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Scanning Electrochemical Microscopy (SECM) has been used as a non-invasive electrochemical technique for studying cellular processes. SECM enables the quantification of cellular metabolites in real-time providing a deeper understanding of cellular responses to external stimuli. SECM imaging of living cells requires maintaining an ideal physiological environment to ensure reliable data collection on cellular reactivity. The cellular response can be directly influenced by physicochemical parameters including cell media composition, temperature and light exposure. This research demonstrates the effect of media composition on the electrochemical current signal of adenocarcinoma cervical cancer (HeLa) cells during SECM measurements using ferrocenemethanol as a redox mediator. Investigated media that are commonly used as electrolyte, are phosphate buffered saline (PBS), and Dulbecco's modified Eagle's medium (DMEM) in the absence and presence of fetal bovine serum (FBS). In addition, this research demonstrates that fluctuating light illumination impacts the stability of the cellular electrochemical current response. Our findings reveal that media composition and illumination are important parameters that must be carefully considered and monitored during SECM live cell imaging. [ABSTRACT FROM AUTHOR]

Fluorescence labeling via fluorescent proteins (FPs) or immunofluorescence has been routinely applied for microscopic imaging of specific proteins. However, due to these over-weight and oversized labels (e.g. GFP, 238 aa, 27 kDa, ∼4 nm in size), the potential physiological malfunctions of the target proteins are largely underestimated in living cells. Herein, for living cells, we report a small and minimally-invasive Raman reporter (about 2 aa and <1 kDa), which can be site-specifically introduced into proteins by genetic codon expansion. After a single unnatural amino acid (UAA) is precisely incorporated into the target protein, the strained alkyne can rapidly undergo copper-free Diels–Alder cycloaddition reactions with the tetrazine-functionalized Raman reporter, which features a fine vibrational spectrum in contrast to fluorescence. In our experimental results, the UAA-based Raman tag was successfully incorporated into vimentin, histone 3.3 and huntingtin (Htt74Q) proteins in living HeLa cells and further utilized for stimulated Raman imaging. The site-specific bioorthogonal fusion of small Raman tags with intracellular proteins will pave the way for minimally-invasive protein labeling and multi-color imaging in living cells. [ABSTRACT FROM AUTHOR]

Sensitive detection of microRNA (miRNA), one of the most promising biomarkers, plays crucial roles in cancer diagnosis. However, the low expression level of miRNA makes it extremely urgent to develop ultrasensitive and highly selective strategies for quantification of miRNA. Herein, a DNA machine is rationally constructed for amplified detection and imaging of low-abundance miRNA in living cells based on the toehold-mediated strand displacement reaction (TMSDR). The isothermal and enzyme-free DNA machine with low background leakage is fabricated by integrating two DNA circuits into a cascade system, in which the output of one circuit serves as the input of the other one. Once the DNA machine is transfected into breast cancer cells, the overexpressed miRNA-203 initiates the first-layer circuit through TMSDR, leading to the concentration variation of fuel strands, which further influences the assembly of hairpin DNA in the second-layer circuit and the occurrence of fluorescence resonance energy transfer (FRET) for fluorescence imaging. Benefiting from the cascade of the two-layer amplification reaction, the proposed DNA machine acquires a detection limit down to 4 fM for quantification of miR-203 and a 10 000-fold improvement in amplification efficiency over the single circuit. Therefore, the two-layer circuit cascade-based DNA machine provides an effective platform for amplified analysis of low-abundance miRNA with high sensitivity, which holds great promise in biomedical and clinical research. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) are extensively used in cellular imaging, single-particle tracking, disease diagnosis, studying membrane protein interaction, and drug delivery. Understanding the dynamics of AuNP uptake in live cells is crucial for optimizing their efficacy and safety. Traditional manual methods for quantifying AuNP uptake are time-consuming and subjective, limiting their scalability and accuracy. The available fluorescence-based techniques are limited to photobleaching and photoblinking. Optical microscopy techniques are limited by diffraction limits. Electron microscopy–based imaging techniques are destructive and unsuitable for live cell imaging. Furthermore, the resulting images may contain hundreds of particles with varied intensities, blurring, and substantial occlusion, making it difficult to manually quantify AuNP uptake. To overcome this issue and measure AuNP uptake by live cells, we annotated a dataset of dark-field images of 50 nanometer–radius AuNPs at different incubation durations. Then, to count the number of particles present in a cell, we created a customized multi-column convolutional neural network (MC-CNN). The customized MC-CNN outperformed typical particle counting architectures when compared to spectroscopy-based counting. This will allow researchers to gain a better understanding of AuNP behavior and interactions with cells, paving the way for advancements in nanomedicine, drug delivery, and biomedical research. The code for this paper is available at the following link: https://github.com/Namerlight/LabelFree_AuNP_Quantification. [ABSTRACT FROM AUTHOR]

Nucleic acids, including DNA and RNA, have been considered as powerful and functional biomaterials owing to their programmable structure, good biocompatibility, and ease of synthesis. However, traditional nucleic acid-based probes have always suffered from inherent limitations, including restricted cell internalization efficiency and structural instability. In recent years, DNA nanotechnology has shown great promise for the applications of bioimaging and drug delivery. The attractive superiorities of DNA nanostructures, such as precise geometries, spatial addressability, and improved biostability, have enabled them to be a novel category of nucleic acid delivery systems for biomedical applications. In this review, we introduce the development of DNA nanotechnology, and highlight recent advances of DNA nanostructure-based delivery systems for cellular imaging and therapeutic applications. Finally, we propose the challenges as well as opportunities for the future development of DNA nanotechnology in biomedical research. [ABSTRACT FROM AUTHOR]

Telomerase as a new valuable biomarker for early diagnosis and prognosis evaluation of cancer has attracted much interest in the field of biosensors, cell imaging, and drug screening. In this review, we mainly focus on different optical techniques and various signal amplification strategies for telomerase activity determination. Fluorometric, colorimetry, chemiluminescence, surface-enhanced Raman scattering (SERS), and dual-mode techniques for telomerase sensing and imaging are summarized. Signal amplification strategies include two categories: one is nucleic acid-based amplification, such as rolling circle amplification (RCA), the hybridization chain reaction (HCR), and catalytic hairpin assembly (CHA); the other is nanomaterial-assisted amplification, including metal nanoclusters, quantum dots, transition metal compounds, graphene oxide, and DNA nanomaterials. Challenges and prospects are also discussed to provide new insights for future development of multifunctional strategies and techniques for in situ and in vivo analysis of biomarkers for accurate cancer diagnosis. [ABSTRACT FROM AUTHOR]

Raman imaging (RI) is an outstanding technique that enables molecular-level medical diagnostics and therapy assessment by providing characteristic fingerprint and morphological information about molecules. However, obtaining high-quality Raman images generally requires a long acquisition time, up to hours, which is prohibitive for RI applications of timely cytopathology and histopathology analyses. To address this issue, image super-resolution (SR) based on deep learning, including convolutional neural networks and transformers, has been widely recognized as an effective solution to reduce the time required for achieving high-quality RI. In this study, a locality enhanced transformer network (LETNet) is proposed to perform Raman image SR. Specifically, the general architecture of the transformer is adopted with the replacement of self-attention by convolution to generate high-fidelity and detailed SR images. Additionally, the convolution in the LETNet is further optimized by utilizing depth-wise convolution to improve the computational efficiency of the model. Experiments on hyperspectral Raman images of breast cancer cells and Raman images of a few channels of brain tumor tissues demonstrate that the LETNet achieves superior 2×, 4×, and 8× SR with fewer parameters compared with other SR methods. Consequently, high-quality Raman images can be obtained with a significant reduction in time, ranging from 4 to 64 times. Overall, the proposed method provides a novel, efficient, and reliable solution to expedite high-quality RI and promote its application in real-time diagnosis and therapy. [ABSTRACT FROM AUTHOR]

Excessive production of potent biological oxidants such as HOCl has been implicated in numerous diseases. Thus, it is crucial to develop highly specific and precise methods to detect HOCl in living systems, preferably with molecules that can show a distinct therapeutic effect. Our study introduces the synthesis and application of a highly sensitive fluorescence "turn-on" probe, Myco-OCl, based on the mycophenolic acid scaffold with exceptional water solubility. The ESIPT-driven mechanism enables Myco-OCl to specifically and rapidly detect (<5 s) HOCl with an impressive Stokes shift of 105 nm (λex = 417 nm, λem = 522 nm) and a sub-nanomolar (97.3 nM) detection limit with the detection range of 0 to 50 μM. The potential of Myco-OCl as an excellent biosensor is evident from its successful application for live cell imaging of exogenous and endogenous HOCl. In addition, Myco-OCl enabled us to detect HOCl in a zebrafish inflammatory animal model. These underscore the great potential of Myco-OCl for detecting HOCl in diverse physiological systems. Our findings thus offer a highly promising tool for detecting HOCl in living organisms. [ABSTRACT FROM AUTHOR]

The discovery and implementation of media that derive from bioinspired designs and bear optical readouts featuring large Stokes shifts are of continued interest to a wide variety of researchers and clinicians. Myco-F, a novel mycophenolic acid precursor–based probe features a cleavable tert-butyldimethylsiloxy group to allow for fluoride detection. Myco-F exhibits high selectivity and specificity towards F− (Stokes shift = 120 nm). All measurements were performed in complete aqueous media (LOD=0.38 μM). Myco-F enables detection of fluoride ions in living HEK293 cells and localizes in the eye region (among other regions) of the zebrafish. DFT calculations support the proposed ESIPT working photomechanism. [ABSTRACT FROM AUTHOR]

Bimodal imaging probes that combine magnetic resonance imaging (MRI) and photoluminescence imaging are quite appealing since they can supply both anatomical and molecular information to effectively ameliorate the accuracy of detection. In this study, an activatable nanoprobe, [Eu(BTD)3(DPBT)]@MnO2, for bimodal time-gated luminescence imaging (TGLI) and MRI has been constructed by anchoring visible-light-excitable Eu3+ complexes on lamellar MnO2 nanosheets. Due to the luminescence quenching effect and non-magnetic resonance (MR) activity of MnO2 nanosheets, the developed nanoprobe presents quite weak TGL and MR signals. After exposure to H2O2 or GSH, accompanied by the transformation from MnO2 to Mn2+, the nanoprobe exhibits rapid, sensitive, and selective "turn-on" responses towards GSH and H2O2 in TGL and MR detection modes. Furthermore, the nanoprobe displays high stability, low cytotoxicity, good biocompatibility and water dispersion. Given the high contents of GSH and H2O2 in cancer cells, the nanoprobe was used for the identification of cancer cells by TGLI of intracellular GSH and H2O2, as well as for the tracing of tumor cells in tumor-bearing mice by tumor-targeting in vivo MRI and TGLI of tumor tissues. The research outcomes proved the potential of [Eu(BTD)3(DPBT)]@MnO2 as a useful nanoprobe for the tracing and accurate detection of cancer cells in vitro and in vivo via bimodal TGLI and MRI. [ABSTRACT FROM AUTHOR]

β-Carotene is a natural antioxidant that has an indispensable effect on the growth and immunity of the human body. For intracellular and in vitro detection of β-carotene, N-doped carbon quantum dots (O-CDs) were prepared by co-heating carbonization of 1,5-naphthalenediamine and nitric acid in ethanol solvent for 2 h at 200 °C. O-CDs have longer wavelength orange light emission, with an optimal excitation peak of 470 nm and an optimal emission peak of 590 nm. According to the principle of the internal filtering effect on which the detection system is based, O-CDs present a good linear relationship with β-carotene within a wide range of 0–2000 μM, and the R2 coefficient of the linear regression equation is 0.999. In addition, O-CDs showed targeting of lysosomes in cell imaging and could be used to detect intracellular lysosomal movement. These experiments show that O-CDs can be used for in vivo and in vitro detection of β-carotene and can serve as a potential substitute to commercial lysosome targeting probes. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) with red fluorescence emission are highly desirable for use in bioimaging and trace- substance detection, with potential applications in biotherapy, photothermal therapy, and tumor visualization. Most CDs emit green or blue fluorescence, thus limiting their applicability. We report a novel fluorescent detection platform based on high-brightness red fluorescence emission carbon dots (R-CDs) co-doped with nitrogen and bromine, which exhibit pH and oxidized L -glutathione (GSSG) dual-responsive characteristics. The absolute quantum yield of the R-CDs was as high as 11.93%. We discovered that the R-CDs were able to detect acidic pH in live cells and zebrafish owing to protonation and deprotonation. In addition, GSSG was detected in vitro over a broad linear range (8–200 μM) using the R-CDs with excitation-independent emission. Furthermore, cell imaging and bioimaging experiments demonstrated that the R-CDs were highly cytocompatible and could be used as fluorescent probes to target lysosomes and nucleolus. These studies highlight the promising prospects of R-CDs as biosensing tools for bioimaging and trace-substance detection applications. [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 contrast to well-established DNA-selective dyes for live cell imaging, RNA-selective dyes have been less developed owing to the challenges of making small molecules have RNA selectivity over DNA. Two kinds of dyes are now commercially available for nucleolar RNA imaging in cells, but these two dyes do not apply to living cells and have limited use in fixed and permeabilized cells. Herein, we report on thiazole orange (TO), a well-known nucleic acid stain, as a promising fluorogenic dye for nucleolar RNA imaging in living cells. TO shows clear response selectivity for RNA over DNA with a significant light-up property upon binding to RNA (λem = 532 nm, I/I0 = 580-fold, and Φbound/Φfree = 380) and is even applicable to wash-free imaging of living cells. More interestingly, 2TO, a regioisomer of TO in which the benzothiazole unit is connected to position 2 in the quinoline ring, performs much better (λem = 532 nm, I/I0 = 430-fold, Φbound/Φfree = 1200), having superior selectivity for RNA in both solution and living cells. The comparison with TO derivatives carrying different substituents at N1 of the quinoline ring reveals that the slight change in the TO framework significantly affects RNA selectivity, photostability and membrane permeability. [ABSTRACT FROM AUTHOR]

The combination of single-cell Raman microspectroscopy (SCRM) and stable isotope probing (SIP) enables in situ tracking of carbon or hydrogen fluxes into microorganisms at the single-cell level. Therefore, it has high potential for the analysis of metabolic processes and biogeochemical cycles. However, especially for high throughput applications such as imaging or cell sorting, it is hampered by low Raman scattering intensities (and therefore long acquisition times). In order to overcome these limitations, this study brings forward a systematic investigation of Resonance Raman (RR) enhanced SCRM for SIP of bacterial carotenoids. Dynamic carbon uptake from 13C-glucose was successfully monitored and quantified utilizing 13C stable isotope-induced red-shifts of RR signals. High single-cell phenotypic heterogeneity was revealed in terms of carbon uptake and, unlike in previous studies, clear evidence for de novo synthesis of carotenoids was found. For the first time, hydrogen uptake into carotenoids was systematically investigated by deuterium labeling (providing a direct probe for metabolic activity of single cells). In carotenoid single-cell Resonance Raman (SCRR) spectra, a unique pattern of signal red-shifts and apparent blue-shifts was observed and quantitatively evaluated. Finally, a novel combined approach for simultaneous monitoring of carbon and hydrogen uptake revealed complementary effects in carotenoid SCRR spectra that can be analyzed in parallel. Overall, it was shown that the high RR intensity, simplicity of spectral features and straightforward signal processing make microbial carotenoids an ideal target for quantitative multi-element SIP, with great potential for high throughput applications. [ABSTRACT FROM AUTHOR]

Foam cell formation and further accumulation in the subendothelial space of the vascular wall is a hallmark of early atherosclerosis (AS). Targeting foam cell formation can be a promising approach for the early detection and prevention of AS. However, only a few studies have actually examined foam cells in vivo, and most methods combined nanotechnology with angiography, which is complex and could cause further damage to the endothelium. Herein, based on methylene blue, a biosafe NIR dye approved by the FDA, an interventional probe (HMB-NA@Mp) triggered by hypochlorous acid (HClO) was designed for imaging foam cells easily, safely, and effectively in the early stage of AS. Here, encapsulation of the probe by foam cells targeted platelet membrane (Mp) increased probe targeting and reduced toxicity. Cell and animal experimental results showed that the probe could accumulate at the lesion site and significantly enhance fluorescence in the early AS model group. Remarkably, at the same time, it could also release the metabolite niacin, which played a role in inhibiting atherosclerosis. Thus, HMB-NA@Mp is expected to be a powerful means for the early detection and timely intervention of early AS in the absence of clinical symptoms. [ABSTRACT FROM AUTHOR]

We successfully constructed a new class of nanoflares based on ultra-thin silica-coated gold nanoparticles (Au@SiO2) with the covalent binding of nucleic acids, which demonstrated more resistance to biothiols than that exhibited in the traditional Au–S binding strategy, for imaging the target miRNA-21 with high fidelity in living cells. [ABSTRACT FROM AUTHOR]

NAD(P)H quinone oxidoreductase1 (NQO1) is a flavoenzyme that regulates the redox potential level in cells. Overexpression of NQO1 has been proven to be relevant to some malignant tumors. Herein a bioluminescent probe NQO1-Luc equipped with an NQO1-targeting group, trimethyl-locked quinone propionic acid (QPA), was constructed. The reduction of NQO1-Luc could be triggered by NQO1, resulting in the release of free D -luciferin, and concomitantly a bright bioluminescence emission. NQO1-Luc exhibits high selectivity and sensitivity toward NQO1 activity and the capability of distinguishing NQO1-overexpressing cells in vitro and in vivo, which offers a promising tool for investigations of NQO1 related biological processes including tumors in living organisms. [ABSTRACT FROM AUTHOR]

Polarity and viscosity, as important microenvironment parameters, play an essential role in cell metabolism. Therefore, 9-acridine carboxaldehyde reacted with cyano compounds to obtain polarity-sensitive probes 1a–b and viscosity-sensitive probes 1c–d. Among them, with the increase in solvent polarity, the maximum emission wavelength of acridine-dicyanoisophorone-based probe 1a red-shifted from 553 nm to 594 nm, the fluorescence quantum yield increased from 0.5% to 35.6%, and the fluorescence intensity enhanced 38 fold. The acridine-cyanofuranone based probe 1b also has a polarity response similar to 1a. Nevertheless, when the solution viscosity increased from 0.89 cP (100% water) to 856 cP (1% water), the fluorescence intensity of the acridine-tricyanodihydrofuran based probe 1c at 430 nm enhanced 5.6 times. The acridine-cyanobenzothiazole based probe 1d also had a viscosity response similar to 1c. In addition, probes 1a–b were used for further HeLa cell imaging experiments due to their good photostability and the results suggested that probe 1a could locate lipid droplets and probes 1b–c could stain lysosomes. Moreover, probes 1a–b could dynamically monitor the changes in intracellular polarity. [ABSTRACT FROM AUTHOR]

Biomass materials have abundant natural resources, renewability and good biochemical compatibility, so biomass-based fluorescent materials prepared from biomass materials have gradually become a research hotspot. In particular, the low cost and environmentally friendly properties of chitosan have been widely used in the field of functional materials. Chitosan-based functional materials have attracted extensive attention in the detection and removal of organic and inorganic pollutants. They have been widely used in biological imaging, environmental detection, drug carriers and other fields. This paper reviews the preparation and application of chitosan-based fluorescent probes, including chitosan-derived fluorescent probe materials and chitosan-based carbon quantum dots. At the same time, it focuses on the application research of chitosan-based carbon quantum dots in the fields of environmental detection, cell imaging, drug carriers, photocatalysis, etc. In addition, it provides new ideas and application prospects for the development and application of chitosan-based fluorescent materials in the future. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) plays a vital role in regulating many important physiological functions. However, H2S-containing industrial wastewater is inevitably pumped into the environment which seriously contaminates water supplies and foodstuffs. So it is crucial to develop a single fluorescent probe for H2S detection with high sensitivity and selectivity. Herein, a colorimetric and turn-on near infrared (NIR) fluorescent probe NRDNP based on benzophenoxazine was designed and synthesized by thiolysis of 2,4-dinitrophenyl (DNP) ether as the specific reaction site strategy to achieve highly specific H2S detection in living systems. The studies demonstrated that the probe NRDNP exhibited excellent sensing performance toward H2S with an about 80-fold NIR fluorescence enhancement, a rapid response within 10 min, excellent sensitivity with a detection limit of 19 nM and good selectivity. Furthermore, the NRDNP is an optical sensor which visually changes in terms of the fluorescence colour/intensity upon sensing gaseous H2S molecules. NRDNP has low cytotoxicity and has been successfully applied in the fluorescence imaging of H2S in living cells, suggesting that it would be an effective tool for H2S detection in living systems. [ABSTRACT FROM AUTHOR]

Adenosine triphosphate (ATP) is a direct energy source in cells and the core of the biochemical system, and is closely related to various metabolic activities in living organisms. Therefore, designing a simple and rapid ATP detection method is significant to study its physiological function. Herein, a dual-channel fluorescent probe RhB-NA for the in situ imaging of ATP in living cells was designed and synthesized. When ATP bound to RhB-NA , the spirolactam in rhodamine B was induced to open, resulting in a new fluorescence response at 589 nm. Notably, in cell imaging, the treatment of HeLa cells with exogenous H2O2 and H2S, which have certain effects on the mitochondria, confirmed that RhB-NA could detect fluctuations in ATP levels after the mitochondrial state was affected. We believe that RhB-NA has far-reaching significance for studying certain physiological diseases caused by abnormal ATP levels. [ABSTRACT FROM AUTHOR]

The change in lysosomal pH is an important physiological indicator in the process of cell autophagy. Herein, a ratiometric fluorescent probe, 4-(2-(1H-benzo[d]imidazol-2-yl)vinyl)-N,N-dimethylaniline (BD), has been synthesized and applied for lysosomal pH detection and cell autophagy imaging. In this probe, the imidazole group and dimethylamino group possess excellent lysosomal targeting ability and the benzimidazole moiety acts as a proton reaction site. BD reveals an obvious ratiometric fluorescence emission with an ideal pKa value of 4.73 and a linear response in the range of 4.06–5.20, which is considered useful for the quantitative detection and imaging of lysosomal pH change. Meanwhile, BD exhibits a larger Stokes shift, good selectivity, strong photostability, good reversibility and good biocompatibility, which makes BD capable of being applied to complex biological environments. Ratiometric fluorescence imaging studies show that BD can selectively monitor the pH in the lysosomes of live cells, and even real-time dynamic monitoring of cell autophagy can be conducted. Moreover, BD also shows excellent application potential in the field of anticounterfeiting. [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]

As a precursor of all reactive oxygen species (ROS), superoxide anions play an important role in organisms. However, excessive superoxide anions can cause various diseases. Thus, it is highly urgent to develop efficient tools for in situ superoxide anion detection. In this work, a novel boric acid-based, mitochondria-targeted fluorescent probe Mito-YX for superoxide anion detection was designed by regulating its intramolecular charge transfer (ICT) effect. The probe exhibited turn-on fluorescence enhancement within 4 min of reaction with the superoxide anion. In addition, Mito-YX also exhibited high selectivity and a low detection limit down to 0.24 μM with good mitochondrial targeting characteristics, which provided a necessary basis for in vivo detection of superoxide anions. What is more, Mito-YX was successfully applied for the in situ monitoring of superoxide anions in living MCF-7 cells, RAW 264.7 cells and a mouse model of lung inflammation stimulated by LPS. This work provided an important and promising tool for rapid in situ diagnosis and research of the progression of pneumonia. [ABSTRACT FROM AUTHOR]

Fluorescence imaging in the near-infrared (NIR) window has great potential for clinical diagnosis and treatment because of its deep penetration and high contrast. Here, a NIR hemicyanine-based probe (CyP) was synthesized for selective detection and imaging of Hg2+ in living cells and animals. Using the rigid xanthene structure as the electron donor, trimethylindolenine as the electron acceptor and diphenylphosphinothioic chloride as the recognition element, the probe CyP could specifically respond to Hg2+ and transform into an activated donor–π-acceptor (D–π-A) motif with a NIR emission maximum at 710 nm. Cell and animal imaging experiments showed that the probe CyP could be activated by Hg2+ and had good concentration dependence in imaging. Meanwhile, animal imaging experiments showed that the activated CyP probe exhibited a higher tissue penetration depth and spatiotemporal resolution. Thus, the probe CyP could be a useful tool for monitoring and visually evaluating Hg2+ in living systems. [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]

A coumarin coupled tetraphenylethylene based AIEgen (TPE-Lac) with an intense greenish-yellow emission has been synthesized and utilized for multipurpose sensing and imaging applications. TPE-Lac acts as a sensitive sensor for the detection of cyanide ions (CN−) with an immediate turn-off response in the presence of many other interfering cations and anions. The limit of detection (LOD) was as low as 33 nM, which is well below the permissible limit set by the World Health Organization (WHO). Cyanide detection in the solid phase was successfully demonstrated by drop-casting the solution of the TPE-Lac probe on TLC plates and measuring and analysing the fluorescence response by ImageJ analysis. TPE-Lac was further employed in the detection of explosive nitroaromatics in solution and solid phases. Also, TPE-Lac was found suitable as an imaging agent and could easily percolate into live H520 cells giving bright fluorescence from the intra-cellular region. Easy and cost-effective synthesis, fast response and low LODs are some of the advantages of this AIEgen over available molecular probes for the same purpose. [ABSTRACT FROM AUTHOR]

As a common gaseous signaling molecule, hydrogen sulfide (H2S) plays a vital role in physiology and pathology. The development of fluorescent probes for detecting H2S has attracted widespread attention. However, most of the reported fluorescent probes with nitrobenzoxadiazole (NBD) as the recognition group have been widely used to simultaneously detect biothiols and H2S, instead of specifically detecting H2S. Herein, a novel NBD-based near-infrared (NIR) fluorescent probe named CX-N for the detection of H2S is synthesized. The selectivity of CX-N for H2S is significantly higher than that for biothiols and other potential interferences. After reacting with H2S, CX-N shows a significant increase in NIR fluorescence (75-fold), large Stokes shift (155 nm) and fast response (4 min). And the possible response mechanism of CX-N to H2S is given and confirmed by HPLC and HRMS. Based on the low cytotoxicity of CX-N, it has been used for H2S imaging in live cells and zebrafish. More importantly, CX-N has also been successfully applied for the real-time imaging of H2S in inflammatory and tumor mice based on its NIR emission, which provides a reliable platform for the specific recognition of H2S in complex biological systems. [ABSTRACT FROM AUTHOR]

In this work, a single particle imaging method based on the total internal reflection (TIR) imaging platform for the sensing and cell imaging of nitrite (NO2−) in the near-infrared region using cyanine dye-assembled composite upconversion nanoparticles (UCNPs) was developed. The NaYF4:Yb,Tm@NaGdF4 UCNPs were synthesized as energy donors, and the cyanine dye IR-798 was prepared as an energy acceptor. Since the absorption spectrum of the cyanine dye IR-798 and the luminescence spectrum of upconversion nanoparticles overlapped effectively, IR-798 quenched the luminescence of the UCNPs. When NO2− was added to the cyanine dye-assembled composite upconversion nanoparticle system, NO2− destroyed the conjugate structure of IR-798, so that the luminous intensity of UCNPs could be restored. Based on the mechanism, a quantitative image analysis with high sensitivity, low sample usage, and fast response time using the TIR single particle imaging platform was developed to determine the content of nitrite in human serum samples. In addition, the UCNPs-IR-798 probe was applied to image the exogenous NO2− content in HeLa living cells based on the single particle imaging platform. [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]

Cellular imaging using carbon dots is an important research method in several fields. Herein, green-emissive carbon quantum dots (G-CDs) with a pretty high absolute quantum yield (QY) were fabricated via a one-step solvothermal method by using m-phenylenediamine and concentrated hydrochloric acid. G-CDs displayed strong green fluorescence with excitation/emission peaks at 460/500 nm, and their absolute quantum yield was as high as 58.65%. Further experiments suggested that the G-CDs we prepared have good solubility, excellent biocompatibility, and the capacity of rapidly imaging HeLa and 4T1 cells. Over expectations, the G-CDs could penetrate cells in only 10 s and the confocal images showed that the G-CDs could target the nucleus of cells. Moreover, by using 920 nm as the excitation wavelength, two-photon imaging has been successfully applied to 4T1 cells, overcoming the inherent limitations of single-photon imaging. The extremely high absolute quantum efficiency, ultra-fast imaging speed, and two-photon imaging capability make the G-CDs have good application potential in biomedical analysis and the clinical diagnostic field. [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]

DNA self-assembling nanoprobes with self-transferability and resistance to nuclease degradation have been developed and applied to live cell bio-imaging. In this work, we constructed a hairpin-functionalized DNA tetrahedron (HFDT) intramolecular catalytic self-assembly platform to detect low-abundance miRNAs by a catalyzed hairpin assembly (CHA). The designed HFDT enhances the CHA reaction efficiency and aggregates into dendrimer structures in the presence of miRNAs. This innovative "small to large" strategy can effectively change the distribution and properties of biomaterials in the organism, thus effectively retaining them inside the tumor and reducing the efflux of nanomaterials, increasing their accumulation in the tumor site and protecting them from the complex physiological environment, which has promising applications in tumor imaging. [ABSTRACT FROM AUTHOR]

Visualization of signaling molecules in single living cells is crucial for understanding cellular metabolism and physiology, which can provide valuable insights into early diagnoses and treatments of diseases. Highly sensitive in situ monitoring of intracellular analytes released from single living cells by virtue of label-free nanosensors is urgently needed, which can avoid interferences from molecular labeling. Here, we proposed an ultrasensitive strategy for in situ imaging of intracellular H2O2 in single living cancer cells by surface-enhanced Raman scattering (SERS) spectroscopy with the utilization of label-free Fe3O4@Ag core–satellite nanoparticles (NPs). The Fe3O4@Ag NPs can efficiently and selectively catalyze the oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. Additionally, they exhibit excellent SERS activity that allows for in situ monitoring of intracellular H2O2 in living cells through establishing the correlation between the H2O2 level and the SERS intensity of the catalytic oxidation product of TMB. The H2O2 concentration is revealed through the SERS intensity of oxidized TMB with a good linear response in a wide range from 1 fM to 1 mM. Moreover, the intracellular H2O2 level in live cancer cells and imaging of the distribution of H2O2 inside single cells can be achieved by using such a label-free nanosensor based strategy. Our work demonstrates that the label-free Fe3O4@Ag NP-based SERS imaging and quantification strategy is a promising and powerful approach to assess intracellular H2O2 in living cells and allows us to monitor single-cell signaling molecules with nanoscale resolution. [ABSTRACT FROM AUTHOR]

Highly efficient monitoring of microRNA is of great significance for cancer research. By attaching aptamers to DNA nanowires through base pairing, here we designed a multivalent self-assembled DNA nanowire for fast quantification of intracellular target miRNAs in special cancer cells. In this work, an aptamer AS1411 and a microRNA-21 anti-sequence labeled with Cy5 were fixed on DNA nanowires, and then a short DNA strand with black hole quencher 2 (BHQ2) hybridizes with the microRNA-21 anti-sequence to quench Cy5. With the aid of AS1411, the probe can recognize and enter the target special cells efficiently. In addition, because of the banding between microRNA-21 and microRNA-21 anti-sequence, short DNA strands with BHQ2 are detached from the DNA nanowire and result in the recovery of Cy5 fluorescence signals. Ultimately, the fluorescence of Cy5 was activated quickly due to the high local concentration of recognition units on the nanowire, resulting in a large number of activated Cy5 dyes in a short time just like DNA nano string lights. Experimental results revealed that the designed DNA nanowire probe shows great performance for specifically and quickly monitoring microRNA-21 in living cells and in vivo. This developed strategy may become a general platform for detecting targets in living cells and possess great potential for biological and diagnostic research. [ABSTRACT FROM AUTHOR]

Double-stranded (ds) biosensors are homogeneous oligonucleotide probes for detection of nucleic acid sequences in biochemical assays and live cell imaging. Locked nucleic acid (LNA) modification can be incorporated in the biosensors to enhance the binding affinity, specificity, and resistance to nuclease degradation. However, LNA monomers in the quencher sequence can also prevent the target-fluorophore probe binding, which reduces the signal of the dsLNA biosensor. This study investigates the influence of LNA modification on dsLNA biosensors by altering the position and amount of LNA monomers present in the quencher sequence. We characterize the fluorophore–quencher interaction, target detection, and specificity of the biosensor in free solution and evaluate the performance of the dsLNA biosensor in 2D monolayers and 3D spheroids. The data indicate that a large amount of LNA monomers in the quencher sequence can enhance the specificity of the biosensor, but prevents effective target binding. Together, our results provide guidelines for improving the performance of dsLNA biosensors in nucleic acid detection and gene expression analysis in live cells. [ABSTRACT FROM AUTHOR]

Imaging biomolecules within a single bacterial cell is crucial for understanding cellular genetic mechanisms. Herein, we exploited a surface-enhanced Raman spectroscopy (SERS) imaging strategy for single cell analysis. Cellular biosynthesized Ag nanoparticles (NPs) provided the necessary enhancement for SERS imaging. Multiple complementary techniques, including high-resolution transmission electron microscopy (HR-TEM), high-angle annular dark-field (HAADF)-scanning transmission electron microscopy (STEM), and energy-dispersive X-ray spectroscopy (EDX), were used to characterize the biogenic Ag NPs in cells. Three-dimensional SERS imaging maps displayed spectral information of biomolecules within the single cell. The multivariate curve resolution (MCR) model and principal component analysis (PCA) model were used to analyze the cellular SERS imaging maps. The MCR model, with a specific constraint of non-negativity, resulted in meaningful identification of biomolecules associated with Ag reduction. Focusing on the molecular level reveals that Pantoea sp. IMH utilizes several mechanisms to synthesize Ag NPs, including cytoplasm reduction by glucose or nicotinamide adenine dinucleotide (NADH)-dependent reductase, and extracellular reduction by an electron transfer chain containing quinone and cytochrome C. Our results shed new light on the Ag NP biosynthesis mechanism and single cell Raman analysis. [ABSTRACT FROM AUTHOR]

Ferric(III) ions (Fe3+) are one of the most abundant metal ions in environmental and biological systems. The determination of Fe3+ has attracted great attention for healthcare concerns. In this work, we have developed a novel fluorescence method for the sensing and intracellular imaging of Fe3+ based on the prepared red-emissive carbon nanodots. The nanoprobes are synthesized via a microwave method using ammonium fluoride and o-phenylenediamine as carbon precursors, which exhibit excellent optical properties and low toxicity. More importantly, the carbon nanodots show high selectivity towards Fe3+ against other interfering ions. The sensitivity is also high with the limit of detection as low as 0.05 μM. Meanwhile, the carbon nanodots have been successfully used for fluorescence imaging of cells and could be quenched by intracellular Fe3+. These results suggest that the red-emissive carbon nanodots have diverse potential utilities in biomedical fields. [ABSTRACT FROM AUTHOR]

Hypochlorous acid (HClO) is an important bactericide, and adjusting the content of HClO helps to improve the host's innate immunity and resist microbial invasion. Aggregation-induced luminescence (AIE) is the opposite of aggregation-induced quenching (ACQ). Compounds with AIE properties emit weakly in a dispersed state in solution and they can emit strong fluorescence in an aggregated state. In this article, we proposed a new AIE fluorescent probe QM-ClO based on the quinoline-malononitrile (QM) fluorophore and dimethylthiocarbamate (DMTC) to detect HClO. The probe QM-ClO showed a fast response time, a low detection limit of 30.8 nM and a large Stokes shift (190 nm). Carbonyl cyanide metachlorophenyl-hydrazone (CCCP) was used to induce cell apoptosis, and then an increase in the HClO content was observed in the cell. It is proved that cell apoptosis can lead to the increase of the HClO content in the cell. This probe provides an effective tool for studying apoptosis-related diseases. [ABSTRACT FROM AUTHOR]

Since it was first proposed in 2007, inertial microfluidics has been extensively studied in terms of theory, design, fabrication, and application. In recent years, with the rapid development of microfabrication technologies, a variety of channel structures that can focus, concentrate, separate, and capture bioparticles or fluids have been designed and manufactured to extend the range of potential biomedical applications of inertial microfluidics. Due to the advantages of high throughput, simplicity, and low device cost, inertial microfluidics is a promising candidate for rapid sample processing, especially for large-volume samples with low-abundance targets. As an approach to cellular sample pretreatment, inertial microfluidics has been widely employed to ensure downstream cell analysis and detection. In this review, a comprehensive summary of the application of inertial microfluidics for high-throughput cell analysis and detection is presented. According to application areas, the recent advances can be sorted into label-free cell mechanical phenotyping, sheathless flow cytometric counting, electrical impedance cytometer, high-throughput cellular image analysis, and other methods. Finally, the challenges and prospects of inertial microfluidics for cell analysis and detection are summarized. [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]

Reactive sulfur species (RSS) play pivotal roles in various pathological and physiological processes. There exists an intricate relevance in generation and metabolism among these substances. Although they are nucleophilic, there are still some differences in their reactivity. There are many methods to detect them by using reactive fluorescent probes, but the systematic study of their reactivity is still lacking. In our study, we designed a multiple reaction site fluorescent probe based on benzene conjugated benzopyrylium and NBD. The study revealed that besides both biothiols and hydrogen sulfide, sulfur dioxide (SO2) can cleave the ether bond. There are two reaction forms for GSH with low reactivity: cutting the ether bond and adding the conjugated double bond of benzopyrylium. Nevertheless, Cys/Hcy with higher activity can further rearrange with NBD after cutting the ether bond. In addition, SO2 can not only cleave the ether bond, but also continue to add the conjugated double bond of benzopyrylium. The above processes lead to multicolor emission of the probe, thus realizing the characteristic analysis of different sulfides. Thus the probe can be used for the detection of sulfide in mitochondria, and further for the imaging of sulfide in cells and zebrafish. This effective analysis method will provide a broad application prospect for practical applications. [ABSTRACT FROM AUTHOR]

Platinum(II) complexes are the most commonly used anticancer drugs and potential optical materials, but the detectability of Pt(II) complex-based probes is seldom reported. In our previous work, a tetradentate Pt(II) complex Pt-CHO was utilised as a 'turn-off' probe to detect ClO− and image cancer cells. However, the recognition mechanism has not been completely clarified and there are still doubts. In this work, three Pt(II) complexes, Pt-H, Pt-CHO and Pt-COOH, were developed to elucidate the mechanism of this class of complexes and refine their property studies. As a result, the UV–visible absorption and luminescence emission experiments, as well as the mass spectrum, proved that the oxidation of Pt(II) to Pt(IV) was the real reason for luminescence quenching, which has nothing to do with aldehyde groups. This first reported mechanism introduces a new type of ClO− probe based on Pt(II) complexes, thereby expanding the application fields of platinum complexes. Moreover, the quantum yield measurements, the effect of biomolecules and reversibility were studied to improve the properties of the probes. Theoretical calculations were used to gain an in-depth understanding of optical characteristics and related mechanisms. The cell imaging of RAW264.7 cells under endogenous ClO− proved the potential of the probes in bioimaging. [ABSTRACT FROM AUTHOR]

With the rapid development of various industries, cyanide (CN−) and hypochlorite (ClO−) have a tremendously adverse effect on the health of humans and animals. In this study, a fluorescent probe HHTB based on a benzaldehyde–indole fused chromophore was designed to detect cyanide and hypochlorite simultaneously. The synthesized probe was found to have strong anti-interference ability. In addition, the designed probe could respond rapidly to ClO− in just 80 s, while the color changed visibly from red to colorless. Moreover, the response time to CN− was longer (about 160 s), with the apparent color change from red to light red. The ratiometric and colorimetric absorbance variation of HHTB was due to the nucleophilic attack of CN− on the indole C＝N functional group and the strong oxidization of ClO− which destroyed the C＝C bonds and the conjugation systems. Furthermore, the probe HHTB responding to ClO− and CN− presented high sensitivity, as the calculated detection limits were 1.18 nM and 1.40 nM, respectively. The probe was also found to have low biological toxicity and was used in living cells successfully. Therefore, it has good application prospect in the field of cell imaging and biomedicine. The binding mechanism of HHTB–CN and the reaction mechanism of HHTB and ClO− were further elucidated by a series of experiments. [ABSTRACT FROM AUTHOR]

Iron, nitrogen-co-doped carbon quantum dots (Fe,N-CDs) were prepared via a simple one-step hydrothermal method. The quantum yield of fluorescence reached about 27.6% and the blue-emissive Fe,N-CDs had a mean size of 3.76 nm. The as-prepared carbon quantum dots showed good solubility, a high quantum yield, good biocompatibility, low cytotoxicity, and high photostability. Interestingly, the as-prepared Fe,N-CDs exhibited good selectivity and sensitivity toward both hematin and ferric ions, and the limit of detection for hematin and ferric ions was calculated to be about 0.024 μM and 0.64 μM, respectively. At the same time, Fe,N-CDs were used for imaging HeLa cells and showed that most Fe,N-CDs were detained in the lysosome. Thus, this fluorescent probe has potential application in the quantitative detection of hematin or Fe3+ in a complex environment and for determining Fe3+ at the cellular level. [ABSTRACT FROM AUTHOR]

Since oxidative stress has been recognized as a major factor contributing to the progression of several neurodegenerative disorders, reactive oxygen species (ROS) including superoxide have received great attention as a representative molecular marker for the diagnosis of Alzheimer's disease (AD). Here, superoxide-sensitive fluorogenic molecular probes, benzenesulfonylated resorufin derivatives (BSRs), were newly devised for optical bioimaging of oxidative events in neurodegenerative processes. BSRs, fluorescence-quenched benzenesulfonylated derivatives of resorufin, were designed to recover their fluorescence upon exposure to superoxide through a selective nucleophilic uncaging reaction of the benzenesulfonyl cage. Among BSRs, BSR6 presented the best sensitivity and selectivity to superoxide likely due to the optimal reactivity matching between the nucleophilicity of superoxide and its electrophilicity ascribed to the highly electron-withdrawing pentafluoro-substitution on the benzenesulfonyl cage. Fluorescence imaging of inflammatory cells and animal models presented the potential of BSR6 for optical sensing of superoxide in vitro and in vivo. Furthermore, microglial cell (Bv2) imaging with BSR6 enabled the optical monitoring of intracellular oxidative events upon treatment with an oxidative stimulus (amyloid beta, Aβ) or the byproduct of oxidative stress (4-hydroxynonenal, HNE). [ABSTRACT FROM AUTHOR]