Biogenic Iron Sulfide Nanoparticles to Enable Extracellular Electron Uptake in Sulfate‐Reducing Bacteria

Microbes synthesize cell‐associated nanoparticles (NPs) and utilize their physicochemical properties to produce energy under unfavorable metabolic conditions. Iron sulfide (FeS) NPs are ubiquitous and are predominantly biosynthesized by sulfate‐reducing bacteria (SRB). However, the biological role of FeS NPs in SRB remains understudied. Now, conductive FeS NPs function is demonstrated as an electron conduit enabling Desulfovibrio vulgaris Hildenborough, an SRB strain, to utilize solid‐state electron donors via direct electron uptake. After forming FeS NPs on the cell surface, D. vulgaris initiated current generation coupled with sulfate reduction on electrodes poised at ?0.4 V versus standard hydrogen electrode. Single‐cell activity analysis showed that the electron uptake and metabolic rate via FeS NPs in D. vulgaris were about sevenfold higher than those via native cell‐surface proteins in other SRB.     

Amperometric Flow‐Biosensor for Cyanide Based on an Inhibitory Effect upon Bioelectrocatalytic Reduction of Oxygen by Peroxidase‐Modified Carbon‐Felt

A novel, simple and relative highly sensitive amperometric flow biosensor for cyanide was developed by using horseradish peroxidase (HRP)‐adsorbed carbon‐felt (CF), based on an inhibitory effect on the HRP‐catalyzed O₂ reduction. The HRP‐CF showed a sufficient bioelecrocatalytic activity for O₂ reduction in the potential region from 0 to ?0.5 V at pH 5.0, due to a direct electron transfer‐based O₂ reduction process via ferrous‐HRP and compound III. This HRP‐catalyzed O₂ reduction was reversibly inhibited by cyanide, which enabled to fabricate a novel and simple reagentless (i.e., no requirement of the ordinary substrate, H₂O₂, and the electron transfer mediators) flow‐biosensor for cyanide. When air‐saturated 0.1 M phosphate buffer (pH 5.0) was used as a carrier under the applied potential of ?0.2 V vs. Ag/AgCl, the steady‐state base‐current due to the HRP‐catalyzed O₂ reduction was reversibly inhibited by the cyanide injection (200 µL), resulting in peak‐shape current responses. The magnitude of the inhibition peak currents linearly increased with increasing concentrations of cyanide up to 1 µM, and the detection limit was found to be 0.04 µM (S/N=2). The apparent inhibition constant K_i′ was estimated to be 0.87 µM.     

Glutathione Peroxidase‐Based Amperometric Biosensor for the Detection of S‐Nitrosothiols

A new biosensor is described for the detection of S‐nitrosothiols (RSNOs) based on their decomposition by immobilized glutathione peroxidase (GPx), an enzyme containing selenocysteine residue that catalytically produces nitric oxide (NO) from RSNOs. The enzyme is entrapped at the distal tip of a planar amperometric NO sensor. The new biosensor shows good sensitivity, linearity, reversibility, and response times towards various RSNO species in PBS buffer, pH 7.4 . In most cases, the response time is less than 5 min, and the response is linear up to 6 μM of the tested RSNO species. The lowest detection limit is obtained for S‐nitrosocysteine (CysNO), at approx. 0.2 μM. The biosensor's sensitivity is not affected by the addition of EDTA as a chelating agent; an advantage over other potential catalytic enzymes that contain copper ion centers, such as CuZn‐superoxide dismutase and xanthine oxidase. However, lifetime of the new sensor is limited, with sensitivity decrease of 50% after two days of use. Nonetheless, the new amperometric GPx based RSNO sensor could prove useful for detecting relative RSNO levels in biological samples, including whole blood.     

Fabrication of Bienzymatic Glucose Biosensor Based on Novel Gold Nanoparticles‐Bacteria Cellulose Nanofibers Nanocomposite

An exploration of gold nanoparticles–bacterial cellulose nanofibers (Au‐BC) nanocomposite as a platform for amperometric determination of glucose is presented. Two enzymes, glucose oxidase (GOx) and horseradish peroxidase (HRP) were immobilized in Au‐BC nanocomposite modified glassy carbon electrode at the same time. A sensitive and fast amperometric response to glucose was observed in the presence of electron mediator (HQ). Both of GOx and HRP kept their biocatalytic activities very well in Au‐BC nanocomposite. The detection limit for glucose in optimized conditions was as low as 2.3 µM with a linear range from 10 µM to 400 µM. The biosensor was successfully applied to the determination of glucose in human blood samples.     

Application of Different Zeolites for Improvement of the Characteristics of a pH‐FET Biosensor Based on Immobilized Urease

Different modifications of the zeolites Na⁺‐Beta and LTA were applied for improving the working characteristics of a urea biosensor. The bioselective membrane of the biosensor was based on urease and different zeolites co‐immobilized with bovine serum albumin on the surface of a pH‐FET. It was shown that the biosensors modified with the zeolites H⁺‐Beta30 and H⁺‐Beta50 are characterized by increased sensitivity to urea. The influence of the zeolite concentration on the sensitivity of the biosensors was studied. The optimal concentration of the zeolites H⁺‐Beta30 and H⁺‐Beta50 in the bioselective membrane was 15 %. Different variants of co‐immobilization of urease and zeolite H⁺‐Beta30 were studied and the optimal method was selected. Thus, a general conclusion is that the urea biosensor sensitivity can be improved using zeolite H⁺‐Beta30 for urease immobilization in the bioselective membrane.     

A New Enzyme Immobilization Technique Based on Thionine‐Bovine Serum Albumin Conjugate and Gold Colloidal Nanoparticles for Reagentless Amperometric Biosensor Applications

A novel enzyme immobilization technique based on thionine‐bovine serum albumin conjugate (Th‐BSA) and gold colloidal nanoparticles (nano‐Au) was developed. Thionine was covalently bound onto the BSA film with glutaraldehyde(GA) as cross‐linker to achieve Th‐BSA conjugate. The free amino groups of thionine were then used to attach nano‐Au for the immobilization of horseradish peroxidase (HRP). Such nano‐Au/Th‐BSA matrix shows a favorable microenvironment for retaining the native activity of the immobilized HRP and thionine immobilized in this way can effectively shuttle electrons between the electrode and the enzyme. The proposed biosensor displays excellent catalytic activity and rapid response for H₂O₂. The linear range for the determination of H₂O₂ is from 4.9×10^?7 to 1.6×10^?3 M with a detection limit of 2.1×10^?7 M at 3σ and a Michaelies‐Menten constant K value of 0.023 mM.     

Design and Development of a Non-Enzymatic Electrochemical Biosensor for the Detection of Glutathione

Glutathione (GSH-reduced form) is a tripeptide that plays a vital role as an antioxidant to remove xenobiotics in the human body and changes in GSH levels are a marker for the progression of various diseases. In this context, a highly sensitive non-enzymatic electrochemical biosensor for the detection of GSH has been developed using reduced graphene oxide Manganese oxide (rGMnO) nanocomposite as the nano-interface. Initially, graphene oxide was synthesized by Hummer's method and then thermally reduced in the presence of MnO₂ in a blast furnace to obtain rGMnO nanocomposite. The nanocomposite was characterized to validate its structure and morphological properties via Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry and amperometry studies showed that upon the addition of GSH, the Pt/rGMnO modified working electrode exhibited a linear response in the range of 1–100 μM at an input voltage of −0.62 V. The developed sensor was found to have a sensitivity of 0.3256 μA μM⁻¹ and LOD of 970 nM with a recovery of 92–104 % in real blood serum samples.     

A Polymer‐Based Electrochemical DNA Biosensor for Salmonella: Preparation,Characterization and Calibration

In this paper, we present the results of the use of bifunctional polymeric films of polystyrene (10.3 KD–49.5 KD) to anchor oligo sequences of various lengths (15, 35 and 70‐mer). The polymers were prepared by radical polymerization with 4,4′‐azobis(4‐cyanovaleric acid) as initiator and 3‐Carboxy PROXYL to control the molecular weight and polydispersity. They were further modified with N‐hydroxysuccinimide to anchor the (5′‐AmMC₁₂) oligos. The anchoring reaction was done on a polymer‐modified glassy carbon electrode. The probes were hybridized with their ferrocene‐labeled complementary sequences. The hybridization reaction was followed by Osteryoung square wave voltammetry (OSWV). The calibration curve showed a narrow and sharp linear range between (5.7–8.0)×10^?7 M and a detection limit around 0.55 µM.     

Detection of Trace Phenol Based on Mesoporous Silica Derived Tyrosinase‐Peroxidase Biosensor

A novel electrochemical biosensor for phenol based on immobilization of tyrosinase‐peroxidase on mesoporous silica is described. The enhanced sensitivity of the tyrosinase‐horseradish peroxidase based biosensor to phenol was observed on comparing with tyrosinase or horseradish peroxidase monoenzyme modified electrodes. Two enzymes retained their enzymatic activities for phenol determination without any mediator. The preparation conditions of the biosensor are discussed. Optimization of the experimental parameters was performed with regard to pH and operating potential. The phenol sensor exhibited a fast response of less than 10 seconds. The sensitivity of the biosensor for phenol was 14 μA μM^?1 cm^?2 with a linear range from 2×10^?7 to 2.3×10^?4 M and a detection limit of 4.1×10^?9 M. The biosensor showed a good stability and reproducibility.     

Lactate Biosensor Based on Hydrotalcite‐Like Compounds: Performances and Application to Serum Samples

A lactate biosensor based on lactate oxidase supported onto a hydrotalcite, electrochemically deposited on a platinum surface, was developed for the first time. For the best electrode configuration, a linear response up to 0.8 mM, with a limit of detection of 14 μM and a sensitivity of 91 mA M^?1 cm^?2, was obtained. The influence of some interferents due to the oxidation of hydrogen peroxide (at +0.35 V vs. SCE) was also studied. By controlling carefully the experimental conditions, the determination of lactate in a commercial serum sample in the presence of interferents was successfully accomplished.     

Amperometric Biosensor for Choline Based on Gold Screen‐Printed Electrode Modified with Electrochemically‐Deposited Silica Biocomposite

A mediator‐free choline biosensor was developed using the electrochemically assisted sol‐gel deposition on gold screen‐printed electrodes. The addition of 12 mM of cationic surfactant CTAB in silica sol allowed enhancing the stability of the sensor. The modified electrode demonstrated catalytic activity and stable amperometric response to choline for over 3 weeks of exploitation with the sensitivity of 6 µA mM^?1 and LOD of 6 µM. The interference of ascorbic acid was reduced by pretreating the analyzed solution with MnO₂ powder. The application of the sensor with the purpose of identifying choline in the baby milk demonstrated satisfactory metrological characteristics.     

Amperometric Detection of 4‐Chlorophenol on Two Types of Expanded Graphite Based Composite Electrodes

The assessment of an expanded graphite‐Ag‐zeolite‐epoxy composite (EG‐Z‐Ag‐Epoxy) electrode for the determination of 4‐chlorophenol (4‐CP) is described and compared to the corresponding expanded graphite‐epoxy composite (EG‐Epoxy) electrode. Cyclic voltammetry was used to characterize the electrochemical behavior and determination of 4‐CP at both electrodes in 0.1 M Na₂SO₄ and 0.1 M NaOH supporting electrolytes. A substantial enhancement of sensitivity for the determination of 4‐CP at the EG‐Z‐Ag‐Epoxy electrode was reached by applying a chemical preconcentration step prior to voltammetric quantification. Also, under these last conditions the lowest limit of detection of 1 μM illustrates the analytical versatility of this electrode in a concentration range where aquatic 4‐chlorophenol pollution is known to occur.     

Amperometric Biosensor Based on Immobilization Acetylcholinesterase on Manganese Porphyrin Nanoparticles for Detection of Trichlorfon with Flow‐Injection Analysis System

A highly sensitive amperometric biosensor for the detection of organophosphate pesticides (OPs) is developed. The biosensor was fabricated by immobilized acetylcholinesterase (AChE) on manganese (III) meso‐tetraphenylporphyrin (MnTPP) nanoparticles (NPs)‐modified glassy carbon (GC) electrode. The MnTPP NPs used in this article were synthesized by mixing solvent techniques. AChE enzyme was immobilized on the MnTPP NPs surface by conjugated with chitosan (CHIT). The electrocatalytic activity of MnTPP NPs led to a greatly improved performance for thiocholine (TCh) product detection. The developed AChE‐CHIT/MnTPPNP/GC biosensor integrated with a flow‐injection analysis (FIA) system was used to monitor trichlorfon (typical OP). A wide linear inhibition response for trichlorfon is observed in the range of 1.0 nM–1.0 mM, corresponding to 10–83% inhibition for AChE with a detection limit of 0.5 nM.     

Impedimetric DNA‐Based Biosensor for Silver Ions Detection with Hemin/G‐Quadruplex Nanowire as Enhancer

A DNA‐based biosensor was reported for detection of silver ions (Ag⁺) by electrochemical impedance spectroscopy (EIS) with [Fe(CN)₆]^4?/3? as redox probe and hybridization chain reaction (HCR) induced hemin/G‐quadruplex nanowire as enhanced label. In the present of target Ag⁺, Ag⁺ interacted with cytosine‐cytosine (C? C) mismatch to form the stable C? Ag⁺? C complex with the aim of immobilizing the primer DNA on electrode, which thus triggered the HCR to form inert hemin/G‐quadruplex nanowire with an amplified EIS signal. As a result, the DNA biosensor showed a high sensitivity with the concentration range spanning from 0.1 nM to 100 µM and a detection limit of 0.05 nM.     

One‐Step Electrochemically Deposited Nanocomposite Film of CS‐Fc/MWNTs/GOD for Glucose Biosensor Application

A simple and controllable electrodeposition approach was proposed for one‐step construction of glucose biosensors by in situ co‐deposition of ferrocene‐branched chitosan derivatives (CS‐Fc), multiwalled carbon nanotubes (MWNTs), and glucose oxidase (GOD) onto electrode surface. The formation of CS‐Fc could not only effectively prevent the leakage of Fc and retain its electrochemical activity, but also provide a biocompatible microenvironment for retaining the native activity of the immobilized biomolecules. Further entrapment of MWNTs into the CS matrix improved electronic conductivity of the biocomposite significantly. The facile procedure of immobilizing GOD and the promising feature of biocomposite will offer a versatile platform to fabricate biosensors and bioelectronic devices.     

Facile Synthesis of Leaf‐Like CuO Nanoparticles and Their Application on Glucose Biosensor

An efficient amperometric biosensor based on well‐crystallized leaf‐like CuO nanoparticles for detecting glucose has been proposed. The leaf‐like CuO nanoparticles, synthesized by a simple one‐step hydrothermal method, were characterized by X‐ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) for the morphology study. Under the optimal condition, the electrochemical behaviour of the leaf‐like CuO nanoparticles modified electrode for detection of glucose exhibited high sensitivity of 246 µA/mM/cm², short response time (within 5 s), linear dynamic range from 1.0 to 170 µM (R²=0.9995), and low limit of detection (LOD) (S/N=3) of 0.91 µM. The high sensitivity, good reproducibility, stability, and fast amperometric sensing towards oxidation of glucose, make this biosensor promising for future application.     

Electrochemical Biosensor Based on Bienzyme and Carbon Nanotubes Incorporated into an Os‐complex Thin Film for Continuous Glucose Detection in Human Saliva

Saliva opens a door for noninvasive and painless glucose testing since it reflects changes in the body physiology of diabetic individuals as compared to healthy ones. In this paper, a unique, disposable saliva biosensor has been developed for accurate, low cost, and continuous glucose monitoring. The biosensor exhibits linear dependence of the catalytic current upon glucose bulk concentration over the 0.05–1.5 mM range (R=0.998). A detection limit of 0.003 mM can be calculated considering three times the standard deviation of the blank signal divided by the sensitivity of the sensor. The selectivity of the biosensor was evaluated by adding the interferent species of lactate, ascorbic acid and uric acid into in 0.5 mM glucose; the nearly negligible interference current indicates its good selectivity. The operational stability of the biosensor was measured in 1 mM glucose over a 2 h period (RSD=3.27 %). A clinical trial on real‐time noninvasive salivary glucose monitoring was carried out on 30 individuals by measuring subjects’ salivary glucose and blood glucose in parallel. The results show that there is a good correlation of glucose levels in saliva and in blood 2 h after breakfast. Thus, the disposable biosensor would be a potential alternative for continuous glucose detection in human saliva.     

Voltammetric Studies on the Recognition of a Copper Complex to Single‐ and Double‐Stranded DNA and Its Application in Gene Biosensor

A mixed‐ligands copper complex [Cu(phendione)(DAP)]SO₄ (phendione=1,10‐phenanthroline‐5,6‐dione, DAP=2,3‐diaminophenazine) was synthesized. Cyclic voltammetry showed that the complex underwent an obvious decrease of redox peak currents and positive shift of formal potential after interaction with double‐stranded DNA (dsDNA), suggesting that the copper complex behaved as a typical metallointercalator for dsDNA, The recognition properties of the copper complex to single‐stranded DNA (ssDNA) and dsDNA were assessed using surface‐based electrochemical methods and the results suggested that the complex had obviously different redox signals at ssDNA and dsDNA modified electrodes. The copper complex was further used as an electroactive indicator for the detection of cauliflower mosaic virus (CaMV) 35S promoter gene.     

An L‐Lactate Amperometric Enzyme Electrode Based on L‐Lactate Oxidase Immobilized in a Laponite Gel on a Glassy Carbon Electrode. Application to Dairy Products and Red Wine

A biosensor based on the immobilization of Lactate oxidase in laponite–organosilasesquioxane films on glassy carbon electrode for the quantification of L ‐lactate in wine and dairy products is presented. The bioelectrode showed a very high sensitivity (0.33±0.01) A cm^?2 M^?1 and a short time response (10 s) for less than 1 U of enzyme. No significant interferences, including ascorbic acid, were detected. For red wine, matrix effects assigned to polyphenols and anthocyanins were observed, which ware easily overcome by sample dilution. Our L ‐lactate determinations were in good agreement with those of two standard methods.