Rajkumar Devasenathipathy

Highly selective amperometric sensor for the trace level detection of hydrazine at bismuth nanoparticles decorated graphene nanosheets modified electrode

A highly selective amperometric sensor was developed for the trace level determination of hydrazine at bismuth nanoparticles (Bi) decorated graphene nanosheets (GR) composite film modified glassy carbon electrode (GCE). GR-Bi nanocomposite has been successfully prepared via simple and facile chemical reduction approach and its structure was characterized by various techniques. Surface morphological and X-ray diffraction studies revealed the formation and high loading of Bi nanoparticles on graphene sheets. GR-Bi nanocomposite modified GCE exhibited greatly enhanced electrocatalytic performance towards electro-oxidation of hydrazine in terms of decrease in overpotential and increase in oxidation peak current (Ip). The kinetic parameters such as electron transfer coefficient (α) and diffusion coefficient (Do) of the hydrazine oxidation were determined to be 0.70 and 2.65×10(-5) cm(2) s(-1), respectively. An amperometric sensor has been fabricated which detects trace level concentration of hydrazine. The sensor exhibited a wide linear range from 20 nM to 0.28 mM and a very low detection limit (LOD) of 5 nM. Remarkably, this is the lowest LOD achieved for the determination of hydrazine in neutral pH among other reported electrochemical hydrazine sensors. In addition, the sensor selectively detects hydrazine even in the presence of 1000 fold excess quantity of common interferrants. The practical feasibility of the sensor has been assessed in water and urine samples with good recoveries. Furthermore, the sensor exhibited appreciable stability, repeatability and reproducibility results.

Glucose biosensor based on glucose oxidase immobilized at gold nanoparticles decorated graphene-carbon nanotubes

Biopolymer pectin stabilized gold nanoparticles were prepared at graphene and multiwalled carbon nanotubes (GR-MWNTs/AuNPs) and employed for the determination of glucose. The formation of GR-MWNTs/AuNPs was confirmed by scanning electron microscopy, X-ray diffraction, UV-vis and FTIR spectroscopy methods. Glucose oxidase (GOx) was successfully immobilized on GR-MWNTs/AuNPs film and direct electron transfer of GOx was investigated. GOx exhibits highly enhanced redox peaks with formal potential of -0.40 V (vs. Ag/AgCl). The amount of electroactive GOx and electron transfer rate constant were found to be 10.5 × 10(-10) mol cm(-2) and 3.36 s(-1), respectively, which were significantly larger than the previous reports. The fabricated amperometric glucose biosensor sensitively detects glucose and showed two linear ranges: (1) 10 μM - 2 mM with LOD of 4.1 μM, (2) 2 mM - 5.2 mM with LOD of 0.95 mM. The comparison of the biosensor performance with reported sensors reveals the significant improvement in overall sensor performance. Moreover, the biosensor exhibited appreciable stability, repeatability, reproducibility and practicality. The other advantages of the fabricated biosensor are simple and green fabrication approach, roughed and stable electrode surface, fast in sensing and highly reproducible.

Immobilization of glucose oxidase on graphene and cobalt phthalocyanine composite and its application for the determination of glucose.

We described a simple and facile chemical reduction strategy for the preparation of graphene (GR)-cobalt phthalocyanine (CoPc) composite and explored it for the enzymatic determination of glucose. CoPc is an active mediator and electrocatalysts for the immobilization of GOx and determination of glucose. However, it is not stable on the electrode surface and also suffers from lack of conductivity. Here, we have employed GR as the suitable support to stabilize CoPc through simple chemical reduction method and the resulting composite has been used for the glucose biosensor application. Scanning electron microscopy, X-ray diffraction and Energy-dispersive X-ray spectroscopy studies confirmed the successful formation of composite. Direct electron transfer of glucose oxidase (GOx) was observed with well defined redox peaks at the formal potential of -0.44 V. The amount of electroactive GOx (Г) and electron transfer rate constant (ks) were calculated to be 3.77×10(-10) mol cm(-2) and 3.57 s(-1), respectively. The fabricated amperometric biosensor detects glucose in wide linear concentration range from 10 μM to 14.8 mM with high sensitivity of 5.0 9μA mM(-1) cm(-2). The sensor offered very low detection limit (LOD) of 1.6 μM. In addition, practical feasibility of the sensor has been explored in screen printing carbon electrode with accurate determination of glucose present in human blood serum and urine samples. Furthermore, the sensor exhibited appreciable stability, repeatability and reproducibility results.

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.

Highly selective determination of cysteine using a composite prepared from multiwalled carbon nanotubes and gold nanoparticles stabilized with calcium crosslinked pectin

AbstractWe describe a glassy carbon electrode (GCE) modified with gold nanoparticles that were stabilized with calcium-crosslinked pectin (CCLP) and electrodeposited on multiwalled carbon nanotubes (MWCNTs) by cyclic voltammetry. The resulting electrode was used for the selective determination of L-cysteine (L-Cys). Its characterization showed that the CCLP acts as a scaffold to form highly stable, uniform and electrochemically active AuNPs. Electrochemical studies showed the MWCNT to significantly promote the electrodeposition of the CCLP-AuNPs. The new GCE exhibited excellent electrocatalytic ability towards oxidation of L-Cys in showing a lower overpotential and giving a higher oxidation peak current. The diffusion coefficient for the oxidation of L-Cys was calculated to be 3.0 × 10−6 cm2 s−1. This amperometric sensor displays a wide linear range (from 0.1 to 1,000 μM), high sensitivity (0.46 μA μM−1 cm−2) and a detection limit as low as 19 nM (at a signal-to-noise ratio of 3). The sensor was applied to specifically detect L-Cys even in the presence of 500-fold excess of interferents. It also is stable and possesses good repeatability and reproducibity, and was successfully applied to the determination of L-Cys in spiked samples of human serum. Graphical abstractCalcium ions cross linked pectin (CCLP) stabilized gold nanoparticles (AuNPs) at multiwalled carbon nanotubes (MWCNT) was electrochemically prepared. The as-prepared nanocomposite was characterized by various methods and employed for the selective determination of L-Cysteine.

A sensitive and selective enzyme-free amperometric glucose biosensor using a composite from multi-walled carbon nanotubes and cobalt phthalocyanine

In the present study, a simple and sensitive amperometric enzyme-free glucose sensor was developed at a multiwalled carbon nanotube and cobalt tetrasulfonated phthalocyanine (MWCNT–CoTsPc) modified electrode. The morphology of the fabricated composite was characterized and confirmed by transmission electron microscopy and UV-Vis spectroscopy. UV-Vis spectroscopy results confirmed that the MWCNT–CoTsPc composite was formed via the strong π–π interaction between CoTsPc and MWCNT. Compared with pristine CoTsPc, the MWCNT–CoTsPc composite modified electrode showed a higher electrocatalytic activity and lower overpotential towards the oxidation of glucose. Amperometric i–t technique was used for the determination of glucose. The response of glucose was linear over the concentration ranging from 10 μM to 6.34 mM with a sensitivity of 122.5 μA mM−1 cm−2. The response time of the sensor was determined to be 2 s with a limit of detection of 0.14 μM (S/N = 3). The fabricated sensor also exhibited a good selectivity in the presence of common interfering species. In addition, the fabricated sensor exhibited special advantages, such as low working potential, good sensitivity along with good repeatability and reproducibility, for the determination of glucose.

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.

Femtomolar detection of mercuric ions using polypyrrole, pectin and graphene nanocomposites modified electrode

Several nanomaterials and techniques for the detection of mercuric ions (Hg(2+)) have been developed in the past decade. However, simple, low-cost and rapid sensor for the detection of heavy metal ions yet remains an important task. Herein, we present a highly sensitive electrochemical sensor for the femtomolar detection of Hg(2+) based on polypyrrole, pectin, and graphene (PPy/Pct/GR) which was prepared by one step electrochemical potentiodyanamic method. The effect of concentration of pectin, polypyrrole and graphene were studied for the detection of Hg(2+). The influence of experimental parameters including effect of pH, accumulation time and accumulation potential were also studied. Different pulse anodic stripping voltammetry was chosen to detect Hg(2+) at PPy/Pct/GR/GCE modified electrode. The fabricated sensor achieved an excellent performance towards Hg(2+) detection such as higher sensitivity of 28.64μAμM(-1) and very low detection limit (LOD) of 4 fM at the signal to noise ratio of 3. The LOD of our sensor offered nearly 6 orders of magnitude lower than that of recommended concentration of Hg(2+) in drinking water by United States Environmental Protection Agency and World Health Organization. Compared to all previously reported electrochemical sensors towards Hg(2+) detection, our newly fabricated sensor attained a very LOD in the detection of Hg(2+). The practicality of our proposed sensor for the detection of Hg(2+) was successfully demonstrated in untreated tap water.

Electropolymerization of cobalt tetraamino-phthalocyanine at reduced graphene oxide for electrochemical determination of cysteine and hydrazine

We describe a simple and elegant electropolymerization method to prepare highly stable tetraamino functionalized cobalt phthalocyanine (pTACoPc) at electrochemically reduced graphene oxide (RGO). The described method efficiently bridges the excellent physicochemical properties of RGO with the rich redox chemistry of TACoPc. Graphene oxide was electrochemically reduced to RGO at the electrode surface along with concominent electropolymerization of TACoPc. The electrochemical studies showed that RGO on pTACoP/GCE increased effective surface area, reduced charge transfer resistance and enhanced electrochemical signal. The RGO-pTACoPc film modified electrode exhibits excellent electrocatalytic ability to oxidize cysteine and hydrazine. To determine cysteine, the RGO-pTACoPc sensor displayed a linear concentration range of 50 nM to 2.0 μM, detection limit of 18.5 nM and sensitivity of 10.19 nA nM−1 cm−2. Besides, the sensor displayed a linear concentration range of 50 nM to 2.6 μM, detection limit of 10 nM and sensitivity of 1.62 nA nM−1 cm−2 to determine hydrazine. The electrocatalytic ability of RGO-pTACoPc shows better performance over other cobalt phthalocyanine derivatives. Furthermore, the described sensor exhibited long-term storage stability, good repeatability and reproducibility. The practical applicability of the sensor has been assessed in biological and water samples.