Organic electrochemical transistors for cell-based impedance sensing

Abstract

Electrical impedance sensing of biological systems, especially cultured epithelial cell layers, is now a common technique to monitor cell motion, morphology, and cell layer/tissue integrity for high throughput toxicology screening. Existing methods to measure electrical impedance most often rely on a two electrode configuration, where low frequency signals are challenging to obtain for small devices and for tissues with high resistance, due to low current. Organic electrochemical transistors (OECTs) are conducting polymer-based devices, which have been shown to efficiently transduce and amplify low-level ionic fluxes in biological systems into electronic output signals. In this work, we combine OECT-based drain current measurements with simultaneous measurement of more traditional impedance sensing using the gate current to produce complex impedance traces, which show low error at both low and high frequencies. We apply this technique in vitro to a model epithelial tissue layer and show that the data can be fit to an equivalent circuit model yielding trans-epithelial resistance and cell layer capacitance values in agreement with literature. Importantly, the combined measurement allows for low biases across the cell layer, while still maintaining good broadband signal.

Controlling the mode of operation of organic transistors through side-chain engineering

“…S8) (16). The hole mobility of the material can be extracted using constant current or impedance matching methods previously reported for OECTs (30,31) which use the hole transit time to determine carrier mobility. This method results in a hole mobility of 0.95 cm 2 /Vs, which is in good agreement with the estimate of transistor saturation mobility (using C i = 0.94 mF/cm 2 , from Fig.…”

Organic transistor platform with integrated microfluidics for in-line multi-parametric in vitro cell monitoring

“…Mechanisms to explain these changes in the cell impedance for FSSstimulated cells may include changes in the cleft height (distance between substrate and cells) and/or paracellular distance of the cells 49 . In the present work, we made use of the equivalent circuit of Figure 3a (right) to model the cell layer covering the transistor channel, adding in series to R s (series electrolyte resistance) and C OECT (transistor channel capacitance), the cell layer resistance (R cl ) and cell layer capacitance (C cl ) in parallel 40 . Notably, the presence of the cleft height offers an additional ionic resistance (R cleft ) that in our model is counted in the series electrolyte resistance R s .…”

“…Measurements parameters were controlled using a customized LabVIEW program. For fitting of the frequencydependent measurements, a MATLAB script was used to extract the cell layer resistance and capacitance as reported previously 40 .…”

Research Update: Electrical monitoring of cysts using organic electrochemical transistors

“…It is worth noting that although we use the −3 dB cut-off value as a proof of concept for this set of experiments, and this method is appropriate to extract relative differences, it prohibits quantitative extraction of physical parameters necessary for comparing different systems. As we have recently demonstrated, 19 the frequency dependent transconductance can be transformed into a complex impedance which can then be fit to an appropriate model. In the present case, assuming the OECT is represented as a capacitor, and the capillary as a resistor and capacitor in parallel, a resistance of 251 kΩ is extracted for the 1 cm long, 160 µm diameter capillary tube, and an OECT channel capacitance of 14 nF.…”

“…1(b) right. The electrical measurements were performed using OECTs, and the frequency dependent normalized transconductance values were plotted as previously detailed, 19 Fig. 1(b) left.…”