Thermal Noise as a Probe for Cell Adhesion

In the adhesion area of cells on solid substrates, there is a narrow cleft filled with electrolyte. The sheet resistance of the cleft is crucial for the interfacing of cells with semiconductors and metals. It can be estimated by applying intracellular or extracellular ac voltages and recording the response of current, of extracellular voltage or of transmembrane voltage. A more elegant approach relies on the Fluctuation-Dissipation Theorem which implies that an electrical resistance is related with voltage fluctuations. It was previously demonstrated that the voltage fluctuations in the area of adhesion can be recorded with transistors and that the resistance of the cell-chip junction can be estimated from the noise spectrum [1].To attain a more reliable interpretation of the voltage noise, we measured spatial maps of the noise spectrum in the adhesion area. We used a Multi-Transistor-Array with a homogeneous surface of titanium dioxide [2]. The bandwidth of recording was 3 MHz at a spatial resolution of 7.8 μm. As a test system we used snail neurons that were cultured on chips coated with polylysine. We found a good agreement between the twodimensional maps of the noise spectra with a theory of thermal noise in a planar core-coat conductor. Sheet resistances on the order of 100 MOhm were obtained. Apart from the effect of the sheet resistance, the noise characteristics revealed changes of the membrane conductance and membrane capacitance. Thus thermal noise recording is a novel probe for the electrical properties of cell adhesion with subcellular resolution, with high bandwidth and without perturbation of the system.[1] M. Voelker and P. Fromherz, Phys. Rev. Lett, 96 (2006) 228102.[2] A. Lambacher et al., Applied Physics A 79 (2004) 1607.