Carbon quantum dots-based fluorescent probe for sensitive and selective detection of glutathione in bacteria and cells

Abstract

Background

The sensitivity of 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) method may not be enough to detect low concentration glutathione (GSH), especially in complex samples, which limits its application in some biologic scenarios. Fluorescent carbon quantum dots (CQDs) have garnered significant interest in bioanalytical applications due to their unique properties, particularly the sensitivity in the detection of complex samples.

Results

In this work, carbon quantum dots (TOCDs) were prepared via pyrolysis method of d-threonine and o-phenylenediamine. Considering advantages of selectivity of DTNB and sensitivity of TOCDs, a simple, fast and sensitive fluorescent sensor based on TOCDs and DTNB was fabricated for selective detection of GSH. In the presence of GSH in the mixture of TOCDs and DTNB, –SH of GSH can interact with DTNB and subsequently affording 5-thio-2-nitrobenzoate (TNB), which can strongly absorb excitation light of TOCDs and lead to fluorescence quenching of TOCDs. As a consequence, quantitative screening of GSH can be achieved through the fluorescence intensity of TOCDs was decreased after the addition of GSH in the system of TOCDs and DTNB. Under optimized conditions, good linear relationships in the range of 2.5–40 nM, 40–150 nM and 150–1000 nM for GSH. TOCDs can effectively detect GSH with a limit of detection (LOD) 1.5408 nM. The feasibility of the TOCDs probe was verified through non-invasive detection of reduced glutathione (GSH) in bacteria and cells. The fluorescence of TOCDs in different living bacteria/cells were yellow fluorescence, while the fluorescence could be ignored after joining GSH and DTNB. The mechanism about quench phenomenon of the fluorescence intensity between TOCDs and DTNB/GSH was the inner-filter effect. These results demonstrated that the presented fluorescent sensor could be a promising sensing platform for GSH analysis.

Significance

This sensing strategy could be expanded to more access to the GSH-induced acute toxicity and disease. The yellow fluorescence carbon quantum dots demonstrated its potential application on GSH detection in bacteria and cells.