Reduction of silver ions in gold nanoparticle suspension for detection of dihydroxybenzene isomers

We have investigated the reduction of silver ions in a gold nanoparticle suspension by dihydroxybenzene isomers: hydroquinone (1,4-dihydroxybenzene), catechol (1,2-dihydroxybenzene), and resorcinol (1,3-dihydroxybenzene). We found that using these isomers as reducing agents resulted in distinctive color changes of suspensions. When hydroquinone was added to suspensions containing cysteamine-modified gold nanoparticles and silver nitrate, the suspension changed from red to yellow because a silver shell formed on the gold nanoparticles. With catechol, the suspension initially turned yellow from formation of core–shell nanoparticles, and then it became black following the polymerization of catechol on the nanoparticle surfaces. This caused charge reversal followed by aggregation of core–shell nanoparticles. The addition of resorcinol, however, did not produce core–shell nanoparticles because its high oxidation peak potential prevented the reduction of silver ions, keeping the suspension color unchanged. Based on the color changes, we could detect the concentration of hydroquinone and catechol with high sensitivity. Moreover, the addition of Fe(III) ions enabled selective detection of hydroquinone in a mixture of dihydroxybenzene isomers by forming a chelate complex with catechol.