Electrochemical impedance spectroscopy (EIS) is becoming more and more relevant for the characterization of biosensors employing interdigitated electrodes. We compare four different sensor topologies for an exemplary use case of ion sensing to extract recommendations for the design optimizations of impedimetric biosensors. Therefore, we first extract how sensor design parameters affect the sensor capacitance using analytical calculations and finite element (FEM) simulations. Moreover, we develop equivalent circuit models for our sensor topologies and validate them using FEM simulations. As a result, the impedimetric sensor response is better understood, and sensitive and selective frequency ranges can be determined for a given sensor topology. From this, we extract design optimizations for different sensing principles.

In this work, we present a novel approach for the fabrication of a fully printed poly(3,4 ethyldioxythiophene)poly(styrenesulfunate) (PEDOT:PSS)-based organic electrochemical transistor (OECT) on textile substrates, that serves as a selective cation sensor, thanks to the combination of both OECT and electrochemical impedance spectroscopy (EIS) response. In particular, the selectivity achieved relies on discerning ion diffusion dynamics at low frequencies during EIS measurements and coupling these with the variations in OECT response associated with ion concentration. Unlike existing literature, our sensor is fabricated using cost-effective techniques, is planar, integrated directly onto textiles, and operates without external gate electrodes. Employing the same device configuration for both OECT and EIS measurements(both methods with a high coefficient of correlation $R^{2} = 89\%$ and $R^{2} > 94\%$ respectively), we demonstrate its efficacy by characterizing the sensor across three different concentrations of potassium chloride (KCl) and sodium chloride (NaCl), establishing a comprehensive 3D calibration space to extract the electrolyte composition in a concentration between 1.25mM and 100mM.

In this letter, a cost-effective, flexible, and fully printable potassium ion (K+) sensor is developed. The sensor consists of two interdigitated gold electrodes covered by a butylacrylate potassium ion-sensitive membrane (ISM). An impedimetric measurement method is chosen to eliminate the need for a reference electrode and to reduce signal drifting. We show the versatility and high reproducibility of the manufacturing process and present first measurement results. Our sensors achieve a sensitivity of 4.553 MΩ/(mmol/L) at 100 mHz and an accuracy of 1.8 mmol/L. The sensors exhibit low cross sensitivity toward sodium ions and show no signal drift.

Poly(3,4-ethylenedioxythiophene )-poly( styrene sulfonate) (PEDOT:PSS) is a conductive polymer yielding promising interface characteristics for biosensor electrodes. In this work, we compare two solution processing methods, namely drop-casting and spray-coating, for the deposition of PEDOT:PSS layers on gold interdigitated electrodes for electrical impedance spectroscopy based biosensing applications in fluid. Both techniques include (3-glycidyloxypropyl) trimethoxysilane (GOPS) as a crosslinker and reveal good stability in electrolytes. On the one hand, spray coating shows higher mechanical robustness, reproducibility, and better layer thickness control. On the other hand, drop-casting yields a 3-fold lower surface roughness and results in improved double-layer characteristics with a capacitance of 157 $\mu \mathrm{F}$ compared to 3 $\mu \mathrm{F}$ of bare gold. Both deposition techniques promise higher electrode reproducibility and improved interface characteristics, especially in the lower frequency range.

This paper introduces an ultra-low noise continuous-time (CT) analog front-end (AFE) interface for ionic spectroscopy applications. The proposed readout technique combines magnitude/phase and lock-in architectures over a relatively wide frequency range, from 10 Hz to 100 kHz. This hybrid architecture enables the extension of the overall dynamic range (DR) to 120 dB. The presented AFE has a programmable transimpedance gain of 12 G$\Omega$ to cover various kinds of electrochemical impedance sensors. Moreover, the input-referred current noise reaches 2.2 fA/$\sqrt{}$Hz. This ensures a resolution of 125 fA rms in a bandwidth of 2.5 kHz, which corresponds to the desired sensitivity of ionic sensing applications. The proposed readout architecture is implemented in 180 nm CMOS technology. It occupies an area of 0.7 $\mathrm{m}\mathrm{m}^{2}$ with a total power consumption equals 3.9 mW from a 1.8 V supply voltage.

In this work, we present a flexible 2-electrode impedimetric potassium ion sensor that does not rely on a reference electrode and reaches a sensitivity of 56.7 $\mathbf{k}\Omega/\mathbf{dec}$ . We directly compare its impedimetric and standard potentiometric performance and show that the detection range can be increased from 3 to 5 decades. Additionally, the signal drift is reduced by more than 13x from 10-20% to 0.6-1.5%. However, the cross-sensitivity towards sodium ions is increased from 0.13 to 0.68. To improve this value, we performed equivalent circuit fitting on the electrochemical impedance spectroscopy data to exploit the increased availability of sensor information. By this, we found that the sensor's double-layer capacitance shows a selectivity of 0.005. Hence, impedance spectroscopy can improve sensor drift and selectivity and thereby enable new application fields.