Preparation of a cyanine-based fluorescent probe for highly selective detection of glutathione and its use in living cells and tissues of mice

Indopolycarbocyanine dyes as perspective analytical reagents for spectrophotometric determination of nitrite by radical nitration

A spectrophotometric method for the quantitative determination of nitrite was developed, based on the radical nitration of indopolycarbocyanine dyes in the presence of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO). The rate of the reaction of the studied dyes with nitrite increases with the lengthening of the polymethine chain and the presence of hydrophilic sulfo groups in the side chain of the dye. TEMPO acts as a co-reagent, significantly accelerating the reaction rate and increasing the sensitivity of nitrite determination. The proposed reaction mechanism is supported by spectrophotometric and HPLC/MS studies. For Ind2 (tetramethine indocarbocyanine cationic dye), the limit of detection for nitrite is 0.50 µM within a linearity range of 1-13 µM. The developed method is sensitive, with a LOD 130 times lower than the maximum contaminant level (MCL) of nitrite in drinking water (65 μM), as specified by the WHO. The method is of low-toxicity and good selectivity, as the determination of nitrite is not significantly affected by the main components of water. The method was successfully applied for the analysis of nitrite in natural and bottled water.

Tailoring the peroxidase-like properties of Mo atom nanoclusters/N-MXene nanozymes for sensitive colorimetric detection of glutathione

Although nanozyme engineering has made tremendous progress, there is a huge gap between them and natural enzymes due to the enormous challenge of precisely adjusting the geometric and electronic structure of active sites. Considering that intentionally adjusting the metal-carrier interactions may bring the promising catalytic activity, in this work, a novel Mo atom nanocluster is successfully synthesized using nitrogen-doped Mxene (MoACs/N-MXene) nanozymes as carriers. The constructed MoACs/N-MXene displays excellent peroxidase-like catalytic activity and kinetics, outweighing its N-MXene and Mo nanoparticles (NPs)-MXene references and natural horse radish peroxidase. This work not only reports a successful example of MoACs/N-MXene nanozyme as a guide for achieving peroxidase-mimic performance of nanozymes for colorimetric glutathione sensing at 0.29 μM, but also expands the application prospects of two-dimensional MXene nanosheets by reasonably introducing metal atomic clusters and nonmetal atom doping and exploring related nanozyme properties.

Facile, green and scalable synthesis of single-layer manganese dioxide nanosheets and its application for GSH and cTnI colorimetric detection

Manganese dioxide (MnO2) nanosheets possess unique physical and chemical properties, making them widely applicable in various fields, such as chemistry and biomedicine. Although MnO2 nanosheets are produced using bottom-up wet chemistry synthesis methods, their scale is below the gram level and requires a long processing time, restricting their effective scale-up from laboratory to market. We report a facile, green and scalable synthesis of MnO2 nanosheets by mixing Shiranui mandarin orange juice and KMnO4 for 30 minutes. We produced more than one gram (1.095) of MnO2 nanosheets with a 0.65 nm mean thickness and a 50 nm mean lateral size. Furthermore, we established a visual colorimetric biosensing strategy based on MnO2 nanosheets for the assay of glutathione (GSH) and cardiac troponin I (cTnI), offering high sensitivity and feasibility in clinical samples. For GSH, the limit of detection was 0.08 nM, and for cTnI, it was 0.70 pg mL-1. Meanwhile, the strategy can be used for real-time analysis by applying a smartphone-enabled biosensing strategy, which can provide point-of-care testing in remote areas.

Flash phase engineering of MoS2 nanofilms for enhanced photoelectrochemical performance

A heterophase structure combining semiconducting 2H- and metallic 1T-MoS2 exhibits significantly enhanced photoelectrochemical performance due to the electrical coupling and synergistic effect between the phases. Therefore, site-selective effective phase engineering is crucial for the fabrication of MoS2-based photoelectrochemical devices. Here, we employed a flash phase engineering (FPE) strategy to precisely fabricate a 2H-1T heterophase structure. This technique allows simple, efficient, and precise control over the micropatterning of MoS2 nanofilms while enabling site-selective phase transition from the 1T to the 2H phase. The detection of reduced glutathione (GSH) showed an approximately 5-fold increase in sensitivity when using the electrode fabricated by FPE.

Fast Antioxidation Kinetics of Glutathione Intracellularly Monitored by a Dual-Wire Nanosensor

The glutathione (GSH) system is one of the most powerful intracellular antioxidant systems for the elimination of reactive oxygen species (ROS) and maintaining cellular redox homeostasis. However, the rapid kinetics information (at the millisecond to the second level) during the dynamic antioxidation process of the GSH system remains unclear. As such, we specifically developed a novel dual-wire nanosensor (DWNS) that can selectively and synchronously measure the levels of GSH and ROS with high temporal resolution, and applied it to monitor the transient ROS generation as well as the rapid antioxidation process of the GSH system in individual cancer cells. These measurements revealed that the glutathione peroxidase (GPx) in the GSH system is rapidly initiated against ROS burst in a sub-second time scale, but the elimination process is short-lived, ending after a few seconds, while some ROS are still present in the cells. This study is expected to open new perspectives for understanding the GSH antioxidant system and studying some redox imbalance-related physiological.

Improved Sensitivity and Selectivity of Glutathione Detection through Target-Driven Electron Donor Generation in Photoelectrochemical Electrodes

Glutathione (GSH) plays a vital role in many physiological processes, and its abnormal levels have been found to be associated with several diseases. In contrast to traditional methods using electron donor-containing electrolytes for photoelectrochemical (PEC) sensing, in this study, a target-driven electron donor generation in a PEC electrode was developed to detect GSH. Using well-aligned TiO2 nanotube arrays (TNTs) as the PEC substrate, mesoporous MIL-125(Ti) was grown in the TNTs through an in situ solvothermal method and subsequent two-step annealing treatment. The accommodation capacity of mesoporous MIL-125(Ti) allows a well loading of cystine and Pt nanoclusters (NCs). Taking advantage of the specific cleavage ability of disulfide bonds by GSH, cystine was converted to cysteine, which served as the electron donor for the PEC process. Benefiting from the confinement effect of mesoporous MIL-125(Ti), cysteine was effectively oxidized to cysteine sulfinic acid by the photogenerated holes. Importantly, the highly active Pt NCs decorated in the mesopores not only improved the charge transfer but also accelerated the above oxidation reaction. The synergistic effect of these factors enabled the efficient separation of the photogenerated electron-hole pairs, which induced a significant photocurrent increase and in turn led to the high-sensitivity detection of GSH. Consequently, the proposed PEC biosensor exhibited excellent performance in the detection of GSH in serum specimens. The target-driven electron donor generation designed in this study might open a new route for developing sensitive and selective PEC biosensors with application in complex biological environments.

Recent progress on near-infrared fluorescence heptamethine cyanine dye-based molecules and nanoparticles for tumor imaging and treatment

Recenly, near-infrared fluorescence heptamethine cyanine dyes have shown satisfactory values in bioengineering, biology, and pharmacy especially in cancer diagnosis and treatment, owing to their excellent fluorescence property and biocompatibility. In order to achieve broad application prospects, diverse structures, and chemical properties of heptamethine cyanine dyes have been designed to develop novel functional molecules and nanoparticles over the past decade. For fluorescence and photoacoustic tumor imaging properties, heptamethine cyanine dyes are equipped with good photothermal performance and reactive oxygen species production properties under near-infrared light irradiation, thus holding great promise in photodynamic and/or photothermal cancer therapies. This review offers a comprehensive scope of the structures, comparisons, and applications of heptamethine cyanine dyes-based molecules as well as nanoparticles in tumor treatment and imaging in current years. Therefore, this review may drive the development and innovation of heptamethine cyanine dyes, significantly offering opportunities for improving tumor imaging and treatment in a precise noninvasive manner. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Bioimaging of glutathione variation for early diagnosis of hepatocellular carcinoma using a liver-targeting ratiometric near-infrared fluorescent probe

Reliable biomarkers are crucial for early diagnosis of diseases and precise therapy. Biological thiols (represented by glutathione, GSH) play vital roles in the antioxidant defense system for maintaining intracellular redox homeostasis in organisms. However, the aberrant variation in the cellular concentration of GSH correlates with diverse diseases including cancer. Here, a ratiometric near-infrared fluorescent probe CyO-Disu is constructed for the specific sensing of GSH variation in live cells and mice models of hepatic carcinoma (HCC). CyO-Disu features three key elements, a response moiety of bis(2-hydroxyethyl) disulfide, a near-infrared fluorescence signal transducer of heptamethine ketone cyanine, and a targeting moiety of D-galactose. By virtue of its liver-targeting capability, CyO-Disu was utilized for evaluating GSH fluctuations in primary and metastatic hepatoma living cells. To evaluate the efficacy of CyO-Disuin vivo, orthotopic HCC and pulmonary metastatic hepatoma mice models were employed for GSH imaging using two-dimensional and three-dimensional fluorescence molecular tomographic imaging systems. The bioimaging results offered direct evidence that GSH displayed varied concentrations during the progression of HCC. Therefore, the as-synthesized probe CyO-Disu could serve as a potential powerful tool for the early diagnosis and precise treatment of HCC using GSH as a reliable biomarker.

Preparation of near-infrared AIEgen-active fluorescent probes for mapping amyloid-β plaques in brain tissues and living mice

Fibrillar aggregates of the amyloid-β protein (Aβ) are the main component of the senile plaques found in brains of patients with Alzheimer's disease (AD). Development of probes allowing the noninvasive and high-fidelity mapping of Aβ plaques in vivo is critical for AD early detection, drug screening and biomedical research. QM-FN-SO3 (quinoline-malononitrile-thiophene-(dimethylamino)phenylsulfonate) is a near-infrared aggregation-induced-emission-active fluorescent probe capable of crossing the blood-brain barrier (BBB) and ultrasensitively lighting up Aβ plaques in living mice. Herein, we describe detailed procedures for the two-stage synthesis of QM-FN-SO3 and its applications for mapping Aβ plaques in brain tissues and living mice. Compared with commercial thioflavin (Th) derivatives ThT and ThS (the gold standard for detection of Aβ aggregates) and other reported Aβ plaque fluorescent probes, QM-FN-SO3 confers several advantages, such as long emission wavelength, large Stokes shift, ultrahigh sensitivity, good BBB penetrability and miscibility in aqueous biological media. The preparation of QM-FN-SO3 takes ~2 d, and the confocal imaging experiments for Aβ plaque visualization, including the preparation for mouse brain sections, take ~7 d. Notably, acquisition and analyses for in vivo visualization of Aβ plaques in mice can be completed within 1 h and require only a basic knowledge of spectroscopy and chemistry.

Sb-doped FeOCl nanozyme-based biosensor for highly sensitive colorimetric detection of glutathione

Nanozymes have been emerging as substitutes for natural enzymes to construct biosensors towards biomolecular detection. However, the detection of glutathione (GSH) by nanozyme-based biosensors still remains a great challenge for research on catalytic activity enhancement and the detection mechanism. In this work, Sb-doped iron oxychloride (Sb-FeOCl) with a well-defined nanorod-like structure is prepared by high-temperature calcination. Sb-FeOCl nanorods have high peroxidase-like activity, which can catalyze the decomposition of H₂O₂ into ·OH and then oxidize 3,3',5,5'-tetramethylbenzidine (TMB). In view of these intriguing observations, a reliable colorimetric method with a simple mixing and detection strategy is developed for the detection of GSH. The linear range of GSH detection is 1-36 μM. The detection limit of GSH reaches a low level of 0.495 μM (3σ/slope). The GSH sensing system also exhibits excellent specificity and anti-interference. Taking advantage of the advantages of the Sb-FeOCl nanorod-based biosensor, it can be used to quantitatively detect GSH levels in human serum. It can be anticipated that the Sb-FeOCl nanorods have broad prospects in the field of enzymatic biochemical reactions.

Fluorescent probes for biomolecule detection under environmental stress

The use of fluorescent probes in visible detection has been developed over the last several decades. Biomolecules are essential in the biological processes of organisms, and their distribution and concentration are largely influenced by environmental factors. Significant advances have occurred in the applications of fluorescent probes for the detection of the dynamic localization and quantity of biomolecules during various environmental stress-induced physiological and pathological processes. Herein, we summarize representative examples of small molecule-based fluorescent probes that provide bimolecular information when the organism is under environmental stress. The discussion includes strategies for the design of smart small-molecule fluorescent probes, in addition to their applications in biomolecule imaging under environmental stresses, such as hypoxia, ischemia-reperfusion, hyperthermia/hypothermia, organic/inorganic chemical exposure, oxidative/reductive stress, high glucose stimulation, and drug treatment-induced toxicity. We believe that comprehensive insight into the beneficial applications of fluorescent probes in biomolecule detection under environmental stress should enable the further development and effective application of fluorescent probes in the biochemical and biomedical fields.

Versatile Construction of Biomimetic Nanosensors for Electrochemical Monitoring of Intracellular Glutathione

The current strategies for nanoelectrode functionalization usually involve sophisticated modification procedures, uncontrollable and unstable modifier assembly, as well as a limited variety of modifiers. To address this issue, we propose a versatile strategy for large-scale synthesis of biomimetic molecular catalysts (BMCs) modified nanowires (NWs) to construct functionalized electrochemical nanosensors. This design protocol employs an easy, controllable and stable assembly of diverse BMCs-poly(3,4-ethylenedioxythiophene) (PEDOT) composites on conductive NWs. The intrinsic catalytic activity of BMCs combined with outstanding electron transfer ability of conductive polymer enables the nanosensors to sensitively and selectively detect various biomolecules. Further application of sulfonated cobalt phthalocyanine functionalized nanosensors achieves real-time electrochemical monitoring of intracellular glutathione levels and its redox homeostasis in single living cells for the first time.

Activatable NIR-II Fluorescence Probe for Highly Sensitive and Selective Visualization of Glutathione In Vivo

Visualization of glutathione (GSH) enables us to understand GSH-related pathophysiological processes in living subjects. Currently, in vivo visualization methods of GSH are based on visible or first near-infrared (NIR-I) window fluorescence (FL) probes, which possess limitations due to their low tissue penetration depth and strong tissue autofluorescence. Herein, we developed a GSH-activatable second near-infrared (NIR-II) window FL probe (denoted as LET-7) for highly sensitive and selective visualization of GSH in vivo. LET-7, composed of an anionic polymethylcyanide skeleton linked with a FL quenching group of 3,5-bis(trifluoromethyl)benzenethiol, can be specifically activated by GSH, thus triggering a significant NIR-II FL emission enhancement with excellent photostability, which enables us to efficiently distinguish GSH from closely related low-molecular-weight biothiols. The limit of detection of LET-7 for GSH was determined to be as low as 85 nM. Most intriguingly, the in vivo studies demonstrated that LET-7 showed high sensitivity and good selectivity toward GSH. Therefore, our study provides a solution to design activatable NIR-II FL probes for in vivo imaging of GSH and other disease-related biomarkers.

Design, Synthesis, and Antibacterial Evaluation of Novel Ocotillol Derivatives and Their Synergistic Effects with Conventional Antibiotics

The improper use of antibiotics has led to the development of bacterial resistance, resulting in fewer antibiotics for many bacterial infections. Especially, the drug resistance of hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) is distinctly serious. This research designed and synthesized two series of 3-substituted ocotillol derivatives in order to improve their anti-HA-MRSA potency and synergistic antibacterial activity. Among the synthesized compounds, 20–31 showed minimum inhibitory concentration (MIC) values of 1–64 µg/mL in vitro against HA-MRSA 18–19, 18–20, and S. aureus ATCC29213. Compound 21 showed the best antibacterial activity, with an MIC of 1 μg/mL and had synergistic inhibitory effects. The fractional inhibitory concentration index (FICI) value was 0.375, when combined with chloramphenicol (CHL) or kanamycin (KAN). The structure–activity relationships (SARs) of ocotillol-type derivatives were also summarized. Compound 21 has the potential to be developed as a novel antibacterial agent or potentiator against HA-MRSA.

Signal Amplification Strategy Using Atomically Gold-Supported VO2 Nanobelts as a Co-reaction Accelerator for Ultrasensitive Electrochemiluminescent Sensor Construction Based on the Resonance Energy Transfer Platform

Luminol, as a classical luminophore, plays a crucial role in electrochemiluminescence (ECL). However, the traditional luminol-H₂O₂ ECL system suffers from the self-decomposition of H₂O₂ at ambient temperature, which hinders its further application in quantitative analysis. In this work, for the first time, we developed atomically gold-supported two-dimensional VO₂ nanobelts (Au/VO₂) as an advanced co-reaction promoter to speed up the reduction of dissolved oxygen to superoxide radicals (O₂^•-), which react with the luminol anion radical and greatly promote the ECL emission. The ECL resonance energy transfer (ECL-RET) between the hollow manganese dioxide nanospheres and luminol results in a conspicuously decreased ECL signal response, and in the presence of glutathione (GSH), effective redox reaction between manganese dioxide and GSH restores the ECL signal. As a consequence, the designed sensor based on ECL-RET-assisted Au/VO₂ signal amplification showed outstanding performance for "signal-on" detection of GSH in the concentration range of 10^-3 to 10^-10 M, and the detection limit was as low as 0.03 nM. The ECL sensor displayed excellent specificity and was successfully utilized to target GSH in real human serum samples. Importantly, this work not only highlights a powerful avenue for constructing an ultrasensitive ECL sensor for GSH but also provides some inspiration for the further design of high-performance co-reaction accelerators using the ECL technique.

Anti-Tumor Metastasis via Platelet Inhibitor Combined with Photothermal Therapy under Activatable Fluorescence/Magnetic Resonance Bimodal Imaging Guidance

Photothermal therapy (PTT) is a promising tumor therapy strategy; however, heterogeneous heat distribution over the tumor often exists, resulting in insufficient photothermal ablation and potential risk of cancer metastasis, which has been demonstrated to be associate with platelets. Herein, a near-infrared (NIR) photothermal agent of IR780 was conjugated with MRI agent of Gd-DOTA via a disulfide linkage (ICD-Gd), which was coassembly with lipid connecting tumor-homing pentapeptide CREKA (Cys-Arg-Glu-Lys-Ala) (DSPE-PEG-CREKA) to encapsulate a platelet inhibitor of ticagrelor (Tic), affording a multistimuli-responsive nanosystem (DPC@ICD-Gd-Tic). The nanosystem with completely quenching fluorescence could specifically target the tumor-associated platelets and showed pH/reduction/NIR light-responsive drug release, which simultaneously resulting in dis-assembly of nanoparticle and fluorescence recovery, enabling the drug delivery visualization in tumor in situ via activatable NIR fluorescence/MR bimodal imaging. Finally, DPC@ICD-Gd-Tic further integrated the photoinduced hyperthermia and platelet function inhibitor to achieve synergistic anticancer therapy, leading to ablation of primary tumor cells and effectively suppressed their distant metastasis. The number of lung metastases in 4T1 tumor bearing mice was reduced by about 90%, and the size of tumor was reduced by about 70%, while half of the mouse was completely cured by this smart nanosystem.

Dimethyl Sulfoxide-Free and Water-Soluble Fluorescent Probe for Detection of Bovine Serum Albumin Prepared by Ionic Co-assembly of Amphiphiles

Detection of bovine serum albumin (BSA) is an important issue in the sense of medical applications and enzymatic reactions; however, the recently developed fluorescent probes require the involvement of dimethyl sulfoxide (DMSO), which may be detrimental to proteins. In this study, we demonstrated a DMSO-free and water-soluble fluorescent probe prepared by ionic co-assembly of amphiphiles. The cationic amphiphile is a newly designed molecule (denoted by DPP-12) bearing a conjugated diketopyrrolopyrrole (DPP) and two tetraphenylethylene groups. It turns out that the fluorescence emission of DPP-12 depends on the amount of anionic amphiphilic sodium dodecyl benzene sulfonate (SDBS). The fluorescence intensity first increases and then decreases with the concentration of SDBS, and each branch presents a linear relationship. BSA consumes SDBS by the formation of complexes, thus leading to an increase of fluorescence intensity of the mixed solution of DPP-12 and SDBS. Therefore, the mixed solution of DPP-12 and SDBS was applied as a fluorescent probe to detect the low concentration of BSA by back-titration. This fluorescent probe does not require DMSO and has good tolerance to metal ions in blood and good photostability. The limit of detection is as low as 940 nM, almost 3 orders of magnitude lower than the content in organisms.

An endoplasmic reticulum-targeting fluorescent probe for discriminatory detection of Cys, Hcy and GSH in living cells

Endoplasmic reticulum, known to us as the ER, is the largest organelle in many kinds of eukaryotic cells and plays vital roles in maintaining the normal function of cells. Biothiols (Cys, Hcy, GSH) in secretory proteins will be modified as they enter the ER and are of great importance in balancing redox state of ER environments. In this article, we have developed the first endoplasmic reticulum-targeting fluorescent probe, ER-CP, for concurrent distinguishment of Cys, Hcy and GSH with favorable sensitivity and selectivity. ER-CP was successfully used in fluorescence imaging of Cys, Hcy and GSH in HeLa cells. In addition, ER-CP exhibited a good ER-targeting property (Pearson's correlation coefficient = 0.90).

BODIPY-based Fluorescent Probe for the Detection of Cysteine in Living Cells

Cysteine (Cys), as one of the important amino acids, plays a vital role in various physiological and pathological processes. Hence, it is meaningful to develop a convenient and sensitive detection method. Herein, a novel BODIPY-based fluorescent probe (BDP-DM) was developed, which had a higher selectivity for Cys than other amino acids, including homocysteine (Hcy) and glutathione (GSH). Ultimately, we concluded that the BDP-DM probe could be used to successfully detected intracellular Cys in living HeLa cells.

High-Yielding Water-Soluble Asymmetric Cyanine Dyes for Labeling Applications

A simple and efficient microwave-assisted synthesis of asymmetric pentamethine cyanine dyes with various functional groups was developed, which allows high-yielding results. The synthesized dyes are modifiable and suitable for single-molecule imaging in biological and medical sciences by application of click chemistry or classic esterification and amidation.

Versatile Electrochemiluminescence and Photoelectrochemical Detection of Glutathione Using Mn2+ Substitute Target by DNA-Walker-Induced Allosteric Switch and Signal Amplification

Glutathione (GSH) serves vital functions in biological systems and associates with various human diseases. In this work, a versatile electrochemiluminence (ECL) and a photoelectrochemical (PEC) "signal on" biosensing platform were developed for a sensitive assay of GSH by a Mn²⁺-powered DNAzyme amplification strategy combined with DNA-walker-triggered allosteric conversion. First, MnO₂ nanosheets were reduced to Mn²⁺ by GSH; then, Mn²⁺ as a substitute target triggered DNAzyme-assisted cleavage-cycling amplification to generate numerous DNA output (s3). Meanwhile, the DNA molecular machine was introduced to bridge signal probes for versatile biosensing, which included hairpin DNA as a track and an arm as a walker. The presence of DNA output (s3) activated the swing arm to hybridize with hairpin DNA and then cut it by Nt.BbvCI, which initiated autonomous walking of the arm for forming a large number of streptavidin (SA) aptamers. Thus, a large number of CdS:Mn-SA tags as versatile signal probes was linked to the electrode by specific SA-aptamer binding, generating highly enhanced ECL and PEC signals for sensitive detection of the target. The present biosensing system take advantage of metal ion-based DNAzyme amplification, a DNA walker machine, multi-signals of QDs, and specificity of aptamers, which can provide a universal and efficient biosensing method for detecting various targets. The designed strategy demonstrated good performance for a GSH assay in human serum samples, showing more promising applications than other reported methods.

Enhanced in vivo Optical Imaging of the Inflammatory Response to Acute Liver Injury in C57BL/6 Mice Using a Highly Bright Near-Infrared BODIPY Dye

Delving deeper is possible in whole-body in vivo imaging using a super-bright membrane-targeting BODIPY dye (BD). The dye was used to monitor homing of ex vivo fluorescently labelled neutrophils to an injured liver of dark-pigmented C57BL/6 mice. In vivo imaging system (IVIS) data conclusively showed an enhanced signal intensity and a higher signal-to-noise ratio in mice receiving neutrophils labelled with the BD dye relative to those labelled with a gold standard dye at 2 h post in vivo administration of fluorescently labelled cells. Fluorescence-activated cell sorting (FACS) confirmed that BD is nontoxic, and an exceptional cell labelling dye that opens up precision deep-organ in vivo imaging of inflammation in mice routinely used for biomedical research. The origin of enhanced performance is identified with the molecular structure and the distinct localisation of the dye within cells that enable remarkable changes in its optical parameters.

Highly sensitive glutathione assay and intracellular imaging with functionalized semiconductor quantum dots

Glutathione (GSH) plays a vital role in biological systems and is associated with human pathology. The engineering of semiconductor quantum dots (QDs) as fluorescent probes for GSH sensing and bioimaging is a potential yet rarely reported approach. Herein, we report the in situ growth of manganese dioxide nanosheets (MnO2) on silica-coated semiconductor quantum dots (QD@SiO2), to prepare a stable and biocompatible fluorescent nanoprobe (QD@SiO2-MnO2) for the selective and sensitive detection of GSH. The modification of QD@SiO2 with MnO2 significantly quenched the fluorescence of CdSe/ZnS QDs, yet the addition of GSH efficiently recovered the fluorescence of the nanoprobe due to the decomposition of MnO2 by GSH. This nanosensor showed a rapid response to GSH with a low detection limit, and high selectivity towards GSH over potential interferences. Furthermore, the MnO2-engineered QDs had good biocompatibility and cellular uptake ability, and were successfully applied for the real-time imaging of intracellular GSH. We envision that semiconductor QD-based probes will stimulate the study of GSH dynamics and facilitate the understanding of GSH-related pathophysiological events.

Novel Ru(bpy)2(cpaphen)2+/TPrA/TiO2 Ternary ECL System: An Efficient Platform for the Detection of Glutathione with Mn2+ as Substitute Target

A sensitive electrochemiluminescence (ECL) biosensor was developed for glutathione (GSH) detection based on a novel Ru(bpy)₂(cpaphen)²⁺/TPrA/TiO₂ ternary ECL system with Mn²⁺ as substitute target for signal amplification. Specifically, the TiO₂ nanoneedles (TiO₂ NNs) were used as the coreaction accelerator for the first time to promote the oxidation process of coreactant tripropylamine (TPrA) in the anode and significantly increase the ECL signal of Ru(bpy)₂(cpaphen)²⁺ for an amplified initial signal. Meanwhile, a novel target conversion strategy for GSH was developed by reducing MnO₂ nanosheets to Mn²⁺ as a substitute target, which played the role of a coenzyme factor for cleaving DNA double strands intercalated with Ru(bpy)₂(cpaphen)²⁺ to markedly weaken initial signal. As a result, the novel "on-off" biosensor achieved a sensitive detection of GSH range from 5 μM to 215 μM with a detection limit of 0.33 μM. Importantly, the proposed strategy enriched the application of Ru complex and TPrA ECL system in bioanalytical applications, and provided a new signal amplification strategy for bioactive small molecules.

Dual-channel fluorescence detection of mercuric (II) and glutathione by down- and up-conversion fluorescence carbon dots

The fluorescent carbon dots (CDs) with high fluorescent quantum yield (φ_f = 62%) and down- and up-conversion fluorescence properties were synthesized by one-pot hydrothermal treatment of citric acid and tris(hydroxymethyl)methyl aminomethane. The CDs displayed the capability to absorb excitation wavelength at 660 nm and 330 nm with fluorescence emission wavelength at 398 nm and 399 nm, respectively. The CDs showed high selectivity towards Hg²⁺ against various metal ions. Around 70% fluorescence was quenched by 40 μM Hg²⁺ through dynamic and static quenching mechanisms. Because of stronger affinity between the thiol and Hg²⁺, over 90% fluorescence was recovered by adding 40 μM glutathione to CDs-Hg²⁺ system. The calibration curves exhibited wide linear region for Hg²⁺ (0-4 μM) and glutathione (0-30 μM). The limits of detection with down- and up-conversion for Hg²⁺ were calculated to be 0.23 μM and 0.25 μM, and for glutathione were 0.28 μM and 0.29 μM, respectively. Inspired by the sensing results, logic gates with Hg²⁺ and glutathione as inputs were also established. Most importantly, this method was applied to detect Hg²⁺ and glutathione in tap water and lake water, and the recovery values were obtained to be 96.2%-110.4% and 93.4%-96.9%.

A series of BODIPY-based probes for the detection of cysteine and homocysteine in living cells

Biothiols, such as glutathione (GSH), homocysteine (Hcy) and cysteine (Cys), are important biomarkers and play crucial roles in many physiological processes. Thus, the detection of biothiols is highly important for early diagnosis of diseases and evaluation of disease progression. Herein, new types of BODIPY-based fluorescent probes (probe 1, probe 2 and probe 3) capable of cysteine (Cys)/homocysteine (Hcy) sensing with high selectivity over other amino acids were developed. In addition, we further studied the influence of different electronegativity substituents on these probes to sensing Cys/Hcy. Ultimately, we concluded that the electron withdrawing group on probe 1 can accelerate the probe response to Cys/Hcy, and probe 1 was successfully applied for selective imaging Cys/Hcy in living cells.

A Fluorescent Cy7-Mercaptopyridine for the Selective Detection of Glutathione over Homocysteine and Cysteine

We describe a near-infrared (NIR) fluorescent probe 1 for the selective detection of GSH over Hcy and Cys under physiological conditions. Probe 1 was composed of Cy7 as a NIR dye and 2-mercaptopyridine as a GSH-reactive site and fluorescence quencher. In the presence of GSH, the 2-mercaptopyridine functionality of probe 1 was replaced by the thiolate group of GSH through a nucleophilic substitution reaction with a fluorescence increase at 818 nm. The probe was found to be highly selective for GSH over Hcy, Cys, and other tested potential interferants, including ROS and metal ions. In addition, probe 1 successfully displayed fluorescence changes in response to changing the GSH concentrations in MDA-MB-231 cells in the presence of external agents i.e., N-acetyl-l-cysteine (NAC; as GSH inducer) or buthionine sulfoximine (BSO; as GSH inhibitor). We envision that probe 1 will serve as a promising sensing tool for monitoring the changes of the GSH level and the understanding of the roles of GSH under physiological and pathological conditions.

Glutathione-driven Cu(i)-O2 chemistry: a new light-up fluorescent assay for intracellular glutathione

Besides its widely known role as an endogenous antioxidant in scavenging free radicals, glutathione (GSH) can also play the role of prooxidant and promote CuO-induced formation of hydroxyl radicals to light up a fluorescent signal through Cu(i)-O2 chemistry without requiring additional H2O2. This approach is independent of the mechanisms of enzyme mimics, such as the well-known oxidase and peroxidase mimetics, providing a new method to simply and effectively analyze intracellular GSH.

Supramolecular glyco-poly-cyclodextrin functionalized thin-layer manganese dioxide for targeted stimulus-responsive bioimaging

We have developed a supramoleuclar imaging probe based on thin-layer manganese dioxide functionalized with a fluorescent, multivalent glyco-poly-cycolodextrin for the targeted, stimulus-responsive bioimaging of cancer cells.