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Abstract: This paper describes the first immunosensing system reported for the detection of bacteria combining immunomagnetic capture and amperometric detection in a one-step sandwich format, and in a microfluidic environment. Detection is based on the electrochemical monitoring of the activity of horseradish peroxidase (HRP), an enzyme label, through its catalysis of hydrogen peroxide (H2O2) in the presence of the mediator hydroquinone (HQ). The enzymatic reaction takes place in an incubation micro-chamber where the magnetic particles (MPs) are confined, upstream from the working electrode. The enzyme product is then pumped along a microchannel, where it is amperometrically detected by a set of microelectrodes. This design avoids direct contact of the biocomponents with the electrode, which lowers the risk of electrode fouling. The whole assay can be completed in 1h. The experiments performed with Escherichia coli evidenced a linear response for concentrations ranging 102–108 cellml−1, with a limit of detection of 55cellsml−1 in PBS, without pre-enrichment steps. Furthermore, 100cellsml−1 could be detected in milk, and with negligible interference by non-target bacteria such as Pseudomonas. [Copyright &y& Elsevier]

The number of CTCs in peripheral blood is of great significance for the early diagnosis, recurrence and prognosis evaluation of tumor patients. Consequently, it is required to develop simple and effective technique to realize the capture and detection of rare number CTCs. Herein, a SiO 2 , gelatin and biotinylated EpCAM aptamer P1 modified Fe 3 O 4 immunomagnetic nanoparticles (IMNs) were prepared for the specific capture and nondestructive release of trace amounts of CTCs. Then, utilizing the peroxidase-like activity of single-walled carbon nanotubes (SWCNTs) and the effect of non-specific DNA sequences on this activity, a colorimetric probe was constructed by modifying the three DNA sequences (mDNA) onto the IMNs. When target cell was present, due to the specific interaction between cells and P1, the conformational structure of P1 was changed. Consequently, the mDNA linked with P1 on IMNs was replaced by the cell and released from IMNs. In this way, the quantification of captured CTCs could be converted to that of released mDNA. This strategy combined the capture and detection of CTCs as a whole and could detect down to 10 cells with a high selectivity. Finally, we achieved the accurate quantification of CTCs in lysed bloods from 12 clinical tumor patients, which exhibited a great promise for further clinical applications. • A colorimetric detection method was established for CTCs. • It utilized the peroxidase activity of SWCNTs and the effect of DNA sequences on this activity. • The CTCs were firstly captured by designed IMNs. • CTCs numbers in 12 tumor patients blood were determined. [ABSTRACT FROM AUTHOR]