Improved on-chip impedimetric immuno-detection of subpopulations of cells toward single-cell resolution

Abstract

Impedance spectroscopy has gained interest for the quantitative detection of specific cells mainly due to a label-free detection and their miniaturization capability required for integration on chip and development of point-of-care diagnostics. In this paper, we report the study of impedimetric microfluidic devices with improved sensitivity targeting the immuno-detection of cells. The sensitivity of our system was evaluated in terms of the capacity to detect monocytes trapped by immune-reaction with CD14 antibody immobilized on micro-electrode surface. All measurements were performed in faradic mode using a redox probe. The sensitivity was evaluated as a function of the impedance increase ΔZ, recorded at 100Hz, caused by the insulating character of the cell trapped on electrodes. Analyses first confirmed that the sensing performances were significantly improved by using microfluidics. This increase could originate from an increase in the probability of cell trapping and a better organization of cells on the electrode due to the laminar flow. The greatest sensitivity was recorded with interdigitated electrodes for which the influence of the gap value was evaluated. The maximal sensitivity was reached with the smallest inter-electrodes gap tested (50μm). This performance was in part attributed to the redox cycling taking place between neighboring fingers that was strongly affected when cells were trapped on the electrodes edges. Furthermore we also demonstrate that the slice of cell concentration for which the sensitivity is maximized is correlated to the area of electrodes. Moreover, the smallest area of interdigitated electrode (0.1mm length) allowed the detection of as low as 5 cells per mL