Raju Khan

Iron oxide nanoparticles–chitosan composite based glucose biosensor

Iron oxide (Fe(3)O(4)) nanoparticles prepared using co-precipitation method have been dispersed in chitosan (CH) solution to fabricate nanocomposite film on indium-tin oxide (ITO) glass plate. Glucose oxidase (GOx) has been immobilized onto this CH-Fe(3)O(4) nanocomposite film via physical adsorption. The size of the Fe(3)O(4) nanoparticles estimated using X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) has been found to be approximately 22 nm. The CH-Fe(3)O(4) nanocomposite film and GOx/CH-Fe(3)O(4)/ITO bioelectrode have been characterized using UV-visible and Fourier transform infrared (FTIR) spectroscopic and scanning electron microscopy (SEM) techniques, respectively. This GOx/CH-Fe(3)O(4)/ITO nanocomposite bioelectrode has response time of 5s, linearity as 10-400 mgdL(-1) of glucose, sensitivity as 9.3 microA/(mgdLcm(2)) and shelf life of about 8 weeks under refrigerated conditions. The value of Michaelis-Menten (K(m)) constant obtained as 0.141 mM indicates high affinity of immobilized GOx towards the substrate (glucose).

Zinc oxide nanoparticles-chitosan composite film for cholesterol biosensor.

Zinc oxide nanoparticles (NanoZnO) uniformly dispersed in chitosan (CHIT) have been used to fabricate a hybrid nanocomposite film onto indium-tin-oxide (ITO) glass plate. Cholesterol oxidase (ChOx) has been immobilized onto this NanoZnO-CHIT composite film using physiosorption technique. Both NanoZnO-CHIT/ITO electrode and ChOx/NanoZnO-CHIT/ITO bioelectrode have been characterized using Fourier transform-infrared (FTIR), X-ray diffraction (XRD), cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) techniques, respectively. The ChOx/NanoZnO-CHIT/ITO bioelectrode exhibits linearity from 5 to 300 mg dl(-1) of cholesterol with detection limit as 5 mg dl(-1), sensitivity as 1.41x10(-4) A mg dl(-1) and the value of Michaelis-Menten constant (K(m)) as 8.63 mg dl(-1). This cholesterol biosensor can be used to estimate cholesterol in serum samples.

Chitosan/polyaniline hybrid conducting biopolymer base impedimetric immunosensor to detect Ochratoxin-A

Chitosan (CS)-polyaniline (PANI) hybrid conducting biopolymer film was obtained on indium-tin-oxide (ITO) electrode using electrochemical polymerization process. Fourier transform infrared (FT-IR) spectra of PANI-CS had showed covalent and hydrogen binding between PANI and CS molecules. Electrochemical impedance spectroscopy (EIS) measurements had showed low charge transfer resistance (R(CT)) of PANI-CS and PANI. Successive rabbit antibody (IgGs) immobilization on PANI-CS, CS and PANI matrixes surface were confirmed with FT-IR and EIS measurements. Ochratoxin-A (OTA) interaction with IgGs had increased R(CT) values and showed linear response up to 10 ng/mL OTA concentration in electrolyte. Relative change in R(CT) was higher in PANI-CS due to higher proportion of carboxylic and hydroxyl functionalities at PANI-CS matrix surfaces. The absolute sensitivity of PANI, CS, and PANI-CS were 16+/-6, 22+/-9 and 53+/-8 Omega mL/ng, respectively derived from slope of linear response up to 10 ng/mL with 1 ng/mL minimum detection limit.

Graphene–polyaniline nanocomposite based biosensor for detection of antimalarial drug artesunate in pharmaceutical formulation and biological fluids

Bioactive electrode of dispersed graphene oxide in polyaniline composite was electrochemically fabricated onto indium tin oxide substrate for pharmaceutical application. Formations of nanocomposite graphene-polyaniline matrix with diameter 67.99 nm were observed with the use of scanning electron microscope and high resolution transmission electron microscope. Electrochemical interfacial properties and immobilization of enzyme onto the graphene-polyaniline electrode have been evaluated and confirmed with the use of Fourier transform infrared spectroscopic, cyclic voltammetry and electrochemical impedance spectroscopic techniques. The graphene-polyaniline-horseradish peroxidase biosensor was further used for sensing artesunate a potent antimalarial drug. The biosensor shows linearity of 0.05-0.40 ng mL(-1) of artesunate with sensitivity of 0.15 µA ng mL(-1). The procedure was applied to the assay of the drug in dosage form, human serum, plasma and urine without matrix interference. The limits of detection for parenteral artesunate, human urine, human serum and human plasma were 0.012 ng mL(-1), 0.013 ng mL(-1), 0.014 ng mL(-1) and 0.014 ng mL(-1) respectively. The mean percentage recoveries obtained were in the range from 98.23% to 100.3% for parental drug, urine, serum and plasma samples. The resultant precision and accuracy as evidenced have shown a promising selectivity in their application.

Mycotoxin detection on antibody-immobilized conducting polymer-supported electrochemically polymerized acacia gum.

Electrochemical polymerization of acacia gum (AG) was initiated by electroactive polyaniline (PANI) monomers by radical cation formation and their coupling reactions with AG molecules. R(CT) values obtained from electrochemical impedance spectroscopy analysis at various AG concentrations with PANI were drastically decreased, confirming formation of conducting AG complexes with PANI. Quantitative analysis of ochratoxin-A (OTA) detection in electrolyte was carried out on rabbit antibody-immobilized PANI and PANI-AG matrices. The observed sensitivities of 50, 150, and 250 mg AG-added PANI matrix-based platforms were 3.3 ± 0.5, 10.0 ± 0.5, and 12.7 ± 0.5 μA/ng/ml, respectively. The sensitivity of only PANI electrodes was 2.6 ± 0.3 μA/ng/ml, which was relatively lower than AG-added PANI. This increase was due to the presence of glycan functional groups in AG molecules that supported the retention of activity of antibodies. In addition, enhanced electron transportation at AG-PANI film surface was observed due to formation of an electroactive polymer film of two different electroactive functions to contribute toward enhancement in the detection sensitivity.

Detection of anticancer drug tamoxifen using biosensor based on polyaniline probe modified with horseradish peroxidase

Amperometric biosensor based on horseradish peroxidase immobilized via glutaraldehyde on the polyaniline modified platinum electrode shows evidenced promising characteristics in detecting anticancer drug tamoxifen. The sensor was fabricated simply by adsorbing horseradish peroxidase enzyme on the electrode surface for which Cyclic Voltammetry was used to monitor the electro-catalytic reduction of tamoxifen under diffusion-adsorption controlled conditions. Fourier Transform Infrared Spectroscopy, Cyclic Voltammetry and Electrochemical Impedance Spectroscopic techniques are used to characterize the electrochemical interfacial properties of surface modified electrodes. The first-hand effort on modified biosensor within Platinum/Polyaniline/Horseradish peroxidase biosensor system has demonstrated excellent electro-analytical properties with biosensor sensitivity of 1.6 μA ng mL(-1). The optimum limit of detection and limit of quantification are 0.07 ng mL(-1) and 0.29 ng mL(-1) respectively for the determination of anticancer drug tamoxifen. It is felt that the present study will help in improving our knowledge of cost-effective quantitative determination of tamoxifen in metabolized biological fluids and other pharmaceutical formulations.

Impedimetric immunosensor for detection of cardiovascular disorder risk biomarker

We report the construction and characterization of a novel, level free impedimetric immunosensor for rapid, sensitive and selective detection of myoglobin (Mb). Monoclonal anti-myoglobin (anti-Mb-IgG) antibody was immobilized on screen-printed multiwalled carbon nanotubes electrode for signal amplification without the need of natural enzymes. The fabrication of resulting immunosensor was extensively characterized by using scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectroscopy, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Electrochemical impedance spectroscopy (EIS) technique offered a linear detection range (0.1-90ngmL(-1)) of myoglobin with sensitivity of 0.74kΩngmL(-1) (correlation coefficient, R(2)=0.97) and detection limit of 0.08ngmL(-1) (S/N=3). The mean percentage recovery of Mb in serum samples using this working biosensor is 97.33%. Furthermore, the proposed strategy can be a promising alternative for detection of Mb related cardiovascular disorders.

Natural polyhydroxyalkanoate-gold nanocomposite based biosensor for detection of antimalarial drug artemisinin

The worrisome trend of antimalarial resistance has already highlighted the importance of artemisinin as a potent antimalarial agent. The current investigation aimed at fabricating a biosensor based on natural polymer polyhydroxyalkanoate-gold nanoparticle composite mounting on an indium-tin oxide glass plate for the analysis of artemisinin. The biosensor was fabricated using an adsorbing horse-radish peroxidase enzyme on the electrode surface for which cyclic voltammetry was used to monitor the electro-catalytic reduction of artemisinin under diffusion controlled conditions. Electrochemical interfacial properties and immobilization of enzyme onto a polyhydroxyalkanoate-gold nanoparticle film were evaluated, and confirmed by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The differential pulse voltammetric peak current for artemisinin was increased linearly (concentration range of 0.01-0.08μg mL(-1)) with sensitivity of 0.26μAμg mL(-1). The greater sensitivity of the fabricated biosensor to artemisinin (optimum limits of detection were 0.0035μg mL(-1) and 0.0036μg mL(-1) in bulk and spiked human serum, respectively) could be of much aid in medical diagnosis.

Electrochemical immunosensor based on poly (3,4-ethylenedioxythiophene) modified with gold nanoparticle to detect aflatoxin B1

Gold nanoparticles (Au-NPs) functionalized Poly (3,4-ethylenedioxythiophene) (PEDOT) bioelectrodes were fabricated layer by layer deposition on ITO electrode for detection of aflatoxin B1. The monoclonal anti-aflatoxin antibodies (Anti-AFB1) were immobilized over the surface of PEDOT/Au-NPs/ITO using EDC/NHS coupling. The surface morphology and characteristics of the modified electrodes were investigated by scanning electron microscope and contact angle measurements. The electrochemical analysis of the fabricated immunoelectrode and the immobilization of the antibodies have been evaluated and confirmed by performing Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Fourier Transform Infrared Spectroscopy (FTIR). Decrease in the value of electron transfer resistance (Ret) and increase in the peak current values after incorporation of Au-NPs signifies the enhanced properties of PEDOT embedded Au-NPs. The heterogeneous rate constant (ks) and transfer coefficient (α) have been determined by using Lavirons method. The fabricated immunosensor exhibits high sensitive amperometric response of 3.72μAngmL-1 towards AFB1 concentration in a linear range of 1-25ngmL-1 with detection limit (LOD) of 0.0045ngmL-1and limit of quantification (LOQ) of 0.0156ngmL-1. The fabricated immunoelectrode shows a reproducibility of 96.13% and 94.5% towards real maize sample spiked with AFB1 of concentration 30ngmL-1and 50ngmL-1, respectively.

NIR upconversion characteristics of carbon dots for selective detection of glutathione

In the current study, we report the near infrared (NIR) upconversion (in the range of 850–950 nm) properties of carbon nanoparticles and their utility as a fluorescence probe for selective and sensitive detection of glutathione (GSH). The fluorescence probe comprises of carbon dots (CDs), which possess the capacity to absorb NIR photons (@930 nm) with consequent emission in the visible region (@520–540 nm). CDs, in the presence of Cu2+, suffer severe quenching of its photoluminescence behavior. As a result, the upconversion green emission at 530 nm gets hindered. However, in the presence of GSH, anti-Stoke emission is reinstated courtesy of prominent complexation between GSH and Cu2+. Correlation between the restored upconversion intensity and GSH concentration shows a linear agreement effective for a wide range (0.5–100 μM) with the limit of detection of 0.35 μM. The developed sensing platform also possesses high selectivity in the presence of other amino acids and thiols. Detection of GSH was further carried out in diluted human serum, which revealed a high percentage of recovery. Thus, this study demonstrates the potential of CDs as a cheap, effective and highly selective NIR upconversion based fluorescence probe for the detection of GSH. Such nanoparticles with stable emission could be utilized as the alternative to conventional upconversion organic dyes and semiconductor quantum dots.