Suram T. Pathirana

Specific and selective biosensor for Salmonella and its detection in the environment

The specific and selective detection of Salmonella typhymurium based on the use of a polyclonal antibody immobilized by the Langmuir-Blodgett method on the surface of a quartz crystal acoustic wave device was demonstrated in liquid samples. These biosensors were selective to S. typhymurium in the presence of large concentrations of Escherichia coli O157:H7. They were also specific to S. typhymurium since bacteria preincubated with free antibody produced no signal. Dark-field and electron microscopy showed that two different antibodies, polyvalent somatic O and flagellar H7, were immobilized on the sensor surface producing two distinct attachments of bacteria at the liquid-solid interface. The somatic O antibody exhibits a rigid, binding, while the flagellar H7 antibody forms a flexible connection allowing a large degree of freedom. When the attachment of bacteria was rigid and strong, the responses of the acoustic wave sensors correlated with changes in the mass of bacteria present at the liquid-solid interface. In contrast, when attachment was flexible, the sensor signals were inversely proportional to the additional mass of bound bacteria. This difference is probably determined by the interfacial viscoelasticity and by acoustic and electromagnetic coupling. The signals of environmentally aged sensors with either predominantly rigid or flexible positioning of bacteria were correlated with changes in mass at the liquid-solid interface. Sensors with O or H type of binding could be used for analytical purposes.

Recognition of cell-specific binding of phage display derived peptides using an acoustic wave sensor

ASSLNIA, a peptide selected for murine myofibers using phage display technology, was immobilized onto an acoustic wave sensor. The sensor responded to murine and feline muscle homogenates indicating crosspieces interactions. Kidney, liver, and brain preparations produced insignificant responses.

Novel methods for storage stability and release of Bacillus spores

Bacillus subtilis spores were immobilized in activated charcoal and tapioca and filled with acacia gum. These formulations were tested for spore stability during storage at temperatures ranging from 40°C to 90°C and for bacterial release. Thermodynamic analysis showed that immobilization of spores in acacia gum significantly increased their viability compared with unprotected spores. The viability was further increased when suspensions of spores in acacia gum were added to granules of charcoal and tapioca. The number of the spores released after storage was also increased when spores were treated with acacia gum prior to immobilization in tapioca and charcoal. Formulations of Bacillus spores with acacia gum and porous carriers (charcoal and tapioca) prolong the anticipated shelf‐life of spores even under ambient temperature and provide slow and steady bacterial release consistent with their high viability.

Inhibition and enhancement of odorant-induced cAMP accumulation in rat olfactory cilia by antibodies directed against Gαs/olf- and Gαi-protein subunits

The odorant‐induced accumulation of cAMP can be inhibited by antibodies directed against Gαs/olf. In contrast, antibodies raised against Gαi‐subunits caused a strong enhancement of the odorant‐induced cAMP accumulation. Western blotting and immunoelectron microscopy revealed the presence of both GαS/olf‐ and Gαi‐subunits in rat cilia preparations. The existence of both stimulatory and inhibitory odorant‐induced regulation of adenylyl cyclase activity in olfactory cilia may indicate that an initial integration of different odorant stimuli begins at the level of primary reactions in the same effector enzyme.

Assembly of cadmium stearate and valinomycin molecules assists complexing of K+ in mixed Langmuir-Blodgett films

The incorporation of valinomycin molecules into cadmium stearate multilayers increased complexation of valinomycin with potassium ions and potassium permeability of the multilayers. Valinomycin-cadmium stearate mixed Langmuir-Blodgett multilayers were exposed to aqueous solutions of KCl, NaCl and KClNaCl mixtures in a concentration range of 0.001–100 mM. The current responses of the multilayers indicated a significant dependence on the K+ concentration but not on the Na+ concentration. A marked preference for K+ over Na+ was observed in mixed ion solutions even when the concentration of Na+ exceeded the concentration of K+ by the factor of 100000. The K+Na+ selectivity was dependent on the concentration of valinomycin in mixed monolayers and was highest at about 9 mol% of valinomycin, at which point the antibiotic molecules were completely surrounded by cadmium stearate molecules. This information may be useful for understanding of fundamental properties of molecular assemblies and antibiotic/cell membrane interactions.