Novel Spectroelectrochemical Sensor

This sensor combines three levels of selectivity in one device: selective partitioning into a film, electrochemical excitation signal, and optical response signal. The sensor structure is essentially a guided wave optic that exhibits multiple internal reflection with an optically transparent electrode (OTE) deposited on it. The OTE is coated with a thin chemically-selective film that serves to enhance detection limit by preconcentrating the analyte. The evanescent field at the points of internal reflection within the guided wave optic penetrates the film so that electrochemical events within the film can be monitored optically. The research has many facets including the development of selective coatings for the sensor, instrumentation, and theory to describe the spectroelectrochemical behavior. We are pursuing applications in biomedical and environmental areas.

Capillary electrophoresis on a microchip

The goal of this research is to significantly improve the determination of trace amounts of biologicals with respect to speed of analysis, selectivity, and limit of detection, versus the standard immunoassay methodology. Aptamer-based assays of polypeptides and proteins are used as illustrative chemical systems, and affinity capillary electrophoresis on a multilane plastic microchip with detection by laser induced fluorescence is the analytical technique. Analysis time is shortened from hours to minutes by the rapid, high-resolution separation of protein-photoaptamer complexes without the need for prior sample preparation.

Additionally, the multilane, disposable plastic chip format provides rapid throughput due to the multiplexing of the analysis and the disposability of the low cost chips.

Nanotube biosensor

Typical immunoassays are multi-step procedures that involve a capture step, multiple rinses, adding a label for detection and/or amplification, and finally detection.  These methods can be very sensitive, and are perfectly suitable for laboratory analysis, but are limited for some applications that require continuous monitoring, rapid response, and portability.  Electrochemical impedance spectroscopy (EIS), coupled with the selectivity and sensitivity of biological recognition molecules such as antibodies promises to be an effective label-free sensing technique for biomolecules.   Carbon nanotubes are being explored as an electrode material for an EIS based biosensor, as their physical, electrical, and chemical properties give them advantages over conventional electrode materials.

Lanthanide-Organic Macrocycles for Anion Sensing

Anions play essential roles in biological and environmental systems. For example, DNA, amino acids, and a majority of enzyme substrates are anionic or have anionic components. The ability to detect the concentration of specific anions in various media is important for monitoring pollutant levels and studying biological processes. Lanthanide metals, particularly europium (Eu³⁺) and terbium (Tb³⁺), have unique luminescent properties and we are interested in taking advantage of their high sensitivity and long luminescent lifetimes to create macromolecules with sensor properties. Through coordination chemistry, these metals have been linked to chromophoric chelating ligands to create highly luminescent porous molecules with host-guest characteristics. The resulting porous molecules can readily act as sensors because the luminescence intensity of the Eu³⁺ atom is easily altered with the inclusion and binding of anionic guests within the molecular pore. We are interested in the rational design of such macrocyclic compounds for specific anionic analytes and forming a mechanistic understanding of the macrocyle-anion binding and energy-transfer phenomena responsible for the luminescent signaling event.

Multivalent carbohydrate ligands

Our main focus is the syntheses of tailored, robust, multivalent carbohydrate ligands for the precise detection and differentiation of select pathogens/toxins.  Carbohydrates represent Nature’s third class of biopolymers and are not well understood.  However, cell surface carbohydrates are often utilized by pathogens as a mode of binding prior to host cell infection.  By designing synthetic ligands that mimic natural receptors and applying them to a number of sensor platforms, we are able to detect pathogens of interest.  A representative example of our research is the biotinylated divalent mannose ligand for the detection of type 1 fimbriated (mannose specific) E. coli.  By applying this ligand to streptavidin-coated paramagnetic beads, we were able to achieve an order of magnitude lower detection limit as compared to commercial antibodies. 

Vapochromic salts