Label-free colorimetric detection of Cu2+ on the basis of Fenton reaction-assisted signal amplification with unmodified gold nanoparticles as indicator

A novel label-free strategy is demonstrated for the amplified detection of copper ions (Cu2+) on the basis of Fenton reaction and unmodified gold nanoparticles (AuNPs). AuNPs are known to stabilise in the presence of single-stranded DNA (ssDNA), which prevents the salt-induced aggregation of AuNPs in solution because of electrostatic repulsion. However, in the presence of a Fenton reagent, Cu2+ catalyses the Fenton reaction to generate hydroxyl free radicals, which cut the ssDNA into different sequence fragments or even single bases to induce AuNP aggregation along with a red-to-blue colour change. Cu2+ is qualitatively and quantitatively detected through this phenomenon, and Cu2+ recycling may amplify the signal transduction based on Fenton reaction with unlabelled sensing strategies. A linear calibration of A700/A525 versus Cu2+ concentration is obtained within 0.1-10 μM, along with a detection limit of 23 nM and relative standard deviation (RSD) of 4.1% (1 μM). Moreover, the sensing system exhibits excellent sensitivity and selectivity for Cu2+, with quantitative spike-recoveries from 88% to 116% in environment water samples.