Colloidal quantum dot chains: self-assembly mechanism and ratiometric fluorescent sensing

Abstract

Precise control of the size, shape, and composition of nanocrystals will be required to fully explore and utilize unique properties of nanomaterials with a broad range. In this manuscript we have designed colloidal QD chains, using carboxyl-modified red fluorescent cadmium telluride (CdTe), which were self-assembled by the mediation of trithiocyanuric acid (TTCA). Furthermore, a ratiometric fluorescent sensor with dual-emissions was constructed by mixing the QD chains with blue fluorescent carbon dots (CDs) for the visual ultrasensitive detection of As(III) in environmental water. In the process of As³⁺ detection, it could react with the third sulfydryl, which resulted in the agglomeration of QD chains and quenching of the red emission of the QDs, while the blue fluorescent CDs were insensitive to the analyte. So the variation of fluorescence intensity ratios produces an obvious change of the fluorescence color from fushia to blue, which can be conveniently observed by the naked eye under a UV lamp without any complicated instrumentation. The LOD of this ratiometric fluorescent probe could reach as low as 1 ppb, which is much lower than the maximum level of 10 ppb As³⁺ in drinking water stipulated by WHO. Following the sensing mechanism, a paper-based sensor has been prepared by printing the ratiometric probe on filter paper, which provides a convenient and simple approach for the visual detection of As³⁺. Therefore, the very simple and effective strategy reported here could be extended to the visual detection of a wide range of analytes in the environment by the construction of highly efficient ratiometric nanoprobes.