SOLID-PHASE IMMOBILIZATION OF OPTICALLY RESPONSIVE LIPOSOMES IN SOL-GEL MATERIALS FOR CHEMICAL AND BIOLOGICAL SENSING

Liposomes enhanced with surface recognition groups have previously bee n found to have high affinity for heavy metal ions and virus particles with unique fluorescent and colorimetric responses, respectively. The se lipid aggregate systems have now been successfully immobilized in a silica matrix via the sol-gel method, affording sensor materials that are robust, are easily handled, and offer optical clarity. The mild p rocessing conditions allow quantitative entrapment of preformed liposo mes without modification of the aggregate structure. Lipid extraction studies of immobilized nonpolymerized liposomes showed no lipid leakag e in aqueous solution over a period of 3 months. Heavy metal fluoresce nt sensor materials prepared with 5% nonyl)-rac-glyceroyl]-3,6-dioxaoc tyl]iminodiacetic acid/distearylphosphatidylcholine liposomes exhibite d a 4-50-fold enhancement in sensitivity to various metal ions compare d to that of the Liposomes in free solution. Through ionic attraction the anionic silicate surface, at the experimental pH of 7.4, may act a s a preconcentrator of divalent metal ions, boosting the gel's interna l metal concentration. Entrapped sialic acid-coated polydiacetylene Li posomes responded with colorimetric signaling to influenza virus X31, although slower than the free Liposomes in solution. The successful tr ansport of the virus (50-100 nm diameter) reveals a large pore diamete r of the gel connecting the liposome to the bulk solution. The porous and durable silica matrix additionally provides a protective barrier t o biological attack (bacterial, fungal) and allows facile recycling of the Liposome heavy metal sensor.