There is a multitude of scenarios that demand more than one channel of a potentio-/galvanostat. The reasons vary greatly – just to name a few typical settings:
- automating sequential multi-sensor probing over
- the need of scaling up experiments to more throughput via parallel experiments
- complex multi-electrode arrangements with need for specific synchronized control
- simultaneous comparison of a single or a set of test targets/sensors to a single or a group of reference sensors
As diverse as the reasons for using multichannel arrangements are the choices for solutions. In general, there are four basic approaches:
A Novel 3D Label-Free Monitoring System of hES-Derived Cardiomyocyte Clusters: A Step Forward to In Vitro Cardiotoxicity Testing
Unexpected adverse effects on the cardiovascular system remain a major challenge in the development of novel active pharmaceutical ingredients (API). To overcome the current limitations of animal-based in vitro and in vivo test systems, stem cell derived human cardiomyocyte clusters (hCMC) offer the opportunity for highly predictable pre-clinical testing. The three-dimensional structure of hCMC appears more representative of tissue milieu than traditional monolayer cell culture. However, there is a lack of long-term, real time monitoring systems for tissue-like cardiac material. To address this issue, we have developed a microcavity array (MCA)-based label-free monitoring system that eliminates the need for critical hCMC adhesion and outgrowth steps. In contrast, feasible field potential derived action potential recording is possible immediately after positioning within the microcavity. Moreover, this approach allows extended observation of adverse effects on hCMC. For the first time, we describe herein the monitoring of hCMC over 35 days while preserving the hCMC structure and electrophysiological characteristics. Furthermore, we demonstrated the sensitive detection and quantification of adverse API effects using E4031, doxorubicin, and noradrenaline directly on unaltered 3D cultures. The MCA system provides multi-parameter analysis capabilities incorporating field potential recording, impedance spectroscopy, and optical read-outs on individual clusters giving a comprehensive insight into induced cellular alterations within a complex cardiac culture over days or even weeks.
A novel 96-well multielectrode array based impedimetric monitoring platform for comparative drug efficacy analysis on 2D and 3D brain tumor cultures
Aggressive cancer entities like neuroblastoma and glioblastoma multiforme are still difficult to treat and have discouraging prognosis in malignant stage. Since each tumor has its own characteristics concerning the sensitivity towards different chemotherapeutics and moreover, can obtain resistance, the development of novel chemotherapeutics with a broad activity spectrum, high efficacy and minimum side effects is a continuous process. Sophisticated in vitro assays for comprehensive prediction of in vivo drug efficacy and side effects represent an actual bottleneck in the drug development process. In this context, we developed a novel in vitro 2D and 3D multiwell–multielectrode device for drug efficacy monitoring based on direct real-time impedance spectroscopy measurement in combination with our unique 96-well multielectrode arrays and microcavity arrays. For demonstration, we used three neuro- and glioblastoma cell lines that were cultured as monolayer and multicellular tumor spheroids for recapitulating in vivo conditions. Using our novel 96-well multielectrode array based system it was possible to detect time and concentration dependent responses concerning treatment with doxorubicin, etoposide and vincristine. While all tested chemotherapeutics revealed high potency for apoptosis induction in neuroblastoma cells, etoposide was ineffective for glioblastoma cell lines. Determination of IC50 values allowed us to compare drug efficacy in 2D and 3D culture models and moreover, revealed chemotherapeutic and tumor cell line specific activity patterns. These pharmacokinetic patterns are of great interest in the context of preclinical drug development. Thus, impedance spectroscopy based monitoring systems could be used for the fast in vitro based in vivo prediction of novel anti-tumor drugs.
Microfluidic platforms capable of complex on-chip processing and liquid handling enable a wide variety of sensing, cellular, and material-related applications across a spectrum of disciplines in engineering and biology. However, there is a general lack of available microscale sensors capable of non-optically monitoring and quantifying on-chip fluid motion. Hence, many microfluidic systems are confined to the laboratory because their use requires optical microscopy. Here, we present a method for dynamically tracking laminar interfacial flows in microfluidic channels non-optically using impedance spectroscopy. Using a microfluidic T-channel, we generate a liquid interface by co-flowing two different electrolyte streams side-by-side. The interface is driven through an array of “displacement” electrodes where it is electrokinetically deflected across the microchannel. The interfacial flow is monitored downstream using an array of interdigitated “impedance” electrodes which dynamically measure the electrochemical impedance near the surface of the flow channel. We demonstrate that the impedance spectrum is sensitively influenced by the position of the deflected interface. While laminar fluid interfaces are ubiquitous to microfluidic flows and used extensively in rheology and biomolecular detection, it is currently difficult to measure their position non-optically. The sensing method presented here enables the interfacial position to be dynamically determined without a microscope and provides a new tool for lowering the barriers to operating microfluidic devices outside the confines of a traditional laboratory.
Through Vial Impedance Spectroscopy (TVIS): A Novel Approach to Process Understanding for Freeze-Drying Cycle Development
Through vial impedance spectroscopy (TVIS) provides a new process analytical technology for monitoring a development scale lyophilization process, which exploits the changes in the bulk electrical properties that occur on freezing and subsequent drying of a drug solution. Unlike the majority of uses of impedance spectroscopy, for freeze-drying process development, the electrodes do not contact the product but are attached to the outside of the glass vial which is used to contain the product to provide a non-sample-invasive monitoring technology. Impedance spectra (in frequency range 10 Hz to 1 MHz) are generated throughout the drying cycle by a specially designed impedance spectrometer based on a 1 GΩ trans-impedance amplifier and then displayed in terms of complex capacitance. Typical capacitance spectra have one or two peaks in the imaginary capacitance (i.e., the dielectric loss) and the same number of steps in the real part capacitance (i.e., the dielectric permittivity). This chapter explores the underlying mechanisms that are responsible for these dielectric processes, i.e., the Maxwell-Wagner (space charge) polarization of the glass wall of the vial through the contents of the vial when in the liquid state, and the dielectric relaxation of ice when in the frozen state. In future work, it will be demonstrated how to measure product temperature and drying rates within single vials and multiple (clusters) of vials, from which other critical process parameters, such as heat transfer coefficient and dry layer resistance, may be determined.