AIE) characteristics. The experimental results indicated that Probe B with good selectivity and a low detection limit (LOD) of 0.02 µM can also exhibit a significant ratiometric fluorescence color change from cyan to dark blue within 2 min in a nearly pure water solvent system after the addition of ClO−. Finally, by virtue of the good photophysical properties and ClO− sensing performance, Probe B and the Probe B loaded portable test paper were successfully applied to live cell imaging and the naked eye recognition of ClO−, respectively. [ABSTRACT FROM AUTHOR]

Transferrin-modified AuNCs (Tf-AuNCs) with two photon-near infrared (TP-NIR) fluorescence were prepared. For the first time, a novel nanoprobe platform, Tf-AuNCs@MnO2, was developed for the TP-NIR fluorescence imaging and magnetic resonance imaging of living cells and tissues. This platform had high spatiotemporal resolution and a tissue-penetration depth of 300 μm. [ABSTRACT FROM AUTHOR]

The single signal amplification strategy is significant for detecting various disease biomarkers but is restricted by its limited accuracy. The multi-signal and multi-mode methods have overcome this deficiency. Acid phosphatase (ACP) is an important intracellular enzyme but one-step cell imaging material-based probes are scarce for ACP. Herein, we designed a one-step self-assembled polymer probe using neutral red (NR), modified-(pyridoxal-5′-phosphate (PLP)) and Eu3+. The polymer exhibited non-emission and excellent stability. Upon the catalytic hydrolysis reaction of ACP, the polymer exhibited two strong fluorescence signals at 373 nm and 613 nm and an appreciable decline of absorbance at 395 nm. The probe has excellent selectivity and higher sensitivity with a limit of detection as low as 0.02 mU mL−1. It possesses favorable biocompatibility and has been successfully used to detect and image intracellular ACP in several living cells. [ABSTRACT FROM AUTHOR]

A new fluorescent probe (Q-lipo) was developed by conjugating a xanthene scaffold with a quinoline moiety for activatable imaging of lipophagy. Q-lipo with acidic pH activated near infrared fluorescence and the lipid droplet targeting ability allowed activatable fluorescence imaging and flow cytometry detection of lipophagy in live cells with high contrast. It was further utilized to study the effect of tumor-microenvironment related conditions on lipophagy. Q-lipo would provide a useful tool for studying lipophagy in live cells. [ABSTRACT FROM AUTHOR]

We describe an intracellular enzyme-powered DNA circuit probe with a tunable amplifier for sensitive and selective detection of miRNA. This approach has been successfully applied for in situ miRNA-21 fluorescence imaging in live cells. Also, we used chemicals to elevate the APE1 expression level rendering a tunable amplification strength for more flexible imaging applications. [ABSTRACT FROM AUTHOR]

To selectively detect H2S based on the thiolysis reaction of 7-nitro-1,2,3-benzoxadiazole (NBD), amines attracted increasing attention since NBD amine is regarded as a new H2S reaction site. Herein, a novel fluorescent probe, triphenylamine piperazine NBD (TPA-Pz-NBD), was developed. The results showed that it exhibited high selectivity towards H2S via fluorescence spectroscopy and solution color. Furthermore, TPA-Pz-NBD not only detected H2S by a dual-channel, turn-on fluorescence signal at 500 nm and turn-off fluorescence signal at 545 nm, respectively, but also displayed a wide detection range of 0–125 μM. In addition, living cell imaging results indicated that TPA-Pz-NBD holds potential for the detection of intracellular H2S. [ABSTRACT FROM AUTHOR]

Evident from numerous studies, cysteine plays a crucial role in cellular function. Reactions with analyte also enables for molecular recognition to adhere to molecular therapeutic potential; integration between synthetic probes therefore allows for a potentially deep therapy-related interogation of biological systems (theranostics). The development of molecular cysteine probes with extremely accurate detection is still a key challenge for the field. The development of water-soluble organic molecular fluorescent probes able to efficiently distinguish common biothiols such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) by chemical recognition means i.e. by (binding, cleavage) in biological systems is a greatly sought research challenge due to the similarity of the small sulfhydryl-containing species. Herein, we have developed a water-soluble and highly cell viable fluorescent organic molecule (log P = 0.82) for the selective detection of cysteine. The probe (Myco-Cys) shows a "turn-on" response with the cleavage ester linkage of the methacrylate as cysteine is encountered in solution. The probe shows strong fluorescence enhancement (16.5-fold) when treated with Cys (1 equiv., 10 μM) compared to closely related species such as amino acids, including HCy/GSH, and the limit of detection was determined as 45.0 nM. DFT calculations helped confirm the photomechanism of Myco-Cys. Furthermore, the sensing ability of the probe was demonstrated by living cell assays through the use of confocal fluorescence microscopy. Myco-Cys could selectively detect cysteine among biothiols. Myco-Cys was able to monitor the cysteine level, apart from the oxidative stress present in the form of H2O2 in A549 cells. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) have demonstrated considerable potential for use in sensing and bioimaging applications based on their unique intrinsic properties. However, CDs have typically been used as fluorescence sensors, as opposed to indicators, based on their ultraviolet absorption and discoloration performance. In this study, orange red-emitting CDs with a high quantum yield (QY) of 53% were constructed from 2,3-diaminopyridine via solvothermal synthesis. Different from the fluorescence quenching behavior reported previously, the constructed CDs demonstrated a unique character in their ultraviolet absorption and fluorescence emission in the presence of Fe3+. The color of the CD solution varied from mauve to orange following the addition of Fe3+ at concentrations exceeding 1 μM, which enabled these CDs to be used in the determination of the presence of Fe3+ in lake water. In addition, due to their negligible cytotoxicity, good solubility, and adequate dispersity, an outstanding cellular probe with near-infrared fluorescence was established. Overall, this study presents a unique CD-based sensor, details its fluorescence mechanism, visual colorimetry, and ultraviolet absorption variations, and confirms its applicability in near-infrared cellular imaging and environmental analyses. [ABSTRACT FROM AUTHOR]

To investigate RNA degradation in live cells, detection methods that do not require RNA extraction from cells are necessary. In this study, we examined the utility of fluorescence lifetime measurements using a probe attached to the end of an RNA molecule for detecting RNA degradation. We optimized a short fluorescein-labeled RNA sequence whose fluorescence lifetime varied significantly before and after degradation. The selected HHG-fluorescein sequence (H = U, C, or A) is a promising RNA labeling unit (fluorescence lifetime probe) for live cell imaging of RNA degradation. [ABSTRACT FROM AUTHOR]

An extensive comprehension of biochemical activities occurring in living systems is crucial for prior detection of diseases and characterization of suitable treatments. To understand the pathological/physiological conditions in living cells, pH monitoring is an important tool. To date, the facile synthesis of nanosensors with strong fluorescence coupled with long emission wavelength and good photostability for pH monitoring is still scanty. In this work, new fluorescent silicon nanoparticles (Si NPs) allowing pH sensing were designed. The Si NPs were obtained from the mixture of 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEEA) and 2-aminophenol in one-pot, and under 480 nm excitation, they emitted yellow fluorescence at 560 nm. The Si NPs exhibited excellent salt and temperature tolerance, robust photo stability, and high contrast fluorescence. Furthermore, the prepared Si NPs had been successfully applied to pH measurement in fruit juice samples and fluorescence imaging of gastric parietal cells in tissue sections, providing a new approach for eosinophilic cell staining. [ABSTRACT FROM AUTHOR]

Fluorescence-capable pyrazine-based polycyclic heteroaromatics for application in bioimaging were synthesized via a simple and concise methodology, and investigation on their fluorescence properties, including the effect of pH on the fluorescence behaviour, and MTT assays were carried out. Interestingly, the fluorescence of the substituted phenanthrenes and triphenylene compounds showed emission in the green to red region and had robust emission that did not get dramatically affected in the biologically relevant pH range. The MTT assay of these compounds on HeLa cells (a human cervical carcinoma cell line) revealed that the compound was well tolerated by cells and was cytocompatible. The molecules were internalized and can be easily used for imaging mammalian cells. [ABSTRACT FROM AUTHOR]

β-Lactoglobulin amyloid fibril (BLGF)-capped gold nanoclusters (Au NCs) with red, green and blue emissions were fabricated via pH-dependent reduction strategy. The BLGF-Au NCs exhibited 3.2 times enhancement of fluorescence (λex = 500 nm, λem = 684 nm), a significant 42 nm red shift, a 11.57% quantum yield and a 1.4 μs decay time compared with native β-lactoglobulin (BLG)-stabilized Au NCs. Meanwhile, the multicolor Au NCs were employed for cell imaging via incubation with A549 cells for 14 h. According to the Michaelis–Menten equation, the kinetic parameters of the BLGF-Au NCs showed a lower Km value (66 μmol L−1) for 3,3,5,5-tetramethylbenzidine (TMB) and a higher vmax (3.74 × 10−8 M s−1) for H2O2, which are comparable with other artificial nanoenzymes and natural peroxidases. Based on the highly intrinsic peroxidase-like activity of the BLGF-Au NCs, a colorimetric method was developed for glucose determination with a detection limit of 1.5 μmol L−1 by determining the variation of the absorption at 652 nm, ranging from 5 to 100 μmol L−1. In addition, the glucose assay method also revealed a 101.02 to 104.16% recovery in a real human serum sample. [ABSTRACT FROM AUTHOR]

Carbon-based dot nanoclusters (CDCs) are reported for the first time. The morphologies of the obtained CDCs are characterized using transmission electron microscopy and atomic force microscopy. It is found that the CDCs are composed of dozens of carbon-based dots (CDs), which are connected together through the sp3-hybridized carbon atoms. When compared with free CDs, the obtained CDCs have higher defect densities. As a result, the UV-vis absorption edge of the CDCs is extended to around 700 nm, and the maximum fluorescence wavelength red-shifts to 570 nm. Furthermore, the CDCs show a high singlet oxygen (1O2)-generation capability (quantum yield of about 0.13) under visible light irradiation. The long-wavelength emission and the excellent photostability give the obtained CDCs great application potential in cell imaging, and the wide UV-vis absorption band and high 1O2-generation capability allow the obtained CDCs to work as effective photosensitizers in photodynamic cancer therapy. [ABSTRACT FROM AUTHOR]

Nitro groups with a strong electron-withdrawing effect can powerfully influence the fluorescence of fluorophores. In this work, through adjusting the nitro group at the HBT fluorophore to construct a phenylhydrazone structure, two probes (HBTN and HBTH) were synthesized to detect OCl−. Consequently, HBTN with the nitro group quenched the fluorescence of HBT and HBTH without the nitro group causing a redshift of the fluorescence, which resulted in enhanced and ratiometric fluorescence signal changes during the detection process. Among them, HBTN shows good ability to selectively detect OCl− in the concentration range of 0–14 μM with the detection limit of 2.06 nM. Based on HBTN, a portable test strip for detecting OCl− was made for the convenient quantification of the OCl− concentration with a spectrophotometer, and exogenous and endogenous OCl− was successfully imaged in cells. [ABSTRACT FROM AUTHOR]

Supramolecular systems are formed by the assembly of two or more molecules to achieve different or better functions with respect to those of the individual molecules. Secondary interactions contribute to the geometry and crystal structure of molecules, and it has been found that in supramolecular systems, the H⋯S interaction plays a pivotal role in molecular organization and properties. Moreover, depending on their arrangement, supramolecular assemblies help to recognize selected tri-positive metal ions. Herein, a 4-(1-naphthylvinyl)pyridine (4-nvp)-appended coordination compound, [Zn(4-nvp)2(SCN)2] (1), was synthesized and characterized by X-ray crystal structure determination. The solid-state structure of compound 1 reveals the formation of a 2D supramolecular architecture via C–S⋯H and C–H⋯π interactions. The compound is weakly emissive in CH3CN/H2O (1 : 1, v/v) and shows selective turn-on fluorescence enhancement in response to trivalent metal ions M3+ (M = Fe, Al, and Cr) over mono- and di-valent metal ions. Very low cytotoxicity and large improvement in the fluorescence intensity of the compound 1 upon the accumulation of tri-positive metal ions make the proposed probe suitable for the bio-imaging of M3+ (M = Al, Fe, and Cr) ions in living cells. [ABSTRACT FROM AUTHOR]

A biotinylated metallacage was prepared via metal-coordination-driven self-assembly, combining fluorescence, anti-cancer and targeted properties into a single entity. The metallacage was successfully employed for targeted cell imaging and therapy, offering a platform for cancer theranostics. [ABSTRACT FROM AUTHOR]

A near-infrared ratiometric fluorescent probe CR-Ac based on a coumarin–benzopyrylium platform has been developed for selective detection of Cu2+. The cell imaging data revealed the capabilities of CR-Ac in monitoring the dynamic changes of subcellular Cu2+ and the quantification of Cu2+ levels in living cells. [ABSTRACT FROM AUTHOR]

Here we report a novel strategy to crosslink the surface of sulfonated-carbon dots (S-CDs) by complexing SnCl4 with sulfonate groups (–SO3−) on the CDs in aqueous solution. The S-CDs show an average photoluminescence (PL) quantum yield of 21% and a mean diameter of 3.8 nm. After being complexed with Sn4+, the as-obtained Sn@S-CDs present a reduced size of 1.8 nm and a higher PL quantum yield of 32%. More interestingly, the Sn@S-CDs show an enhanced singlet oxygen (1O2) quantum yield as high as 37% compared to that of the S-CDs (27%). In the HepG2 cell line as a model, the Sn@S-CDs exhibit a remarkable cell imaging effect and in vitro PDT efficiency. Therefore, our study proposes a simple but effective cross-linking strategy to synthesize CDs incorporated with metal ions, for the purpose of achieving an enhanced fluorescence intensity and a higher 1O2 quantum yield. [ABSTRACT FROM AUTHOR]

A new FRET probe has been prepared for ratiometric fluorescence detection of hydroxyl radicals. It has been successfully used for detecting mitochondria-localized drug activation in living cells and imaging endogenous hydroxyl radicals in zebrafish gastrointestinal (GI) tracts under normal culturing conditions. [ABSTRACT FROM AUTHOR]

Nitroreductase (NTR) with a high expression level in tumors has been considered as a biomarker of highly aggressive hypoxia tumors. Thus, it is important to develop powerful tools for tumor hypoxia detection. Here, we developed a two-photon fluorescent probe hTP-NNO2 for NTR detection. The probe with one-step synthesis exhibited high yield. hTP-NNO2 showed high selectivity and sensitivity for NTR and the detection limit was as low as 43 ng mL−1. hTP-NNO2 also showed low cytotoxicity and high stability, indicating that hTP-NNO2 is suitable for NTR detection in real-time and in situ under physiological conditions. hTP-NNO2 was used for NTR imaging in hypoxia cells and the fluorescence intensity of hTP-NNO2 increased with decreasing oxygen concentration. Benefiting from the advantages of two-photon fluorescent probes, we performed NTR detection in deep brain tissue with an imaging depth of up to 100 μm. hTP-NNO2 was further successfully applied for NTR detection in zebrafish and tumors. These results indicated that we developed a promising fluorescence imaging tool for NTR detection in vitro and in vivo. [ABSTRACT FROM AUTHOR]

We developed a new method for the de novo formation of fluorophores based on citrate (DNFC) in biological samples. Use of an amide coupling reagent and microwave irradiation greatly facilitates the fluorophore formation on peptides and proteins with N-terminal cysteine or serine. Since N-terminal cysteine and serine can form thiazolopyridone- or oxazolopyridone-based fluorophores emitting blue and green fluorescence, respectively, by the DNFC staining, each organelle, cell and tissue exhibited a characteristic fluorescence distribution. The DNFC staining is able to provide a new potential protocol for future cell imaging, histology and diagnosis. [ABSTRACT FROM AUTHOR]

A rhodamine based chemosensor, 3-(((2-(3′,6′-bis(ethylamino)-2′,7′-dimethyl-3-oxospiro[isoindoline-1,9′-xanthen]-2-yl)ethyl)imino)methyl)-2-hydroxy-5-methylbenzaldehyde (HL-CHO), has been developed for the detection of Al3+, Cr3+ and Fe3+ ions. The absorbance of HL-CHO at 528 nm increases significantly in HEPES buffer in methanol : water (9 : 1, v/v) (pH 7.4) in the presence of Al3+, Cr3+ and Fe3+ ions with the alteration of solution color from colorless to pink. The fluorescence intensity of the probe at 550 nm enhances by 1465, 588 and 800 fold in the presence of Al3+, Cr3+ and Fe3+ ions, respectively. To the best of our knowledge, this huge increase in fluorescence intensity with Al3+ and Cr3+ has not been observed for other rhodamine based chemosensing systems. The weak fluorescence and no coloration of the probe are due to the existence of a spirolactam ring. The trivalent cations induce the opening of the spirolactam ring and consequently change the color and the fluorescence intensity followed by the 1 : 1 complex formation with HL-CHO which are evident from Job's analysis, ESI mass spectral analysis and elemental analysis. The quantum yield and lifetime of HL-CHO have increased considerably in the presence of the trivalent cations. The high sensitivity of the probe towards all the cations is evident from the nM order of LOD values. This has been used in living cell imaging studies with the human neuroblastoma SH-SY5Y cell line. Having appended –CHO groups for Schiff-base condensation with other amines, HL-CHO could be a potential precursor for future chemosensors. [ABSTRACT FROM AUTHOR]

A novel recyclable ratiometric fluorescent probe based on MOFs was designed and synthesized by a one-step approach, which was realized by assembling Al-MOFs in an aqueous solution containing rhodamine B (RhB) as a fluorescent reagent and Fe3O4 as a magnetically recyclable reagent. The obtained fluorescent probe (Fe3O4/RhB@Al-MOFs) has two emissions under excitation at 330 nm, in which the emission at 440 nm is attributed to the Al-MOFs and the emission at 610 nm presumably originates from the RhB dye. It was noted that the probe displays responses to Mg2+ ions with fluorescence enhancement at 440 nm, whereas the fluorescence at 610 nm would be a constant reference fluorescence signal. The existence of RhB significantly improves the detection accuracy and broadens the linear range. As a result, the selectivity of Fe3O4/RhB@Al-MOFs towards Mg2+ compared to other metal ions is excellent. When the Mg2+ ions (262.5 ppm) are added, the ratio of fluorescence intensity (I440/I610) is changed from 2.47 to 11.5. The Fe3O4/RhB@Al-MOFs show a rapid detection process (90 s), high fluorescence enhancement (up to 5-fold) and a low detection limit of Mg2+ ions (8 × 10−7 M). In particular, the magnetic Fe3O4 endows Fe3O4/RhB@Al-MOFs with a high magnetic responsiveness, thus, facilitating the separation procedures. As expected, it can be easily separated and recycled without a significant loss of recognition performance after being used many times, and thus, exhibits good reusability. Meanwhile, the cell cytotoxicity experiments suggest that Fe3O4/RhB@Al-MOFs is nearly non-toxic and in vitro cell imaging experiments demonstrate that the probe is capable of successfully enhancing fluorescence from the intracellular area in HL-7702 and A375 cellular systems. Hence, it has the potential for the detection of Mg2+ ions inside biosystems. [ABSTRACT FROM AUTHOR]

Synthetic host–guest complexes are inherently dynamic as they employ weak and reversible noncovalent interactions for their recognition processes. We strategically exploited dynamic supramolecular recognition between fluorescently labeled guest molecules to complementary cucurbit[7]uril hosts to obtain stochastic switching between fluorescence ON- and OFF-states, enabling PAINT-based nanoscopic imaging in cells and tissues. [ABSTRACT FROM AUTHOR]

A rational design of a benzoperylene probe BP-3 with positive charge allows for turn-on excimer emission, and wash-free cell membrane imaging. BP-3 possesses excellent chemical, thermal and photo stability. And the Stokes shift of the excimer emission is considerably large (90–100 nm), which very much avoids the background fluorescence interference. [ABSTRACT FROM AUTHOR]

The anticancer mechanism of NO is difficult to study owing to its short lifetime and high reactivity. Thus, a theranostic anticancer NO donor assembled with NO on-demand release abilities, accurate lysosome location capabilities and signal feedback behavior was developed. Profiting from the theranostic properties, the specific mechanism was comprehensively studied. Spectral and cell imaging studies revealed that the as prepared NO donors could release NO in solution or within cancer cells. Fluorescence co-dyeing experiments demonstrated that Mo-Nap-NO entered lysosomes specifically and disrupted them after being triggered by light. Upon irradiation with 460 nm visible light, both the donors demonstrated considerable in vitro anticancer effects. A further mechanistic study showed that after entering the lysosome and being triggered by 460 nm irradiation, NO ruptured the lysosome, resulting in the release of cathepsin D into the cytosol, which activated the caspase3 mediated apoptosis pathway. [ABSTRACT FROM AUTHOR]

Protein C receptor (PROCR) is a recently discovered transmembrane biomarker for several tissue stem cells and is highly expressed in triple-negative breast cancer (TNBC) patient-derived xenografts. Herein, to enrich the toolbox for the biochemical evaluation of PROCR, we have developed a peptide-functionalized fluorogenic 2D material based on the self-assembly between a fluorescent peptide probe and thin-layer molybdenum disulfide. The material developed was suitable for the sensitive detection of PROCR recombinant protein in buffer solution and the fluorescence imaging of TNBC cells that express high levels of PROCR. [ABSTRACT FROM AUTHOR]

A metal-free cascade reaction was developed for the synthesis of indolo[1,2-a]quinoline derivatives from arylsulfonyl hydrazides and 1-(2-(arylethynyl)phenyl)indoles in the presence of TBAI/TBHP. Impressively, these products exhibit excellent fluorescence properties, which is promising for cell imaging. [ABSTRACT FROM AUTHOR]

A one-dimensional homochiral coordination polymer (CP), [ZnCl2(1,3-BPEB)]n, (denoted as polymer 1) with helical structure was synthesized from ZnCl2 and achiral ligand 1,3-bis[2-(4-pyridyl)ethenyl]benzene (1,3-BPEB). X-ray crystallography study reveals that CP 1 crystallizes in the tetragonal system P43212 chiral space group. It exhibits good thermal stability and its skeleton can be maintained even after being heated to 400 °C. The UV-vis spectrum shows that 1 has a maximal absorption onset at 310 nm with a band gap of 3.1 eV, indicating a wide band-gap semiconductor. As expected, the participation of the fluorescent ligand 1,3-BPEB endows 1 with strong fluorescence emission. Nanoparticles with strong red fluorescence based on CP 1 can be applied to the field of biological imaging, achieving a good imaging effect. [ABSTRACT FROM AUTHOR]

A novel Schiff base fluorescence probe (HL) was synthesized by the condensation of salicylaldehyde and an 8-aminoquinoline derivative. This probe acts as a "turn-on" dual selectivity fluorescence probe for Zn2+ and Al3+ ions, providing different colors and detection limits (DL) of 11.5 and 23.5 nM, respectively. Moreover, when Zn2+ and Al3+ co-exist, HL exhibits a preference for Al3+ by displacing Zn2+ from the HL-Zn2+ complex, realizing a dual-channel signal output for Al3+. The HL-Al3+ system could further discern F− by a "turn-off" fluorescence response with a DL of 86.0 nM. Furthermore, the probe HL was capable of monitoring intracellular Al3+, Zn2+ and F− in living PC12 cells in vitro through fluorescence imaging, which proved its value in potential in vivo applications. [ABSTRACT FROM AUTHOR]