Dye-sensitized biosystem sensing using macroporous semiconducting metal oxide films

Transparent semiconducting oxide (TiO2, SnO2 and ZnO) films having highly interconnected pores in the range of 30–200 nm were fabricated in one-pot using polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer. Such porous structures were helpful for efficient transport of bulky guest species such as proteins. Biosensing protocols were constructed in the films by using bulky biomolecules, namely, adsorbed DNA, adsorbed antibody and adsorbed antigen–antibody (immunoassay). In the DNA-based system, the macroporous TiO2 film was the most useful among porous anatase films such as mesoporous and mesoporous/PS beads derived macroporous ones, leading to significant detection of 125 times higher photocurrent generated from a dye (Cy5) attached to DNA than those observed for the others. Macroporous SnO2 and ZnO films were also available for the construction of similar biomolecule immobilized electrodes. Extremely complicated immunoassay reactions involving bulky proteins (antigen, antibody, etc.) were also established using the macroporous TiO2 and SnO2 films. Especially photocurrent for electron transfer from Cy5 attached to the second antibody was successfully detected by using the SnO2 film for exceptionally selective sensing applications.