Electrocatalytic Nitrite Determination Using Iron Phthalocyanine Modified Gold Nanoparticles

Electrochemical detection of nitrite was achieved via electrodeposition of gold nanoparticles (AuNPs) onto glassy carbon electrodes, followed by 3‐mercaptopropionic acid (MPA) self‐assembly, enabling attachment of an iron(III) monoamino‐phthalocyanine (FeMAPc) catalyst via amide bond formation. The use of scanning electron microscopy, energy dispersive X‐ray spectroscopy and ultraviolet‐visible spectroscopy realised surface characterisation while cyclic voltammetry and electrochemical impedance spectroscopy techniques were applied for electrochemical interrogation. The electrochemical behaviour of nitrite at the bare (GCE), AuNPs/GCE, FeMAPc/GCE and FeMAPc‐MPA/AuNPs/GCE was further scrutinised using differential pulse voltammetry in phosphate buffer solution (0.1 M PBS, pH 5.8). Overall the FeMAPc‐MPA/AuNPs/GCE resulted in sensitivity 14.5 nA/µM, which was double that of AuNPs/GCE, 2.4 times FeMAPc/GCE and 3.5 times the response at a bare GCE, with linear range 1.9 µM–2.04 mM (PBS, pH 5.8) and LOD 0.21 µM. An interference study revealed that the proposed sensor (FeMAPc‐MPA/AuNPs/GCE) exhibited a selective response in the presence of interfering anions and the analytical capability of the sensor was demonstrated via nitrite ion determination in real water samples.     

Development of Simple Electrochemical Sensor for Selective Determination of Methadone in Biological Samples Using Multi‐walled Carbon Nanotubes Modified Pencil Graphite Electrode

The electrochemical sensor was developed for determination of methadone (MTD) using multi‐walled carbon nanotubes (MWCNT) modified pencil graphite electrode (MWCNT‐PGE). It was found that the oxidation peak current of MTD at the MWCNT‐PGE was greatly improved compared with that of the bare‐PGE. At the MWCNT‐PGE, well‐defined anodic peak of MTD was observed at about 0.7 V (in pH 7 solution). The influence of several parameters on the determination of MTD was investigated. At optimum experimental conditions, differential pulse voltammetry (DPV) was used for determination of MTD, which exhibited a linear calibration graph of Ip versus MTD concentration in the range of 0.1–15 µM with a correlation coefficient of 0.9992. The calculated detection limit for S/N = 3 was 87 nM. It has been shown that the peaks obtained for oxidation of ascorbic acid (AA), uric acid (UA) and MTD in their mixture could be well resolved by differential pulse voltammetry, permitting us to develop a sensitive and selective electrochemical sensor for determination of MTD in the presence of AA and UA. Finally, MWCNT‐PGE was used for determination of MTD in biological samples, such as human serum and urine, using the standard addition procedure and the results were quite promising.     

A Simple and Sensitive Poly‐1,5‐Diaminonaphthalene Modified Sensor for the Determination of Sulfamethoxazole in Biological Samples

Sulfamethoxazole (SMZ), an antibacterial sulfonamide drug, has been selectively determined using poly‐1,5‐diaminonaphthalene (p‐DAN) modified glassy carbon electrode (GCE). The modified sensor was characterized by field emission scanning electron microscopy (FE‐SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). SMZ showed linear response in the concentration range of 0.5–150 µM by using square wave voltammetry (SWV) and the detection limit was found to be 0.05 nM with sensitivity of 0.085 µA µM^?1. The proposed sensor has been successfully employed to determine SMZ in the pharmaceutical tablets and human urine samples.     

Electrosynthesis of Molecularly Imprinted Poly‐o‐phenylenediamine on MWCNT Modified Electrode for Selective Determination of Meldonium

In this study, a molecularly imprinted polymer (MIP) was synthesized by electrochemical polymerization and used to construct an electrochemical sensor for determination of meldonium (MEL) selectively for the first time. The polymer film was generated by using o‐phenylenediamine (o‐PD) as a monomer on the surface of carboxylic acid functionalized multiwalled carbon nanotube (MWCNT) modified pencil rod electrode in the presence of MEL as a template. MEL imprinted (MEL‐imp) and non‐imprinted (N‐imp) polymer films and coated electrodes were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), profilometry, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Voltammetric measurements were carried out in a ferrocyanide/ferricyanide redox probe solution for MEL‐imp and N‐imp electrodes in the presence and absence of template molecule. The decrease in peak current of redox probe was linear with the concentration of MEL in the range of 0.1–5 μg/mL and the limit of detection (3 s/b) was found to be 0.066 μg/mL under optimized experimental conditions. The proposed sensor was successfully applied for selective determination of MEL in human urine sample with long term stability and good reproducibility.     

Investigation of plasma-functionalized multiwalled carbon nanotube film and its application of DNA sensor for Legionella pneumophila detection

A novel multiwall carbon nanotube (MWCNT) electrode functionalized with oxygen plasma treatment was prepared and characterized, and its DNA sensing ability for Legionella pneumophila (L. pneumophila) detection was examined using electrochemical measurement. A well-patterned MWCNT working electrode (WE) on a Pt track was fabricated using photolithography, transfer methods and an etching technique. The MWCNT WE was functionalized by oxygen plasma treatment prior to applying for DNA sensor. The surface morphology of the plasma-functionalized MWCNT (pf-MWCNT) WEs were observed by scanning electron microscope (SEM) and the change of chemical composition was characterized by X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were performed using CV with ferricyanide/ferrocyanide redox couple. Effective areas of working electrodes were calculated to be 0.00453 cm² for pristine MWCNT electrode and 0.00747-0.00874 cm² for pf-MWCNT electrodes with different plasma treatment times. Differential pulse voltammetry (DPV) was carried out in methylene blue solution for DNA sensing. The pf-MWCNT based DNA sensor was successfully operated in a target concentration range of 10 pM to 100 nM and had a lower detection limit than a pristine MWCNT based DNA sensor.     

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.     

Gold‐Iron Bimetallic Nanoparticles Impregnated Reduced Graphene Oxide Based Nanosensor for Label‐free Detection of Biomarker Related to Non‐alcoholic Fatty Liver Disease

We report for the first time a microwave assisted, one pot, direct, and facile synthesis of monodispersed iron‐gold bimetallic nanoparticles (BNP_Au‐Fe) using glucose as a reducing agent in merely 90 s. The as such synthesized BNP_Au‐Fe were thoroughly characterized using UV‐Vis, XRD, TEM, EDX, elemental mapping, and raman spectroscopy. These BNP_Au‐Fe were further impregnated with reduced graphene oxide (rGO) and coated onto glassy carbon electrode (GCE) to develop a sensor probe for label free electrochemical detection of acetaminophen, which is considered to be a most potent biomarker related to non‐alcoholic fatty liver disease. The sensor probe was systematically characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The BNP_Au‐Fe‐rGO nanocomposite matrix showed the sensing of acetaminophen with a wide dynamic range between 50 and 800 nM with detection limit (DL) of 0.14 nM (±0.05) nM (RSD<4.12 %) that was lower compared to previously reported acetaminophen sensors. To show the practical application of the sensor probe, acetaminophen was detected in human urine samples, which showed the percentage recovery between 86.65 % and 91.32 %. To the best of our knowledge, this is the first report where BNP_Au‐Fe impregnated rGO was used to detect acetaminophen. Interferences due to various molecules such as glucose, serum albumin, glycine, glutamic acid, alanine, citric acid, and ascorbic acid were tested individually and in mixed sample. Long‐term stability of sensor probe was examined which was found to be stable up to 12 weeks. The sensor fabricated using BNP_Au‐Fe‐rGO nanocomposite has many attractive features such as; simplicity, rapidity, and label free detection, hence it could be a method of choice for acetaminophen detection in clinical settings.     

Design and Development of Ultrafast Sinapic Acid Sensor Based on Electrochemically Nanotuned Gold Nanoparticles and Solvothermally Reduced Graphene Oxide

We report for the first time sinapic acid (SA) sensing based on nanocomposite comprising electrochemically tuned gold nanoparticles (EAuNPs) and solvothermally reduced graphene oxide (rGO). The synthesized EAuNPs, rGO, and EAuNPs‐rGO nanocomposite were characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), particle size analysis, and Raman spectroscopy. A proof‐of‐concept electrochemical sensor for SA was developed based on synthesized EAuNPs‐rGO nanocomposite, which was characterized by electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The developed sensor detected SA with a linear dynamic range (LDR) between 20 μM and 200 μM and detection limit (DL) of 33.43 (±0.21) nM (RSD<3.32 %). To show the useful purpose of the sensor probe in clinical applications, SA was detected in human urine samples, which showed the percentage recovery between 82.6 % and 92.8 %. Interferences due to various molecules such as L‐cystine, glycine, alanine, serum albumin, uric acid, citric acid, ascorbic acid, and urea were tested. Long‐term stability of the sensor probe was examined, which was found to be stable up to 6 weeks. The sensor fabricated using EAuNPs‐rGO nanocomposite has many attractive features such as; simplicity, rapidity, and label‐free detection; hence, it could be a method of choice for SA detection in various matrices.     

Reduced Graphene Oxide/Carbon Nanotube/Gold Nanoparticles Nanocomposite Functionalized Screen‐Printed Electrode for Sensitive Electrochemical Detection of Endocrine Disruptor Bisphenol A

We fabricated a highly sensitive electrochemical sensor for the determination of bisphenol A (BPA) in aqueous solution by using reduced graphene oxide (RGO), carbon nanotubes (CNT), and gold nanoparticles (AuNPs)‐modified screen‐printed electrode (SPE). GO/CNT nanocomposite was directly reduced to RGO/CNT on SPE at room temperature. AuNPs were then electrochemically deposited in situ on RGO/CNT‐modified SPE. Under optimized conditions, differential pulse voltammetry (DPV) produced linear current responses for BPA concentrations of 1.45 to 20 and 20 to 1,490 nM, with a calculated detection limit of an ultralow 800 pM. The sensor response was unaffected by the presence of interferents such as phenol, p‐nitrophenol, pyrocatechol, 2,4‐dinitrophenol, and hydroquinone.     

In situ synthesis of gold nanoparticles on porous polyacrylonitrile nanofibers for sensing applications

A simple and cost-effective method was reported to synthesize small size (6 nm) gold nanoparticles (AuNPs) on polyacrylonitrile (PAN) electrospun nanofibers (AuNPs/PAN). The formation of AuNPs is attributed to the in situ reduction of Au(III) to Au(0) by 4-(dimethylamino)benzaldehyde doped in the PAN nanofibers. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) confirmed that the AuNPs/PAN nanofibers showed good conductivity. The AuNPs/PAN nanofibers were used to immobilize tris(2,2'-bipyridyl)ruthenium(II) ions (Ru(bpy)(3)(2+)) to form an electrochemiluminescence (ECL) sensor. The AuNPs on the PAN nanofibers exhibited an excellent catalytic effect on the ECL of Ru(bpy)(3)(2+) which could be employed to detect low concentrations of phenolic compounds. The linear response range of the ECL sensor to hydroquinone is 0.55-37 μM with limit of detection of 80 nM (S/N = 3). This sensor has been successfully applied to determine the hydroquinone content in photographic developer samples. Our work provides a very simple and cost-effective method to synthesize AuNPs on polymer nanofibers which shows great potential in the field of electrocatalysis and chemo/biosensors.     

An Electrochemical Sensor Based on Gold Nanoparticles Incorporated in Mesoporous MFI Zeolite for Determination of Purine Bases in DNA

An electrochemical sensor was developed based on gold nanoparticles incorporated in mesoporous MFI zeolite for the determination of purine bases. Au nanoparticles (AuNPs) were incorporated into the mesoporous MFI zeolite (AuNPs/m‐MFI) by post‐grafting reaction. The composite materials were characterized by transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and electrochemical methods. Au nanoparticles with a size of 5‐20 nm are uniformly dispersed in the pores of mesoporous MFI zeolite. And the morphology of MFI zeolite can be perfectly kept after pore expansion and Au nanoparticles incorporation. The electrocatalytic oxidation of purine bases (guanine and adenine in DNA) is investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The surface‐confined Au nanoparticles provide the good catalytic activity for oxidation of purine bases. The simultaneous detection of guanine and adenine can be achieved at AuNPs/m‐MFI composites modified glassy carbon electrode (GCE). The electrochemical sensor based on AuNPs/m‐MFI exhibits wide linear range of 0.5–500 μM and 0.8–500 μM with detection limit of 0.25 and 0.29 μM for guanine and adenine, respectively. Moreover, the electrochemical sensor is applied to evaluation of guanine and adenine in herring sperm DNA samples with satisfactory results.     

Ag ion irradiated based sensor for the electrochemical determination of epinephrine and 5-hydroxytryptamine in human biological fluids

A promising and highly sensitive voltammetric method has been developed for the first time for the determination of epinephrine (EP) and 5-hydroxytryptamine (5-HT) using 120 MeV Ag ion irradiated multi-walled carbon nano tube (MWCNT) based sensor. The MWCNT were irradiated at various fluences of 1e12, 3e12 and 1e13 ions cm⁻² using palletron accelerator. The simultaneous determination of EP and 5-HT has been carried out in phosphate buffer solution of pH 7.20 using square wave voltammetry and cyclic voltammetry. Experimental results suggested that irradiation of MWCNT by Ag ions enhanced the electrocatalytic activity due to increase in effective surface area and insertion of Ag ions, leading to a remarkable enhancement in peak currents and shift of peak potentials to less positive values as compared to the unirradiated MWCNT (pristine). The developed sensor exhibited a linear relationship between peak current and concentration of EP and 5-HT in the range 0.1–105 μM with detection limit (3σ/b) of 2 nM and 0.75 nM, respectively. The practical utility of irradiation based MWCNT sensor has been demonstrated for the determination of EP and 5-HT in human urine and blood samples.     

Highly Sensitive Molecularly Imprinted Sensor Based on Platinum Thin‐film Microelectrode for Detection of Chloramphenicol in Food Samples

A highly sensitive and selective electrochemical biomimetic sensor was fabricated for fast detection of chloramphenicol (CAP) in honey and milk samples. Platinum thin‐film microelectrode (Pt TFME), which could provide unique electrochemical properties and achieve measurement using very limited solution volumes, was surface‐modified by electropolymerizing o‐phenylenediamine. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the preparation process of CAP‐imprinted poly(o‐phenylenediamine) film and rebinding ability of CAP into the imprinted cavities. The electrochemical properties of the sensor were further investigated with square wave voltammetry (SWV) by using K₃Fe(CN)₆ as an electroactive probe. The current difference of oxidation peaks of K₃Fe(CN)₆ had a good linear relationship with the concentration of CAP in the range of 0.9–10 nM. The detection limit was 0.39 nM based on the signal to noise ratio of 3. The developed sensor was successfully applied to determine CAP in honey and milk samples, and the result was in good agreement with that obtained by high performance liquid chromatography‐mass spectrometry (HPLC‐MS). The sensor showed high sensitivity and excellent selectivity to CAP in comparison to other structurally related and/or normally existing antibiotics, and demonstrated great promise for the rapid quantification of CAP in real food samples and field analysis.     

Molecularly Imprinted Electrochemical Sensor Based on Modified Reduced Graphene Oxide‐gold Nanoparticles‐polyaniline Nanocomposites Matrix for Dapsone Determination

This work was designed to develop an electrochemical sensor based on molecular imprinted polyaniline membranes onto reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) modified glassy carbon (GC) electrode for dapsone (DDS) determination. The prepared RGO/AuNPs/PANI‐MIPs nanocomposite was characterized by Ultra‐Violet‐Visible (UV‐Vis), Fourier transform infrared spectroscopy (FT‐IR) and scanning electronic microscopy (SEM) images. The feature of the imprinted electrode was evaluated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and impedance spectroscopy (IS). Throughout this study several analytical parameters, such as incubation time, pH value, concentration of monomer/template molecules and electro‐polymerization cycles were investigated. Under the optimized conditions, the experimental results showed best analytical performances for DDS detection with a sensitivity of 0.188 Ω/mol L^?1, a linear range from 1.0×10^?7 M to 1.0×10^?3 M and a detection limit of 6.8×10^?7 M. The bioanalytical sensor was applied to the determination of dapsone in real samples with high selectivity and recovery.     

Electrochemical Sensor Based on Multiwalled Carbon Nanotube,Alizarine Red S and Chitosan for Simultaneous Determination of Oxomemazine Hydrochloride,Paracetamol and Guaifenesin

A simple and highly sensitive sensor has been used for the determination of oxomemazine hydrochloride (OXO) in presence of paracetamol (PAR) and guaifenesin (GU). Carbon paste electrode was modified with multiwalled carbon nanotube (MWCNT), alizarine red S (AZ) and chitosan (CH). Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to characterize the nanostructure and performance of the sensor. Under the optimized experimental conditions OXO gave linear response over the range of 2.00×10⁻⁶–1.00×10⁻⁴ mol L⁻¹. The detection limit was found to be 4.35×10⁻⁷ mol L⁻¹. The practical application of the modified electrode was demonstrated by measuring the concentration of OXO in pharmaceutical samples and urine. This revealed that suggested sensor shows excellent analytical performance for the determination of OXO in terms of a very low detection limit, high sensitivity and selectivity.     

Nanohybrid Comprising Gold Nanoparticles – MoS2 Nanosheets for Electrochemical Sensing of Folic Acid in Serum Samples

Folic acid (FA) deficiency is associated with several clinical conditions such as megaloblastic anemia, neuropsychiatric, and pregnancy-related syndromes, this makes FA an important metabolite to be monitored. We have fabricated an electrochemical biosensor based on gold nanoparticles decorated molybdenum disulfide nanosheets (AuNPs−MoS₂NSs) nanocomposite as a transducer matrix for specific and rapid electrochemical detection of FA. Differential pulse voltammetry (DPV) studies displayed a rapid analytical response of the fabricated AuNPs−MoS₂NSs/GCE sensor probe towards FA in a wide concentration range of 0.001–100 μM with a very low detection limit of 0.72±0.03 nM. The selectivity of the fabricated sensor probe has been examined in the presence of interferents such as dopamine, uric acid, ascorbic acid, glucose, and urea. The clinical potential of the fabricated biosensor was established by monitoring FA in human serum samples. The developed AuNPs−MoS₂NSs/GCE sensor probe showed high reproducibility and stability, indicating its promise for FA detection in clinical settings.     

Sensing Lorazepam with a glassy carbon electrode coated with an electropolymerized-imprinted polymer modified with multiwalled carbon nanotubes and gold nanoparticles

We report on an electrode for the amperometric determination of lorazepam. A glassy carbon electrode was coated with a molecular imprint made by electropolymerization of ortho-phenylenediamine and filled with multiwalled carbon nanotubes and gold nanoparticles, which enhances the transmission of electrons. The sensor was studied with respect to its response to hexacyanoferrate (III) as a probe and by electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry. The linear response range to Lorazepam is from 0.5 nM to 1.0 nM and from 1.0 nM to 10.0 nM, with a detection limit of 0.2 nM (at an S/N of 3). The electrode was successfully applied to determine Lorazepam in spiked human serum.

Aptamer‐Assisted Gold Nanoparticles/PEDOT Platform for Ultrasensitive Detection of LPS

Neatly arranged gold nanoparticles (AuNPs) were directly electrodeposited on an electrochemically polymerized self‐assembled monolayer (SAM) of thiol‐functionalized 3,4‐ethylenedioxythiophene (EDOT) derivative, EDTMSHA. A thiolated single‐stranded DNA (ssDNA) aptamer with high specificity to LPS was immobilized on the AuNPs/conducting polymer composite film, serving as sensing platform for LPS detection. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscope (SEM), and atomic force microscopy (AFM) were utilized to characterize the modification and detection processes. The electron transfer resistance was found to have a linear relationship with LPS concentration from 0.1 pg/mL to 1 ng/mL.     

Improved Performance of an Amperometric Biosensor with Polydiaminonaphthalene on Electrochemically Deposited Au Nanoparticles

The performance of an enzyme sensor fabricated through covalent bond formation on the HRP‐bonded poly(1,8‐diaminonaphthalene) (polyDAN) layer with gold nanoparticles (AuNPs) was applied to catalyze the electrochemical reduction of H₂O₂. The surface characteristics of the sensor probe were studied using cyclic voltammetry, SEM, XPS, QCM, and impedance spectroscopy. The AuNP‐deposited surface resulted in higher conductivity and sensitivity for H₂O₂ detection in phosphate buffer solution. A linear calibration plot was obtained in the H₂O₂ concentration range between 10.0 μM and 25.0 mM with detection limit 5.0±1.25 μM. The lifetime of HRP/polyDAN/AuNP/GC probe was over 70 days without response loss.     

Construction of an electrochemical sensor based on the electrodeposition of Au-Pt nanoparticles mixtures on multi-walled carbon nanotubes film for voltammetric determination of cefotaxime

Mixtures of gold-platinum nanoparticles (Au-PtNPs) are fabricated consecutively on a multi-walled carbon nanotubes (MWNT) coated glassy carbon electrode (GCE) by the electrodeposition method. The surface morphology and nature of the hybrid film (Au-PtNPs/MWCNT) deposited on glassy carbon electrodes is characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The modified electrode is used as a new and sensitive electrochemical sensor for the voltammetric determination of cefotaxime (CFX). The electrochemical behavior of CFX is investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results of voltammetric studies exhibited a considerable improvement in the oxidation peak current of CFX compared to glassy carbon electrodes individually coated with MWCNT or Au-PtNPs. Under the optimized conditions, the modified electrode showed a wide linear dynamic range of 0.004-10.0 μM with a detection limit of 1.0 nM for the voltammetric determination of CFX. The modified electrode was successfully applied for the accurate determination of trace amounts of CFX in pharmaceutical and clinical preparations.