Dual metal ion (Fe3+ and As3+) sensing and cell bioimaging using fluorescent carbon quantum dots synthesised from Cynodon dactylon

Abstract

In this study, water dispersible fluorescent carbon quantum dot (CQD) has been synthesised, having an average size of 8.6 ± 0.4 nm using Cynodon dactylon (CD) following microwave assisted green synthetic one-step method. As-prepared CQD fluoresces strongly at 444 nm having a quantum yield of 1% in water when excited at 350 nm. This fluorescence of CQD is sensitive toward As³⁺ and Fe³⁺ metal ions. These CQD are utilized for dual metal ion fluorescence sensing; turn-on fluorescence sensing for As³⁺ and turn-off fluorescence sensing for Fe³⁺ ions. Limit of detection for As³⁺ and Fe³⁺ ions has been found to be 19 nM and 0.10 μM respectively, which is the lowest value reported for As³⁺ without any functionalization. The adsorption kinetics of As³⁺ and Fe³⁺ ions on CQD have been examined using pseudo-first-order-kinetic model revealing that physical adsorption is dominant over chemical processes in this work. For 0.41 g/L and 1.90 g/L dose of CQD, the equilibrium adsorption capacity was found to be 1.57 × 10^-6 mg/g, 2.91 × 10^-7 mg/g, and 1.01 × 10^-5 mg/g, 1.69 × 10^-6 mg/g respectively for As³⁺ and Fe³⁺ ions. Despite having low quantum yield in water, as-prepared CQD showed low cytotoxicity and good tolerance against photodegradation of biological cells at concentrations lower than 62.5 μg/mL and when the cells are illuminated up to 12 h. Owing to this, the synthesised CQD have been utilized as fluorescent probes for in itro cell imaging.

Keywords: CQD; Cytotoxicity; Fluorescence; Heavy metal; Sensing.