Publications

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Crucial to low-level detection of biowarfare agents in aqueous environments is the mass sensitivity optimization of Love-wave acoustic sensors. The present work is an experimental study of 36{sup o} YX cut LiTaO{sub 3} based Love-wave devices for detection of pathogenic spores in aqueous conditions. Given that the detection limit (DL) of Love-wave based sensors is a strong function of the overlying waveguide, two waveguide materials have been investigated, which are polyimide and polystyrene. To determine the mass sensitivity of Love-wave sensor, bovine serum albumin (BSA) protein was injected into the Love-wave test cell while recording magnitude and phase shift across each sensor. Polyimide had the lowest mass detection limit with an estimated value of 1-2 ng/cm{sup 2}, as compared to polystyrene where DL = 2.0 ng/cm{sup 2}. Suitable chemistries were used to orient antibodies on the Love-wave sensor using adsorbed protein G. The thickness of each biofilm was measured using ellipsometry from which the surface concentrations were calculated. The monoclonal antibody BD8 with a high degree of selectivity for anthrax spores was used to capture the non-pathogenic simulant B. thuringiensis B8 spores. Bacillus Subtilis spores were used as a negative control to determine whether significant non-specific binding would occur. Spore aliquots were prepared using an optical counting method, which permitted removal of background particles for consistent sample preparation. This work demonstrates that Love-wave devices can be used to detect B. anthracis simulant below reported infectious levels.

Impedance based, planar chemical microsensors are the easiest sensors to integrate with electronics. The goal of this work is a several order of magnitude increase in the sensitivity of this sensor type. The basic idea is to mimic biological chemical sensors that rely on changes in ion transport across very thin organic membranes (supported Bilayer Membranes: sBLMs) for the sensing. To improve the durability of bilayers we show how they can be supported on planar metal electrodes. The large increase in sensitivity over polyelectrolytes will come from molecular recognition elements like antibodies that bind the analyte molecule. The molecular recognition sites can be tied to the lipid bilayer capacitor membrane and a number of mechanisms can be used to modulate the impedance of the lipid bilayers. These include coupled ion channels, pore modification and double layer capacitance modification by the analyte molecule. The planar geometry of our electrodes allows us to create arrays of sensors on the same chip, which we are calling the ''Lipid Chip''.