Biological self-assembled monolayers for photosynthetic solar cell and sensing applications

Photosynthetic sub-cellular plant structures called thylakoid were immobilized onto a gold electrode surface that had been functionalized by bioelectrocatalytic self-assembled monolayers (bio-SAMs) of cystamine and pyrroloquinoline quinone (PQQ). The goal is to achieve direct transfer of electrons from thylakoids to the electrode via the bio-SAMs to increase the electrical output of MEMS photosynthetic fuel cells. The immobilization technique could also be used in MEMS bio-sensing and microbial fuel cell applications. Quartz crystal microbalance with dissipation (QCM-D) was used to monitor the deposition kinetics of cystamine, PQQ, and thylakoids. Using QCM-D, the surface coverage of these three layers was determined to be, respectively, 7.9 × 10^-10 mol/cm², 3.3 × 10^-10 mol/cm², and 1.5 × 10⁶ thylakoids/cm². The cystamine and PQQ monolayers formed within 5 min, while the thylakoid layer required over 1 h. Each layer was shown to be covalently linked to the substrate or layer underneath and thus was able to survive repeated rinsing in water or buffer.