Nano-carriers of fluorescent probes and enzymes

Cascade Blue, Sulforhodamine G and yeast alcohol dehydrogenase were encased inside nano-sized silicate shell and their absorption and fluorescence spectrophotometric properties, and the enzyme activity investigated. The stabilized molecules have potential as biosensors, in drug delivery, and recyclable catalysts. Cascade Blue and Sulforhodamine G were attached to 85 nm diameter colloidal gold, encased with silicate, and the gold core dissolved. Fluorescence quenched by the gold was recovered for both dyes, but the peak emission was red-shifted from that in water for Cascade Blue and blue-shifted for Sulforhodamine G. The fluorescence excitation spectra of these dyes showed similar shifts, reflecting their interaction with the shell interior. The spectrofluorometric results for alcohol dehydrogenase bound to 15 nm diameter colloidal gold were similar. The substrate ethanol and cofactor NAD were permeable to the silicate shell. Only 20% of enzyme activity of ADH was lost after binding to gold and an additional 20% lost by encasing with silicate. Subsequent rate of loss of activity was significantly lowered. This study demonstrated that dyes and enzymes could be encased within silicate shells. Whether the shell protects these molecules from the environment, and how the thickness of silicate shell affects the rate of enzyme reaction remain to be investigated.