Simultaneous Electrochemical Determination of Glutathione and Glutathione Disulfide at a Nanoscale Copper Hydroxide Composite Carbon Ionic Liquid Electrode

Synthesis of Ag nanoparticles for selective dual detection of glutathione and dopamine using N, N-dimethyl-p-phenylenediamine mediated colorimetric probe

We report a simple and easy method to synthesize Ag nanoparticles (Ag NPs) and demonstrate its potential for the detection of glutathione (GSH) and dopamine (DA) via colorimetric assay. The Ag NPs were found to be monodispersed and spherical with a size of 5 ± 2 nm. The X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM) investigations revealed the formation of crystalline Ag NPs. The colour of N, N-dimethyl-p-phenylenediamine assay changed from dark pink to colourless when the concentration of GSH was increased from 1 to 40 μM. Notably, the suspension colour changed from dark pink to blue when a similar set of experiments were performed with DA. The UV/Visible and interference experiments of Ag NPs exhibited excellent sensitivity and selectivity against both GSH and DA even after the addition of 40 μM of different interference biomolecules. The calculated limit of detection (LOD) was 141 and 245 nM for GSH and DA, respectively. The real-time analysis with serum samples showed satisfactory recovery percentages of >95 and 80-90% for GSH and DA, respectively. Hence, the Ag NPs reported here have huge potential to serve as a sensitive and selective colorimetric sensor for the detection of GSH and DA for diverse applications ranging from catalysis to cancer therapy and theranostics.

In vivo monitoring of glutathione in a live rat brain based on the ratiometric signal output of 2D Cu-TCPP(Fe) nanosheets

Herein, a novel ratiometric electrochemical platform was developed for in vivo analysis of GSH based on the dual signal output of 2D Cu-TCPP(Fe) nanosheets. Our method with high selectivity and high accuracy enabled GSH monitoring in a live rat brain, and accurate GSH concentrations were firstly reported in different brain regions upon global cerebral ischemia.

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.

Covalent organic framework-MnO2 nanoparticle composites for shape-selective sensing of bithiols

Covalent organic frameworks (COFs) for detecting biological macromolecules in water or biological environments are generally challenging. In this work, a composite material IEP-MnO₂ is obtained by combining manganese dioxide (MnO₂) nanocrystals and a fluorescent COF (IEP), which is synthesized by using 2,4,6-tris(4-aminophenyl)-s-triazine and 2,5-dimethoxyterephthalaldehyde. By the addition of biothiols, such as glutathione, cysteine or homocysteine with different sizes, the fluorescence emission spectra of IEP-MnO₂ changed ("turn-on" or "turn-off") via different mechanisms. The fluorescence emission of IEP-MnO₂ increased in the presence of GSH by the elimination of the FRET (Förster resonance energy transfer) effect between MnO₂ and IEP. Surprisingly, due to the formation of a hydrogen bond between Cys/Hcy and IEP, the fluorescence quenching for IEP-MnO₂ + Cys/Hcy may be explained via the photoelectron transfer (PET) process, which endows IEP-MnO₂ with specificity in distinguishing the detection of GSH and Cys/Hcy compared to other MnO₂ complex materials. Therefore, IEP-MnO₂ was used to detect GSH and Cys in human whole blood and serum, respectively. The limit of detection for GSH in whole blood and Cys in human serum was calculated to be 25.58 μM and 4.43 μM, which indicates that IEP-MnO₂ can be used to investigate some diseases related to GSH and Cys concentration. Moreover, the research expands the application of covalent organic frameworks in the fluorescence sensing field.

Anodic SnO2 Nanoporous Structure Decorated with Cu2O Nanoparticles for Sensitive Detection of Creatinine: Experimental and DFT Study

Advanced anodic SnO₂ nanoporous structures decorated with Cu₂O nanoparticles (NPs) were employed for creatinine detection. Anodization of electropolished Sn sheets in 0.3 M aqueous oxalic acid electrolyte under continuous stirring produced complete open top, crack-free, and smooth SnO₂ nanoporous structures. Structural analyses confirm the high purity of rutile SnO₂ with successful functionalization of Cu₂O NPs. Morphological studies revealed the formation of self-organized and highly-ordered SnO₂ nanopores, homogeneously decorated with Cu₂O NPs. The average diameter of nanopores is ∼35 nm, while the average Cu₂O particle size is ∼23 nm. Density functional theory results showed that SnO₂@Cu₂O hybrid nanostructures are energetically favorable for creatinine detection. The hybrid nanostructure electrode exhibited an ultra-high sensitivity of around 24343 μA mM^-1 cm^-2 with an extremely lower detection limit of ∼0.0023 μM, a fast response time (less than 2 s), and wide linear detection ranges of 2.5-45 μM and 100 μM to 15 mM toward creatinine. This is ascribed to the creation of highly active surface sites as a result of Cu₂O NP functionalization, SnO₂ band gap diminution, and the formation of heterojunction and Cu(1)/Cu(ll)-creatinine complexes through secondary amines which occur in the creatinine structure. The real-time analysis of creatinine in blood serum by the fabricated electrode evinces the practicability and accuracy of the biosensor with reference to the commercially existing creatinine sensor. The proposed biosensor demonstrated excellent stability, reproducibility, and selectivity, which reflects that the SnO₂@Cu₂O nanostructure is a promising candidate for the non-enzymatic detection of creatinine.

Construction of an aggregation-induced electrochemiluminescent sensor based on an aminal-linked covalent organic framework for sensitive detection of glutathione in human serum

We demonstrate the construction of an aggregation-induced electrochemiluminescent (AIECL) sensor for glutathione (GSH) assay by integrating an aminal-linked covalent organic framework (A-COF) with manganese dioxide (MnO₂) nanosheets. The AIECL of the A-COF is quenched by the MnO₂ nanosheets via electrochemiluminescent resonance energy transfer (ERET) from the excited A-COF to MnO₂. The presence of GSH can reduce the MnO₂ nanosheets into Mn²⁺, restoring the AIECL emission of the A-COF. This AIECL sensor has the characteristics of fast response, high sensitivity, and good selectivity toward GSH, and it can accurately measure GSH in human serum.

Voltammetric studies of glutathione transfer across arrays of liquid-liquid microinterfaces for sensing applications

The simple and facilitated transfer of tripeptide glutathione across the water/2-nitrophenyl octhyl ether interface was studied via cyclic voltammetry at interface between two immiscible electrolyte solutions (ITIES). The micro-perforated membrane prepared with a laser with a femtosecond pulse was used for mechanical stabilization of the interface. The method of cyclic voltammetry was used to study the passive and facilitated interfacial transfer of glutathione and its complex with the crown ether dibenzo-18-crown-6 (DB18C6).The glutathione mass transfer mechanism was established and substantiated, the diffusion coefficients, thermodynamic characteristics of interphase transfer and the constant of complexation of the glutathione by DB18C6 were determined. Square wave voltammetry based on facilitated transfer was used for more accurate and sensitive determination of glutathione low detection limit (0.8 μM) with wide linear dynamic range (from 3.0 to 80 μM) was reached. The influence of various potentially interfering ions on the voltammetric determination of glutathione has also been investigated. The method developed was applied to determine glutathione in aqueous solutions and malt extract.

Synthesis of a Novel Electrochemical Probe for the Sensitive and Selective Detection of Biothiols and Its Clinical Applications

The ability to estimate and quantify biothiols in biological fluids is very significant for attaining a detailed understanding of biothiols-related pathological diseases. Most of the developed methods for biothiols detection are not suitable for this purpose owing to their low sensitivity, poor selectivity, and long experimental procedures. In this study, a novel and simple structure electrochemical probe has been synthesized for the first time for the selective determination of biothiols. The developed probe is based on using 2,4-dinitrobenzenesulfonyl moiety (DNBS) as a selective recognition moiety for biothiols. The electrochemical probe was successfully fabricated through a facile one-step reaction between 2,4-dinitrobenzenesulfonyl chloride (DNBS-Cl) and p-aminophenol. The successful synthesis of the probe was confirmed by using different characterization techniques such as an NMR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and mass spectrometry. Biothiols can selectively cleave the DNBS moiety through an aromatic nucleophilic substitution (ANS) reaction within 10 min to release p-aminophenol, which is a highly electrochemical active molecule that can be selectively detected easily by cyclic voltammetry at low potential. The probe has been employed for the quantification of cysteine, glutathione, and homocysteine with a LOD of 1.50, 3.48, and 4.67 μM, respectively. Excellent recoveries have been achieved in the range of 95.44-98.71% for the determination of the total biothiols in the human plasma sample.

Highly selective and sensitive detection of glutathione over cysteine and homocysteine with a turn-on fluorescent biosensor based on cysteamine-stabilized CdTe quantum dots

In this work, cysteamine (CA) stabilized CdTe quantum dots (QDs) (CA-CdTe QDs) and sodium citrate stabilized gold nanoparticles (AuNPs) were prepared. Because of the strong electrostatic interaction and spectral overlap of emission spectrum of CA-CdTe QDs and absorption spectrum of AuNPs, a highly effective fluorescence resonance energy transfer (FRET) system was formed and the fluorescence of CA-CdTe QDs was strongly quenched. The synthesized CA-CdTe and AuNPs were self-assembled to large clusters due to the electrostatic attraction and the fluorescence of CA-CdTe was sharply quenched as a result of FRET. Under the optimum pH of 5.5, the positive GSH could assemble with negative AuNPs through electrostatic interaction and destroy the FRET system of CA-CdTe and AuNPs, due to the red shift of absorption wavelength of AuNPs caused by aggregation. The fluorescence of CA-CdTe recovered, and the recovered fluorescence efficiency shows a linear function against the GSH concentrations from 6.7 nM to 0.40 μM, with a detecting limit of 3.3 nM. The quenched emission of CA-CdTe could be recovered attributed to the aggregation of AuNPs by GSH. Under optimal conditions, the sensing system was successfully applied in the detection of GSH in real human blood plasma samples with a recovery of 99.5-102.3%, showing a promising future for the highly sensitive and selective GSH detection in the human blood plasma samples.

Electrochemical sensing platform for the detection of methyl parathion applying highly biocompatible non-covalent functionalized phosphonium-based ionic liquid@MWCNTs hybrid to immobilize hemoglobin

A hydrophobic carboxyl functionalized phosphonium-based ionic liquid (IL) ((5-carboxypentyl) triphenylphosphonium bis (trifluoromethyl)sulfonyl) amide, TPP-HA[TFSI]) was synthesized through a simple hydrothermal approach. Based on the π-π and cation-π interactions with multi-wall carbon nanotubes (MWCNTs), a TPP-HA[TFSI]@MWCNTs hybrid was prepared to immobilize hemoglobin (Hb) to fabricate a simple and effective electrochemical sensing platform for the detection of methyl parathion (MP) in vegetables. Spectroscopic and electrochemical results show that TPP-HA[TFSI]@MWCNTs substrate synergistically provided a good biocompatible microenvironment for Hb, and the hydrophobicity of TPP-HA[TFSI] and the π-π interaction and hydrogen bonding between TPP-HA[TFSI]@MWCNTs, Hb and nafion (NF) were conducive to maintain the stability and integrity of the modified electrode interface. The TPP-HA[TFSI]@MWCNTs with large surface area and high conductivity promoted the exposure of the electroactive center of Hb and the direct electron transfer between Hb and the electrode, which effectively amplified the electrochemical signal and improved the sensitivity of MP detection. The constructed electrochemical sensing platform had a wider linear range (2-14 ng mL^-1) and a lower detection limit (0.62 ng mL^-1) for MP, and had acceptable repeatability, reproducibility, stability and anti-interference ability. This results indicated that the phosphonium-based ILs functionalized MWCNTs was an effective substrate for the immobilization of biological components, which have broad prospect in the construction of electrochemical sensing interfaces.

Highly sensitive and selective detection of glutathione using ultrasonic aided synthesis of graphene quantum dots embedded over amine-functionalized silica nanoparticles

Glutathione (GSH) is the most abundant antioxidant in the majority of cells and tissues; and its use as a biomarker has been known for decades. In this study, a facile electrochemical method was developed for glutathione sensing using voltammetry and amperometry analyses. In this study, a novel glassy carbon electrode composed of graphene quantum dots (GQDs) embedded on amine-functionalized silica nanoparticles (SiNPs) was synthesized. GQDs embedded on amine-functionalized SiNPs were physical-chemically characterized by different techniques that included high resolution-transmission electron microscopy (HR-TEM), X-ray diffraction spectroscopy (XRD), UV-visible spectroscopy, Fourier-transform infrared spectroscopy(FTIR), and Raman spectroscopy. The newly developed electrode exhibits a good response to glutathione with a wide linear range (0.5-7 µM) and a low detection limit (0.5 µM) with high sensitivity(2.64 µA µM-1). The fabricated GQDs-SiNPs/GC electrode shows highly attractive electrocatalytic activity towards glutathione detection in the neutral media at low potential due to a synergistic surface effect caused by the incorporation of GQDs over SiNPs. It leads to higher surface area and conductivity, improving electron transfer and promoting redox reactions. Besides, it provides outstanding selectivity, reproducibility, long-term stability, and can be used in the presence of interferences typically found in real sample analysis.

Potent Acrylamide Determination in Food Products Using Ion-Selective Electrode Technique

A potent selective acrylamide liquid sensor based on the reaction of acrylamide with 2-(5-Bromo-2-pyridylazo)-5-[N-n-Propyl-N-(3-Sulfopropyl) amino] aniline reagent is successfully designed. The characteristics slope (52.33 mV/decade), linearity usable range from 1.0 × 10⁻⁷–1.0 × 10⁻¹ molar, limit of detection (1.6 × 10⁻⁸) molar, selectivity attitude to several inorganic cations, amino acids and sugars, time of response (8 s), lifetime (four months), pH effect on the electrode potential and the basic validation parameters were studied. The desirable pH applicable range was 3.0–6.5, and the restraint of the developed sensor is independent on this working pH range. The deployed electrode was effectively applied for rapid inexpensive analysis of acrylamide cations in food products with comparison to high-performance liquid chromatographic method and the results were agreeable with each other. The obtained data by the suggested electrode were treated statistically and compared with the various recently published acrylamide sensors.

Recent advances of the ionic chiral selectors for chiral resolution by chromatography, spectroscopy and electrochemistry

Ionic chiral selectors have been received much attention in the field of asymmetric catalysis, chiral recognition, and preparative separation. It has been shown that the addition of ionic chiral selectors can enhance the recognition efficiency dramatically due to the presence of multiple intermolecular interactions, including hydrogen bond, π-π interaction, van der Waals force, electrostatic ion-pairing interaction, and ionic-hydrogen bond. In the initial research stage of the ionic chiral selectors, most of work center on the application in chromatographic separation (capillary electrophoresis, high-performance liquid chromatography, and gas chromatography). Differently, more and more attention has been paid on the spectroscopy (nuclear magnetic resonance, fluorescence, ultraviolet and visible absorption spectrum, and circular dichroism spectrum) and electrochemistry in recent years. In this tutorial review as regards the ionic chiral selectors, we discuss in detail the structural features, properties, and their application in chromatography, spectroscopy, and electrochemistry.

Cyclic Voltammetry in Biological Samples: A Systematic Review of Methods and Techniques Applicable to Clinical Settings

Oxidative stress plays a pivotal role in the pathogenesis of many diseases, but there is no accurate measurement of oxidative stress or antioxidants that has utility in the clinical setting. Cyclic Voltammetry is an electrochemical technique that has been widely used for analyzing redox status in industrial and research settings. It has also recently been applied to assess the antioxidant status of in vivo biological samples. This systematic review identified 38 studies that used cyclic voltammetry to determine the change in antioxidant status in humans and animals. It focusses on the methods for sample preparation, processing and storage, experimental setup and techniques used to identify the antioxidants responsible for the voltammetric peaks. The aim is to provide key information to those intending to use cyclic voltammetry to measure antioxidants in biological samples in a clinical setting.

Smart phone assisted quinoline-hemicyanine based fluorescent probe for the selective detection of glutathione and the application in living cells

Quinoline appended hemicyanine 6MIM with strong ICT character was successfully synthesized through simple condensation reaction of 6-methoxy-2-chloro-3-formyl quinoline with 2-benzothiazolinium iodide. The photophysical characteristics of synthesized probe revealed that it would selectively detect glutathione (GSH) when it compared with different amino acids including biothiols and the detection limit is found to be 100 nM. The turn off sensor is due to thiol-halogen S_NAr nucleophilic substitution between 6MIM and thiol group in glutathione. More importantly, the biosensor 6MIM was effectively applied in the fluorescence bioimaging of GSH in living cells with low cell toxicity. The colorimetric detectable color change of 6MIM-GSH has been effectively integrated with smartphone assisted RGB color value application with lowest detection value of 120 nM.

ABTS radical-based single reagent assay for simultaneous determination of biologically important thiols and disulfides

Both the total amount of biothiols and thiol/disulfide ratio are wellness indicators of oxidative balance that play an important role in antioxidant defense system. Oxidized biothiols in disulfide form cannot be determined by conventional ABTS assay due to the biphasic kinetic pattern of the reaction between biothiols and ABTS radical cation (ABTS^•+), necessitating the initial reduction of disulfides to thiols prior to measurement. In this study, direct simultaneous determination of biothiols (RSH) and their disulfides (RSSR) by using a single reagent of ABTS^•+ was achieved without preliminary chemical reduction. Thus, conventional problems of preliminary operations arising from direct borohydride reduction of disulfides to thiols, followed by formaldehyde removal of borohydride excess and complications caused by formaldehyde-thiol reactions were effectively overcome with the use of a single reagent (ABTS^•+). Box-Behnken statistical experimental design was employed to specify the optimal incubation temperature and time as 60 °C and 60 min, respectively. The detection limits (LOD) of the proposed assay for biothiols were compared to those of the widely used DTNB (Ellman) reference assay known to be nonresponsive to disulfides, and were found to be much lower (4-70 times). The proposed biothiol assay was successfully applied to some pharmaceutical samples and synthetic serum without preliminary treatment, and the results were highly compatible with the HPLC findings. The proposed assay was demonstrated to have superior features such as simplicity, rapidity and higher sensitivity over the widely applied Ellman thiols assay.

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.

Chemically Responsive Photonic Crystal Hydrogels for Selective and Visual Sensing of Thiol-Containing Biomolecules

Intracellular thiols (e.g., cysteine, homocysteine, and glutathione) play critical roles in biological functions. Glutathione is the most abundant cellular thiol which is important for preserving redox homeostasis in biosystems. Herein, we demonstrated the fabrication of responsive photonic crystals (RPCs) for selective detection of thiol-containing biomolecules through the combination of self-assembly of monodisperse carbon-encapsulated Fe3O4 nanoparticles (NPs) and in situ photopolymerization. Typically, the polyacrylamide-based PCs were prepared by a cross-linking agent containing disulfide bonds. Interestingly, the specific chemical reaction between the disulfide bonds and thiol-containing biomolecules leads to the decrease of the cross-linking degree for the RPCs, triggering the swelling of the hydrogel and increase of the NP lattice spacing. The reduced glutathione (10-6 to 10-2 mol/L) can be determined by measuring the diffracted wavelength or visually observing the structural color change. Moreover, the RPCs can be used to detect different kinds of thiol-containing biomolecules by a simple color variation due to different reaction rates between disulfide bonds and different thiol-containing biomolecules. This study provides a facile yet effective strategy for visualized determination of the thiol-containing biomolecules.

A novel ultrasensitive electrochemiluminescence biosensor for glutathione detection based on poly-L-lysine as co-reactant and graphene-based poly(luminol/aniline) as nanoprobes

In this work, an ultrasensitive electrochemiluminescence (ECL) biosensor was constructed using poly-L-lysine (PLL) as a novel co-reactant of luminol and poly(luminol/aniline) nanorods loaded reduced graphene oxide (PLA@rGO) as nanoprobe, which enable highly sensitivity detection of glutathione (GSH). To the best of our knowledge, it is the first time that PLL was used for the co-reactant of luminol. Notably, about a 5-fold enhancement was obtained compared with the individual PLA@rGO using GCE. Due to the remarkable quenching effect between the excited state of PLL and the reduced form of GSH in the ECL system of luminol/PLL, the ECL sensing platform exhibited wide linear ranges of 1.0 × 10^-9-1.0 × 10^-4 M and 1.0 × 10^-4-1.0 × 10^-2 M and a low detection limit of 7.7 × 10^-10 M. Simultaneously, the biosensor was also successfully applied to detect GSH in human serum sample with high recoveries. Hence, this work would open a new platform for the wide application of PLL in immunoassay and various sensors.

Novel molecularly imprinted polymer (MIP) multiple sensors for endogenous redox couples determination and their applications in lung cancer diagnosis

Multiplex electrochemical sensors for amperometric detection of glutathione disulfide (GSSG), glutathione (GSH), cysteine (Cys), cystine (Cyss), β-nicotinamide adenine dinucleotide phosphate (NADP⁺) and coenzyme II reduced tetrasodium salt (NADPH) were developed, in which analysis of Cyss, NADP⁺ and NADPH are the first report using this sensing system. Specificity of these sensors were ensured by a layer of molecularly imprinted polymer (MIP) which was electropolymerized in situ with the analytes as template. All the sensors were tested with standard buffers and mouse blood samples, showing satisfactory performance towards the corresponding analytes. Dynamic concentration for the six analytes was in the range of 10^-11-10^-8 mol/L with the detection limit down to 20 pmol/L. In addition, artificially synthesized MIP film on the electrodes allowed for good selectivity and stability. Real blood sample measurement proved that the sensors owned decent accuracy with recovery value ranging from 92%~112%. More importantly, blood samples from lung cancer patients and healthy donors were assayed by using the proposed sensors. Redox potentials (Ehc) were calculated based on the contents of these endogenic substances, which were utilized to reflect the health status of human body and help diagnose lung cancer. The levels of GSH, NADPH and the absolute value of Ehc_(GSH/GSSG) in patients with lung cancer are significantly lower (P < 0.01) than those in healthy people, while the contents of GSSG (P < 0.01) are higher. The blood test results suggested that the content of GSH, NADPH, NADP⁺ and Ehc_(GSH/GSSG) might serve as biomarkers for lung cancer prediagnosis. These novel sensors for liquid biospy of cancer have cost-benefit and scalability advantage over current techniques, potentially enabling broader clinical access and efficient population screening.

The synthesis of thiol-stabilized silver nanoparticles and their application towards the nanomolar-level colorimetric recognition of glutathione

The synthesis and characterization of 5-methyl-1,3,4-thiadiazole-2-thiol fabricated silver nanoparticles and their application to detect glutathione.

Nanomaterials: Electrochemical Properties and Application in Sensors

The unique properties of nanoparticles make them an extremely valuable modifying material, being used in electrochemical sensors. The features of nanoparticles affect the kinetics and thermodynamics of electrode processes of both nanoparticles and redox reactions occurring on their surface. The paper describes theoretical background and experimental studies of these processes. During the transition from macro- to micro- and nanostructures, the analytical characteristics of sensors modify. These features of metal nanoparticles are related to their size and energy effects, which affects the analytical characteristics of developed sensors. Modification of the macroelectrode with nanoparticles and other nanomaterials reduces the detection limit and improves the degree of sensitivity and selectivity of measurements. The use of nanoparticles as transducers, catalytic constituents, parts of electrochemical sensors for antioxidant detection, adsorbents, analyte transporters, and labels in electrochemical immunosensors and signal-generating elements is described.

Nitrogen-Doped Carbon Nanoparticles Derived from Silkworm Excrement as On⁻Off⁻On Fluorescent Sensors to Detect Fe(III) and Biothiols

On⁻off⁻on fluorescent sensors based on emerging carbon nanoparticles (CNPs) or carbon dots (CDs) have attracted extensive attention for their convenience and efficiency. In this study, dumped silkworm excrement was used as a novel precursor to prepare fluorescent nitrogen-doped CNPs (N-CNPs) through hydrothermal treatment. The obtained N-CNPs showed good photoluminescent properties and excellent water dispersibility. Thus, they were applied as fluorescence “on⁻off⁻on” probes for the detection of Fe(III) and biothiols. The “on⁻off” process was achieved by adding Fe(III) into N-CNP solution, which resulted in the selective fluorescence quenching, with the detection limit of 0.20 μM in the linear range of 1⁻500 μM. Following this, the introduction of biothiols could recover the fluorescence efficiently, in order to realize the “off⁻on” process. By using glutathione (GSH) as the representative, the linear range was in the range of 1⁻1000 μM, and the limit of detection was 0.13 μM. Moreover, this useful strategy was successfully applied for the determination of amounts of GSH in fetal calf serum samples.

Fluorescence detection of glutathione and oxidized glutathione in blood with a NIR-excitable cyanine probe

Cyanine has been widely utilized as a near infrared (NIR) fluorophore for detection of glutathione (GSH). However, the excitation of most of the reported cyanine-based probes was less than 800 nm, which inevitably induce biological background absorption and lower the sensitivity, limiting their use for detection of GSH in blood samples. To address this issue, here, a heptamethine cyanine probe (DNIR), with a NIR excitation wavelength at 804 nm and a NIR emission wavelength at 832 nm, is employed for the detection of GSH and its oxidized form (GSSG) in blood. The probe displays excellent selectivity for GSH over GSSG and other amino acids, and rapid response to GSH, in particular a good property for indirect detection of GSSG in the presence of enzyme glutathione reductase and the reducing agent nicotinamideadenine dinucleotide phosphate, without further separation prior to fluorescent measurement. To the best of our knowledge, this is the first attempt to explore NIR fluorescent approach for the simultaneous assay of GSH and GSSG in blood. As such, we expect that our fluorescence sensors with both NIR excitation and NIR emission make this strategy suitable for the application in complex physiological systems.

Facile electrochemiluminescence sensing platform based on high-quantum-yield gold nanocluster probe for ultrasensitive glutathione detection

This report outlines a highly sensitive and facile electrochemiluminescence (ECL) sensing platform based on a novel high-quantum-yield Au-nanocluster (AuNC) probe for glutathione (GSH) detection. Owing to the prominent quenching effect of GSH on the ECL of the AuNCs, the proposed ECL nanosensor showed a wide response to GSH in the ranges of 1.0 × 10^-9-1.0 × 10^-5M and 1.0 × 10^-5-1.0 × 10^-1M and a low detection limit of 3.2 × 10^-10M. In addition, the proposed system exhibited good selectivity for GSH in the presence of other chemical/biological interferences. Moreover, since no further functionalization of AuNC-based sensor interface was necessary, together with the stability, high sensitivity and selectivity of the proposed nanosensor, this convenient approach was able to successfully detect GSH in both of human urine samples and blood samples with excellent recoveries, which indicated its promising application under physiological conditions. Of significant importance is that this study not only helps in gaining a better understanding of the applicability of the ECL properties of AuNCs, but also provides a new avenue for the design and development of ECL sensors based on the novel high-quantum-yield AuNC-based probe and other functional-metal-based NC probes.

Biothiols induced colour change of silver nanoparticles: A colorimetric sensing strategy

A sensor for the detection and determination of bio-thiols (glutathione (GSH) and cysteamine (Cyste)) has been developed by integrating the distinguished distance related optical characteristics of silver nanoparticles with the simplicity of colorimetric technique. In presence of these analytes, shift in surface plasmon resonance (SPR) absorption of silver nanoparticles (AgNPs) with change in its colour was observed. Yellow coloured AgNPs solution becomes colourless in presence of GSH and changes to red in presence of Cyste. FTIR, TEM and DLS studies were used to confirm the mechanism. The difference in absorption of AgNPs in the absence and presence of GSH was found to vary linearly in the range 1.00×10^-5M to 5.00×10^-7M concentration range with limit of detection at 3.68×10^-7M. The method can also be applied to quantify Cyste in the range 1.10×10^-6M to 5.00×10^-8M with limit of detection at 1.80×10^-8M. The utility of the proposed colorimetric assay is validated by determination of GSH and Cyste in artificial blood serum.

Chemical analysis in saliva and the search for salivary biomarkers – a tutorial review

A review of the uses of saliva biomarkers, detection methods and requirements for new biomarkers.

Sonochemical synthesis of silver nanoparticles anchored reduced graphene oxide nanosheets for selective and sensitive detection of glutathione

Developed here an eco-friendly, one-pot approach toward rapid synthesis of silver nanoparticles anchored reduced graphene oxide (AgNPs_(TMSPED)-rGO) nanosheets via sonochemical irradiation method, using an aqueous solution mixture of GO and AgNO₃ in the presence of N-[3(trimethoxysilyl)propyl] ethylenediamine (TMSPED) without any reducing agent. As synthesized decorated nanosheets was thoroughly characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Pristine AgNPs_(TMSPED), pristine rGO_(TMSPED) and as prepared AgNPs_(TMSPED)-rGO materials were employed to modify the glassy carbon (GC) electrode and demonstrated its excellent electrocatalytic activities towards glutathione (GSH). Voltammetry and amperometry measurements were utilized to assess the electrochemical properties towards the glutathione detection. When the Ag nanoparticles were anchored onto the rGO surface, the observed results illustrated that the electrocatalytic properties of rGO might be enhanced. The resulting sensor exhibits excellent repeatability and long-term stability. Furthermore, AgNPs_(TMSPED)-rGO/GC electrode able to be employed for the selective determination of GSH in amperometric analysis in the presence of ascorbic acid (AA), dopamine (DA), uric acid (UA) and glucose. Finally, this modified electrode was effectively applied to determine glutathione in real samples with good recoveries.

Introducing Ratiometric Fluorescence to MnO2 Nanosheet-Based Biosensing: A Simple, Label-Free Ratiometric Fluorescent Sensor Programmed by Cascade Logic Circuit for Ultrasensitive GSH Detection

Glutathione (GSH) plays crucial roles in various biological functions, the level alterations of which have been linked to varieties of diseases. Herein, we for the first time expanded the application of oxidase-like property of MnO₂ nanosheet (MnO₂ NS) to fluorescent substrates of peroxidase. Different from previously reported fluorescent quenching phenomena, we found that MnO₂ NS could not only largely quench the fluorescence of highly fluorescent Scopoletin (SC) but also surprisingly enhance that of nonfluorescent Amplex Red (AR) via oxidation reaction. If MnO₂ NS is premixed with GSH, it will be reduced to Mn²⁺ and lose the oxidase-like property, accompanied by subsequent increase in SC's fluorescence and decrease in AR's. On the basis of the above mechanism, we construct the first MnO₂ NS-based ratiometric fluorescent sensor for ultrasensitive and selective detection of GSH. Notably, this ratiometric sensor is programmed by the cascade logic circuit (an INHIBIT gate cascade with a 1 to 2 decoder). And a linear relationship between ratiometric fluorescent intensities of the two substrates and logarithmic values of GSH's concentrations is obtained. The detection limit of GSH is as low as 6.7 nM, which is much lower than previous ratiometric fluorescent sensors, and the lowest MnO₂ NS-based fluorescent GSH sensor reported so far. Furthermore, this sensor is simple, label-free, and low-cost; it also presents excellent applicability in human serum samples.

Comparison of glutathione levels measured using optimized monochlorobimane assay with those from ortho-phthalaldehyde assay in intact cells

Fluorometric glutathione assays have been generally preferred for their high specificity and sensitivity. An additional advantage offered by fluorescent bimane dyes is their ability to penetrate inside the cell. Their ability to react with glutathione within intact cells is frequently useful in flow cytometry and microscopy. Hence, the aims of our study were to use monochlorobimane for optimizing a spectrofluorometric glutathione assay in cells and then to compare that assay with the frequently used ortho-phthalaldehyde assay. We used glutathione-depleting agents (e.g., cisplatin and diethylmalonate) to induce cell impairment. For glutathione assessment, monochlorobimane (40μM) was added to cells and fluorescence was detected at 394/490nm. In addition to the regularly used calculation of glutathione levels from fluorescence change after 60min, we used an optimized calculation from the linear part of the fluorescence curve after 10min of measurement. We found that 10min treatment of cells with monochlorobimane is sufficient for evaluating cellular glutathione concentration and provides results entirely comparable with those from the standard ortho-phthalaldehyde assay. In contrast, the results obtained by the standardly used evaluation after 60min of monochlorobimane treatment provided higher glutathione values. We conclude that measuring glutathione using monochlorobimane with the here-described optimized evaluation of fluorescence signal could be a simple and useful method for routine and rapid assessment of glutathione within intact cells in large numbers of samples.

Glassy carbon electrode modified with 7,7,8,8-tetracyanoquinodimethane and graphene oxide triggered a synergistic effect: Low-potential amperometric detection of reduced glutathione

A sensitive electrochemical sensor based on the synergistic effect of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and graphene oxide (GO) for low-potential amperometric detection of reduced glutathione (GSH) in pH 7.2 phosphate buffer solution (PBS) has been reported. This is the first time that the combination of GO and TCNQ have been successfully employed to construct an electrochemical sensor for the detection of glutathione. The surface of the glassy carbon electrode (GCE) was modified by a drop casting using TCNQ and GO. Cyclic voltammetric measurements showed that TCNQ and GO triggered a synergistic effect and exhibited an unexpected electrocatalytic activity towards GSH oxidation, compared to GCE modified with only GO, TCNQ or TCNQ/electrochemically reduced GO. Three oxidation waves for GSH were found at -0.05, 0.1 and 0.5V, respectively. Amperometric techniques were employed to detect GSH sensitively using a GCE modified with TCNQ/GO at -0.05V. The electrochemical sensor showed a wide linear range from 0.25 to 124.3μM and 124.3μM to 1.67mM with a limit of detection of 0.15μM. The electroanalytical sensor was successfully applied towards the detection of GSH in an eye drop solution.