(A) Optical characteristics of multi-spot gold-capped nanoparticle array chip with localized-surface plasmon resonance (LSPR) absorbance peak: (1) slide glass substrate, (2) after gold deposition on slide glass substrate, (3) after silica nanoparticle array on the gold-deposited substrate, and (4) gold-capped nanoparticle array chip. Absorbance peak of multi-spot gold-capped nanoparticle array chip was observed at 540 nm. (B) Absorbance spectrum of LSPR properties obtained after binding of 100 μg/mL gold binding peptide (GBP)–AIa with 1 μg/mL anti-AI antibody in wavelength region (from 450 nm to 850 nm). LSPR properties of bare substrate (black line), GBP–AIa-immobilized on the multi-spot chip surface (red line), binding reaction between GBP–AIa and anti-AI antibody on the multi-spot chip surface (green line). Inset represents the 60 multi-spot gold-capped nanoparticle array chip with one spot of 2 mm in diameter. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article). (C) Superimposed absorbance spectrum curves obtained from GBP–AIa immobilized on the surface of multi-spot chip in the presence of anti-AI antibody with concentrations ranging from 1 fg/mL to 1 μg/mL. (D) Calibration curve for absorbance dependence on anti-AI antibody concentration by using GBP–AIa-immobilized multi-spot chip. (Reproduced with permission from [68], published by Elsevier, 2012).