Self-assembly of the light-harvesting complex of photosystem II (LHCII) on alkanethiol-modified gold electrodes

A light-harvesting complex of photosystem II (LHCII), isolated from spinach, was immobilized onto a gold electrode modified with self-assembled monolayers (SAMs) of alkanethiols, NH2–(CH2)n–SH, n = 2, 6, 8, 11; HOOC–(CH2)7–SH; and CH3–(CH2)7–SH; and a bare electrode. The extent of LHCII complex adsorption according to surface treatment decreased in the order amino groups > carboxylic acid groups > methyl groups and increased with the methylene chain length in NH2–(CH2)n–SH. Interestingly, the photocurrent density depended on the terminal group and the methylene chain length in NH2–(CH2)n–SH and decreased in the order amino groups > methyl groups > carboxylic acid groups. An efficient photocurrent response of the LHCII complex on SAMs of NH2–(CH2)n–SH, n = 8 was observed upon illumination at 680 nm. These results indicated that the LHCII complexes were well organized on the cationic surfaces of the gold electrodes modified with amino alkanethiols. The quantum yield depended on the methylene chain length (n), where the maximum photocurrent response was observed at n = 8, which corresponded to a distance of 1.7 nm between the terminal amino group in NH2–(CH2)8–SH and the gold surface.