Abstract
Fluorescent dye staining combined with fluorescence microscopy or flow cytometry is becoming a routine way to monitor microorganism viability that is necessary for food safety, antibiotic development, and human health. However, the conventional live/dead assay dyes suffer from high cost, inconvenient staining steps, and high cytotoxicity, which is urgently needed to overcome. Herein, cheap carbon dots, CDs-EPS605, were reported to successfully assess microbial viability in a convenient way with neglectable cytotoxicity. The fluorescent N-doped CDs-EPS605 could be facilely prepared from bacterial amino exopolysaccharide (EPS) by one-step hydrothermal carbonization, which is cost-effective and sustainable. The negatively charged CDs-EPS605 consisted of C, H, O, N, P, and S, and featured various functional groups, including -COOH, -OH, -CONH-, and -NH2. CDs-EPS605 were observed to sensitively and selectively stain dead microorganisms instead of live ones to enable discrimination of live/dead microorganisms. The labeling method with CDs-EPS605 did not require protection from light, or washing, which is convenient. Additionally, CDs-EPS605 displayed better photostability and much less cytotoxicity compared to the commercial counterpart. Altogether, CDs-EPS605 represent a simple, yet powerful staining agent for microbial viability assessment, and at the same time enrich the current applications of microbial EPS.
Highlights
Microbial viability assessment is commonly performed during pathogen detection, antibiotic development and microbial monitoring in both industrial and biomedical fields (Breeuwer and Abee, 2000)
We considered microbial exopolysaccharide EPS-605 as an excellent raw material for Carbon dots (CDs) synthesis, given that it contains elements C, H, O, S, P, and N (Li et al, 2017), providing both the major carbon framework and other elements for doping to produce CDs without the utilization of passive agents (Reckmeier et al, 2016)
We reported amino EPS from lactate acid bacteria (LAB) was first time explored as a single precursor to produce fluorescence N-doped CDs viz. CDs-EPS605 through simple onestep hydrothermal reaction without any dopants and passivation agents
Summary
Microbial viability assessment is commonly performed during pathogen detection, antibiotic development and microbial monitoring in both industrial and biomedical fields (Breeuwer and Abee, 2000). Other methods like atomic force microscopy (AFM) (Fantner et al, 2010), fourier transform infrared spectroscopy (FT-IR) (Notingher et al, 2003), surface-enhanced raman scattering (Zhou et al, 2015) and nucleic acid sequence-based amplification (Keer and Birch, 2003) have been under development to gain higher accuracy, but they are time-consuming and costly, requiring pretreatment of organisms. Compared to these methods, fluorescent dye staining paired with fluorescence microscopy or flow cytometry. Developing desirable dyes for microbial viability evaluation is of great value
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