Electrocatalytic Biosensor Research Articles

Direct electrocatalytic sensing of myoglobin using an annealed Au-implanted electrode

Ion implantation is a versatile and green material surface modification technology that modifies the structure of target-neat surface by bombardment of non-metal or heavy metal ions. A new Au nanoparticle loaded ITO (AuNPs/ITO) electrodes was prepared by ion implantation and thermal annealing method in this work. The obtained nanoparticles were characterized by Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical methods. The direct electrocatalysis of Myoglobin (MB) was reported. It was found that after annealing at 500 °C for 2 h, the damage part of the implanted sample was eliminated. The surface coverage of MB on the MB/AuNPs/ITO electrode and the MB/annealed-AuNPs/ITO electrode was 4.35× 10−11 mol·cm−2 and 1.23 × 10−10 mol·cm−2, respectively. The results show that this composite method can be used to fabricate an electrocatalytic biosensor.

All-printed multiplexed electrocatalytic biosensors with rationally designed nanoparticle inks

Inkjet printing, capable of rapid and template-free fabrication with high resolution and low material waste, is a promising method to construct electrochemical biosensor devices. However, the construction of fully inkjet-printed electrochemical biosensor remains a challenge owing to the lack of appropriate inks, especially the sensing inks of bioactive materials. Herein, we demonstrate a fully inkjet-printed, integrated and multiplexed electrochemical biosensor by combining rationally designed nanoparticle Inks. The stable gold (Au) nanoparticles ink with lower sintering temperature is prepared by using L-cysteine as stabilizer, and it is used to print the interconnects, the counter electrodes, and the working electrodes. The SU-8 ink is used to serve as dielectric layer for the biosensor, whereas the silver electrode is printed on the Au electrode by using commercially silver nanoparticles ink before it is chlorinated to prepare Ag/AgCl reference electrode. Moreover, we synthesize an inkjet-printable and electroactive ink, by the ‘one-pot method’, which is composed of conductive poly 6-aminoindole (PIn-6-NH2) and gold–palladium (Au–Pd) alloy nanoparticle (Au–Pd@PIn-6-NH2) to enhance the sensing performance of gold electrode towards hydrogen peroxide (H2O2). Especially, the amino groups in PIn-6-NH2 can be further used to immobilizing glucose oxidase (GOx) and lactic acid oxidase (LOx) by glutaraldehyde to prepare printable sensing ink for the detection of glucose and lactate. The fully inkjet-printed electrochemical biosensor enabled by advanced inks can simultaneously detect glucose and lactate with good sensitivity and selectivity, as well as facile and scalable fabrication, showing great promise for metabolic monitoring.

A dual-responsive electrochemical biosensor based on artificial protein imprinted polymers and natural hyaluronic acid for sensitive recognition towards biomarker CD44

Two main challenges for biosensors facing may be analytical sensitivity and selectivity. Ultra-highly specific protein molecularly imprinted polymers (MIPs) with characteristics of easy preparation, chemical stability, convenient assembly with transducer, offer unprecedented opportunities for high-performance recognition towards targets. A dual-responsive electrochemical biosensor was demonstrated, where integrated both artificial protein MIPs and natural hyaluronic acid (HA) probes into one flexible electrode to detect biomarker CD44. Their efficacy towards target of two types of probes were elucidated and contrasted. Dual-channel screen-printed electrodes (SPEs) were designed innovatively. As one responsive channel, protein MIPs were synthesized through a polymerization procedure between functional monomer of alginate gel, a biocompatible antifouling chemical, and template protein CD44. Natural HA probes were immobilized to produce the other responsive channel. Such binary channels realized highly sensitive and selective target quantifying with lower limit of detections (LODs) of 1.41 × 10−5 ng/mL for MIPs-based and 1.51 × 10−5 ng/mL for HA-based channels, attributing to superior specificity, antifouling property and biocompatibility of MIPs and HA, satisfying stability of SPEs, high sensitivity of electrochemical techniques. The dual-responsive strategy can be extended to other batched integration of functionalized materials and active biomolecules into electrochemical and electro-catalytic biosensors towards multiple components to monitor physical signs and diagnose human diseases.

Programming a hollow core-shell CuS@CuSe heteromicrocubes synergizing superior multienzyme activity function as enhanced biosensing platforms

Introducing heterostructures combined by different building blocks (transition metal chalcogenides) enables the regulation of composition and architecture towards boosting electrocatalytic sensing performance. Herein, a successful transformation from well-defined Cu2O microcubes to hollow core-shell CuS@CuSe heteromicrocubes are performed via a template-directed in-situ sulfuration and selenization reaction at room temperature and further defined as bifunctional nanozymes to detect H2O2 reduction and DA oxidation, of which the ultrathin CuSe nanosheets vertically wrapping on hollow CuS microcube-like core created plenty of exposed active sites, rich ion-transfer channels, as well as remarkable structural stability, while the existence of interfacial effect between two components can facilitate fast ion/electron transfer to execute cooperative catalytical capacity, thus harvesting highly efficient electrochemical sensor features for catalyzing H2O2 and DA, as reflected by high sensitivity (1005.2 μA mM−1 cm−2 and 60.44 μA μM−1 cm−2), low LOD (30 nM and 0.38 nM), favorable working potential (−0.25 V and 0.20 V) as well as excellent selectivity, powerful long-term stability and outstanding repeatability/reportability. Such preeminent performance is not only superior to single CuS and CuSe counterparts and most designed nanozymes, but also creates satisfactory recoveries and expected accuracy in real human serum samples. Then, designing heterogeneous nanomaterials with matching functions and structures and investigating their potential prospects in electrocatalytic biosensors would guide the exploitation of nanozymes to fulfill the versatile requirements.

In situ deposition of MOF-74(Cu) nanosheet arrays onto carbon cloth to fabricate a sensitive and selective electrocatalytic biosensor and its application forthe determination of glucose in human serum.

A new electrocatalytic biosensor (MOF-74(Cu) NS-CC) based on the in situ deposition of MOF-74(Cu) nanosheet on carbon cloth via a bottom-up synthetic approach in a glass tube was developed. The electrocatalytic activity of the deposited MOF-74(Cu) NS was demonstrated in the oxidation of glucose to gluconate under alkaline conditions. Theresults revealed that the proposedmethod of in situ formation of MOF-74(Cu) NS onto a carbon cloth surface in a multi-layer solution is capable to generate a stable MOF-74(Cu) NS-CC electrode with excellent sensing performance. When the as-synthesized MOF-74(Cu) NS-CC was applied directly as the working electrode for glucose sensing, it showed much higher conductivity and redox activity than MOF-74(Cu) NS-GCE. With the potential applied at 0.55V (vs. Ag/AgCl), this new electrocatalytic biosensor exhibits an excellent linear relationship between current density and concentration of glucose. Moreover, a wide linear range of detection (1.0 to 1000μM) was observed. The limit of detection was found to be 0.41μM (S/N = 3). The response sensitivity is 3.35mAmM-1cm-2 when the concentration of glucose is in the range 1-100μM and 3.81mAmM-1cm-2 for the 100-1000μMconcentration range. This study provides a low-cost, easy to prepare, and reproducible methodology for the synthesis of highly redox-active nanomaterials based on the in situ formation of two-dimensional MOF-74(Cu) NS for the development of new electrocatalytic biosensors. Graphical abstract.

Highly electrocatalytic biosensor based on Hemin@AuNPs/reduced graphene oxide/chitosan nanohybrids for non-enzymatic ultrasensitive detection of hydrogen peroxide in living cells

A non-enzymatic and highly electrocatalytic H2O2 biosensor was proposed by using a novel electrode composed of hemin-capped biomineralized gold nanoparticles (Hem@AuNPs), reduced graphene oxide (rGO) and chitosan (CS). Owing to the excellent electrocatalytic activity of Hem@AuNPs and great conductivity of rGO, this developed biosensor is capable of ultrasensitive measuring H2O2 in real-time. In addition, the introduction of CS resulted in a film on the electrode, which can enhance the stability by protecting the biosensor from external disturbances. Taking advantages of the peroxidase-like activities of the nanohybrids, the developed electrode exhibited outstanding electrochemical performance toward H2O2 with high selectivity, fast response, superior sensitivity and good stability. More importantly, the lower determination limit of 9.3 nM and wider linear ranges of 5 orders of magnitude enable this biosensor to detect H2O2 releasing from living Hela cells accurately. This work provides tremendous potential for real-time monitoring the secretion of H2O2 in living cells.

Single-step multivalent capture assay for nucleic acid detection with dual-affinity regulation using mutation inhibition and allosteric activation.

The rational modulation of receptor affinity through distal-site mutation and allosteric control is valuable in biosensor designing to tune the useful dynamic range. Our ability to programmatically engineer dual-affinity regulation into diverse affinities of target binding and activities of hybridization chain reaction, however, remains limited. By programmable engineering of the switching equilibria of the recognition hairpin using distal-site mutation inhibition and allosteric activation, we obtained a set of receptors varying significantly in affinities of target binding and activities of the hybridization chain reaction. For the first time, we developed an electrocatalytic biosensor for nucleic acid detection with a tunable dynamic range based on a conformational switch triggered bidirectional hybridization chain reaction and blocker assisted multivalent binding. This designable biosensor thus enables single-step incubation, diverse affinities of target binding, diverse efficiencies of signal amplification and diverse single nucleotide discrimination for quantitative analyses of nucleic acids of various lengths in serum, which holds great potential as a compelling platform suitable for liquid biopsy.

Protein-mimicking nanowire-inspired electro-catalytic biosensor for probing acetylcholinesterase activity and its inhibitors

A highly sensitive electrochemical biosensor based on the synthetized L-Cysteine-Ag(I) coordination polymer (L-Cys-Ag(I) CP), which looks like a protein-mimicking nanowire, was constructed to detect acetylcholinesterase (AChE) activity and screen its inhibitors. This sensing strategy involves the reaction of acetylcholine chloride (ACh) with acetylcholinesterase (AChE) to form choline that is in turn catalytically oxidized by choline oxidase (ChOx) to produce hydrogen peroxide (H2O2), thus L-Cys-Ag(I) CP possesses the electro-catalytic property to H2O2 reduction. Herein, the protein-mimicking nanowire-based platform was capable of investigating successive of H2O2 effectively by amperometric i-t (current-time) response, and was further applied for the turn-on electrochemical detection of AChE activity. The proposed sensor is highly sensitive (limit of detection is 0.0006 U/L) and is feasible for screening inhibitors of AChE. The model for AChE inhibition was further established and two traditional AChE inhibitors (donepezil and tacrine) were employed to verify the feasibility of the system. The IC50 of donepezil and tacrine were estimated to be 1.4 nM and 3.5 nM, respectively. The developed protocol provides a new and promising platform for probing AChE activity and screening its inhibitors with low cost, high sensitivity and selectivity.

Nanospheres and nanoleaves of γ-Fe2O3 architecturing for magnetic and biomolecule sensing applications

Acicular 1D iron oxide nanostructures such as needles, nanorods, and nanowires are attracted much attention owing to their enhanced optical, magnetic, catalytic and mechanical properties over spherically shaped nanoparticles. In this article, we have reported the highly crystalline monodispersed thermally stable γ-Fe2O3 nanosphere (20nm) and γ-Fe2O3 nanoleaves (8μm) and FeO nanospheres (20nm) synthesis using a facile nanoarchitecturing biosurfactant method. Characteristics of the iron oxide nanostructures were examined with field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimeteric analysis/differential thermogravimetric analysis (TG/DTA), fourier transform infrared spectroscopy (FTIR), Vibrating sample magnetometer (VSM) and cyclic voltammetry (CV) electrochemical analysis. Taking advantage of the saponin with big polar head and long hydrocarbon chain, it has become possible to template the synthesis of γ-Fe2O3 nanosphere and Aloe Vera Leaf (AVL) like nanostructures controlling the reaction time and Sapinduss Mukkorossi Fruit Extract (SMFE) concentration. The satellite peaks appeared at 718.5eV and 716eV respectively and XRD confirmed the formed γ-Fe2O3 nanodots are unidirectionally colloid and coalescence via 303 plane to form γ-Fe2O3 nanoleaves at lower surfactant, however at higher surfactant FeO spheres. Defect free γ-Fe2O3 nanoleaves demonstrates a higher magnetization of 13.8–9emu/g due to the absence of coherent rotation of the magnetic moment caused by the larger width of nanoleaves. It was revealed that the γ-Fe2O3 nanoleaves and γ-Fe2O3 nanospheres exhibite the uric acid oxidation at a reduced potential of 303±3mV with 150% and 80% enhanced electrocatalytic current respectively than GCE. This facile synthetic approach offers a greener alternative route for the synthesis of iron oxide nanostructures that are devoid of cellular and toxic chemical components. The synthesized nanomateials will find usage in magnetic storage devices, biomedical and electrocatalytic biosensor fields.

Prussian blue-Au nanocomposites actuated hemin/G-quadruplexes catalysis for amplified detection of DNA, Hg2+ and adenosine triphosphate.

In this paper, horseradish peroxidase-mimicking DNAzyme (HRP-DNAzyme) and Prussian blue (PB)-gold (Au) nanocomposites were designed as versatile electrochemical sensing platforms for the amplified detection of DNA, Hg(2+) and adenosine triphosphate (ATP). By the conjugation of the target probe with the capture probe, a conformational change resulted in the formation of HRP-DNAzyme on the PB-Au modified electrode. The redox of HRP-DNAzyme (red) was efficiently carried out in the presence of H2O2, in which PB acted as a mediator stimulating the biocatalytic functions of HRP-DNAzyme and actuated a catalytic cycle bringing an amplified signal. Specific recognition of the target DNA, Hg(2+) and ATP allowed selective amperometric detection of the target molecule. The detection limits of DNA, Hg(2+) and ATP were 50 nM, 30 pM and 3 nM, respectively. The highlight of this work is that the catalytic cycle between PB-Au nanocomposites and HRP-DNAzyme was adequately utilized in the amplification platform for versatile sensing. The novel electrocatalytic biosensor involving only one-step incubation exhibited a wide linear range, low detection limit, and satisfactory selectivity and operational stability. The proposed approach provided an ease-of-use and universal reporting system with a simple design and easy operations.

Electrodeposited nitrogen-doped graphene/carbon nanotubes nanocomposite as enhancer for simultaneous and sensitive voltammetric determination of caffeine and vanillin

A nitrogen-doped graphene/carbon nanotubes (NGR–NCNTs) nanocomposite was employed into the study of the electrochemical sensor via electrodeposition for the first time. The morphology and structure of NGR–NCNTs nanocomposite were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Meanwhile, the electrochemical performance of the glassy carbon electrode (GCE) modified with electrodeposited NGR–NCNTs (ENGR–NCNTs/GCE) towards caffeine (CAF) and vanillin (VAN) determination was demonstrated by cyclic voltammetry (CV) and square wave voltammetry (SWV). Under optimal condition, ENGR–NCNTs/GCE exhibited a wide linearity of 0.06–50μM for CAF and 0.01–10μM for VAN with detection limits of 0.02μM and 3.3×10−3μM, respectively. Furthermore, the application of the proposed sensor in food products was proven to be practical and reliable. The desirable results show that the ENGR–NCNTs nanocomposite has promising potential in electrocatalytic biosensor application.

English

In this paper the results for the construction of a gold/mercaptobenzothiazole/polyaniline/ acetylcholinesterase/polyvinylacetate (Au/ MBT/PANI/AChE/PVAc) thick-film biosensor for the determination of certain carbamate pesticide solutions in selected aqueous organic sol- vent solutions are reported. AChE biosensors are designed to complement the classical analytical methods of pesticide detection. The Au/ MBT/PANI/AChE/PVAc electrocatalytic biosensor device was constructed by encapsulating acetylcholinesterase (AChE) enzyme in the PANI polymer composite, followed by the coating of poly(vinyl acetate) (PVAc) on top to secure the biosensor film from disintegration in the organic solvents evaluated. The electroactive substrate called acetylthiocholine (ATCh) was employed to provide the movement of electrons in the amperometric biosensor. The voltammetric results have shown that the current shifts more anodically as the Au/MBT/PANI/AChE/PVAc bio- sensor responded to successive acetylthiocholine (ATCh) substrate addition under anaerobic conditions in 0.1 M phosphate buffer, KCl (pH 7.2) solution and aqueous organic solvent solutions. For the Au/MBT/PANI/AChE/PVAc biosensor, various performance and stability parame- ters were evaluated. These factors include the optimal enzyme loading, effect of pH, long-term stability of the biosensor, temperature stability of the biosensor, the effect of polar organic solvents, and the effect of non-polar organic solvents on the amperometric behavior of the biosen- sor. The biosensor constructed in this study offered a reasonable linear range between 0.25 to 3.45 nM for the detection of carbofuran, al- dicarb and dioxacarb pesticide solutions. The detection limits for the individual carbamate pesticides were 0.249 nM for carbofuran, followed by 1.209 nM for aldicarb and 1.572 nM for dioxacarb.

Mercaptobenzothiazole-on-gold organic phase biosensor systems: 1. Enhanced organosphosphate pesticide determination

This paper reports the construction of the gold/mercaptobenzothiazole/polyaniline/acetylcholinesterase/polyvinylacetate (Au/ MBT/PANI/AChE/PVAc) thick-film biosensor for the determination of certain organophosphate pesticide solutions in selected aqueous organic solvent solutions. The Au/MBT/PANI/AChE/PVAc electrocatalytic biosensor device was constructed by encapsulating acetylcholinesterase (AChE) enzyme in the PANI polymer composite, followed by the coating of poly(vinyl acetate) (PVAc) on top to secure the biosensor film from disintegration in the organic solvents evaluated. The electroactive substrate called acetylthiocholine (ATCh) was employed to provide the movement of electrons in the amperometric biosensor. The voltammetric results have shown that the current shifts more anodically as the Au/MBT/PANI/AChE/PVAc biosensor responded to successive acetylthiocholine (ATCh) substrate addition under anaerobic conditions in 0.1 M phosphate buffer, KCl (pH 7.2) solution and aqueous organic solvent solutions. For the Au/MBT/PANI/AChE/PVAc biosensor, various performance and stability parameters were evaluated. These factors include the optimal enzyme loading, effect of pH, long-term stability of the biosensor, temperature stability of the biosensor, the effect of polar organic solvents, and the effect of non-polar organic solvents on the amperometric behavior of the biosensor. The biosensor was then applied to detect a series of 5 organophosphorous pesticides in aqueous organic solvents and the pesticides studied were parathion-methyl, malathion and chlorpyrifos. The results obtained have shown that the detection limit values for the individual pesticides were 1.332 nM (parathion-methyl), 0.189 nM (malathion), 0.018 nM (chlorpyrifos).

Electrocatalytic sulfite biosensor with human sulfite oxidase co-immobilized with cytochrome c in a polyelectrolyte-containing multilayer.

An efficient electrocatalytic biosensor for sulfite detection was developed by co-immobilizing sulfite oxidase and cytochrome c with polyaniline sulfonic acid in a layer-by-layer assembly. QCM, UV–Vis spectroscopy and cyclic voltammetry revealed increasing loading of electrochemically active protein with the formation of multilayers. The sensor operates reagentless at low working potential. A catalytic oxidation current was detected in the presence of sulfite at the modified gold electrode, polarized at +0.1 V (vs. Ag/AgCl 1 M KCl). The stability of the biosensor performance was characterized and optimized. A 17-bilayer electrode has a linear range between 1 and 60 µM sulfite with a sensitivity of 2.19 mA M−1 sulfite and a response time of 2 min. The electrode retained a stable response for 3 days with a serial reproducibility of 3.8% and lost 20% of sensitivity after 5 days of operation. It is possible to store the sensor in a dry state for more than 2 months. The multilayer electrode was used for determination of sulfite in unspiked and spiked samples of red and white wine. The recovery and the specificity of the signals were evaluated for each sample.FigureSchematic of the bioelectrocatalytic sulfite sensor: sulfite oxidase (green) oxidizes sulfite to sulfate and transfers electrons via heme b5 to cyt c (red) and thence to the gold electrode

An electro-catalytic biosensor fabricated with Pt–Au nanoparticle-decorated titania nanotube array

A Gold–Platinum nanoparticle-decorated titania nanotubular electrode is fabricated by electrochemically depositing Au and Pt nanoparticles onto a highly-oriented titania nanotube array. The prepared electrode, characterized by SEM and EDX, shows remarkably improved catalytic activities in the oxidation of hydrogen peroxide. By modifying the electrode with glucose oxidase (GOx) the resultant glucose biosensor exhibits a high sensitivity to glucose in the range of 0 to 1.8 mM with a response time of 3 s and detection limit of 0.1 mM.

TTF‐TCNQ Functionalized Ormosil Based Electrocatalytic Biosensor: A comparative study on Bioelectrocatalysis

AbstractA novel electrocatalytic biosensor for glucose is reported that incorporate encapsulation of tetrathifulvalene‐tetracyanoquinodimethane (TTF‐TCNQ) functionalized organically modified sol gel glass (ormosil). The new ormosil is made using palladium‐linked glycidoxypropyltrimethoxysilane precursor, trimethoxysilane, HCl and TTF‐TCNQ powder at 25 °C. The ormosil is converted into fine powder and incorporated within graphite paste electrode along with glucose oxidase. The bioelectrochemistry of GOD and TTF‐TCNQ functionalized ormosil is examined based on cyclic voltammetry and amperometric measurements. A large electrocatalytic current to the order of 8000 μA/cm2 is recorded on the addition of 300 mM glucose. Typical responses of new biosensor are reported. The sensitivity of glucose analysis is found relatively much better as compared to earlier reported glucose biosensors. The role of palladium and TTF‐TCNQ introduction within ormosil and its advantages on bioelectrocatalysis are discussed.

A Novel Ferrocene-Encapsulated Palladium-Linked Ormosil-Based Electrocatalytic Biosensor. The Role of the Reactive Functional Group

A novel palladium-linked ormosil material with encapsulated ferrocene is reported along with its application in bioelectrocatalysis. The Pd-glycidoxypropyltrimethoxysilane is made by mixing an aqueous solution of palladium chloride and glycidoxypropyltrimethoxysilane. The linkage of palladium with glycidoxypropyltrimethoxysilane is confirmed by UV-vis, mass, and 13C spectroscopy. It is suggested that Pd is sandwiched between two molecules of glycidoxypropyltrimethoxysilane replacing oxygen. The new ormosil is made using Pd-linked silane precursor containing ferrocene monocarboxylic acid, trimethoxysilane and HCl. The formation of ormosil at two different temperatures (10 and 30 °C) is also studied, with the result that the ormosil formed at 10 °C does not show electrocatalysis of glucose oxidase whereas the ormosil made at 30 °C is found to be an efficient bioelectrocatalyst. The cyclic voltammetry results show peak separation of 57–59 mV of encapsulated ferrocene made at 30 °C and relatively large peak separation of the one made at 10 °C. The performance, stability, and reproducibility of the new ormosil based glucose biosensor are discussed. Another important investigation in support of the above outcome is reported showing the self-assembly of palladium on the reactive solid state ormosil surface. The reactive ormosil is developed using a mixture of trimethoxysilane and 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane in acidic medium.

A Novel Ormosil Based Electrocatalytic Biosensor for Glucose/Ethanol Based on Dehydrogenase Modified Electrode

A novel ormosil material for designing electrocatalytic biosensors for glucose and ethanol based on dehydrogenase catalyzed reactions is reported. The electrode material is prepared using palladium-linked glycidoxypropyltrimethoxysilane, ferrocene monocarboxylic acid, trimethoxysilane and HCl. The ormosil prepared from these ingredients shows reversible electrochemistry of ormosil encapsulated ferrocene. The electrocatalytic oxidation of NADPH/NADH and subsequently novel dehydrogenase based biosensors for glucose and ethanol are developed. The results based on cyclic voltammetry and amperometry are reported. The enzyme sensors are developed based on the modification of electrode material by dehydrogenase enzymes. The modification of electrode material is made by two approaches of enzyme immobilization: immobilization of dehydrogenase within polyvinyl alcohol and sandwiching the dehydrogenase within two layers of ormosils among which the first layer being the electrode material itself and the second layer of ormosil prepared without palladium linkage precursor and ferrocene. The biosensor made by the second approach shows high stability and much better reproducibility of enzyme electrode performance. The results on glucose and alcohol sensing based on electrochemical measurements are reported.

A novel ferrocene encapsulated palladium-linked ormosil-based electrocatalytic dopamine biosensor

A novel finding on the development of electrocatalytic biosensor for dopamine is reported. The new electrocatalytic dopamine biosensor is developed using ferrocene encapsulated palladium (Pd)-linked organically-modified sol–gel glass (ormosil). The alkoxy precursors used for the preparation of new ormosil-based electrocatalytic biosensor are palladium-linked glycidoxypropyltrimethoxysilane and trimethoxysilane. The optimum concentrations of these precursors are added in aqueous solution of ferrocene monocarboxylic acid and HCl followed by gelation for 30 h at 25°C to form ormosil. The ferrocene encapsulated ormosil is characterized based on cyclic voltammetric measurements. The CV results shows peak separation of 57–59 mV and a linear relation between peak current and square root of scan rate suggesting well behaved reversible electrochemistry of ormosil encapsulated ferrocene. The CV results and the detection of ferrocene in working medium shows that ferrocene is not leached out of ormosil matrix. The tyrosinase is immobilized within polyvinyl alcohol over the ferrocene encapsulated new ormosil and finally mounted using nucleopore membrane. The electrocatalytic response of immobilized tyrosinase over new ormosil is observed and the results are reported. The performance, stability, and reproducibility of new ormosil-based dopamine biosensor are reported.

An Organically Modified Silicate-Based Ethanol Biosensor

A novel electrocatalytic ethanol biosensor using ferrocene-encapsulated palladium (Pd)-linked organically modified sol–gel glass (ormosil) is reported. The alkoxy precursors used to prepare the new ormosil-based electrocatalytic biosensor are Pd-linked glycidoxypropyltrimethoxysilane and trimethoxysilane. Pd-glycidoxypropyltrimethoxysilane (black solution) is made by mixing aqueous solutions of palladium chloride and glycidoxypropyltrimethoxysilane. The new ormosil is made using a Pd-linked silane precursor, trimethoxysilane, an aqueous solution of ferrocene monocarboxylic acid, and HCl. Alcohol dehydrogenase (ADH) is assembled over the ferrocene–ormosil layer using polyvinyl alcohol and then protecting the immobilized enzyme layer using Millipore filter membranes (pore size 1 μm). The electrocatalytic response of immobilized ADH, soluble nicotinamide adenine dinucleotide, and Pd-linked ormosil-encapsulated ferrocene is then observed. The electrocatalytic oxidation of NADH and the subsequent ADH-catalyzed formation of NADH are monitored electrochemically. Typical results recorded after the addition of varying concentrations of ethanol are reported; however, the sensor is sensitive to other alcohol and known ADH-sensitive substrates. The stability and reproducibility of the new ethanol biosensor are reported.