Breast tumor cell detection at single cell resolution using an electrochemical impedance technique

Gold micro-electrodes with various diameters (25, 50, 75, 100 and 250 mu m) were manufactured using standard micro-fabrication techniques and optimized for counting of MCF-7 cells (breast tumor cells) with single cell resolution. For specific cell capture, anti-EpCAM was immobilized on 11-mercaptoundecanoic acid (11-MUA)-3-mercaptopropionic acid (3-MPA) mixed self-assembled monolayer (SAM) modified gold surface of micro-electrodes. Electrodes were characterized using optical, cyclic voltammetry and electrochemical impedance spectroscopic (EIS) techniques. Cell capture response recorded using EIS suggested that optimum electrode dimensions should be analogous to desired cell size. For MCF-7 cells with an average diameter of 18 +/- 2 mu m, an electrode with 25 mu m diameter was established as the optimum electrode size for precise single cell recognition and enumeration. In EIS investigation, the 25 mu m electrode exhibited an impedance change of similar to 2.2 x 10(7) Omega in response to a single tumor cell captured on its surface. On the other hand other electrodes (250, 100, 75 and 50 mu m) showed much less response for a single tumor cell. In future, the use of high density arrays of such electrodes with surface modifications will result in miniaturized lab on a chip devices for precise counting of MCF-7 cells with single cell resolution.