Size-dependent inhibition and enhancement by gold nanoparticles of luminol-ferricyanide chemiluminescence

It was found that gold nanoparticles of small size (< 5 nm) could inhibit the chemiluminescence (CL) of the luminol-ferricyanide system, whereas gold nanoparticles of large size (> 10 nm) could enhance this CL, and the most intensive CL signals were obtained with 25-nm-diameter gold nanoparticles. The luminophor was identified as the excited-state 3-aminophthalate anion. The studies of UV-visible spectra, CL spectra, X-ray photoelectron spectra, effects of concentrations of luminol and ferricyanide solution, and fluorescence quenching efficiency of gold colloids were carried out to explore the CL inhibition and enhancement mechanism. The CL inhibition by gold nanoparticles of small size was supposed to originate from the competitive consumption of ferricyanide by gold nanoparticles and the relatively high quenching efficiency of the luminophor by gold nanoparticles. In contrast, the CL enhancement by gold nanoparticles of large size was ascribed to the catalysis of gold nanoparticles in the electron-transfer process during the luminol CL reaction and the relatively low quenching efficiency of the luminophor by gold nanoparticles. This work demonstrates that gold nanoparticles have the size-dependent inhibition and enhancement in the CL reaction, proposing a perspective for the investigation of new and efficient nanosized inhibitors and enhancers in CL reactions for analytical purposes.