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We developed an electrochemical impedance spectroscopy (EIS) biosensor based on bacteriophage long tail fibre proteins (LTFPs) to capture and detect Salmonella. First, based on the genetic information of a Salmonella enterica bacteriophage (SEP37), we found that the genes ORF99, ORF100, and ORF256 encode proteins associated with host recognition. We used the pETdue1 plasmid to construct ORF99–ORF100 and ORF256 co-expression vectors to express (LTFPs) in Escherichia coli and used purified LTFPs as specific biorecognition elements. Then, we fixed gold nanoparticles (AuNPs), cysteamine (Cys), and LTFPs on a gold disk electrode surface via layer-by-layer assembly to construct an EIS biosensor. Salmonella in the sample can be captured by LTFPs on the electrode surface and reduce the electron transfer sites. We applied the EIS biosensor to detect Salmonella spiked in lake water. It showed a good linear relationship within the concentration range of 10 ∼ 1 × 106 colony-forming units (CFU)/mL. The detection limit was 9 CFU/mL. This method based on bacteriophage LTFPs does not require complex pretreatment steps and extends the application of tail fibre proteins as a biorecognition element in the detection field. [Display omitted] • ORF99-100 and ORF256 were inserted into plasmid to construct co-expression vector. • The long tail fibre protein of phage SEP37 was co-expressed in E. coli. • This protein was used as bio-recognition element to construct an EIS biosensor. • This biosensor can quickly detect Salmonella in lake water samples. • This method allowed a detection limit of 9 CFU/mL for Salmonella. [ABSTRACT FROM AUTHOR]

Atractylodis Macrocephalae Rhizoma (AMR) is a bulk herbal foods, which can invigorate spleen and supplement Qi to help health. The accurate identification of the authenticity and origin of AMR is a prerequisite for the safe use and quality control. Herein, a dual-channel colorimetric sensor based on metal ions mediated color transformation of gold nanoparticles (AuNPs) was constructed to identify the authenticity and origin of AMR. The Ag+ / cetyltrimethylammonium chloride modified AuNPs (CTAC-AuNPs) sensing channel and Cr3+ / trisodium citrate modified AuNPs (TCA-AuNPs) sensing channel were rationally designed based on two mechanisms that are the silver deposition and the induced aggregation, respectively. When AMR extracts from different origins or its counterfeits were added to the colorimetric sensor, significantly different terpenoids in extracts can bind to Ag+ or Cr3+ to produce different color transformations. AMR samples from three origins (Zhejiang, Hunan and Anhui) and the counterfeit samples (Gynura japonica (Thunb.) Juel., and Atractylodis Rhizoma) were all accurately classified using the dual-channel colorimetric sensor combined with PLSDA. Our sensor has obvious advantages of simple and instrument-free analysis procedure, which will provide a new idea for the convenient identification of AMR and other herbal foods. [Display omitted] • AuNPs-based dual-channel colorimetric sensor for identifying AMR and its origin. • Two color change systems of AuNPs mediated by Ag+ and Cr3+ were developed in sensor. • The complexation between extracts and metal ions resulted in different color changes. • AMR authenticity and origin can be accurately identified by naked eye or PLSDA. • This method is convenient, accurate and instrument-free, suitable for on-site assay. [ABSTRACT FROM AUTHOR]