Vindhya Kunduru

Biogenic nanoporous silica-based sensor for enhanced electrochemical detection of cardiovascular biomarkers proteins

The goal of our research is to demonstrate the feasibility of employing biogenic nanoporous silica as a key component in developing a biosensor platform for rapid label-free electrochemical detection of cardiovascular biomarkers from pure and commercial human serum samples with high sensitivity and selectivity. The biosensor platform consists of a silicon chip with an array of gold electrodes forming multiple sensor sites and works on the principle of electrochemical impedance spectroscopy. Each sensor site is overlaid with a biogenic nanoporous silica membrane that forms a high density of nanowells on top of each electrode. When specific protein biomarkers: C-reactive protein (CRP) and myeloperoxidase (MPO) from a test sample bind to antibodies conjugated to the surface of the gold surface at the base of each nanowell, a perturbation of electrical double layer occurs resulting in a change in the impedance. The performance of the biogenic silica membrane biosensor was tested in comparison with nanoporous alumina membrane-based biosensor and plain metallic thin film biosensor. Significant enhancement in the sensitivity and selectivity was achieved with the biogenic silica biosensor, in comparison to the other two, for detecting the two protein biomarkers from both pure and commercial human serum samples. The sensitivity of the biogenic silica biosensor is approximately 1 pg/ml and the linear dose response is observed over a large dynamic range from 1 pg/ml to 1 microg/ml. Based on its performance metrics, the biogenic silica biosensor has excellent potential for development as a point of care handheld electronic biosensor device for detection of protein biomarkers from clinical samples.

Electrokinetic Formation of “Microbridges” for Protein Biomarkers as Sensors

We demonstrate a technique to detect protein biomarkers contained in vulnerable coronary plaque using a platform-based microelectrode array (MEA). The detection scheme is based on the property of high specificity binding between antibody and antigen similar to most immunoassay techniques. Rapid clinical diagnosis can be achieved by detecting the amount of protein in blood by analyzing the proteins electrical signature. Polystyrene beads which act as transportation agents for the immobile proteins (antigen) are electrically aligned by application of homogenous electric fields. The principle of electrophoresis is used to produce calculated electrokinetic movement among the anti-C-reactive protein (CRP), or in other words antibody funtionalized polystyrene beads. The electrophoretic movement of antibody-functionalized polystyrene beads results in the formation of “Microbridges” between the two electrodes of interest which aid in the amplification of the antigen—antibody binding event. Sensitive electrical equipment is used for capturing the amplified signal from the “Microbridge” which essentially behaves as a conducting path between the two electrodes. The technique circumvents the disadvantages of conventional protein detection methods by being rapid, noninvasive, label-free, repeatable, and inexpensive. The same principle of detection can be applied for any receptor—ligand-based system because the technique is based only on the volume of the analyte of interest. Detection of the inflammatory coronary disease biomarker CRP is achieved at concentration levels spanning over the lower microgram/milliliter to higher order nanogram/milliliter ranges.

Carbon Nanotubes: Synthesis and Characterization

Carbon can form various types of structurally different frameworks due to the ability of the carbon atoms to form different species of valence bonds. The extremely organized coagulation process of carbon molecules resulting in the formation of the perfectly symmetric fullerene molecule despite the chaotic environment of the carbon arc is truly fascinating. Although many formation theories for the buckyball structure have been suggested, the “pentagon road model” is the most popular amongst many molecular physicists. The prominent features of this model are that carbon sheets have the tendency to accumulate isolated pentagonal carbon ring structures and grow into a carbon sheet with a large number of pentagons supporting its structure.

Characteristics of Carbon Nanotubes for Nanoelectronic Device Applications

Carbon has the incredible ability to combine with itself in varied proportions to form molecules of distinctly disparate physical structures. The evolution of modern organic chemistry began with the growing interest amongst scientists to experiment with carbon clusters formed during synthesis of carbon compounds. These studies on carbon-related compounds began with the support of rigid understanding of a common form of carbon–graphite. Carbon molecule C60 which was discovered in trace amounts in the carbon clusters was a soccer-shaped fullerene molecule which had 60 carbon atoms arranged in a way that each atom was placed at a vertex of a truncated icosahedron [1]. The discovery of Kratschmer et al. to produce C60 in bulk served as a platform for extensive study on carbon-related molecules by scientists, chemists, and material science experts all over the world.

MULTIWALLED CARBON NANOTUBE-BASED AROMATIC HYDROCARBON SENSOR USING ELECTRONIC DIPOLE SPECTROSCOPY

A novel electronic spectroscopy technique based on dipole-dipole interactions for the identification of chemical analytes has been developed. This technique is based on the measurement of the charge transfer of chemical analytes to a multiwalled carbon nanotube mat-based sensing system. This technique was used for the identification of three aromatic hydrocarbons, namely, benzene, toluene, and xylene, at 100 parts-per-billion concentration. This technique was evaluated with multiwalled carbon nanotube mats for rapid, reliable, and robust identification of the three chemicals that belong to the same genre. The technique involves the identification of electronic spectral signatures of these chemicals using frequency domain analysis of the voltage signals generated by the binding of the chemical analytes onto the multiwalled carbon nanotube mat surfaces. This technique has the potential for rapid and accurate identification of multiple chemical analytes in a multiplexed fashion using a single-sensor device. In addition, this particular device configuration in conjunction with the electronic dipole spectroscopy results is a powerful lab-on-a-chip device for chemical and biological sensing applications.