Diketopyrrolopyrrole Amphiphile-Based Micelle-Like Fluorescent Nanoparticles for Selective and Sensitive Detection of Mercury(II) Ions in Water

Abstract

A technique for encapsulating fluorescent organic probes in a micelle system offers an important alternative method to manufacture water-soluble organic nanoparticles (ONPs) for use in sensing Hg²⁺. This article reports on a study of a surfactant-free micelle-like ONPs based on a 3,6-di­(2-thienyl)-2,5-dihydro­pyrrolo­[3,4-<i>c</i>]­pyrrole-1,4-dione (TDPP) amphiphile, (2-(2-(2-methoxy­ethoxy)­ethyl)-3,6-di­(2-thiophyl)-2,5-dihydro­pyrrolo­[3,4-<i>c</i>]­pyrrole-1,4-dione (NDPP) fabricated to monitor Hg²⁺ in water. NDPP was synthesized through a simple one-step modification of a commercially available dye TDPP with a flexible and hydrophilic alkoxy. This study reports, for the first time, that TDPP dyes can respond reversibly, sensitively, and selectively to Hg²⁺ through TDPP–Hg–TDPP complexation, similar to the well-known thymine­(T)–Hg–thymine­(T) model and the accompanying molecular aggregation. Interestingly, transmission electron microscopy (TEM) and dynamic light scattering (DLS) confirmed that, in water, NDPP forms loose micelle-like fluorescent ONPs with a hydrohobic TDPP portion encapsulated inside. These micelle-like nanoparticles offer an ideal location for TDPP–Hg complexation with a modest molecular aggregation, thereby providing both clear visual and spectroscopic signals for Hg²⁺ sensing. An estimated detection limit of 11 nM for Hg²⁺ sensing with this NDPP nanoparticle was obtained. In addition, NDPP ONPs show good water solubility and high selectivity to Hg²⁺ in neutral or alkalescent water. It was superior to most micelle-based nanosensors, which require a complicated process in the selection or synthesis of suitable surfactants. The determinations in real samples (river water) were made and satisfactory results were achieved. This study provides a low-cost strategy for fabricating small molecule-based fluorescent nanomaterials for use in sensing Hg²⁺. Moreover, the NDPP nanoparticles show potential ability in Hg²⁺ ion adsorption and recognization of cysteine using NDPP-Hg composite particle