Self-Immolative Electrochemical Redox Substrates: Emerging Artificial Receptors in Sensing and Biosensing.

The development of artificial receptors has great significance in measurement science and technology. The need for a robust version of natural receptors is getting increased attention because the cost of natural receptors is still high along with storage difficulties. Aptamers, imprinted polymers, and nanozymes are some of the matured artificial receptors in analytical chemistry. Recently, a new direction has been discovered by organic chemists, who can synthesize robust, activity-based, self-immolative organic molecules that have artificial receptor properties for the targeted analytes. Specifically designed trigger moieties implant selectivity and sensitivity. These latent electrochemical redox substrates are highly stable, mass-producible, inexpensive, and eco-friendly. Combining redox substrates with the merits of electrochemical techniques is a good opportunity to establish a new direction in artificial receptors. This Review provides an overview of electrochemical redox substrate design, anatomy, benefits, and biosensing potential. A proper understanding of molecular design can lead to the development of a library of novel self-immolative redox molecules that would have huge implications for measurement science and technology.

Porous Laser-Scribed Graphene Electrodes Modified with Zwitterionic Moieties: A Strategy for Antibiofouling and Low-Impedance Interfaces.

Laser-scribed graphene electrodes (LSGEs) are promising platforms for the development of electrochemical biosensors for point-of-care settings and continuous monitoring and wearable applications. However, the frequent occurrence of biofouling drastically reduces the sensitivity and selectivity of these devices, hampering their sensing performance. Herein, we describe a versatile, low-impedance, and robust antibiofouling interface based on sulfobetaine-zwitterionic moieties. The interface induces the formation of a hydration layer and exerts electrostatic repulsion, protecting the electrode surface from the nonspecific adsorption of various biofouling agents. We demonstrate through electrochemical and microscopy techniques that the modified electrode exhibits outstanding antifouling properties, preserving more than 90% of the original signal after 24 h of exposure to bovine serum albumin protein, HeLa cells, and Escherichia coli bacteria. The promising performance of this antifouling strategy suggests that it is a viable option for prolonging the lifetime of LSGEs-based sensors when operating on complex biological systems.

Polyoxometalate-cyclodextrin supramolecular entities for real-time in situ monitoring of dopamine released from neuroblastoma cells.

Optimized and sensitive biomarker detection has recently been shown to have a critical impact on quality of diagnosis and medical care options. In this research study, polyoxometalate-γ-cyclodextrin metal-organic framework (POM-γCD MOF) was utilized as an electrocatalyst to fabricate highly selective sensors to detect in-situ released dopamine. The POM-γCD MOF produced multiple modes of signals for dopamine including electrochemical, colorimetric, and smartphone read-outs. Real-time quantitative monitoring of SH-SY5Y neuroblastoma cellular dopamine production was successfully demonstrated under various stimuli at different time intervals. The POM-CD MOF sensor and linear regression model were used to develop a smartphone read-out platform, which converts dopamine visual signals to digital signals within a few seconds. Ultimately, POM-γCD MOFs can play a significant role in the diagnosis and treatment of various diseases that involve dopamine as a significant biomarker.

Metal-Organic Frameworks Meet Molecularly Imprinted Polymers: Insights and Prospects for Sensor Applications.

The use of porous materials as the core for synthesizing molecularly imprinted polymers (MIPs) adds significant value to the resulting sensing system. This review covers in detail the current progress and achievements regarding the synergistic combination of MIPs and porous materials, namely metal/covalent-organic frameworks (MOFs/COFs), including the application of such frameworks in the development of upgraded sensor platforms. The different processes involved in the synthesis of MOF/COF-MIPs are outlined, along with their intrinsic properties. Special attention is paid to debriefing the impact of the morphological changes that occur through the synergistic combination compared to those that occur due to the individual entities. Thereafter, the strategies used for building the sensors, as well as the transduction modes, are overviewed and discussed. This is followed by a full description of research advances for various types of MOF/COF-MIP-based (bio)sensors and their applications in the fields of environmental monitoring, food safety, and pharmaceutical analysis. Finally, the challenges/drawbacks, as well as the prospects of this research field, are discussed in detail.

Ruthenium and Nickel Molybdate-Decorated 2D Porous Graphitic Carbon Nitrides for Highly Sensitive Cardiac Troponin Biosensor.

Two-dimensional (2D) layered materials functionalized with monometallic or bimetallic dopants are excellent materials to fabricate clinically useful biosensors. Herein, we report the synthesis of ruthenium nanoparticles (RuNPs) and nickel molybdate nanorods (NiMoO4 NRs) functionalized porous graphitic carbon nitrides (PCN) for the fabrication of sensitive and selective biosensors for cardiac troponin I (cTn-I). A wet chemical synthesis route was designed to synthesize PCN-RuNPs and PCN-NiMoO4 NRs. Morphological, elemental, spectroscopic, and electrochemical investigations confirmed the successful formation of these materials. PCN-RuNPs and PCN-NiMoO4 NRs interfaces showed significantly enhanced electrochemically active surface areas, abundant sites for immobilizing bioreceptors, porosity, and excellent aptamer capturing capacity. Both PCN-RuNPs and PCN-NiMoO4 NRs materials were used to develop cTn-I sensitive biosensors, which showed a working range of 0.1-10,000 ng/mL and LODs of 70.0 pg/mL and 50.0 pg/mL, respectively. In addition, the biosensors were highly selective and practically applicable. The functionalized 2D PCN materials are thus potential candidates to develop biosensors for detecting acute myocardial infractions.

Graphitic Carbon Nitride and IGZO Bio-FET for Rapid Diagnosis of Myocardial Infarction.

Acute myocardial infarction (AMI), commonly known as a heart attack, is a life-threatening condition that causes millions of deaths every year. In this study, a transistor-based biosensor is developed for rapid and sensitive detection of cardiac troponin-I (cTnI), a diagnostic biomarker of AMI. A biosensing technique based on a field effect transistor (FET), which uses indium gallium zinc oxide (IGZO) as an excellent semiconducting channel, is integrated with nanosheet materials to detect cTnI. Porous carbon nitride (PCN) decorated with gold nanoparticles (Au NPs) is used as a bridge between the solid-state device and the biorecognition element. We demonstrate that this biosensor is highly sensitive and has an experimental limit of detection of 0.0066 ng/mL and a dynamic range of 0.01 ng/mL-1000 ng/mL. This is the first report of a semiconducting metal oxide FET cardiac biomarker sensor combined with PCN for the detection of cTnI. The reported compact microsystem paves the way for rapid and inexpensive detection of cardiac biomarkers.

Multiplexed sensing techniques for cardiovascular disease biomarkers - A review.

Cardiovascular diseases (CVDs) are the number one cause of death worldwide, taking 17.9 million lives each year. The rapid, sensitive, and accurate determination of cardiac biomarkers is vital for the timely diagnosis of CVDs. For accurate diagnosis, dependence on a single biomarker is unreliable because each one has also been linked to other diseases. To overcome this problem, the multiplexed determination of two or more markers has emerged as a promising alternative to single-marker analysis. Over the last 5 years, research interest in the development of biosensors for targeting multiple cardiac markers has increased. In this study, we critically reviewed the various multiplexed biosensing approaches reported during the last 5 years, categorizing them by signal readouts. Prospective detection configurations, capture probes, electrode design strategies, electrode types, nanomaterials, reporter tags, and assay types were reviewed, tabulated, and critically discussed. Then, their advantages and limitations were highlighted. For each category, we provided our perspective as well as the overall critical discussion. Lastly, we summarized potential commercial multiplexed cardiac biosensors and commented on the challenges and future prospects for such sensors.

Inherent Surface Activation of Laser-Scribed Graphene Decorated with Au and Ag Nanoparticles: Simultaneous Electrochemical Behavior toward Uric Acid and Dopamine.

Laser-scribed graphene electrodes (LSGEs) have attracted great attention for the development of electrochemical (bio)sensors due to their excellent electronic properties, large surface area, and high porosity, which enhances the electrons' transfer rate. An increasing active surface area and defect sites are the quickest way to amplify the electrochemical sensing attributes of the electrodes. Here, we have found that the activation procedure coupled to the electrodeposition of metal nanoparticles resulted in a significant amplification of the active area and the analytical performance. This preliminary study is supported by the demonstration of the simultaneous electrochemical sensing of dopamine (DA) and uric acid (UA) by the electrochemically activated LSGEs (LSGE*s). Furthermore, the electrodeposition of two different metal nanoparticles, gold (Au) and silver (Ag), was performed in multiple combinations on working and reference electrodes to investigate the enhancement in the electrochemical response of LSGE*s. Current enhancements of 32, 27, and 35% were observed from LSGE* with WE:Au/RE:LSG/CE:LSGE, WE:Au/RE:Au/CE:LSGE, and WE:Au/RE:Ag/CE:LSGE, compared to the same combinations of LSGEs without any surface activation. A homemade and practical potentiostat, KAUSTat, was used in these electrochemical depositions in this study. Among all of the combinations, the surface area was increased 1.6-, 2.0-, and 1.2-fold for WE:Au/RE:LSG/CE:LSGE, WE:Au/RE:Au/CE:LSGE, and WE:Au/RE:Ag/CE:LSGE prepared from LSGE*s, respectively. To evaluate the analytical performance, DA and UA were detected simultaneously in the presence of ascorbic acid. The LODs of DA and UA are calculated to be ∼0.8 and ∼0.6 µM, respectively. Hence, this study has the potential to open new insights into new surface activation strategies with a combination of one-step nanostructured metal depositions by a custom-made potentiostat. This novel strategy could be an excellent and straightforward method to enhance the electrochemical transducer sensitivity for various electrochemical sensing applications.

Design and Fabrication of Yttrium Ferrite Garnet-Embedded Graphitic Carbon Nitride: A Sensitive Electrocatalyst for Smartphone-Enabled Point-of-Care Pesticide (Mesotrione) Analysis in Food Samples.

As the use of pesticides in agriculture is increasing at an alarming rate, food contamination by pesticide residues is becoming a huge global problem. It is essential to develop a sensitive and user-friendly sensor device to quantify trace levels of pesticide and herbicide residues in food samples. Herein, we report an electrocatalyst made up of yttrium iron garnet (Y3Fe5O12; YIG) and graphitic carbon nitride (GCN) to attain picomolar-level detection sensitivity for mesotrione (MTO), which is a widely used herbicide in agriculture. First, YIG was prepared by a hydrothermal route; then, it was loaded on GCN sheets via a calcination method. The surface structures, composition, crystallinity, and interfacial and electrocatalytic properties of the YIG and YIG/GCN were analyzed. As the YIG/GCN displayed better surface and catalytic properties than YIG, YIG/GCN was modified on a screen-printed carbon electrode to fabricate a sensor for MTO. The YIG/GCN-modified electrode displayed a detection limit of 950 pM for MTO. The method was demonstrated in (spiked) fruits and vegetables. Then, the modified electrode was integrated with a miniaturized potentiostat called KAUSTat, which can be operated wirelessly by a smartphone. A first smartphone-based portable sensor was demonstrated for MTO that is suitable for use in nonlaboratory settings.

Simple and selective optical biosensor using Ultrasonicator synthesis of 5-((anthracen-9-ylmethylene) amino)-2,3-dihydrophthalazine-1,4-dione for direct detection of ascorbic acid in vegetables and fruits.

We report an optical biosensor using imine, 5-((anthrcene-9-ylmethylene) amino)-2,3dihydrophthalazine) 1-4-dione (ADD) for direct detection of ascorbic acid (AA) via FRET quenched. The ADD was successfully prepared by using simple ultra - sonication method, which was characterized by various spectroscopic techniques. The fluorescence intensity of ADD probe was drastically quenched in presence of AA, and shown excellent selectivity towards the detection of AA in presence of possible biological active interferences. A wide linear range from 0.25 to 190 µM was achieved towards the detection of AA with a LOD of 10 nM. The occurrence of FRET mechanism is due to intermolecular hydrogen bonding between ADD and AA, which was confirmed by Density Functional Theory calculations. Moreover, the biosensor was successfully applied for the detection of AA in real samples such as fruits and vegetables to demonstrate the practicability. In addition, the developed biosensor could be a simple and economically cheap platform for the detection of AA in food samples.

Growth of large-scale MoS2 nanosheets on double layered ZnCo2O4 for real-time in situ H2S monitoring in live cells.

There is an urgent need to develop in situ sensors that monitor the continued release of H2S from biological systems to understand H2S-related pathology and pharmacology. For this purpose, we have developed a molybdenum disulfide supported double-layered zinc cobaltite modified carbon cloth electrode (MoS2-ZnCo2O4-ZnCo2O4) based electrocatalytic sensor. The results of our study suggest that the MoS2-ZnCo2O4-ZnCo2O4 electrode has excellent electrocatalytic ability to oxidize H2S at physiological pH, in a minimized overpotential (+0.20 vs. Ag/AgCl) with an amplified current signal. MoS2 grown on double-layered ZnCo2O4 showed relatively better surface properties and electrochemical properties than MoS2 grown on single-layered ZnCo2O4. The sensor delivered excellent analytical parameters, such as low detection limit (5 nM), wide linear range (10 nM-1000 µM), appreciable stability (94.3%) and high selectivity (2.5-fold). The practicality of the method was tested in several major biological fluids. The electrode monitors the dynamics of bacterial H2S in real-time for up to 5 h with good cell viability. Our research shows that MoS2-ZnCo2O4-ZnCo2O4/carbon cloth is a robust and sensitive electrode to understand how bacteria seek to adjust their defense strategies under exogenously induced stress conditions.

Sonochemical synthesis and fabrication of perovskite type calcium titanate interfacial nanostructure supported on graphene oxide sheets as a highly efficient electrocatalyst for electrochemical detection of chemotherapeutic drug.

In green approaches for electrocatalyst synthesis, sonochemical methods play a powerful role in delivering the abundant surface areas and nano-crystalline properties that are advantageous to electrocatalytic detection. In this article, we proposed the sphere-like and perovskite type of bimetal oxides which are synthesized through an uncomplicated sonochemical procedure. As a yield, the novel calcium titanate (orthorhombic nature) nanoparticles (CaTiO3 NPs) decorated graphene oxide sheets (GOS) were obtained through simple ultrasonic irradiation by a high-intensity ultrasonic probe (Titanium horn; 50 kHz and 60 W). The GOS/CaTiO3 NC were characterized morphologically and chemically through the analytical methods (SEM, XRD, and EDS). Besides, as-prepared nanocomposites were modified on a GCE (glassy carbon electrode) and applied towards electrocatalytic and electrochemical sensing of chemotherapeutic drug flutamide (FD). Notably, FD is a crucial anticancer drug and also a non-steroidal anti-androgen chemical. Mainly, the designed and modified sensor has shown a wide linear range (0.015-1184 µM). A limit of detection was calculated as nanomolar level (5.7 nM) and sensitivity of the electrode is 1.073 µA µM-1 cm-2. The GOS/CaTiO3 modified electrodes have been tested in human blood and urine samples towards anticancer drug detection.

Rapid One-Pot Synthesis of Polydopamine Encapsulated Carbon Anchored with Au Nanoparticles: Versatile Electrocatalysts for Chloramphenicol and Folic Acid Sensors.

Designing and engineering nanocomposites with tailored physiochemical properties through teaming distinct components is a straightforward strategy to yield multifunctional materials. Here, we describe a rapid, economical, and green one-pot microwave synthetic procedure for the preparation of ternary nanocomposites carbon/polydopamine/Au nanoparticles (C/PDA/AuNPs; C = carbon nanotubes (CNTs), reduced graphene oxide (rGO)). No harsh reaction conditions were used in the method, as are used in conventional hydrothermal or high-temperature methods. The PDA unit acts as a non-covalent functionalizing agent for carbon, through π stacking interactions, and also as a stabilizing agent for the formation of AuNPs. The CNTs/PDA/AuNPs modified electrode exhibited excellent electrocatalytic activity to oxidize chloramphenicol and the resulting sensor exhibited a low detection limit (36 nM), wide linear range (0.1-534 µM), good selectivity (against 5-fold excess levels of interferences), appreciable reproducibility (3.47%), good stability (94.7%), and practicality (recoveries 95.0%-98.4%). Likewise, rGO/PDA/AuNPs was used to fabricate a sensitive folic acid sensor, which exhibits excellent analytical parameters, including wide linear range (0.1-905 µM) and low detection limit (25 nM). The described synthetic route includes fast reaction time (5 min) and a readily available household microwave heating device, which has the potential to significantly contribute to the current state of the field.

A composite film prepared from titanium carbide Ti3C2Tx (MXene) and gold nanoparticles for voltammetric determination of uric acid and folic acid.

In this study, a solution-processing based galvanic deposition approach is described for in-situ deposition of gold nanoparticles (AuNP) on delaminated titanium Ti3C2Tx nanosheets under ultrasonication. The nanocomposite (AuNP@Ti3C2Tx) was placed on a glassy carbon electrode (GCE) and then applied to electrochemically with label-free, and simultaneously sense uric acid (UA), and folic acid (FA) at physiological pH. The modified GCE has attractive figures of merit: (i) The working potentials for UA and AA are well separated (+0.35 V and 0.70 V vs. Ag|AgCl); (ii) wide linear responses (from 0.03-1520 µM for UA and from 0.02-3580 µM for FA; (iii) good electrochemical sensitivities for both UA and FA (0.53 and 0.494 µAµM-1.cm-2, respectively), and (iv) detection limits of 11.5 nM (UA) and 6.20 nM (FA). The electrode exhibited good repeatability (RSD = 4.4%), acceptable reproducibility (RSD = 4.1%), and excellent stability (91.8% over one-month storage). The method was applied to analyze spiked serum samples, and modified GCE is shown appreciable recoveries (97.1-98.8% and 96.8-98.0% for UA, and FA, respectively). Graphical abstractA photograph (top left) of colloidal suspension of gold nanoparticles (AuNPs). They were grown on the delaminated titanium carbide Ti3C2Tx MXene nanosheet via galvanic displacement deposition method, and their corresponding a low-resolution transmission electron microscopy micrograph (top right) of AuNP@Ti3C2Tx. The graphical representation of AuNP@Ti3C2Tx drop-casted on glassy carbon electrode (GCE) (bottom left), and their voltammetric measurement were applied in the presence of both uric acid and folic acid with increasing the concentration of both analytes (bottom right).

Bisintercalating DNA redox reporters for real-time electrochemical qLAMP.

The electrochemical detection methods have emerged as a potential alternative to the bench-top optical systems in monitoring nucleic acid amplification. DNA intercalating redox reporters play a crucial role in such monitoring schemes. Here, a series of bisintercalating redox probes have been tailor-made to meet specific requirements of electrochemical quantitative loop-mediated isothermal amplification (qLAMP). The probes composed of two naphthoquinone-imidazole (NQIM) derivatives as signal motifs that are covalently bridged by different linkers (R). They are bis-NQIM-R; R = Alkane (Ak), ethylene glycol (EG) and phenyl (Ph). The linkers allow the probes to be fine-tuned for securing ideal redox reporter. DNA binding studies via electrochemical and fluorescence techniques demonstrate that the bis-NQIM-R probes possess better ds-DNA bisintercalating ability compared to their mono-analogs. The bis-NQIM-Ph was implemented in a real-time electrochemical qLAMP, for which a prototype custom-made device that can perform fully automated multiplexed analyses is devised. A single copy of Salmonella DNA was quantified in just 10 min and the performance is comparable to the benchtop fluorescence method. Thus, the bisintercalating redox reporters incorporated electrochemical detection schemes hold great promise in qLAMP.

Axial Coordination Site-Turned Surface Confinement, Electron Transfer, and Bio-Electrocatalytic Applications of a Hemin Complex on Graphitic Carbon Nanomaterial-Modified Electrodes.

Understanding the relation between the chemical bonding and the electron-transfer (ET) reaction of surface-confined hemin (a five-coordinated Fe-porphyrin-with-chlorine complex) is a special interest in the biomimicking studies of heme proteins. Owing to the difficulty in ET function, scanty electrochemical reports of hemin in aqueous solution were reported. It has been noticed that in most of the reported procedures, the sixth axial coordination position of the hemin complex has been unknowingly turned by attaching with water molecules (potential cycling in alkaline conditions or heating), solvents such as ethanol and dimethyl sulfoxide, and nitrogen-donating compounds that have helped for the heme ET reaction. In this work, a systematic effort has been taken to find out the contribution of hemin and its axial bond coordination with π-π interaction, hydrogen bonding, and hydrophobic binding systems toward the ET reaction. Various graphitic carbons such as graphitized mesoporous carbon (GMC), mesoporous carbon-hydrophilic and hydrophobic units, graphite nanopowder, graphene oxide, single-walled carbon, multiwalled carbon nanotube (MWCNT), and carboxylic acid-functionalized MWCNT (as a source for π-π interaction, hydrogen bonding, and hydrophobic environment) along with the amino functional group of chitosan (Chit; as an axial site coordinating system) have been tested by modifying them as a hemin hybrid on a glassy carbon electrode (GCE). In addition, a gold nanoparticle (Aunano) system was combined with the above matrix as a molecular wiring agent, and its role was examined. A highly stable and well-defined redox peak at an apparent formal potential (Eo') of -320 mV versus Ag/AgCl with the highest surface excess of 120 × 10-10 mol cm-2 was noticed with the GCE/Aunano-GMC@hemin-Chit hybrid system, wherein all interactive features have been utilized. Omitting any of the individual interactions resulted in either decreased (with Aunano) or nil current response. As applications, efficient bio-electrocatalytic reduction and sensing of dissolved oxygen and hydrogen peroxide have been demonstrated.

Synthesis of robust electrochemical substrate and fabrication of immobilization free biosensors for rapid sensing of salicylate and ß-hydroxybutyrate in whole blood.

An electrochemical latent redox probe, SAF 5 was designed, synthesized and characterized. A rapid and sensitive solution-based assay was demonstrated for salicylate hydroxylase (SHL). In presence of NADH at aerobic conditions, SHL catalyzed the decarboxylative hydroxylation of SAF and released a redox reporter amino ferrocene (AF 6). The release of AF 6 was monitored at interference free potential region (-50 mV vs. Ag|AgCl) using differential pulse voltammetry as signal read-out. The current signal generated by this process is highly specific, and insensitive to other biological interfering compounds. Next, the SAF incorporated SHL assay was extended to fabricate immobilization-free biosensors for rapid sensing of salicylic acid (SA) and ß-hydroxybutyrate (ß-HB) in whole blood. The described method rapidly detects SA in a linear range of 35-560 µM with detection limit of 5.0 µM. For ß-HB determination, the linear range was 10-600 µM and detection limit was 2.0 µM. Besides, the assay protocols are simple, fast, reliable, selective, sensitive and advantageous over existing methods. The whole blood assay did not required cumbersome steps such as, enzyme immobilization, pre-treatments and holds great practical potential in clinical diagnosis.

Core-shell heterostructured multiwalled carbon nanotubes@reduced graphene oxide nanoribbons/chitosan, a robust nanobiocomposite for enzymatic biosensing of hydrogen peroxide and nitrite.

A robust nanobiocomposite based on core-shell heterostructured multiwalled carbon nanotubes@reduced graphene oxide nanoribbons (MWCNTs@rGONRs)/chitosan (CHIT) was described for the fabrication of sensitive, selective, reproducible and durable biosensor for hydrogen peroxide (H2O2) and nitrite (NO2-). The excellent physicochemical properties of MWCNTs@rGONRs such as, presence of abundant oxygen functionalities, higher area-normalized edge-plane structures and chemically active sites in combination with excellent biocompatibility of CHIT resulting in the versatile immobilization matrix for myoglobin (Mb). The most attractive property of MWCNTs@rGONRs which distinguishes it from other members of graphene family is its rich edge density and edge defects that are highly beneficial for constructing enzymatic biosensors. The direct electron transfer characteristics such as, redox properties, amount of immobilized active Mb, electron transfer efficiency and durability were studied. Being as good immobilization matrix, MWCNTs@rGONRs/CHIT is also an excellent signal amplifier which helped in achieving low detection limits to quantify H2O2 (1 nM) and NO2- (10 nM). The practical feasibility of the biosensor was successfully validated in contact lens cleaning solution and meat sample.

One-pot synthesis of three-dimensional Mn3O4 microcubes for high-level sensitive detection of head and neck cancer drug nimorazole.

We described a three-dimensional Mn3O4 microcubes (3D-Mn3O4MCs) synthesised via a facile hydrothermal route for the determination of nimorazole (NMZ), an important drug that used in the treatment of head and neck cancer. The 3D-Mn3O4 MCs possess large active area and high conductivity, and 3D-Mn3O4 MCs film modified screen-printed carbon electrode (3D-Mn3O4MCs/SPCE) was fabricated which displayed excellent electrocatalytic ability towards NMZ. Under optimised working conditions, the modified electrode responded linearly to NMZ in the 0.025-8060µM concentration range and the detection limit was 6nM. A rapid, sensitive, selective, reproducible, and durable sensor was described. The practical feasibility of the sensor was demonstrated in human serum and NMZ tablet samples. The obtained results revealed the potential real-time applicability of the sensing device in biological analysis and pharmaceutical formulations.

Electrochemical latent redox ratiometric probes for real-time tracking and quantification of endogenous hydrogen sulfide production in living cells.

Hydrogen sulfide (H2S) was discovered as a third gasotransmitter in biological systems and recent years have seen a growing interest to understand its physiological and pathological functions. However, one major limiting factor is the lack of robust sensors to quantitatively track its production in real-time. We described a facile electrochemical assay based on latent redox probe approach for highly specific and sensitive quantification in living cells. Two chemical probes, Azido Benzyl ferrocene carbamate (ABFC) and N-alkyl Azido Benzyl ferrocene carbamate (NABFC) composed of azide trigger group were designed. H2S molecules specifically triggered the release of reporters from probes and the current response was monitored using graphene oxide film modified electrode as transducer. The detection limits are 0.32µM (ABFC) and 0.076µM (NABFC) which are comparable to those of current sensitive methods. The probes are successful in the determination of H2S spiked in whole human blood, fetal bovine serum, and E. coli. The continuous monitoring and quantification of endogenous H2S production in E. coli were successfully accomplished. This work lays first step stone towards real-time electrochemical quantification of endogenous H2S in living cells, thus hold great promise in the analytical aspects of H2S.