Sa. Yamanaka et al., SOLID-PHASE IMMOBILIZATION OF OPTICALLY RESPONSIVE LIPOSOMES IN SOL-GEL MATERIALS FOR CHEMICAL AND BIOLOGICAL SENSING, Langmuir, 13(19), 1997, pp. 5049-5053
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.