Selection and characterization of bispecific aptamers against malachite green and leucomalachite green

In order to develop multi-residues rapid detection, the bispecific aptamers against malachite green (MG) and leucomalachite green (LMG) were isolated by the capture systematic evolution of ligands by exponential enrichment (Capture-SELEX). After thirteen rounds of selection, the enriched ssDNA pools were sent for high -throughput sequencing. Nine aptamer candidates (A1-A9) were picked out to test their specificity by gold nanoparticles (AuNPs) colorimetric assay. Three aptamers (A2, A3, A5) with good selectivity were truncated to verify their affinity by fluorescence assay. Finally, three truncated aptamers (A2-a, A3-a, A5-a) with bispecificity and high affinity were identified. For LMG, the dissociation constant (Kd) of them were 8.4 +/- 0.8 nM, 8.2 +/- 1.2 nM, and 13.7 +/- 1.4 nM, respectively. For MG, Kd of them were 3.4 +/- 0.3 mu M, 2.3 +/- 0.2 mu M, 3.0 +/- 0.2 mu M. Among them, A3-a is the best. Our work will provide novel probes for the development of multi-residues rapid detection as well as opportunities for multiple target aptamer discovery.