Browsing by Author "Raj, Vidya"

Now showing 1 - 3 of 3
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    Detection of cholesterol by digitonin conjugated gold nanoparticles
    (BIOSENSORS & BIOELECTRONICS, 2011)
    Functionalized colloidal gold is widely used for qualitative and quantitative detection of specific analytes. We report here a novel modification of gold nanoparticles by digitonin, a glycoside used for precipitating membrane cholesterol. The specific molecular recognition of cholesterol by digitonin gold nanoparticles (DGNP), make it an attractive alternative to the existing enzymatic methods for cholesterol sensing. To enable cholesterol binding, we modified mercapto modified GNPs with digitonin, by a simple esterification reaction. The blue shift in the plasmon absorption spectra of DGNP with different cholesterol concentrations accompanied by a decrease in the absorbance is the principle applied here for the estimation. The observed size reduction followed by cholesterol binding is reasoned due to the enhanced hydophobicity of the surface which in turn expels the water layers associated with the particles prior to cholesterol binding. The method exhibited linearity between concentration of cholesterol and the corresponding absorbance of the plasmon peak, in the range of 160-600 ng/mL with a detection limit of 100 +/- 9 ng/mL. Other steroids did not show any binding affinity towards DGNP. The method depicted here has potential for development as an enzyme free sensor for cholesterol although many factors need to be addressed to transform it for assaying samples like blood. (C) 2011 Elsevier B.V. All rights reserved.
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    Selective detection and estimation of C-reactive protein in serum using surface-functionalized gold nano-particles
    (ANALYTICA CHIMICA ACTA, 2010)
    A new method for the detection of C-reactive protein (CRP) in serum using functionalized gold nano-particles (GNP) is reported. The affinity towards CRP is imparted to GNP by tethering O-phosphorylethanolamine (PEA) onto their surface. GNP and modified GNP were characterized using TEM, particle size analysis, zeta potential measurements, absorption spectroscopy and FT-IR techniques. The event of binding of CRP onto the PEA-GNP is followed by visibly observable colour change. We observed a red shift as well as a decrease in absorption in the plasmon peak of the modified GNP with the concentration of CRP. When the concentration of CRP exceeded 450 ng mL(-1), particles were aggregated and the solution became turbid. The method exhibited a linear range for CRP from 50 to 450 ng mL(-1) with a detection limit of 50 ng mL(-1). The colour change and the variation in absorption of the GNP were highly specific to CRP even in the presence of albumin. We estimated CRP in blood serum collected from patients and the results obtained compared well with the estimation using the technique of nephelometry based on the antibody-antigen interaction. (C) 2010 Elsevier B.V. All rights reserved.
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    Use of chemically modified thermoresponsive copolymers for the detection of C-reactive protein
    (ANALYTICA CHIMICA ACTA, 2007)
    Fluorescence intensity of N-isopropylacrylamide-glycidyl methacrylate (NIPAAm-GMA) copolymer conjugated with fluoreseinamine isomer1 was found to decrease considerably in the presence of NIPAAm-GMA copolymer containing O-phosphorylethanolamine (PEA), the specific ligand of C-reactive protein (CRP). The decrease in the emission intensity was reasoned due to the quenching of the fluorescence through the interaction of the polymer chains. The emission intensity was, however, found to increase rapidly when CRP was added in to the solution containing the polymers. The intensity of fluorescence emission was increased by five-fold in the presence of CRP as low as 20 ng mL(-1). Albumin, the major blood protein, did not show any interference in the emission. The presence of a low molecular protein, cytochrome c, on the fluorescence spectra was also studied and this protein also found not have any influence in binding of CRP onto the ligand indicating that other proteins irrespective of their molecular weights did not influence the measurement. A definite correlation was found between the concentration of CRP and the fluorescence intensity. The method appears to be very sensitive and easy to perform. The study reflects, for the first time, the scope of using copolymeric combinations for the measurement of CRP without the use of antibody. (C) 2007 Elsevier B.V. All rights reserved.