The hybridization was incubated
at 45 ◦C for 1 h with shaking. After the sandwich structure (MNP-
2pDNA/tDNA/1pDNA-AuNP-bDNA-NTs) was formed, the solution
was put on the magnetic separator for 3min and then the super natant was removed. The sandwich structures were washed five
times with 500L of assay buffer in order to effectively remove the
excess 1pDNA-AuNP-bDNA-NTs complex that was not specifically
bound to the MNP-2pDNA/tDNA complex through hybridization.
The washed sandwich structure was dissolved in 10L of 1Mnitric
acid to release the NT ions (Pb2+ or Cd2+). After addition of 90L
of acetate buffer solution (0.1 M, pH 4.5) with 1mg/L bismuth, the
released NT ions were ready for electrochemical measurement. The
attractive characteristic of bismuth is attributed to the formation
of multi-component bismuth alloys with numerous heavy metals,
such as Pb2+, Cd2+, and Zn2+, while facilitating the electrodeposition
of heavy metals.