The presence of hydroquinone (HQ), a phenol
ubiquitous in nature and widely used in industry, needs to be
monitored because of its toxicity to the environment. Here we
demonstrate efficient detection of HQ using simple, fast, and
noninvasive electrochemical measurements on indium tin
oxide (ITO) electrodes modified with nanoparticles comprising
bimetallic Au−In cores and mixed Au−In oxide shells.
Whereas bare ITO electrodes show very low activity for the
detection of HQ, their modification with Au−In core−shell
nanoparticles induces a pronounced shift of the oxidation peak
to lower potentials, i.e., facilitated oxidation. The response of
the different electrodes was correlated with the initial composition of the bimetallic nanoparticle cores, which in turn determined
the amount of Au and In stabilized on the surface of the amorphous Au−In oxide shells available for the electrochemical reaction.
While adding core−shell nanostructures with different compositions of the alloy core facilitates the electrocatalytic (reduction-)
oxidation of HQ, the activity is highest for particles with AuIn cores (i.e., a Au:In ratio of 1). This optimal system is found to
follow a single pathway, the two-electron oxidation of the quinone−hydroquinone couple, which gives rise to high oxidation
peaks and is most effective in facilitating the electrode-to-analyte charge transfer and thus detection. The limits of detection
(LOD) decreased when increasing the amount of Au exposed on the surface of the amorphous Au−In oxide shells. The LODs
were in the range of 10−5−10−6 M and were lower than those obtained using bulk Au.
