DNA walker coupled with nicking endonuclease for sensitive electrochemical detection of saxitoxin†

Saxitoxin (STX) as one of the paralytic shellfish toxins has become a serious public health and environmental issue. In this regards, developing highly sensitive and selective biosensors may help find a solution. Herein, a ferrocene (Fc)-labeled DNA walker coupled with nicking endonuclease Nb.BbvCI was used to construct a sensitive electrochemical aptasensor for STX detection. First, an amplified DNA, aptamer and DNA walker formed a sandwich structure on a gold electrode. This structure was disintegrated when STX was added, resulting in the hybridization of the amplified DNA and DNA walker. Thereafter, the DNA walker was activated by Nb.BbvCI to achieve stepwise cleavage of the hybridized amplified DNA. The released Fc-amplified DNA generated an electrochemical signal that decreased linearly with the logarithm value of STX concentration in the range of 1 pM–100 nM with a detection limit of 0.58 pM. Meanwhile, the proposed aptasensor exhibited good selectivity and recovery rate. The DNA walker coupled with the nicking endonuclease provides effective signal amplification for the detection of toxins and fabrication of sensitive aptasensors.