The electrochemical detection of cell lines of MCF-7 (human breast cancer) has 
been reported, using magnetic beads for the separation tool and high-affinity 
DNA aptamers for signal recognition. The high specificity was obtained by using 
the magnetic beads and aptamers, and the good sensitivity was realized with the 
signal amplification of DNA capped CdS or PbS nanocrystals. The ASV (anodic 
stripping voltammetry) technology was employed for the detection of cadmic 
cation and lead ions, for electrochemical assay of the amount of the target 
cells and biomarkers on the membrane of target cells, respectively. This 
electrochemical method could respond to as low as 100 cells mL(-1) of cancer 
cells with a linear calibration range from 1.0×10(2) to 1.0×10(6) cells mL(-1), 
showing very high sensitivity. Moreover, the amounts of HER-3 which were 
overexpressed on MCF-7 cells were calculated correspond to be 3.56×10(4) 
anti-HER-3 antibody molecules. In addition, the assay was able to differentiate 
between different types of target and control cells based on the aptamers and 
magnetic beads used in the assay, indicating the wide applicability of the assay 
for early and accurate diagnose of cancers.