Abstract
The current study is focused on the application of water-soluble, fluorescent, and pH-sensitive carbon dots (CDs) as a nanoprobe for sensitive detection of pathogenic bacteria in milk and sewage water. The CDs were facilely synthesized through the controlled carbonization of sucrose using sulfuric acid and characterized through XRD, FTIR, TEM, UV-Vis Spectroscopy, and fluorescent analysis. The as-synthesized CDs were highly water-soluble, stable, and pH-sensitive fluorescent nanomaterials. The pH-related fluorescence study showed that the ratio of fluorescence intensity (Log[IF410/IF350]) changed linearly in the pH range between 4.9 and 6.9 in the Britton-Robison buffer. By determining the pH variation of the growth medium caused by the released acidic metabolites, the CDs-based ratiometric nanoprobe and MALDI-TOF mass spectrometry (MS) were used for the detection and identification of Escherichia coli O157:H7, respectively. The practical applicability of the pH-sensitive fluorescent CDs-based ratiometric nanoprobe was evaluated to detect Escherichia coli O157:H7 in real samples, i.e., milk and sewage water using agar count plate method with a limit of detection (LOD) up to 1 colony-forming unit per mL (CFU/mL).
Highlights
Escherichia coli O157:H7 (E. coli O157:H7) is a common enterohemorrhagic bacteria and the main causative agent of food and water-borne diseases [1]
Dye-doped fluorescent silica nanoparticles composite [15], CdTe/CdS quantum dots (QDs) [16], time-resolved fluorescent nanobeads (TRFN) [17], fluorescent microspheres (FM) [18], and aggregation-induced emission (AIE)-based materials [19] have been reported for E. coli O157:H7 sensing
The fluorescent carbon dots (CDs) solution was synthesized by successive carbonization of sucrose as reported [33] and optimized fluorescently under variable pH values during the synthesis (Figure S1)
Summary
Escherichia coli O157:H7 (E. coli O157:H7) is a common enterohemorrhagic bacteria and the main causative agent of food and water-borne diseases [1]. The culture-reliant conventional E. coli O157:H7 detection approach is laborious, suffering from the interference of complex food matrices, and time-consuming, taking 1–3 days [3,4], and needing skilled operators [5] To overcome such limitations, polymerase chain reaction (PCR) [6] has been developed but this method used for E. coli O157:H7 detection needs a detection time of about 24 h [7]. Several bioanalytical techniques have been developed over the last few years, like surface-enhanced raman spectroscopy (SERS) [8], flow cytometry [9], fluorescent methods [10], lateral flow immunoassay [11], hybridization chain reaction (HCR) [12], and amperometric immune sensors [13] Among these approaches, the fluorescent technique has drawn a great deal of attention from researchers owing to its outstanding selectivity, extraordinary sensitivity, cost-effectiveness, and is non-disparaging [14]. The inorganic hybrid nanomaterials, such as QDs [22] or lanthanide-loaded silica nanoparticles [23], are photo-stable substitutes as compared to the stained nanoparticles; the range of their in vivo practical applications remain narrow due to their tedious and multistep synthesis procedures as well as concerns related to their toxicity [24]
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