Platinization: A novel technique to anchor photosystem I reaction centres onto a metal surface at biological temperature and pH

Photosystem I (PSI) reaction centre core antenna complexes containing about 40 chlorophylls per P700 (PSI-40) are 6 nm biological photovoltaic devices. PSI particles carry positively-charged domain(s) and can therefore interact electrostatically with a negatively-charged surface. PSI particles were platinized by reduction of [PtCl6](-2) at neutral pH and 20 degrees C. The presence of metallic platinum on PSI particles was observed directly by scanning tunnelling microscopy (STM). The platinized PSI particles were larger than control PSIs (without platinization), due to the presence of metallic platinum. The electric properties of PSI and metallic platinum were characterized by STM tunnelling conductance (I-V) measurements. Diodic response was obtained in platinized PSI. Metallic platinum formed during the reduction of [PtCl6](2-) caused bonding between PSI particles and a gold metal surface. Using the technique of chemical platinization, PSI particles can be ''welded'' onto gold plates under biologically compatible conditions, resulting in a 2-dimensional spatial array of PSI particles anchored on the metal surface. Metallic platinum is not only a good conductor but also an active catalyst. This platinization ''welding'' technique is potentially important for both bioelectronics and biometallocatalysis.