DMSO-mediated ag lateral coated Au nanobipyramids: Ultrafast colormetric detection platform for Fe³⁺ with uniform etching

Colorimetric detection by etching based on metal nanoparticles is one of the most commonly portable detection methods, but there are problems such as poor particle controllability and irregular etching. In this paper, a novel Ag lateral coated Au nanobipyramids nanostructure (Au@Ag LCNBPs) for multi-colorimetric detection of Fe³⁺ is prepared through the mediation of dimethyl sulfoxide (DMSO). When DMSO is used to cover the surface of Au nanobipyramids (Au NBPs), it greatly affects the way Ag coated Au NBPs. When the volume ratio of DMSO is 25%, Ag is no longer deposited at the tip, but gradually deposited on the side of the Au NBPs to form the Au@Ag LCNBPs. The long axis cross-section of the Au@Ag LCNBPs takes the shape of a hexagon. As the Ag content increases, the width of the Ag layer gradually increases, the cross-section gradually converts to a positive hexagonal shape, and the aspect ratio of the whole structure decreases, leading to the blueshift of the longitudinal LSPR peak. This mode of deposition is different from the longitudinal deposition reported in the previous literature. A multi-colorimetric detection method for Fe³⁺ using the etching of the Ag layer by Au@Ag LCNBPs has been developed. This method exhibits a good exponential correlation in the concentration range of 1–210 μM with the detection limit of 200 nM. With the increase of Fe³⁺, the colloid color shows the change of yellow, orange, red, purple, blue, green and colorless. The etching process can be completed in about 30 s. This nanostructure achieves two etching modes of the Ag layer by Fe³⁺, uniform etching and concave etching. Moreover, it demonstrates that the enormous potential of Au@Ag LCNBPs in colorimetric etching detection.