Thymine functionalized silicon quantum dots for selective detection of melamine and Hg2+

Abstract

Quantum dots (QDs) are tiny particles or nanocrystals of a semiconducting material in the size range of 2-10 nanometers. QDs have size dependent emission wavelength tunability and show unique luminescence properties, which can be exploited to use them in ion and molecular detection. The luminescence method is one of the most promising approaches for ion and molecular recognition owing to its high sensitivity. The luminescence or fluorescence of the QDs gets quenched when they interact with other molecules or ions. The extent of this quenching depends linearly on the concentration of the analytes. For this reason QDs are being popular as fluorescent tags for the detection of ions or molecules involved in many biological and biomedical fields. QDs have been successfully employed for the detection of heavy metal ions, formaldehyde, dopamine, glucose, pesticides etc. In comparison to other QDs, silicon quantum dots (SiQDs) have attracted much interest due to wide availability of low cost, inert source materials, favorable biocompatibility, low cytotoxiciy and unique optical and electronic properties. However, the selective detection of Hg2+ and melamine at sub-ppm level using SiQDs has not been well explored yet. Herein, we exploited the specific interaction strategy of Hg2+ and melamine with thymine and carried out thymine modification of SiQDs. The presence of melamine or Hg2+ caused very rapid and significant fluorescence quenching of SiQDs-Thy leading to the qualitative detection. From the fluorescence intensity ratio change quantitative analysis was also possible and the limit of detection was as low as 0.005 µM for both Hg2+ and melamine. Such lower limit detection of Hg2+ and melamine with QDs has not been reported yet. With increasing the concentration of Hg2+ or melamine, the fluorescence intensity decreased gradually and such response was observed over a wide concentration range. Moreover, SiQDs-Thy showed noticeable selectivity towards Hg2+ and melamine compared to other ions and biomolecules. SiQDs-Thy thus show great promise as a potential sensing platform for Hg2+ and melamine.