Signal “on-off-off” strategy for improving the sensitivity of BRCA1 electrochemical detection by combining gold substrate amplification, DNA conformational transformation and DSN enzymatic hydrolysis dual reduction

In this article we proposed a new signal amplification strategy based on signal "on-off-off" for improving the detection sensitivity of breast cancer 1 (BRCA1) electrochemical sensor. First, the stem-loop structured captured DNA (C-DNA) modified by 5' sulfhydryl group and 3' methylene blue (MB), was self-assembled on electrodeposited nanoAu surface through Au-S reaction. Electrodeposition of nanoAu increased electrode area and strengthened MB electrochemical signal, which indicated "signal on". Then, BRCA1 hybridization with C-DNA made MB away from nanoAu surface, and reduced the MB signal due to the formation of stiff C-DNA/BRCA1 hybridized structure, which indicated "signal off". Finally, the double strand specific nuclease (DSN) was used to cleave C-DNA/BRCA1, and led to the further decrease of MB signal, which also indicated "signal off". Results showed that the designed sensor based on signal "on-off-off" had excellent detection sensitivity for BRCA1. The relative percentage change of MB reduction peak current was linear with BRCA1 concentration from 5 nM to 70 nM, and a low detection limit of 52 pM was achieved. The proposed sensor could distinguish single base mismatch BRCA1, two base mismatch BRCA1, and non-complementary DNA well. In addition, the sensor showed good reproducibility and stability.