Improving Impedance Cell Analysis: High Frequency Dielectric Spectroscopy in Combination with Multivariate Data Analysis and Complementary Assays

We have developed a novel lab-on-a-chip system for continuous and non-invasive monitoring of microfluidic cell cultures using integrated high-frequency contactless impedance spectroscopy (see Figure 1 ). Electrically insulated (passivated) microfabricated interdigitated electrode structures [1] were embedded into four individually addressable microchambers to reliably and reproducibly detect cell-substrate interactions, cell viability and intracellular conductivity changes. Additionally, multivariate data analysis method such as partial least square (PLS) is implemented to analyze impedance spectra (1 kHz to 10 MHz), thus providing sensitive and selective information on intracellular pathway activation, up and down-regulation of protein synthesis as weil as global cellular stress responses. Performance evaluation include the sensing of cellular responses to (a) repeated starvation, (b) sub-lethal concentrations of the cytotoxic compound cisplatin, (c) inhibition of the cellular protein biosynthesis activity using cycloheximide (CHX) and (d) targeted activation of ßadrenergic receptors using isoproterenol. Practical application is demonstrated by combining high-frequency contactless impedance spectroscopy with time-resolved ELISA for IL-6 quantitation in the cell culture supernatant to analyze stress responses of connective tissue cells (human dermal and synovial fibroblasts) to systemic stress factors. The ability to identify transient cell responses to circulating proinflammatory cytokines IL-1ß and TNFa using integrated high-frequency impedance spectroscopy in microfluidic cell cultures could provide cell biologists with a new tool to characterize the onset of chronic inflammation under physiologically relevant measurement conditions .