Alkaline earth metal effect on the size and color transition of citrate-capped gold nanoparticles and analytical implications in periodate-luminol chemiluminescence

Citrate-modified gold nanoparticles were found to undergo size and color transition upon interaction with alkaline earth metals. At low concentrations, metal ions coordinate with AuNPs via citrate boding inducing aggregation which results in size increase as evidenced by the decrease in their plasmon bandwidth. As the concentration increases further, color transition from red to blue is observed which is no longer attributed to aggregation but to specific ion adsorption phenomena. The response of gold nanoparticles to these changes linearly depends on cation concentration in both the UV and Vis regions, a feature that was exploited for the assessment of alkaline earth metal concentrations in water samples. Based on these findings, the modification of the surface properties of metal-coated AuNPs were investigated with regard to their potential influence on the catalytic oxidation of luminol by periodate. Interestingly, a significant amplification of the CL emission signal was recorded when metal ions were associated with AuNPs, even for chemiluminescence “inert” cations like calcium and magnesium. The analytical implications of these findings for the improvement of CL sensitivity and its potential analytical applications are also discussed.