The efficiency of current microcystin detection methods has been hampered by the low detection limits required in drinking water and that routine detection is restricted to a few of the congeners with high degree of undesired cross-reactivity. Here, we report the development of novel microcystin-targeting molecules and their application in microcystin detection. We have selected DNA aptamers from a diverse random library that exhibit high affinity and specificity to microcystin-LR, -YR, and -LA. We obtained aptamers that bind to all chosen congeners with high affinity with K(D) ranging from 28 to 60 nM. More importantly, we also obtained aptamers that are selective among the different congeners, with selectivity from 3-folds difference in binding affinity to total discrimination (K(D) of 50 nM versus nonspecific binding). Electrochemical aptasensors constructed with the selected aptamers were able to achieve sensitive and congener-specific microcystin detection with detection limit as low as 10 pM.

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Here, we integrate two complementary detection strategies for the identification and quantification of Escherichia coli based on bacteriophage T4 as a natural bioreceptor for living bacteria cells. The first approach involves screening and viability assays, employing bacteriophage as the recognition element in label-free electrochemical impedance spectroscopy. The complementary approach is a confirmation by loop-mediated isothermal amplification (LAMP) to amplify specifically the E. coli Tuf gene after lysis of the bound E. coli cells, followed by detection using linear sweep voltammetry. Bacteriphage T4 was cross-linked, in the presence of 1,4-phenylene diisothiocyanate, on a cysteamine-modified gold electrode. The impedimetric biosensor exhibits specific and reproducible detection with sensitivity over the concentration range of 10(3)-10(9) cfu/mL, while the linear response of the LAMP approach was determined to be 10(2)-10(7) cfu/mL. The limit of detection (LOD) of 8 × 10(2) cfu/mL in less than 15 min and 10(2) cfu/mL within a response time of 40 min were achieved for the impedimetric and LAMP method, respectively. This work provides evidence that integration of the T4-bacteriophage-modified biosensor and LAMP can achieve screening, viability, and confirmation in less than 1 h.

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The objective of this study was to develop a biosensor using the cell wall binding domain (CBD) of bacteriophage-encoded peptidoglycan hydrolases (endolysin) immobilized on a gold screen printed electrode (SPE) and subsequent electrochemical impedance spectroscopy (EIS) for a rapid and specific detection of Listeria cells. The endolysin was amine-coupled to SPEs using EDC/NHS chemistry. The CBD-based electrode was used to capture and detect the Listeria innocua serovar 6b from pure culture and 2% artificially contaminated milk. In our study, the endolysin functionalized SPEs have been characterized using X-ray photoelectron spectroscopy (XPS). The integration of endolysin-based recognition for specific bacteria and EIS can be used for direct and rapid detection of Listeria cells with high specificity against non-Listeria cells with a limit of detection of 1.1 × 10(4) and 10(5) CFU mL(-1) in pure culture and 2% milk, respectively.