Nano-gold biosynthesis by silica-encapsulated micro-algae: a "living" bio-hybrid material

Klebsormidium flaccidum algal cells exhibiting the ability to form gold nanoparticles intra-cellularly in suspension were encapsulated within silica gels. Optical and electronic microscopy indicate that entrapped cells maintain their ability to reduce gold salts. A difference in the kinetics of gold colloid formation within silica in the absence or presence of cells could be followed by UV-visible absorption spectroscopy, confirming the bio-mediated nature of the reduction process. Study of the photosynthetic activity of the algae showed that the encapsulation process protects the cells from lethal effects arising from gold toxicity. Moreover, the first in situ imaging of entrapped cells using Raman spectroscopy allowed the investigation of the influence of the gold colloids on the photosynthetic system of the algae, in particular through modification of chlorophyll fluorescence and carotenoid signals. Such a coupling of sol-gel encapsulation and Raman imaging should allow the future development of novel photosynthesis-based cellular biosensors.