Antibodies were linked to the amine-modified spheres by an 1-ethyl-3-(3-dimethylaminopropyl)- carbodiimide (EDC) coupling reaction in 1× phosphate buffered saline (PBS). A total of 0.0001 g of TiO2 spheres and 40 μL of antibody (1 wt %) were added to 450 μL of PBS at 4 °C for half an hour for premixing.