Colorimetric aggregation based cadmium(II) assay by using triangular silver nanoplates functionalized with 1-amino-2-naphthol-4-sulfonate

A colorimetric method is described for sensitive and low-cost detection of Cd(II). It is based on the use of triangular silver nanoplates (tri-AgNPs) modified with 1-amino-2-naphthol-4-sulfonate (ANS) acting as a colorimetric probe. ANS is first linked to the tri-AgNPs via electrostatic interaction of the sulfo groups. In the absence of analyte, ANS on the surface of tri-AgNPs protects them from aggregation. In the presence of Cd(II), the tri-AgNPs aggregate due to the interaction between ANS and Cd(II). This results in a distinct color change from blue (absorption peak at 710 nm) to green (peak at 770 nm). UV-vis spectrometry and image analyses demonstrate that this method exhibits selective and sensitive colorimetric response to Cd(II). The color change can be easily detected with bare eyes. Response is linear in the 30 to 70 mu M concentration range, and the detection limit is 30 nM.