Simultaneous detection of foodborne pathogenic bacteria in milk by fluorescence immunoassay

Sensitive colorimetric detection of Escherichia coli in milk using Au@Ag core-shell nanoparticles

Escherichia coli (E. coli) is a prevalent pathogen that is frequently associated with the foodborne illness. It causes various infections and poses a significant threat to human health. A rapid and sensitive assay for detecting E. coli is essential for timely diagnosis. Herein, a simple and sensitive colorimetric analysis method for detecting E. coli was developed based on the formation of Au@Ag core-shell nanoparticles facilitated by p-benzoquinone (BQ). E. coli reduced p-benzoquinone to generate hydroquinone (HQ), which could reduce the added Tollens' reagent to silver elemental and grow on the surface of gold nanoparticles (AuNPs). As the E. coli concentration increased, the silver layer thickess on the AuNPs surface growed, resulting in a stronger silver absorption peak observed at 390 nm. The color of the solution changed from red to orange, which could be used to detect E. coli by the naked eye. As a result, E. coli was detected with a linear range from 1.0 × 101 to 1.0 × 107 CFU/mL based on the absorbance intensity. In addition, this method accurately detected E. coli in real milk sample, demonstrating promising applications in foodborne pathogen detection. With satisfactory accuracy, the proposed colorimetric method holds excellent prospects in detecting pathogens in actual food samples.

An all-in-one microfluidic SlipChip for power-free and rapid biosensing of pathogenic bacteria

Point-of-care testing of pathogens is becoming more and more important for the prevention and control of food poisoning. Herein, a power-free colorimetric biosensor was presented for rapid detection of Salmonella using a microfluidic SlipChip for fluidic control and Au@PtPd nanocatalysts for signal amplification. All the procedures, including solution mixing, immune reaction, magnetic separation, residual washing, mimicking catalysis and colorimetric detection, were integrated on this SlipChip. First, the mixture of the bacterial sample, immune magnetic nanobeads (IMBs) and immune Au@PtPd nanocatalysts (INCs), washing buffer and H2O2-TMB chromogenic substrate were preloaded into the sample, washing and catalysis chambers, respectively. After the top layer of this SlipChip was slid to connect the sample chamber with the separation chamber, the mixture was moved back and forth through the asymmetrical split-and-recombine micromixer by using a disposable syringe to form the IMB-Salmonella-INC sandwich conjugates. Then, the conjugates were captured in the separation chamber using a magnetic field, and the top layer was slid to connect the washing chamber with the separation chamber for washing away excessive INCs. Finally, the top layer was slid to connect the catalysis chamber with the separation chamber, and the colorless substrate was catalyzed by the INCs with peroxidase-mimic activity to generate color change, followed by using a smartphone app to collect and analyze the image to determine the bacterial concentration. This all-in-one microfluidic biosensor enabled simple detection of Salmonella as low as 101.2 CFU mL-1 within 30 min and was featured with low cost, straightforward operation, and compact design.

A novel fluorescent probe based on carbazole-thiophene for the recognition of hypochlorite and its applications

A carbazole thiophene-aldehyde and 4-methylbenzenesulfonhydrazide conjugate CSH was synthesized by introducing 5-thiophene aldehyde at the 3-position of the carbazole group as the precursor and then condensing it with 4-methylbenzenesulfonhydrazide. CSH has high selectivity and sensitivity towards ClO-, which can specifically identify ClO- by UV-Vis and fluorescence spectroscopy. CSH can rapidly respond to ClO- in the physiological pH range through a fluorescence quenching pattern, accompanied by the color of CSH changing markedly from turquoise to yellowish green under the 365 nm UV light. Probe CSH exhibits a quantitative response to ClO- (0-11 μM) with a low detection limit (1.16 × 10-6 M). Cell imaging experiments have shown that CSH can capture fluorescent signals in the cyan and yellow channels of HeLa cells through fluorescence confocal microscopy, and can successfully identify exogenous ClO- in HeLa cells. In addition, probe CSH can also be used to detect ClO- in environmental water samples. These results indicate that CSH has potential application prospects in the environmental analysis and biological aspects.