Highly selective and sensitive paper-based colorimetric sensor using thiosulfate catalytic etching of silver nanoplates for trace determination of copper ions

• Novel, highly selective and sensitive μPAD for determination of Cu2+ was achieved.
• The limit of detection was found to be very low at 1.0 ng mL−1 by visual detection.
• This method was successfully applied for determination of Cu2+ in real samples.

A novel, highly selective and sensitive paper-based colorimetric sensor for trace determination of copper (Cu2+) ions was developed. The measurement is based on the catalytic etching of silver nanoplates (AgNPls) by thiosulfate (S2O32−). Upon the addition of Cu2+ to the ammonium buffer at pH 11, the absorption peak intensity of AuNPls/S2O32− at 522 nm decreased and the pinkish violet AuNPls became clear in color as visible to the naked eye. This assay provides highly sensitive and selective detection of Cu2+ over other metal ions (K+, Cr3+, Cd2+, Zn2+, As3+, Mn2+, Co2+, Pb2+, Al3+, Ni2+, Fe3+, Mg2+, Hg2+ and Bi3+). A paper-based colorimetric sensor was then developed for the simple and rapid determination of Cu2+ using the catalytic etching of AgNPls. Under optimized conditions, the modified AgNPls coated at the test zone of the devices immediately changes in color in the presence of Cu2+. The limit of detection (LOD) was found to be 1.0 ng mL−1 by visual detection. For semi-quantitative measurement with image processing, the method detected Cu2+ in the range of 0.5–200 ng mL−1(R2 = 0.9974) with an LOD of 0.3 ng mL−1. The proposed method was successfully applied to detect Cu2+ in the wide range of real samples including water, food, and blood. The results were in good agreement according to a paired t-test with results from inductively coupled plasma-optical emission spectrometry (ICP-OES).

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