L-cysteine-regulated in situ formation of Prussian blue/Turnbull’s blue nanoparticles as the colorimetric probe for the detection of copper ion

A fast, simple, sensitive, and selective colorimetric method for the detection of Cu2+ was developed using Prussian blue/Turnbull’s blue nanoparticles (PBNPs/TBNPs) as the probe. The colorimetric sensor is based on the following principle. Cu2+ can induce the aggregation of L-cysteine (L-cys) modified-PBNPs/TBNPs (L-cys-PBNPs/TBNPs), resulting in an obvious red shift of its maximum absorption peak. Thus, the concentration of Cu2+ can be determined based on the peak shift in the UV–Vis spectra. The optimal pH, concentration of L-cys, reaction temperature between L-cys-PBNPs/TBNPs and Cu2+, the formation time of L-cys-PBNPs/TBNPs, and the reaction time between L-cys-PBNPs/TBNPs and Cu2+ of the method were determined to be pH 4.5, 2.0 mM, 20 °C, 5.0 min, and 2.0 min, respectively. A good linearity for the colorimetric determination of Cu2+ at the range of 0.25–2.5 μM (R2 = 0.986) was obtained, with a limit of detection (LOD) of 0.12 μM. Moreover, the negligible response of other metal ions demonstrates good selectivity and specificity of the sensor. In addition, the method was employed in the detection of Cu2+ in lake water samples, and the spiked recoveries are in the range of 96.7–106.6% with a relative standard deviation less than 7.4%. Therefore, the colorimetric method is applicable for Cu2+ detection in real water samples of high sensitivity and selectivity.