A Novel Enzymatic Glucose Biosensor and Nonenzymatic Hydrogen Peroxide Sensor Based on (3‐Aminopropyl) Triethoxysilane Functionalized Reduced Graphene Oxide

In the present study, a novel enzymatic glucose biosensor using glucose oxidase (GOx) immobilized into (3‐aminopropyl) triethoxysilane (APTES) functionalized reduced graphene oxide (rGO‐APTES) and hydrogen peroxide sensor based on rGO‐APTES modified glassy carbon (GC) electrode were fabricated. Nafion (Nf) was used as a protective membrane. For the characterization of the composites, Fourier transform infrared spectroscopy (FTIR), X‐ray powder diffractometer (XRD), and transmission electron microscopy (TEM) were used. The electrochemical properties of the modified electrodes were investigated using electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry. The resulting Nf/rGO‐APTES/GOx/GC and Nf/rGO‐APTES/GC composites showed good electrocatalytical activity toward glucose and H₂O₂, respectively. The Nf/rGO‐APTES/GC electrode exhibited a linear range of H₂O₂ concentration from 0.05 to 15.25 mM with a detection limit (LOD) of 0.017 mM and sensitivity of 124.87 μA mM⁻¹ cm⁻². The Nf/rGO‐APTES/GOx/GC electrode showed a linear range of glucose from 0.02 to 4.340 mM with a LOD of 9 μM and sensitivity of 75.26 μA mM⁻¹ cm⁻². Also, the sensor and biosensor had notable selectivity, repeatability, reproducibility, and storage stability.     

Fe‐enriched Clay‐coated and Reduced Graphene Oxide‐modified N‐doped Polymer Nanocomposite: A Natural Recognition Element‐based Sensing Electrode for DNT

Dinitrotoluene (DNT) is a signature material of all nitro‐aromatic explosives including the lethal 2,4,6‐trinitrotoluene (TNT). A clay‐modified reduced graphene oxide (rGO)‐polymer nanocomposite was prepared as sensing electrode for the detection of (DNT) in the aquatic systems. rGO was in situ dispersed in the electro‐conductive N‐doped phenol/formaldehyde polymer and the clay ‘montmorillonite’ was coated on the nanocomposite. The clay, containing iron as one of its mineral components, served as the recognition element for DNT. Tested using electrochemical measurement techniques – cyclic voltammetry and differential pulse voltammetry, the prepared sensing electrode exhibited a low detection limit (0.0016 μM) on signal to noise ratio basis (S/N=3) and excellent linearity (R²=0.997) over 0.02–10 mg L^?1 with high sensitivity value (428 μA mM^?1 cm^?2) for DNT. The electrode showed negligible interference with the gravimetric and volumetric salts commonly present in seawater, and also, with explosive derivatives. The separate tests performed in a simulated seawater confirmed the suitability of the prepared electrode for use in field applications.     

Electrochemical Detection of Nitrite Using Glassy Carbon Electrode Modified with Silver Nanospheres (AgNS) Obtained by Green Synthesis Using Pre‐hydrolysed Liquor

Silver nanospheres (AgNS) with SPR band ∼417 nm was synthesized by Green synthesis, using a pre‐hydrolysed liquor (PHL) of Nilgiri wood without any pretreatment. The synthesis was carried out at room temperature and was complete within three hours. The reduction and stabilization of silver is brought about by hemicelluloses present in the pre‐hydrolysed liquor. Electrochemical oxidation of nitrite on glassy carbon electrode (GCE) modified with the AgNS in 0.1 M phosphate buffer solution (PBS) of pH 7.0 was found to occur at 0.86 V with respect to Ag/AgCl. Electrochemical sensing experiments with AgNS/GCE showed a linear range of detection between 0.1 to 8 μM, with detection limit of 0.031 μM and a sensitivity of 580 μA mM⁻¹cm⁻².     

Determination of Explosives Using Electrochemically Reduced Graphene

A graphene‐based electrochemical sensing platform for sensitive determination of explosive nitroaromatic compounds (NACs) was constructed by means of electrochemical reduction of graphene oxide (GO) on a glassy carbon electrode (GCE). The electrochemically reduced graphene (ER‐GO) adhered strongly onto the GCE surface with a wrinkled morphology that showed a large active surface area. 2,4‐Dinitrotoluene (2,4‐DNT), as a model analyte, was detected by using stripping voltammetry, which gave a low detection limit of 42 nmol L⁻¹ (signal‐to‐noise ratio=3) and a wide linear range from 5.49×10⁻⁷ to 1.1×10⁻⁵ M . Further characterizations by electrochemistry, IR, and Raman spectra confirmed that the greatly improved electrochemical reduction signal of DNT on the ER‐GO‐modified GC electrode could be ascribed to the excellent electrocatalytic activity and high surface‐area‐to‐volume ratio of graphene, and the strong π–π stacking interactions between 2,4‐DNT and the graphene surface. Other explosive nitroaromatic compounds including 1,3‐dinitrobenzene (1,3‐DNB), 2,4,6‐trinitrotoluene (TNT), and 1,3,5‐trinitrobenzene (TNB) could also be detected on the ER‐GO‐modified GC electrode at the nM level. Experimental results showed that electrochemical reduction of GO on the GC electrode was a fast, simple, and controllable method for the construction of a graphene‐modified electrode for sensing NACs and other sensing applications.     

Ferrocene Decorated N-doped Carbon Modified Electrode with Enhanced Electrocatalytic Activity towards Non-enzymatic Glucose Detection

The nitrogen doped carbon (NDCN) have been synthesized by flame synthetic method to prepare ferrocene decorated NDCN. The hydrolysis product (FC-SH) of ferrocene benzyne derivative (FC-SAc) was immobilized onto NDCN modified GCE and used for glucose detection with high sensitivity. Cyclic voltammetric analysis reveal that FC-S-NDCN/GCE exhibit excellent activity for glucose oxidation when compared to FC/GCE. The FC-S-NDCN/GCE with wide linear responses range from 0.001 to 0.01 mM with the regression co-efficient of 0.998. The FC-S-NDCN/GCE show low detection limit (LOD) of 0.08 μM and exhibit sensitivity of 1580 μA mM⁻¹ cm⁻². The FC-S-NDCN glucose sensor exhibit wide linear range, high sensitivity and lower detection limit on determination of glucose.     

The Hybrid of Gold Nanoparticles and 3D Flower‐like MnO2 Nanostructure with Enhanced Activity for Detection of Hydrogen Peroxide

3D Flower‐like manganese dioxide (MnO₂) nanostructure with the ability of catalysis for hydrogen peroxide (H₂O₂) and super large area that can support gold nanoparticles (AuNPs) with enhanced activity of electron transfer have been developed. The nanostructure of hybrids was prepared by directly mixing citric‐capped AuNPs and 3‐aminopropyltriethoxysilane (3‐APTES)‐capped nano‐MnO₂ using an electrostatic adsorption strategy. The Au‐MnO₂ composite was extensively characterized by scanning electron microscope (SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), the Brunauer‐Emmett‐Teller (BET) method and X‐ray photoemission spectroscopy (XPS). Electrochemical properties were evaluated through cyclic voltammetry (CV) and amperometric method. The prepared sensor showed excellent electrochemical properties towards H₂O₂ with a wide linear range from 2.5×10⁻³∼1.39 mM and 3.89∼13.89 mM. The detection limit is 0.34 μM (S/N=3) with the sensitivities of 169.43 μA mM⁻¹ cm⁻² and 55.72 μA mM⁻¹ cm⁻². The detection of real samples was also studied. The result exhibited that the prepared sensor can be used for H₂O₂ detection in real samples.     

Electrode Modification through Click Chemistry Using Ni and Co Alkyne Phthalocyanines for Electrocatalytic Detection of Hydrazine

This work reports on the development of sensors for the detection of hydrazine using glassy carbon electrodes (GCE) modified with phthalocyanines through click chemistry. Tetrakis(5‐hexyn‐oxy) cobalt(II) phthalocyanine (complex 2 ) and tetrakis(5‐hexyn‐oxy) nickel(II) phthalocyanine (complex 3 ) were employed as electrode modifiers for hydrazine detection. The GCE was first grafted via the in situ diazotization of a diazonium salt, rendering the GCE surface layered with azide groups. From this point, the 1, 3‐dipolar cycloaddition reaction, catalysed by a copper catalyst was utilised to “click” the phthalocyanines to the surface of the grafted GCE. The modified electrodes were characterized by scanning electrochemical microscopy, X‐ray photoelectron spectroscopy and cyclic voltammetry. The electrografted CoP 2 ‐clicked‐GCE and NiP 3 ‐clicked‐GCE exhibited electrocatalytic activity towards the detection of hydrazine. The limit of detection (LoD) for the CoPc‐GCE was 6.09 μM, while the NiPc‐GCE had a LoD of 8.69 μM. The sensitivity was 51.32 μA mM⁻¹ for the CoPc‐GCE and 111.2 μA mM⁻¹ for the NiPc‐GCE.     

Choline Oxidase Based Composite ZrO2@AuNPs with Cu2O@MnO2 Platform for Signal Enhancing the Choline Biosensors

A novel metal composite material based on zirconium dioxide decorated gold nanoparticles (ZrO₂@AuNPs), copper (I) oxide at manganese (IV) oxide (Cu₂O@MnO₂) and immobilized choline oxidase (ChOx) onto a glassy carbon electrode (GCE) (ChOx/Cu₂O@MnO₂-ZrO₂@AuNPs/GCE) has been developed for enhancing the electro-catalytic property, sensitivity and stability of the amperometric choline biosensor. The ChOx/Cu₂O@MnO₂-ZrO₂@AuNPs/GCE displayed an excellent electrocatalytic response to the oxidation of the byproduct H₂O₂ from the choline catalyzed reaction, which exhibited a charge transfer rate constant (K_s) of 0.97 s⁻¹, a diffusion coefficient value (D) of 4.50×10⁻⁶ cm² s⁻¹, an electroactive surface area (A_e) of 0.97 cm² and a surface concentration (γ) of 0.54×10⁻⁸ mol cm⁻². The modified electrode also provided a wide linear range of choline concentration from 0.5 to 1,000.0 μM with good sensitivity (97.4 μA cm⁻² mM⁻¹) and low detection limit (0.3 μM). The apparent Michaelis-Menten constant was found to be 0.08 mM with I_max of 0.67 μA. This choline biosensor presented high repeatability (%RSD=2.9, n=5), excellent reproducibility (%RSD=2.9, n=5), long time of use (n=28 with %I>50.0 %) and good selectivity without interfering effects from possible electroactive species such as ascorbic acid, aspirin, amoxicillin, caffeine, dopamine, glucose, sucrose and uric acid. This optimal method was successfully applied for choline measurement in prepared human blood samples which demonstrated accurate and excellent reliability in the recovery range from 96.7 to 102.0 %.     

Electropolymerized Diphenylamine on Functionalized Multiwalled Carbon Nanotube Composite Film and Its Application to Develop a Multifunctional Biosensor

Diphenylamine (DPA) monomers have been electropolymerized on the amino‐functionalized multiwalled carbon nanotube (AFCNT) composite film modified glassy carbon electrode (GCE) by cyclic voltammetry (CV). The surface morphology of PDPA‐AFCNT was studied using field‐emission scanning electron microscopy (FE‐SEM). The interfacial electron transfer phenomenon at the modified electrode was studied using electrochemical impedance spectroscopy (EIS). The PDPA‐AFCNT/GCE represented a multifunctional sensor and showed good electrocatalytic behavior towards the oxidation of catechol and the reduction of hydrogen peroxide. Rotating‐disk electrode technique was applied to detect catechol with a sensitivity of 1360 µA mM^?1 cm^?2 and a detection limit of 0.01 mM. Amperometric determination of hydrogen peroxide at the PDPA‐AFCNT film modified electrode results in a linear range from 10 to 800 µM, a sensitivity of 487.1 µA mM^?1 cm^?2 and detection limit of 1 µM. These results show that the nano‐composite film modified electrode can be utilized to develop a multifunctional sensor.     

Carbon Quantum Dots Co‐catalyzed with ZnO Nanoflowers and Poly (CTAB) Nanosensor for Simultaneous Sensitive Detection of Paracetamol and Ciprofloxacin in Biological Samples

A novel platform based incorporation of carbon quantum dots (CQDs) and zinc oxide nanoflowers (ZnO‐NFs) decorated with poly cetyltrimethylammonium bromide (CTAB) was developed as electrochemical sensor for the sensitive and selective simultaneous detection of Paracetamol (PAR) and Ciprofloxacin (CIP) in biological samples. For this, CQDs and ZnO‐NFs were first deposited on a glassy carbon electrode (GCE) and subsequently a Poly (CTAB) layer was grown onto their surfaces through electro‐polymerization. The synthesized nanostructures and the corresponding fabricated sensor were characterized by the techniques of TEM, XRD, FE‐SEM, and EDX analysis. Moreover electrochemical characterization by CV and DPV were performed to elucidate the construction process and electron transfer abilities of the CQDs/ZnO‐NFs/Poly(CTAB)/GCE. Increased sensitivity and efficiency of this sensing system was obtained due to the synergistic effects of CQDs, ZnO‐NFs and Poly (CTAB) with multi‐signal amplification. Under the optimum conditions, the DPV response of proposed sensor to PAR and CIP was linear at 0.05–30.0 μM and 0.01–30.0 μM, with the detection limit of 2.47 nM and 1.97 nM respectively. The sensor possessed high stability, reproducibility, sensitivity, and selectivity toward PAR and CIP detection, over potential interferents and presented high recovery percentage in the real sample matrices.     

Magnetite Nanorods Stabilized by Polyaniline/Reduced Graphene Oxide as a Sensing Platform for Selective and Sensitive Non‐enzymatic Hydrogen Peroxide Detection

In this study, magnetite nanorods stabilized on polyaniline/reduced graphene oxide (Fe₃O₄@PANI/rGO) was synthesized via a wet‐reflux strategy. The possible formation of Fe₃O₄@PANI/rGO was morphologically and structurally verified by field emission scanning electron microscopy (FE‐SEM), Fourier transform infrared (FT‐IR) spectroscopy, Raman spectroscopy, X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). Furthermore, the thermal stability of Fe₃O₄@PANI/rGO was measured by a thermogravimetric analyzer (TGA); the composite had good thermal stability owing to the ceramic nature of Fe₃O₄. The Fe₃O₄@PANI/rGO has been applied as a potential sensing platform for electrochemical detection of hydrogen peroxide (H₂O₂). By the combined efforts of extended active surface area, active carbon support, more catalytic active sites and high electrical conductivity, the Fe₃O₄@PANI/rGO exhibited an improved performance toward the non‐enzymatic detection of H₂O₂ in 0.5 M KOH with a fast response time (5 s), high sensitivity (223.7 μA mM^?1 cm^?2), low limit of detection (4.45 μM) and wide linear range (100 μM–1.5 mM). Furthermore, the fabricated sensor exhibited excellent recovery rates (94.2–104.0 %) during real sample analysis.     

Nanostructured NiCu LDHs/polypyrrole nanotubes composite for nonenzymatic glucose sensing in human serum

Nanostructured NiCu layered double hydroxides (NiCu LDHs) are synthesized in situ on polypyrrole nanotubes through convenient co-precipitation and hydrothermal synthesis. The nanostructured composite (NiCu LDHs/PPy) shows high electrocatalytic activities towards the glucose oxidation reaction in alkaline electrolyte so that a nonenzymatic glucose sensor is developed. It is demonstrated that the sensor offers a wide linear range from 1.5 μM to 1.0 mM with a high sensitivity of 525.8 μA mM⁻¹ cm⁻² and a low limit of detection of 66 nM (S/N = 3). The nonenzymatic sensor has been successfully applied to real blood samples for glucose monitoring with high accuracy.     

Synthesis of Ag Nanoparticle Doped MnO2/GO Nanocomposites at a Gas/Liquid Interface and its Application in H2O2 Detection

Ag/MnO₂/GO nanocomposites were synthesized via the method of gas/liquid interface based on silver mirror reaction, and a non‐enzymatic H₂O₂ sensor was fabricated through immobilizing Ag/MnO₂/GO nanocomposites on GCE. The composition and morphology of the nanocomposites were studied by energy‐dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Electrochemical investigation indicated that it exhibited a favorable performance for the H₂O₂ detection. Its linear detection range was from 3 μM to 7 mM with a correlation coefficient of 0.9960; the sensitivity was 105.40 μA mM^?1 cm^?2 and the detection limit was estimated to be 0.7 μM at a signal‐to‐noise ratio of 3.     

Sensitive Electrochemical Determination of Trifluralin at a Disposable Pencil Graphite Electrode

A sensitive differential pulse (DP) voltammetric method has been proposed for the determination of trifluralin (TFA) based on both its reduction and oxidation at a disposable pencil graphite electrode (PGE). DP voltammograms recorded under optimized conditions show that oxidation and reduction peak currents increased linearly in the range from 1.0 to 75.0 μM and from 0.50 to 100.0 μM TFA, respectively. LOD and sensitivity values have been determined as 0.39 μM and 11170 μA mM⁻¹ cm⁻² for oxidation and as 0.20 μM and 22167 μA mM⁻¹ cm⁻² for reduction. The acceptable recovery values (95.2–104.8 %) were obtained from real water samples.     

A Non‐Enzymatic Hydrogen Peroxide Sensor Based on Gold Nanoparticles/Carbon Nanotube/Self‐Doped Polyaniline Hollow Spheres

In this study, a novel non‐enzymatic hydrogen peroxide (H₂O₂) sensor was fabricated based on gold nanoparticles/carbon nanotube/self‐doped polyaniline (AuNPs/CNTs/SPAN) hollow spheres modified glassy carbon electrode (GCE). SPAN was in‐site polymerized on the surface of SiO₂ template, then AuNPs and CNTs were decorated by electrostatic absorption via poly(diallyldimethylammonium chloride). After the SiO₂ cores were removed, hollow AuNPs/CNTs/SPAN spheres were obtained and characterized by transmission electron microscopy (TEM), field‐emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). The electrochemical catalytic performance of the hollow AuNPs/CNTs/SPAN/GCE for H₂O₂ detection was evaluated by cyclic voltammetry (CV) and chronoamperometry. Using chronoamperometric method at a constant potential of ?0.1 V (vs. SCE), the H₂O₂ sensor displays two linear ranges: one from 5 µM to 0.225 mM with a sensitivity of 499.82 µA mM^?1 cm^?2; another from 0.225 mM to 8.825 mM with a sensitivity of 152.29 µA mM^?1 cm^?2. The detection limit was estimated as 0.4 µM (signal‐to‐noise ratio of 3). The hollow AuNPs/CNTs/SPAN/GCE also demonstrated excellent stability and selectivity against interferences from other electroactive species. The sensor was further applied to determine H₂O₂ in disinfectant real samples.     

Enzyme‐free Glucose Sensor Fabricated by Nanorods Decorated Nanopore Arrays on Biomedical Stainless Steel

A novel enzyme‐free glucose sensor was proposed by preparation of nanorods decorated nanopore arrays (NRs/NPAs) on 316L stainless steel simply by electrochemical treatments. The NRs/NPAs sensor displays two linear ranges towards glucose determination, one range from 1 μM to 1.2 mM with a sensitivity of 202.2 μA ? cm^?2 ? mM^?1, another range from 1.2 mM to 7.7 mM with a sensitivity of 59.18 μA?cm^?2 ? mM^?1. The detection limit is 0.5 μM. The NRs/NPAs electrode exhibits excellent stability, good selectivity and reproducibility, rendering it suitable for glucose monitoring.     

Manganese Oxide Nanoparticles/Reduced Graphene Oxide as Novel Electrochemical Platform for Immobilization of FAD and its Application as Highly Sensitive Persulfate Sensor

In this study, manganese oxide nanoparticles/reduced graphene oxide(MnOxNPs/rGO) was used as support for strong immobilization of flavin adenine dinucleotide(FAD). A thin film of rGO cast on the electrode surface, followed by performing electrodeposition of MnOxNPs at applied constant potential of +1.4 V vs. Ag/AgCl for 200 s. Finally, FAD was electrodeposited onto the rGO/MnOxNPs film by potential cycling between 1.0 to ?1.0 V in solution containing 1 mg ml^?1 FAD. Electrochemical properties and catalytic activity of GCE/rGO‐MnOxNPs/FAD toward persulfate (S₂O₈^2?) reduction was investigated. Under optimized condition, the concentration calibration range, detection limit, and sensitivity were 0.1 μM–2 mM, 90 nM and 125.8 nA/μM, respectively, using hydrodynamic amperometry technique.     

Novel Enzymatic Rhodium Modified Poly(styrene‐g‐oleic amide) Film Electrode for Hydrogen Peroxide Detection

Newly synthesized poly(styrene‐g‐oleic amide) was coated onto a rhodium nanoparticle modified glassy carbon (GC) surface for the fabrication of horseradish peroxidase based biosensor used for hydrogen peroxide detection. The rhodium modifed electrode presented ten times higher signal than unmodified electrode even at low elecrtroactive enzyme quantity by enhancing the electron transfer rate at the applied potential of −0.65 V. The biosensor designed by under the optimized rhodium electrodeposition time exhibited a fast response less than 5 s, an excellent operational stability with a relative standard deviation of 0.6 % (n=6), an accuracy of 96 % and a large linear range between 50 μM and 120 mM for hydrogen peroxide. Detection limit and the sensitivity parameters were calculated to be 44 μM and 57 μA mM⁻¹ cm⁻², respectively by preserving its entire initial response up to the 15 days, while only 20 % of its initial response was lost at the end of one month.     

Investigation of electrocatalytic and analytical ability of Pt nanoparticles supported on active carbon modified electrode to analytical determination of glucose

The electrocatalytic and analytical ability to glucose on a highly dispersed Pt nanoparticles supported on active carbon (Pt/C) modified electrode was investigated. The Pt/C nanocomposite was synthesized using a microwave method. The structural characterization and surface morphology of the prepared Pt/C nanocomposite was examined using X-ray diffraction, energy-dispersive X-ray, scanning and transmission electron microscopy. The results show that the Pt nanoparticles with 3–10 nm in diameter are well dispersed on the surface of active carbon. The electrocatalytic and analytical ability of Pt nanoparticles supported on active carbon modified electrode (Pt/C/GCE) was studied using cyclic voltammetry (CV) and chronoamperommetry. The Pt/C/GCE exhibits strong electrocatalytic activity to the glucose oxidation. Under optimal conditions, the Pt/C/GCE performed a current response towards glucose oxidation at a broad concentration range from 0.05 to 11.95 mM. Two linear regions could be observed at 0.05 to 3.5 mM with a sensitivity of 1.29 μA mM^–1 cm^–2 and at 3.5 to 11.95 mM with a sensitivity of 0.85 μA mM^–1 cm^–2, respectively. The Pt/C/GCE exhibits sufficient sensitivity and abilities of anti-interference.     

Facile Synthesis of Graphene/Cobalt Oxide Nanohexagons for the Selective Detection of Dopamine

This work presents a simple green approach for the chemical synthesis of cobalt oxide nano hexagons (Co₃O₄ NHs) with an average size of 160±40 nm incorporated graphene nanosheets (GR). The techniques used to confirm the formation of GR−Co₃O₄ NHs are transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX), and X‐ray diffraction spectroscopy (XRD). The dopamine (DA) sensor was fabricated by drop casting GR−Co₃O₄ NHs on the pre‐cleaned glassy carbon electrode (GCE). GR−Co₃O₄ modified GCE displayed a sensitive and selective electrochemical determination of DA compared to only GR and Co₃O₄ NHs modified GCE. Our fabricated sensor showed a wide linear range from 0.2 to 3443 μM with low limit of detection (84 nM) towards the determination of DA. The sensitivity of our fabricated sensor was calculated to be 108 μA mM⁻¹ cm⁻². As well, a significant storage stability, repeatability and reproducibility were attained by GR−Co₃O₄ NHs modified GCE. Human urine samples were targeted for the demonstration of practicality of our sensor.