A visual electrochemiluminescence resonance energy transfer/surface plasmon coupled electrochemiluminescence nanosensor for Shiga toxin-producing Escherichia coli detection

In this work, we used a microwave method to synthesize green, pollution-free BN quantum dots (QDs). In order to explore new high-performance electrochemiluminescence (ECL) sensors, a BN QDs-based ECL biosensor was established with an ECL resonance energy transfer (ECL-RET)/surface plasmon coupled ECL (SPC-ECL) sensing mode in this work. Firstly, BN QDs and Au NPs were bound to the ends of hairpin DNA, respectively. Therefore, the Au NPs effectively quenched the ECL signal of the BN QDs due to ECL-RET. When hairpin DNA identified the target DNA, the hairpin structure transformed to a linear conformation, and the distance between BN QDs and Au NPs enlarged. As a result, the SPC-ECL effect took the place of ECL-RET. The ECL signal was enhanced, by about six times higher than BN QDs-Au NPs-hairpin DNA conjugates. The new ECL-RET/SPC-ECL sensing mode greatly improved the sensitivity and accuracy of the QDs-based ECL sensor. The proposed biosensor could accurately quantify the Shiga toxin-producing Escherichia coli (STEC) gene from 1 pmol L-1 to 5 nmol L-1 with a limit of detection (LOD) of 0.3 pmol L-1. The new ECL biosensor showed excellent selectivity, stability and high sensitivity, and it was applied in spiked human serum samples with satisfactory results. Moreover, the change of the BN QDs ECL signal could be easily observed with the help of a smartphone camera. Benefiting from the ECL-RET/SPC-ECL sensing mode, to the best of our knowledge, this is the first time that visual QDs ECL signals were directly observed by a household smartphone CMOS.