Synthesis of biocompatible and highly fluorescent N-doped silicon quantum dots from wheat straw and ionic liquids for heavy metal detection and cell imaging

Silane-based precursors for the synthesis of water-dispersible silicon quantum dots (SiQDs) present harmful effects on both researchers and the environment, due to their high toxicity. Though waste wheat straw is an abundant source of natural silicon, its application towards the synthesis of biocompatible SiQDs for metal detection has not yet been explored. In this study, N-doped SiQDs demonstrating uniform spherical morphologies, excellent water dispersity and strong fluorescence emission with a quantum yield of 28.9% were facilely synthesized by using wheat straw (WS) as silicon source and allyl-3-methylimidazolium chloride (AMIMCl) as nitrogen source. The wheat straw based SiQDs (WS-SiQDs) showed linear fluorescence quenching ((F-0-F)/F) with Cr(VI) and Fe(III) concentration in the range of 0-6x10(-4) M. Following immobilization on hydrophilic silica hydrogels, WS-SiQDs@silica hydrogels demonstrated enhanced fluorescence emission which can selectively detect Cr(VI) and Fe (III) to the limits of 142 and 175 nM, respectively. Moreover, cell imaging results reflected thatWS-SiQDs can penetrate the membranes of dental pulp stem cells and react with the nucleuses of the stem cells. The stem cells maintained high viability under the conditions of 24 h incubation and SiQD concentration below 50 mg.L-1, thus indicating low cytotoxicity ofWS-SiQDs. The as-prepared SiQDs demonstrated notable structural and fluorescent properties, therefore representing promising biocompatible fluorescent nanomaterials for metal detection and cell imaging. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

In this study, SiQDs doped with nitrogen were successfully synthesized using waste wheat straw and allyl-3-methylimidazolium chloride. These SiQDs showed excellent water dispersity and strong fluorescence emission, making them suitable for metal detection and cell imaging. The SiQDs displayed linear fluorescence quenching with Cr(VI) and Fe(III) concentrations, and when immobilized on hydrophilic silica hydrogels, they exhibited enhanced fluorescence emission and selective detection abilities. Cell imaging results showed low cytotoxicity of the SiQDs, indicating their potential as biocompatible fluorescent nanomaterials.