Fluorescence turn-on and colorimetric dual readout assay of glutathione over cysteine based on the fluorescence inner-filter effect of oxidized TMB on TMPyP

Oxygen-functionalized Fe3O4@o-polypyrrole acting as high-efficiency oxidase mimics and their application in glutathione colorimetric sensing

The enzyme-like properties of nanozymes may be considerably affected by the structure and surface groups, which thus need to be optimized. Here, through a simple NaOH chemical corrosion method, the chemical structure similar to N-Methylpyrrolidone (NMP), which possessed intrinsic oxidase-like activity, was introduced into polypyrrole (PPy), and then this nanomaterial became oxygen-functionalized PPy (o-PPy) with excellent oxidase-like activity from PPy without this property. Furthermore, after compounding magnetic Fe3O4, the obtained nanocomposites Fe3O4@o-PPy nanoparticles (Fe3O4@o-PPy NPs) showed superiorities in separation during synthesis and real-time control of enzyme catalysis. Studies have found that the enzymatic activity of Fe3O4@o-PPy NPs depended on the amount of functionalized oxygen and the conjugation extent of o-PPy. Fe3O4@o-PPy NPs had efficient oxidase-like activity under a wide range of pH and temperature. Based on the oxidase-like activity of Fe3O4@o-PPy NPs, a colorimetric sensor for glutathione (GSH), which presented rich color changes and satisfactory colorimetric resolution by adding the amaranth, was realized. We believe that the functional modification and structural regulation of PPy can not only realize its wider application but also promote the discovery of novel and efficient nanozymes.

Construction and Application of Copper Ion and Amino Acid Probe Based on Functionalized Metal-Organic Framework Probe

The rapid development of fluorescence probe technology has promoted in-depth research in fields such as environment and life medicine. Traditional single channel fluorescent probes can achieve highly sensitive detection of targets, but they appear powerless in complex environments. In addition, in today's deteriorating resource environment, implementing multi target detection with one probe can effectively save preparation resources, which is in line with the development direction of fluorescent probes. To achieve this goal, designing and preparing multi-site probes is undoubtedly the first choice, but the complexity of their preparation is daunting. Herein, we propose the concept of cascade detection for the first time. After the probe completes the first target detection, the complex between the probe and the first target is achieved based on the characteristics of the first target to achieve subsequent target detection. Based on this, a metal-organic framework was used as a basic skeleton and the concept of serial reactions was applied. First, copper ions were detected through coordination. Then, the specificity of copper for sulfur-containing amino acids was utilized to detect the three types of amino acids, and the practical applications of the three probes were studied separately.

A novel highly sensitive inner filter effect-based fluorescence immunoassay with quantum dots for bioanalysis of zolbetuximab, a monoclonal antibody used for immunotherapy of gastric and gastroesophageal junction adenocarcinoma

Zolbetuximab (ZOL) is a groundbreaking monoclonal antibody targeting CLDN 18.2, a cancer cell surface protein. It is a first-in-class therapy for gastric and gastroesophageal junction adenocarcinoma. However, there is currently any immunoassay available for bioanalysis of ZOL, hindering its pharmacokinetic studies, therapeutic monitoring, and safety profile refinement. To address this gap, this study presents the development and validation of a novel highly sensitive inner filter effect-based fluorescence immunoassay (IFE-FIA) with quantum dots (QDs) as a probe. This assay enables the quantitative determination of ZOL in plasma samples. The assay involved non-competitive capturing of ZOL from the samples using a specific antigen (CLDN 18.2 protein) immobilized on assay plate microwells. A horseradish peroxidase (HRP)-labelled anti-human IgG was used to measure the immune complex. The assay's detection system relies on the formation of a light-absorbing colored product through an HRP-catalyzed oxidative reaction with the substrate 3,3',5,5'-tetramethylbenzidine. This light absorption efficiently quenched the fluorescence of QDs via the IFE. The measured fluorescence signals corresponded to the concentrations of ZOL in the samples. The conditions of the IFE-FIA and its detection system were refined, and the optimum procedures were established. Following the guidelines of immunoassay validation for bioanalysis, the assay was validated, and all the validation criteria were acceptable. The assay demonstrates high sensitivity, accurately quantifying ZOL at concentrations as low as 10 ng/mL in plasma samples, with acceptable precision. Importantly, it avoids interferences from endogenous substances and plasma matrix. The recoveries in spiked human plasma ranged from 96.8 % to 104.5 %, with relative standard deviations of 4.1 %-6.5 %. The proposed IFE-FIA represents a valuable tool for quantifying ZOL in clinical settings, enabling assessment of its pharmacokinetics, therapeutic drug monitoring, and safety profile refinement.

Development of highly sensitive dual-enhanced fluorescence quenching immunochromatographic test strips based on Pt nanoprobes

The fluorescence-quenching method is crucial in vitro analysis, particularly for immunochromatographic test strips (ICTs) using noble metal nanoparticles as probes. However, ICTs still fall short in meeting the requirements for the detection of traces biomarkers due to the noble metal nanoparticles can only quench fluorescence of the dyes within a confined distance. Interestingly, noble metal nanoparticles, such as Pt NPs cannot only perform fluorescence-quenching ability based on the Förster resonance energy transfer (FRET), but also show perfect oxidase-like catalytic performance on many kinds of substrates, such as 3,3',5,5' -tetramethylbenzidine (TMB). We observed that the oxTMB (the oxidation products of TMB) exhibited notable effectiveness in quenching Cy5 fluorescence by the strong inner filter effect (IFE), which obviously improved the fluorescence-quenching efficiency with extremely low background signal. Through the dual-enhanced fluorescence quenching mechanism, the fluorescence quenching constant (Kn) was 661.24-fold that of only Pt NPs on the NC membrane. To validate the feasibility of this technique, we employed two types of biomarkers, namely microRNA (miR-15a-5p) and the signature protein (PSA). The sensitivity of miR-15a-5p was 9.286 × 10-18 mol/L and 17.5-fold more than that based on Pt NPs. As for the PSA, the LOD (0.6265 pg/mL) was 15.5-fold enhancement more sensitive after catalysis. Overall, the dual-enhanced fluorescence quenching rFICTs could act as a practical detection for biomarker in real samples.

A spectroscopy based prototype for the noninvasive detection of diabetes from human saliva using nanohybrids acting as nanozyme

The recent prediction of diabetes to be a global pandemic invites a detection strategy preferably non-invasive, and bloodless to manage the disease and the associated complications. Here, we have synthesized chitosan polymer functionalized, organic-inorganic bio-compatible nano-hybrids of Mn3O4 nanoparticles, and characterized it by utilizing several optical methodologies for the structural characterization which shows the Michaelis Menten (MM) kinetics for glucose and alpha-amylase protein (well-known diabetes biomarkers). We have also studied the potentiality for the detection of alpha-amylase in human salivary secretion which is reported to be strongly correlated with uncontrolled hyperglycemia. Finally, we have developed a prototype for the measurement of glucose (LOD of 0.38 mg/dL, LOQ of 1.15 mg/dL) and HbA1c (LOD of 0.15% and LOQ of 0.45%) utilizing the basic knowledge in the study for the detection of uncontrolled hyperglycemia at the point-of-care. With the limited number of clinical trials, we have explored the potential of our work in combating the diabetic pandemic across the globe in near future.

Ratio fluorescence sensor based on CD/Cu-MOFs for detection of Hg2

Trace detection of toxic heavy metals is a very important and difficult problem in several areas: convenience, sensitivity, and reliability. Herein, we develop an innovative fluorescence resonance energy transfer (FRET)-based ratio fluorescence sensor for the detection of heavy metal mercury ion (H g ²⁺). The sensing platform is composed of coumarin derivatives (CDs) and a copper metal-organic framework (Cu-MOF) named CD/Cu-MOF. The constructed CD/Cu-MOFs ratio fluorescence sensor exhibits dual emission peaks at 430 and 505 nm under the single excitation wavelength of 330 nm. With the addition of H g ²⁺, the fluorescence intensity of the system at 430 nm gradually increased, and the fluorescence intensity at 505 nm remained stable, resulting in a change in the fluorescence ratio. There is a good logarithmic relationship between the H g ²⁺ concentration in the range from 2×10^-8 to 0.001 nM and the ratio of the fluorescence emission intensity of the system (F ₄₃₀/F ₅₀₅) (R ²=0.9901), and its calculated detection limit is 3.76×10^-9 n M. In addition, the CD/Cu-MOFs ratio fluorescence sensor has achieved a good recovery rate of standard addition in the actual food sample recovery experiment, which provides an effective method for the detection of H g ²⁺ in food samples.

Dual-readout fluorescence quenching immunochromatographic test strips for highly sensitive simultaneous detection of chloramphenicol and amantadine based on gold nanoparticle-triggered photoluminescent nanoswitch control

Herein, a novel fluorescence quenching immunochromatographic test strip (FQICTS) for simultaneous detection of chloramphenicol (CAP) and amantadine (AMD) was developed on the basis of inner filter effect (IFE), with the combination of gold nanoparticles (AuNPs) and highly luminescent green-emitting gold nanoclusters (AuNCs) as the IFE quencher/donor pair. The AuNPs could quench the excitation light and emission light of AuNCs and achieve a high IFE efficiency due to dual spectral overlapping. Under optimal conditions, the "turn-on" mode of the AuNCs-based dual-readout FQICTS showed good linearity for CAP detection in chicken samples from 0.05 ng/g to 10 ng/g, with a limit of detection (LOD) of 0.043 ng/g. The linear range of AMD is 0.5-50 ng/g, with LOD of 0.45 ng/g. The visual LODs of CAP and AMD in "turn-on" mode were 200 and 10 times lower than that in "turn-off" mode, respectively. The "turn-on" mode of FQICTS showed high recovery for detecting CAP (82.5-94.5%) and AMD (81.9-110.7%) spiked into chicken samples. The performance and practicability of the established method were verified with commercial enzyme-immunoassay kits, and good correlations were observed. Overall, the newly developed AuNCs-based dual-readout FQICTS is a promising on-site screening tool for rapid, high-sensitivity detection of multiple food contaminants in practical applications.

Combination of Capped Gold Nanoslit Array and Electrochemistry for Sensitive Aqueous Mercuric Ions Detection

Label-free surface plasmon resonance (SPR) detection of mercuric ions in various aqueous solutions, using capped gold nanoslit arrays combined with electrochemical (EC) sensing technique, is demonstrated. The nanoslit arrays are fabricated on flexible cyclo-olefin polymer substrates by a nanoimprinting lithography method. The EC and SPR signals for the investigation of current responses and transmission SPR spectra are simultaneously measured during metal ions electrodeposition. Glycerol-water solution is studied to evaluate the resonant peak wavelength sensitivity (480.3 nm RIU^-1) with a FOM of 40.0 RIU^-1 and the obtained intensity sensitivity is 1819.9%. The ferrocyanide/ferricyanide redox couple performs the diffusion controlled electrochemical processes (R² = 0.99). By investigating the SPR intensity changes and wavelength shifts of various mercuric ion concentrations, the optical properties are evaluated under chronoamperometric conditions. The sensors are evaluated in the detection range between 100 μM and 10 nM with a detection limit of 1 μM. The time dependence of SPR signals and the selectivity of 10 μM Hg²⁺ in the presence of 10 μM interfering metal ion species from Ca²⁺, Co²⁺, Ni²⁺, Na⁺, Cu²⁺, Pb^{2 +} and Mn²⁺ are determined. The capped gold nanoslit arrays show the selectivity of Hg²⁺ and the EC sensing method is effectively utilized to aqueous Hg²⁺ detection. This study provides a label-free detection technique of mercuric ions and this developed system is potentially applicable to detecting chemicals and biomolecules.

A novel self-enhanced carbon nitride platform coupled with highly effective dual-recycle strand displacement amplifying strategy for sensitive photoelectrochemical assay

In this work, a novel self-enhanced photoelectric active material, Na⁺, K⁺-codoped carbon nitride (NaKCN), was synthesized for constructing sensitive photoelectrochemical (PEC) biosensor to detect target miRNA-182-5p. Ingeniously, the NaKCN displayed glucose oxidase (GOx)-mimicking photocatalytic property, which catalyzed glucose to in situ generate high levels of H₂O₂ as its own electron donor for enhancing photocurrent. Moreover, the Na⁺, K⁺ co-doping could reduce energy gap of carbon nitride material, effectively improving the optical absorptivity and photocatalytic efficiency. Additionally, a novel highly effective dual-recycle TSD amplifying strategy was constructed to convert a small amount of target into plentiful two types of output DNAs labeling with sensitizer MB to enhance photocurrent of NaKCN. As a result, this PEC biosensor achieved a high sensitivity with low detection limit of 3.3 fM, which provided a new avenue for improving sensitivity of bioanalysis and diagnosis of diseases.

A turn-on fluorescence strategy for cellular glutathione determination based on the aggregation-induced emission enhancement of self-assembled copper nanoclusters

As a class of ideal fluorescent nanomaterials, self-assembled copper nanoclusters (CuNCs) have attracted increasing interest. Unfortunately, most of these CuNCs only possessed bright luminescence in acidic solution, which limited their practical applications in a physiological environment. Retaining the strong fluorescence of these CuNCs in neutral or alkaline solution is still a challenging task. In this strategy, self-assembled CuNCs were prepared by using 4-methylthiophenol as the protecting ligand. The self-assembled CuNCs display stable and bright luminescence with excitation/emission maxima at 330/605 nm even in neutral and alkaline environments. Interestingly, with the addition of glutathione (GSH), the fluorescence intensity of CuNCs is enhanced strongly through the GSH-controlled aggregation-induced emission enhancement of self-assembled CuNCs. The turn-on fluorescence strategy can determine the GSH concentration in the range from 1 to 100 μM with a limit of detection of 300 nM. In addition, the method is employed for the determination of GSH levels in cells. Therefore, the turn-on fluorescence strategy is reliable, sensitive and suitable for the determination of cellular GSH levels.

Novel and Reliable Chemosensor Based on C. dots from Sunflower seeds for the Distinct Detection of Picric Acid and Bilirubin

Based on the green chemistry approach, highly fluorescent and novel carbon dots (C. dots) were synthesized from naturally available and cost effective sunflower seeds. The obtained C. dots showed a fluorescence quantum yield (Q.Y) of 9.5% with high water dispersibility and photostability. The obtained C. dots were employed for the detection of picric acid (PA) and bilirubin. A good linear relationship in the range of 20-60 nM was obtained for PA with a limit of detection (LOD) as low as 3.86 nM. C. dots were successfully incorporated in the agarose matrix which enabled them to be employed as a solid platform for the in situ detection of PA. The fluorescence of C. dots was selectively quenched by bilirubin compared to other biomolecules with a LOD of 2.03 μM. Use of C. dots as potential candidate for bilirubin detection was verified by real sample analysis. Further, the separation of C. dots was performed using column chromatography and the optical properties of the two different fractions obtained were studied. The blue fraction of C. dots was found to exhibit a higher fluorescence Q.Y and excitation independent emission, with an improved detection of PA and bilirubin.

Fluorescence copolymer-based dual-signal monitoring tyrosinase activity and its inhibitor screening via blue-green emission transformation

Tyrosinase (TYR) is a crucial enzyme in melanin metabolism and catecholamine production, its abnormal overexpression is closely associated with many human diseases involving melanoma cancer, vitiligo, Parkinson's disease and so on. Herein, a dual-signal fluorescence sensing system for monitoring TYR activity is constructed depending on the transformation of blue-green fluorescence emission of copolymer. The developed sensing system is based on TYR catalyzing the hydroxylation of mono-phenol to o-diphenol and the conversion of fluorescence copolymer (FCP) blue emission (430 nm) and green emission (535 nm) in the presence of PEI. In the system, both blue and green emission exhibit a high selectivity and sensitivity (S/B up to 300 and 30 for blue and green emission, respectively) toward TYR in the range from 0.5 to 2.5 U/mL with the detection limit of 0.002 U/mL and 0.06 U/mL, respectively. Additionally, this assay is used to detect TYR in human serum with excellent recovery even at 30% human serum concentrations. Furthermore, it still has been successfully applied to TYR inhibitor screening by taking kojic acid as a model. We believe that our developed sensor has great potential application in TYR-associated disease diagnosis and treatment and drug discovery.

A highly sensitive and adjustable colorimetric assay of hydrogen sulfide by signal amplification based on G-quadruplex-Cu2+ peroxidase mimetics

This work reports the first example of a colorimetric H2S sensor constructed through G-quadruplex-Cu2+ (G4-Cu2+) peroxidase mimetics employing Cu2+ ions and G-rich DNA with signal amplification. In the hydrogen peroxide (H2O2)-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), the catalytic capacity of Cu2+ can be greatly improved in the presence of 22AG DNA, where 22AG DNA acts as a signal amplifier. However, G4-Cu2+ peroxidase mimetics lose their catalytic abilities after reacting with H2S. This is employed to develop a colorimetric assay of H2S without complex synthesis and instrumentation, with a linear range from 0.01 μM to 150 μM and a detection limit of 7.5 nM. The sensitivity of the sensor can also be adjusted by changing the concentration of Cu2+. Moreover, the developed sensor is successfully applied for the quantitative determination of H2S in human serum samples.

An inner filter effect based sensing system for the determination of caffeine in beverage samples

In this work, the inner filter effect (IFE) of caffeine (CF) over the fluorescence signal of glibenclamide (GLB) was used for the determination of CF in beverage samples. The system worked in a turn-off mode since the absorption spectrum of CF overlaps the excitation band of GLB resulting in a decline in its fluorescence signal (λexc = 234 nm, λem = 350 nm). No changes in the fluorescence lifetime of GLB (0.29 ns) were observed in the presence of CF up to 127.6 mg L-1 concentration. The parameters that affect the fluorescence intensity were investigated, such as fluorophore concentration (16 mg L-1), pH (3.2) and temperature (25 °C). Under optimized conditions, the IFE-based approach can determine CF in a range between 1.00 and 100.0 mg L-1, with a detection limit (LOD) of 0.10 mg L-1. The relative standard deviation (% RSD) values for the intra-day and inter-day precision were 0.75 and 1.24, respectively. The new method was successfully tested in the determination of the target analyte in beverage samples without previous treatment. The results were compared with those obtained by a reference method, leading to the conclusion that there were no significant differences at the studied confidence level (α = 0.05).

Natural Polyphenol-Vanadium Oxide Nanozymes for Synergistic Chemodynamic/Photothermal Therapy

The selection of suitable nanozymes with easy synthesis, tumor specificity, multifunction, and high therapeutics is meaningful for tumor therapy. Herein, a facile one-step assembly approach was employed to successfully prepare a novel kind of natural polyphenol tannic acid (TA) hybrid with mixed valence vanadium oxide nanosheets (TA@VO_x NSs). In this system, VO_x is assembled with TA through metal-phenolic coordination interaction to both introduce superior peroxidase-like activity and high near infrared (NIR) absorption owing to partial reduction of vanadium from V⁵⁺ to V⁴⁺ . The presence of mixed valence vanadium oxide in TA@VO_x NSs is proved to be the key for the catalytic reaction of hydrogen peroxide (H₂ O₂ ) to ^. OH, and the corresponding catalytic mechanism of H₂ O₂ by TA@VO_x NSs is proposed. Benefitting from such peroxidase-like activity of TA@VO_x NSs, the overproduced H₂ O₂ of the tumor microenvironment allows the realization of tumor-specific chemodynamic therapy (CDT). As a valid supplement to CDT, the NIR absorption enables TA@VO_x NSs to have NIR light-mediated conversion ability for photothermal therapy (PTT) of cancers. Furthermore, in vitro and in vivo experiments confirmed that TA@VO_x NSs can effectively inhibit the growth of tumors by synergistic CDT/PTT. These results offer a promising way to develop novel vanadium oxide-based nanozymes for enhanced synergistic tumor-specific treatment.

Porphyrins as Colorimetric and Photometric Biosensors in Modern Bioanalytical Systems

Advances in porphyrin chemistry have provided novel materials and exciting technologies for bioanalysis such as colorimetric sensor array (CSA), photo-electrochemical (PEC) biosensing, and nanocomposites as peroxidase mimetics for glucose detection. This review highlights selected recent advances in the construction of supramolecular assemblies based on the porphyrin macrocycle that provide recognition of various biologically important entities through the unique porphyrin properties associated with colorimetry, spectrophotometry, and photo-electrochemistry.

Light-activated semiconducting polymer dots as mimic oxidases with remarkable catalytic efficiency: characteristics, mechanisms, and applications

Herein we demonstrate the characteristics, mechanisms, and applications of light-activated semiconducting polymer dots as mimic oxidases with remarkable catalytic efficiency.

Highly specific monitoring and imaging of endogenous and exogenous cysteine in living cells

Cys is one of the important biothiols and its abnormal concentration may pose a threat to human health. Therefore, the monitoring of Cys in organisms is of great significance. GSH and Hcy, as the other two biothiols, have similar chemical structures and active sites to Cys. Consequently, developing fluorescent probes to independently detect Cys has become a challenging problem. Keeping this in mind, α-β unsaturated ketone as a recognition group was integrated into the coumarin group skeleton to synthesize a fluorescent probe SC. After the nucleophilic addition reaction of Cys with SC, the conjugated system of SC was blocked and the fluorescent enhanced obviously. SC was able to detect Cys specifically under the same excitation with a low detection limit (11.1 nM). SC showed a rapid respond to Cys (120 s) and good fluorescent stability over a wide pH range. In addition, it achieved extracorporeal circulation in the presence of H₂O₂ or NEM. In the end, SC could be applied to detecting endogenous and exogenous Cys under biological condition due to its slight cytotoxicity and good biocompatibility. This provided a powerful tool for studying the physiological function of Cys exclusively.

Self-Referenced Ratiometric Detection of Sulfatase Activity with Dual-Emissive Urease-Encapsulated Gold Nanoclusters

In this study, on the basis of the biomineralization capability of urease, a facile, one-step, and green synthetic method has been proposed for the fabrication of gold nanoclusters (AuNCs). The prepared urease-encapsulated AuNCs (U-AuNCs) exhibited strong red fluorescence emission (λ_em = 630 nm) with a quantum yield as high as 17%. Interestingly, at a low concentration, the U-AuNC solution was found to be a dual-emissive system with the blue emission of the dityrosine (diTyr) residues of urease and the red emission of the embedded AuNCs. Further experiments demonstrated that p-nitrophenol (PNP) can selectively suppress the 410 nm emission of the diTyr residues of U-AuNCs without affecting the red emission of the U-AuNCs. The fluorescence quenching mechanism between U-AuNCs and PNP was systematically studied, and the leading role of the inner filter effect (IFE) was identified. Additionally, based on the sulfatase-catalyzed hydrolysis of p-nitrophenyl sulfate (PNPS) to release PNP, a self-referenced ratiometric detection method for sulfatase, which plays a crucial role in sulfur cycling, degradation of sulfated glycosaminoglycans and glycolipids, and extracellular remodeling of sulfated glycosaminoglycans, was developed by using dual-emissive U-AuNCs as the signal readout, in which the diTyr residues served as the probe and the AuNCs functioned as the internal reference. This IFE-based ratiometric sensing strategy showed a good linear relationship over the range of 0.01-1 U/mL ( R² = 0.997). The detection limit for sulfatase activity was 0.01 U/mL. The developed protocol was successfully used to detect sulfatase activity in human serum samples. The simplicity, rapidity, low cost, high credibility, good reproducibility, and excellent selectivity of the detection platform serve as an inspiration for further applications of fluorescent AuNCs in chemo/biosensing.

Colorimetric determination of glutathione by using a nanohybrid composed of manganese dioxide and carbon dots

A kind of single-layer carbon based dots (CDs) with abundant carboxyl functional groups was hybridized with manganese dioxide (MnO₂). The resulting nanohybrid is stable and can be well dispersed in water. MnO₂ is capable of oxidizing the substrate 3,3'5,5'-tetramethylbenzidine (TMB) to form a blue product whose absorption (peaking at 655 nm) fades in the presence of glutathione (GSH). A sensitive and selective colorimetric GSH assay was worked out that has a linear response in the 10 to 0.1 µM GSH concentration range, with a 0.095 μM detection limit. The method was applied to the determination of GSH in spiked fetal calf serum where it gave excellent recoveries. Graphical abstract Schematic of the preparation of a nanohybrid composed of manganese dioxide and carbon based dots (MnO₂/CDs). They can be used for the colorimetric detection of glutathione (GSH) based on the color change of 3,3'5,5'-tetramethylbenzidine (TMB).

Novel chemiluminescent immunochromatographic assay using a dual-readout signal probe for multiplexed detection of pesticide residues

A novel immunochromatographic assay utilizing luminol-reduced Au nanoparticles as a colorimetric/chemiluminescent dual-readout signal probe was developed for multiplexed detection of pesticide residues.

Highly sensitive fluorescent detection of glutathione and histidine based on the Cu(ii)-thiamine system

A novel fluorescence method for the simultaneous detection of glutathione and histidine based on their inhibitory effects on the oxidation of thiamine by Cu(ii) is proposed.

Inner filter effect-based fluorescent sensing systems: A review

Inner filter effect (IFE) was previously considered as an error in fluorescence measurement. In recent years, it has been developed as an important non-irradiation energy conversion model of spectroscopic technique and found wide applications in the fields of chemical sensing and biosensing. In comparison with traditional techniques based on forster resonance energy transfer (FRET), the IFE-based fluorescent approach is more flexible and straightforward without the link of absorber with fluorescer. The present review for the first time introduces the state of the art in the progress of the IFE-based fluorescent sensing systems, including sensing strategy, essential conditions, materials option, and their applications for the detection of various target analytes, e.g., ionic species, small molecules, and macromolecules. In addition, the benefits and limitations of the IFE-based fluorescent sensing systems are also critically discussed and highlighted.

Luminescent Lanthanide-Based Organic/Inorganic Hybrid Materials for Discrimination of Glutathione in Solution and within Hydrogels

Glutathione (GSH) as a biothiol is an essential peptide related to various diseases. Although multiple strategies for biothiols detection have been developed, there is increasing demand for sensors that can differentiate GSH from cysteine (Cys) and homocysteine (Hcy), owing to the similar structures and thiol groups in these amino acids. Herein, we report a novel Eu³⁺/LAPONITE (Lap)-based organic/inorganic hybrid material for selective detection of GSH via an "off-on" process. The fluorescence of Eu(DPA)₃@Lap-Tris can be quenched by Cu²⁺ through photoinduced electron transfer (PET). The addition of GSH into the Eu(DPA)₃@Lap-Tris/Cu²⁺ system induces the removal of Cu²⁺ from Eu(DPA)₃@Lap-Tris and blocks PET, resulting in the recovery of fluorescence. This proposed assay demonstrates higher selectivity toward GSH than Cys and Hcy, and showed a detection limit of 162 nM within a linear range of 0.5-30 μM. Unlike other GSH selective sensors, this platform could be formed into a hydrogel while its sensitivity was maintained. The sensitive response to GSH in serum samples makes this platform an efficient tool for biological applications because of its ease of preparation, high selectivity, good biocompatibility, and low toxicity.

A phenazine-barbituric acid based colorimetric and ratiometric near-infrared fluorescent probe for sensitively differentiating biothiols and its application in TiO2 sensor devices

A colorimetric and ratiometric NIR fluorescent probe based on phenazine-barbituric acid was developed for biothiols and applied to detect in cells and construct TiO₂ sensor devices.