Mani Govindasamy

Molybdenum disulfide nanosheets coated multiwalled carbon nanotubes composite for highly sensitive determination of chloramphenicol in food samples milk, honey and powdered milk

We have described a hybrid material that consists of molybdenum disulfide nanosheets (MoS2) coated on functionalized multiwalled carbon nanotubes (f-MWCNTs) for sensitive and selective determination of chloramphenicol (CAP). The MoS2/f-MWCNTs nanocomposite was successfully prepared through a hydrothermal process and its structure was characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The MoS2/f-MWCNTs nanocomposite holds excellent electrochemical properties and it displays excellent electrocatalytic ability to CAP. Under optimized working conditions, the nanocomposite film modified electrode responds linearly to CAP in the concentration range of 0.08-1392μM. The detection limit was obtained as 0.015μM (±0.003). The electrode has high level of selectivity in presence of large excess concentrations of interfering species. In addition, the modified electrode offers satisfactory repeatability, reproducibility and stability. The practical applicability of the electrode was demonstrated in food samples such as, milk, powdered milk and honey samples and the recoveries are agreeable which clearly revealed its practical feasibility in food analysis.

Green synthesized gold nanoparticles decorated graphene oxide for sensitive determination of chloramphenicol in milk, powdered milk, honey and eye drops.

A simple and rapid green synthesis using Bischofia javanica Blume leaves as reducing agent was developed for the preparation of gold nanoparticles (AuNPs). AuNPs decorated graphene oxide (AuNPs/GO) was prepared and employed for the sensitive amperometric determination of chloramphenicol. The green biosynthesis requires less than 40s to reduce gold salts to AuNPs. The formations of AuNPs and AuNPs/GO were evaluated by scanning electron and atomic force microscopies, UV-Visible and energy dispersive X-ray spectroscopies, X-ray diffraction studies, and electrochemical methods. AuNPs/GO composite film modified electrode was fabricated and shown excellent electrocatalytic ability towards chloramphenicol. Under optimal conditions, the amperometric sensing platform has delivered wide linear range of 1.5-2.95μM, low detection limit of 0.25μM and high sensitivity of 3.81μAμM(-1)cm(-2). The developed sensor exhibited good repeatability and reproducibility, anti-interference ability and long-term storage stability. Practical feasibility of the sensor has been demonstrated in food samples (milk, powdered milk and honey) and pharmaceutical sample (eye drops). The green synthesized AuNPs/GO composite has great potential for analysis of food samples in food safety measures.

Electrodeposition of gold nanoparticles on a pectin scaffold and its electrocatalytic application in the selective determination of dopamine

A simple electrochemical deposition strategy is proposed for the preparation of gold nanoparticles (Au NPs) at the electrode surface using biopolymer pectin as stabilizing agent. The formation of the nanoparticles was confirmed by scanning electron microscopy (SEM), UV-visible spectroscopy and X-ray diffraction (XRD) studies. A pectin-stabilized, gold nanoparticle film-modified glassy carbon electrode (pectin–Au NP/GCE) was prepared, which exhibited excellent electrocatalytic ability towards oxidation of dopamine (DA). At the pectin–Au NP/GCE, the redox couple corresponding to the redox reaction of DA was observed at the formal potential of 0.20 V with highly enhanced peak currents. A thin layer of nafion coating was applied on the pectin–Au NP composite to improve its selectivity. Two linear ranges of detection were found: (1) 20 nM to 0.9 μM with a limit of detection (LOD) of 6.1 nM, (2) 0.9 μM to 1 mM with a LOD of 0.64 μM. The fabricated sensor selectively detects DA even in the presence of high concentrations of interferents. Moreover, practical feasibility of the sensor was addressed in pharmaceutical samples, which presented appreciable recovery results. The main advantages of the sensor are its very simple and green fabrication approach, roughed and stable structure, and fast and highly reproducible detection of dopamine.

Methyl parathion detection in vegetables and fruits using silver@graphene nanoribbons nanocomposite modified screen printed electrode

We have developed a sensitive electrochemical sensor for Organophosphorus pesticide methyl parathion (MP) using silver particles supported graphene nanoribbons (Ag@GNRs). The Ag@GNRs nanocomposite was prepared through facile wet chemical strategy and characterized by TEM, EDX, XRD, Raman, UV-visible, electrochemical and impedance spectroscopies. The Ag@GNRs film modified screen printed carbon electrode (SPCE) delivers excellent electrocatalytic ability to the reduction of MP. The Ag@GNRs/SPCE detects sub-nanomolar concentrations of MP with excellent selectivity. The synergic effects between special electrocatalytic ability of Ag and excellent physicochemical properties of GNRs (large surface area, high conductivity, high area-normalized edge-plane structures and abundant catalytic sites) make the composite highly suitable for MP sensing. Most importantly, the method is successfully demonstrated in vegetables and fruits which revealed its potential real-time applicability in food analysis.

Novel hydrothermal synthesis of MoS2 nanocluster structure for sensitive electrochemical detection of human and environmental hazardous pollutant 4-aminophenol

Herein, we have demonstrated a new electrochemical sensor for trace level detection of environmentally hazardous 4-aminophenol (4-AP) using a glassy carbon electrode (GCE) modified with MoS2 nanoclusters. The MoS2 nanoclusters were fabricated by a simple hydrothermal treatment without using any other organic templates or surfactants. The formation of MoS2 nanoclusters was confirmed by X-ray diffraction, FT-infrared, Raman and energy dispersive X-ray spectroscopies, scanning electron and transmission electron microscopies and selected area electron diffraction studies. The MoS2 modified GCE (MoS2/GCE) shows good electrocatalytic activity towards the redox reaction of 4-AP by means of cyclic voltammetry and differential pulse voltammetry. The DPV detection of 4-AP using MoS2/GCE delivers excellent sensitivity with a low detection limit of 0.03 (±0.008) μM and good linearity in the range of 0.04–17 μM. The sensitivity of the developed electrode is 4.278 (±0.058) μA mM−1 cm−2. The developed sensor displayed good repeatability, reproducibility and selectivity. Moreover, the practical applicability of the MoS2/GCE is demonstrated in water samples which delivered satisfactory recoveries.

Electrochemical determination of morin in Kiwi and Strawberry fruit samples using vanadium pentoxide nano-flakes

Herein, we report the synthesis of Vanadium Pentoxide Nanoflakes (V2O5 NF) using ionic liquid and employed the V2O5 NF in electrochemical determination of Morin (MR) in fruit samples. The V2O5 NF were characterized by Powder X-ray diffraction (PXRD), scanning electron microscope (SEM), energy-dispersive X-ray analyzer (EDX), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). Remarkably, the as-synthesized V2O5 NF exhibited excellent electrochemical behavior and electrochemical ability towards MR. The CV and DPV studies were recognized that the electrochemical performance of V2O5 NF film modified glassy carbon electrode (V2O5 NF/GCE) towards detection of MR is outstanding in comparison with unmodified GCE. The proposed MR sensor shows a wide linear range, high sensitivity, and low limit of detection are 0.05-10.93μm, 1.130μAμM-1cm-2, and 9nM respectively. The fabulous analytical parameters of the developed sensor surpassed the previously reported modified electrodes, rendering the potential application of V2O5 NF in environmental, biomedical, and pharmaceutical samples.

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

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

Simultaneous determination of dopamine and uric acid in the presence of high ascorbic acid concentration using cetyltrimethylammonium bromide–polyaniline/activated charcoal composite

We describe a simple, low-cost and mass producible composite made up of cetyltrimethylammonium bromide (CTAB) functionalized polyaniline (PANI) and activated charcoal (CTAB–PANI/AC) for simultaneous determination of dopamine (DA) and uric acid (UA). The composite formation was verified through scanning electron microscopy, electrochemical impedance spectroscopy and electrochemical methods. The CTAB–PANI/AC composite was used to modify a glassy carbon electrode (GCE) and the resulting modified electrode displayed excellent electrocatalytic activity to DA and UA and successfully separates their overlapped voltammetric peaks. The composite completely inhibits the AA signal and does not produce any voltammetric signal for AA up to 2 mM. The DA and UA can be selectively detectable up to detection limits of 0.06 (±0.006) μM and 0.20 (±0.008) μM, respectively. The effects of kinetics, analyte concentration and pH of the supporting electrolyte were investigated and optimized. The modified electrode has appreciable stability, repeatability and reproducibility. Besides, the practical feasibility of the sensor is demonstrated in biological samples, which delivered satisfactory recovery results.

Highly sensitive determination of non-steroidal anti-inflammatory drug nimesulide using electrochemically reduced graphene oxide nanoribbons

The excess use of nimesulide (NIM) causes acute side effects to gastrointestinal, central nervous and genitourinary systems and hence its rapid, sensitive determination is highly important. We describe a robust electrochemical sensor based on electrochemically reduced graphene oxide nanoribbons (ER-GONRs) modified on a screen-printed carbon electrode (SPCE) for detecting NIM in pharmaceutical formulations and biological medium. Compared with parental multiwalled carbon nanotubes (MWCNTs), ER-GONRs possess rich edge defects, abundant functional groups, high area-normalized edge-plane structures and chemically active sites and hence they can be a superior electrocatalyst and signal amplifier for electroanalytical applications. ER-GONRs/SPCE exhibited excellent sensing performance towards NIM. The linear range was 1.0 × 10−8 to 1.50 × 10−3 M and the detection limit was 3.50 (±1.57) nM. In addition, the ER-GONRs/SPCE showed excellent real-time sensing applications in NIM tablet and human urine samples, which could find potential applicability in drug and clinical analysis. The combined advantages of SPCE technology and ER-GONRs make this method a robust, low-cost, reproducible, sensitive and easy-to-use sensor.

A facile graphene oxide based sensor for electrochemical detection of prostate anti-cancer (anti-testosterone) drug flutamide in biological samples

A novel electrochemical sensor based on graphene oxide (GO) modified glassy carbon electrode (GCE) has been successfully developed for the determination of anti-cancer drug flutamide for the first time. The morphology and structure of the prepared GO were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), UV-visible spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), field emission-scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The electrochemical properties of the GO were studied by electrochemical impedance spectroscopy (EIS). GO modified GCE was fabricated and utilized to study the electrochemical performance of flutamide by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). As an electrochemical sensor, GO modified GCE exhibited strong electrocatalytic activity towards the reduction of flutamide. Interestingly, the electrochemical sensor displayed an excellent current response for the detection of flutamide with wide linear response range, excellent limit of detection and good sensitivity of 0.009 to 1.9 μM, 6 nM and 29.55 μA μM−1 cm−2, respectively. The proposed sensor has good repeatability, reproducibility, stability and selectivity even in the presence of biologically co-interfering substances. GO modified GCE sensor was successfully used for the detection of flutamide (spiked) in various blood serum samples.