For conjugation, the antibody was adsorbed on the surface of
gold nanoparticles. The UV–vis spectra of antibody–gold nanoparticles
exhibited maximum absorbance at a wavelength of 520 nm,
and there was no significant variation in the absorption spectrum
between antibody–gold nanoparticles and gold nanoparticles
(Fig. 2A). Therefore, it could be explained that gold remained nanosized
after binding with antibody (Dungchai et al., 2008).