Frank Sommerhage

Ion-sensitive field-effect transistor (ISFET) arrays combine the spatial multiplexing of microelectrode arrays with intrinsic chemical selectivity, allowing them to read out proton dynamics that are invisible to conventional metal electrodes. We report here the use of SiO2-gate ISFETs to analyze the CLC-type Cl⁻/H⁺ antiporter ClC-4 in voltage-clamped, stably transfected HEK293 cells. Step depolarizations (+120 mV, 500 ms) evoke acidification of the picolitre-sized cleft between cellular membranes and transistor gates that the ISFET resolves within ≤ 500 ms. This is an order of magnitude faster than dye-based or micro-electrode approaches. Altering the bath buffer (0.1–10 mM HEPES) confirms the inverse relationship between buffer capacity and sensor amplitude. The method is remarkably sensitive and versatile, and may be useful for the functional characterization of various H+-coupled transporters.

Microfabrication and assembly of 3D MEA based on a glass-stainless steel platform is shown utilizing non-traditional “Makerspace Microfabrication” techniques featuring cost-effective, rapid fabrication and an assorted biocompatible material palette.

The widespread adaptation of 3D printing in the microfluidic, bioelectronic, and Bio-MEMS communities has been stifled by the lack of investigation into the biocompatibility of commercially available printer resins. By introducing an in-depth post-printing treatment of these resins, their biocompatibility can be dramatically improved up to that of a standard cell culture vessel (99.99%). Additionally, encapsulating resins that are less biocompatible with materials that are common constituents in biosensors further enhances the biocompatibility of the material. This investigation provides a clear pathway toward developing fully functional and biocompatible 3D printed biosensor devices, especially for interfacing with electrogenic cells, utilizing benchtop-based microfabrication, and post-processing techniques.

Microelectrode Arrays are established platforms for biosensing applications; however, limitations in electrode impedance and cell-electrode coupling still exist. In this paper, the SNR of 25 μm diameter gold (Au) microelectrodes was improved by decreasing the impedance with precision electrodeposition. SEM determined that N-P Pt. microelectrodes had nano-porous structures that filled the insulation cylinders. EIS, CV, and RMS noise measurements concluded that the optimized electrodeposition of N-P Pt. led to a lowered impedance of 18.36 kΩ ± 2.6 kΩ at 1 kHz, a larger double layer capacitance of 73 nF, and lowered RMS noise of 2.08 ± 0.16 μV as compared to the values for Au of 159 kΩ ± 28 kΩ at 1 kHz, 17nF, and 3.14 ± 0.42 μ V, respectively. Human motoneurons and human cardiomyocytes were cultured on N-P Pt. devices to assess their biocompatibility and signal quality. In order to improve the cell-electrode coupling, a precision plating technique was used. Both cell types were electrically active on devices for up to 10 weeks, demonstrated improved SNR, and expected responses to precision chemical and electrical stimulation. The modification of Au microelectrodes with nanomaterials in combination with precision culturing of human cell types provides cost effective, highly sensitive, well coupled and relevant biosensing platforms for medical and pharmaceutical research. [2018-0187]

Microelectrode arrays (MEAs) with evenly distributed multiple sensor spots have been designed for specific applications. Using the MEAs, we determined the relative profiles of potassium channel openers (KCOs) on cultured embryonic Sprague-Dawley rat cardiac myocytes. KCO, pinacidil (PIN), cromakalim (CROM), SDZ PCO400 (SDZ), or its vehicle, was added to the myocytes cumulatively. The action potential signal shapes in the presence of PIN and SDZ show that the changes in voltage over time and the magnitudes of the associated voltage change were reduced concentration-dependently. CROM affected sodium influx more than PIN and SDZ. The comparisons of changes in the rate of beating and propagation speed in the presence of KCOs were made using their corresponding pD₂ values (the negative log of EC₅₀). All KCOs caused concentration-dependent reductions in the rate of beating and propagation speed, with SDZ being the most potent. In addition to the signal shapes, rate of beating, and propagation speed, the origin of excitation and the excitation pattern inside the culture can be also extracted. The results show that the present system can differentiate the effects of different KCOs on myocytes. It might be possible to utilise the MEA as a means to classify drug action based upon a combined interpretation of the three different datasets gained from the extracellular recordings. The combination of these observations might be used as ‘drug signatures’ when profiling drugs in the future.