Anjum Qureshi

Label-free capacitive biosensor for sensitive detection of multiple biomarkers using gold interdigitated capacitor arrays

In this study, a highly sensitive and label-free multianalyte capacitive immunosensor was developed based on gold interdigitated electrodes (GID) capacitor arrays to detect a panel of disease biomarkers. C-reactive protein (CRP), TNFalpha, and IL6 have strong and consistent relationships between markers of inflammation and future cardiovascular risk (CVR) events. Early detection of a panel of biomarkers for a disease could enable accurate prediction of a disease risk. The detection of protein biomarkers was based on relative change in capacitive/dielectric properties. Two different lab-on-a-chip formats were employed for multiple biomarker detection on GID-capacitors. In format I, capacitor arrays were immobilized with pure forms of anti-CRP, -TNFalpha, and -IL6 antibodies in which each capacitor array contained a different immobilized antibody. Here, the CRP and IL6 were detected in the range 25 pg/ml to 25 ng/ml and 25 pg/ml to 1 ng/ml for TNFalpha in format I. Sensitive detection was achieved with chips co-immobilized (diluted) with equimolar mixtures of anti-CRP, -IL6, and -TNFalpha antibodies (format II) in which all capacitors in an array were identical and tested for biomarkers with sequential incubation. The resulting response to CRP, IL6, and TNFalpha in format II for all biomarkers was found to be within 25 pg/ml to 25 ng/ml range. The capacitive biosensor for panels of inflammation and CVR markers show significant clinical value and provide great potential for detection of biomarker panel in suspected subjects for early diagnosis.

Dielectric Properties of Polymer Composites Filled with Different Metals

Electrically conductive composite systems based on polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) filled with metal powders of Al and Cu have been studied. The composite preparation conditions allow the formation of a random distribution of metallic particles in the polymer matrix. Dependence of the dielectric and conductivity properties of the PVC and PMMA/fillers was studied over a broad range of frequency and volume fraction of metal fillers. The experimental results could be explained by means of the conductivity of fillers and the interface polarization between polymers and fillers. Percolation was also seen in this study when the volume fraction of conducting fillers was close to critical value, in which the composites undergo an insulator‐conductor transition. The relation among the dielectric property and the fillers with different conductivity was proposed.

An aptamer based competition assay for protein detection using CNT activated gold-interdigitated capacitor arrays.

An aptamer can specifically bind to its target molecule, or hybridize with its complementary strand. A target bound aptamer complex has difficulty to hybridize with its complementary strand. It is possible to determine the concentration of target based on affinity separation system for the protein detection. Here, we exploited this property using C-reactive protein (CRP) specific RNA aptamers as probes that were immobilized by physical adsorption on carbon nanotubes (CNTs) activated gold interdigitated electrodes of capacitors. The selective binding ability of RNA aptamer with its target molecule was determined by change in capacitance after allowing competitive binding with CRP and complementary RNA (cRNA) strands in pure form and co-mixtures (CRP:cRNA=0:1, 1:0, 1:1, 1:2 and 2:1). The sensor showed significant capacitance change with pure forms of CRP/cRNA while responses reduced considerably in presence of CRP:cRNA in co-mixtures (1:1 and 1:2) because of the binding competition. At a critical CRP:cRNA ratio of 2:1, the capacitance response was dramatically lost because of the dissociation of adsorbed aptamers from the sensor surface to bind when excess CRP. Binding assays showed that the immobilized aptamers had strong affinity for cRNA (K(d)=1.98 μM) and CRP molecules (K(d)=2.4 μM) in pure forms, but low affinity for CRP:cRNA ratio of 2:1 (K(d)=8.58 μM). The dynamic detection range for CRP was determined to be 1-8 μM (0.58-4.6 μg/capacitor). The approach described in this study is a sensitive label-free method to detect proteins based on affinity separation of target molecules that can potentially be used for probing molecular interactions.

Surface modification of polycarbonate by plasma treatment

The surfaces of polycarbonate films were treated by nitrogen plasma, in order to understand the effect of low energy ions on the surface modification of polycarbonate. The modified samples were characterized by micro-hardness tester, optical micrograph/atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and FTIR spectroscopy. It was observed that the hardness of the film increases as fluence increases. This may be attributed to the cross-linking effect as corroborated with FTIR spectra. XPS analysis indicates that chemical bonding on the surface of the film, especially C=O, C-O and C-C/C-H functional groups, was found to change due to plasma treatment. AFM analysis reveals that average surface roughness increases from 5.9 nm to 42.7 nm as fluence increases.

Ion Beam Modification of Polymethyl methacrylate (PMMA) Polymer Matrix Filled with Organometallic Complex

A Nickel Dimethylglyoxime (Ni‐DMG) compound was dispersed in polymethyl methacrylate (PMMA) films at different concentrations. PMMA was synthesized by a solution polymerization technique. These films were irradiated with 120 MeV Ni10+ ions at the fluences of 1×1011 and 1×1012 ions/cm2. The radiation induced changes in dielectric properties and average surface roughness were investigated by using an LCR meter in the frequency range 50 Hz to 10 MHz and atomic force microscopy (AFM), respectively. The electrical properties of irradiated films are found to increase with the fluence and also with the concentration of Ni‐DMG. From the analysis of frequency, f, dependence of dielectric constant, ϵ, it has been found that the dielectric response in both pristine and irradiated samples obey the Universal law given by ϵ α f n−1. The dielectric constant/loss is observed to change significantly due to the irradiation. This suggests that ion beam irradiation promotes (i) the metal to polymer bonding (ii) convert the polymeric structure in to hydrogen depleted carbon network due to the emission of hydrogen gas and/or other volatile gases. Atomic force microscopy (AFM) shows that the average surface roughness and surface morphology of irradiated films are observed to change.

Quantum dot conjugated S. cerevisiae as smart nanotoxicity indicators for screening the toxicity of nanomaterials

In this study, we have evaluated the toxicity of different forms of carbon nanotubes (CNTs) using S. cerevisiae-QD (SQD) bioconjugates as a novel fluorescent biological nanotoxicity indicator. A CNT mediated effect in SQD bioconjugates was used as an indicator for the changes occurring at the cell-membrane interfaces that induced disruption of membrane bound QDs resulting in the loss of fluorescence. Single, double and multiwalled carbon nanotubes (SWCNTs, DWCNTs and MWCNTs) were tested for their toxicities imposed on SQD bioconjugates. Bioconjugates exposed to varying concentrations of different forms of CNTs exhibited different modes of toxicities on SQD bioconjugates. SQD bioconjugates were highly responsive in the 0.1-10 μg mL-1 CNT concentration range after 1 h of exposure. The toxicity of CNTs was linked to the number of CNT walls. These results were further confirmed by SEM analysis and cell-viability tests that were consistent with the toxicity assays using fluorescent bioconjugates with different types of CNTs. SWCNTs imposed more severe cellular toxicity followed by MWCNTs and DWCNTs and the order of increasing cellular-damage by CNTs followed DWCNTs < MWCNTs < SWCNTs. This study speculates that the cell-injury by CNTs depends on their physical properties, such as layers of walls, non-covalent forces and dispersion states. Our results demonstrated a facile optical strategy that enables rapid and real-time cytotoxicity screening with yeast as model living-cells for engineering nanomaterials.

E. coli–quantum dot bioconjugates as whole-cell fluorescent reporters for probing cellular damage

A quantum dot (QD) conjugated whole-cell E. coli biosensor (E. coli-QD bioconjugates) was developed as a new molecular tool for probing cellular damage. The E. coli-QD bioconjugates were viable and exhibited fluorescence emission at 585 nm. Scanning electron microscopy (SEM) analysis of E. coli-QD bioconjugates revealed that the QDs were immobilized on the cell-surfaces and the fluorescence emission from QDs present on cell-surfaces was visualized by confocal microscopic examination. The E. coli-QD bioconjugates were employed as whole-cell fluorescent reporters that were designed to function as fluorescence switches that turn-off when cellular damage occurs. In this study, multi-walled carbon nanotubes (CNTs) were utilized as a model nanomaterial to probe cellular damage. Fluorescence spectra were recorded after the exposure of E. coli-QD bioconjugates with CNTs. We observed a strong correlation between fluorescence emission spectra, SEM and confocal microscopic analysis demonstrating that CNTs induced a dose and exposure time-dependent cellular toxicity. This toxicity mainly occurred by the physical interaction and cellular trafficking mechanisms that led to the collapse of the cellular structure and thus loss of fluorescence. The responses of E. coli-QD bioconjugates against CNTs were also visualized by simply exposing the cells to UV light and therefore rapid toxicity analysis and screening can be made. Our study demonstrated an easy and simple method to determine an important mechanistic perspective for the biological toxicity of chemicals or nanomaterials (NMs).

Electrical and Thermal Studies on the Polyvinylchloride/Carbon Black Composites Induced by High Energy Ion Beam

Modification induced by energetic ion in polyvinylchloride (PVC)/carbon black (CB) composites was studied using impedance gain-phase analyzer, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Different concentrations of CB were dispersed in PVC films. These films were irradiated with 140 MeV Ag11+ ions at the fluences of 1 × 1011 and 1 × 1012ions/cm2. The ac electrical conductivity and dielectric response were studied as a function of filler, frequency and ion fluence. It was found that ac electrical conductivity increases with increasing the percentage of CB, frequency and ion fluence. The observed enhancement in ac electrical conductivity is attributed to the increase in the number of conduction paths created by the carbon black contents in the composites to give a higher electrical conductivity. An increase in dielectric constant was observed with the ion fluence and also with the carbon black content, which is attributed to the interfacial polarization of heterogeneous systems. Differential scanning calorimetry (DSC) analysis showed that the glass transition temperature (Tg) shifted towards lower temperature with increasing the ion fluence. It may be attributed to the scissioning of polymer chains and as a result increase of free radicals, unsaturation etc., which lead to the transformation of polymer into amorphous phase. Atomic force microscopy (AFM) studies revealed that the surface average roughness of the composites increases as filler concentration increases and decreases upon irradiation. SEM micrographs showed that carbon black particles organized into aggregates of micro spherical voids and decreased its size upon irradiation.

Radiation-induced modification of organometallic compound dispersed polymer composites

Polymethyl methacrylate (PMMA) was synthesized by solution polymerization technique. Films of polymer composites were prepared by dispersion of different concentrations of nickel dimethylglyoxime in PMMA. These films were irradiated with 3 MeV proton beam at a dose of 1.48×105 Gy. The dielectric, structural properties and surface morphology of pristine and irradiated samples were studied by means of an LCR meter, X-ray diffraction (XRD) analysis and atomic force microscopy (AFM), respectively. The dielectric properties are observed to enhance with increase in metal compound concentration as well as with irradiation dose. This may be due to metal/polymer bonding and conversion of polymeric structure into hydrogen-depleted carbon network. AFM shows that the surface average roughness decreases after irradiation. Crystallite size of organometallic compound is observed to decrease after irradiation as revealed from XRD analysis.

Nanomaterial resistant microorganism mediated reduction of graphene oxide

In this study, soil bacteria were isolated from nanomaterials (NMs) contaminated pond soil and enriched in the presence of graphene oxide (GO) in mineral medium to obtain NMs resistant bacteria. The isolated resistant bacteria were biochemically and genetically identified as Fontibacillus aquaticus. The resistant bacteria were allowed to interact with engineered GO in order to study the biotransformation in GO structure. Raman spectra of GO extracted from culture medium revealed decreased intensity ratio of ID/IG with subsequent reduction of CO which was consistent with Fourier transform infrared (FTIR) results. The structural changes and exfoliatied GO nanosheets were also evident from transmission electron microscopy (TEM) images. Ultraviolet-visible spectroscopy, high resolution X-ray diffraction (XRD) and current-voltage measurements confirmed the reduction of GO after the interaction with resistant bacteria. X-ray photoelectron spectroscopy (XPS) analysis of biotransformed GO revealed reduction of oxygen-containing species on the surface of nanosheets. Our results demonstrated that the presented method is an environment friendly, cost effective, simple and based on green approaches for the reduction of GO using NMs resistant bacteria.