Nonaqueous Micro Free-Flow Electrophoresis for Continuous Separation of Reaction Mixtures in Organic Media.

The continuous separation mechanism of micro free-flow electrophoresis (µFFE) is a straightforward, suitable tool for microscale purification of reaction mixtures. However, aqueous separation buffers and organic reaction solvents limit the applicability of this promising combination. Herein, we have explored nonaqueous micro free-flow electrophoresis for this purpose and present its suitability for a continuous workup of organic reactions performed in acetonitrile. After successful nonaqueous FFE separation of organic dyes, the approach was applied to continuously recover the photocatalyst [Ru(bpy)3]2+ from a homogeneous, acetonitrile-based reaction mixture. This approach opens up possibilities for further downstream processing of purified products and is also attractive for recycling of precious catalyst species.

Electrically Switchable Monostable Actuatoric Polymer-Based Nanovalve Arrays with a Long-Term Stability.

Here we present a novel electrically switchable nanovalve array based on an intrinsic conductive polymer that has the capabilities to change its volume depending on its redox state. The polymer is created by anodic deposition of a sodium dodecylbenzenesulfonate (DBS)-doped polypyrrole (PPy). Optimization of the DBS-doped PPy layers revealed an actuatoric performance of up to 10% out of plane volume change. More interestingly, the electrochemical characterization revealed an actuatoric monostable polymer that could be used to fabricate nanovalve arrays that have a native opened state when no potential is applied and that can be closed when a reductive potential is applied. As a proof of concept, Atto488-labeled biotin (Biotin-Atto488) was used as a model compound and defined nanovalve arrays with nanopores in the range of 10 nm in diameter (opened state) were fabricated. Afterward, we were able to successfully prove the functionality of our nanovalve array by monitoring the flow-through rates of the Biotin-Atto488. More strikingly, we could demonstrate for the first time the robust and long-term stability of our nanovalve array without any performance loss for at least 72 h and retention capabilities of up to 90%. Furthermore, the demonstrated long-term stability was achieved under biocompatible conditions without the need of toxic dopant supplementation of the flow-through solution. Thus, our novel functional long-term stable nanovalve array offers the capabilities for practical applications.

Large-Ring Cyclodextrins as Chiral Selectors for Enantiomeric Pharmaceuticals.

Large-ring cyclodextrins (CD) are cyclic glucans composed of 9 or more α-1,4-linked glucose units. They are minor side products of bacterial glucanotransferases (CGTases, EC 2.4.1.19) and have previously been available only in very small amounts for studies of their properties in supramolecular complex formation reactions. We engineered a CGTase to synthesize mainly large-ring CD facilitating their preparation in larger amounts. By reversed phase chromatography, we obtained single CD samples composed of 10 to 12 glucose units (CD10, CD11, and CD12) with a purity of >90 %. Their identity was confirmed by high resolution mass spectrometry and fragmentation analysis. We demonstrated the non-toxicity of CD10-CD12 for human cell lines by a cell proliferation assay and impedimetric monitoring. We then showed that CD10 and CD11 are efficient chiral selectors for the capillary electrophoretic separation of the enantiomeric pharmaceuticals fluvastatin, mefloquine, carvedilol, and primaquine.

Continuous purification of reaction products by micro free-flow electrophoresis enabled by large area deep-UV fluorescence imaging.

Microreactors have gained increasing attention in their application toward continuous micro flow synthesis. An unsolved problem of continuous flow synthesis is the lack of techniques for continuous product purification. Herein, we present a micro free-flow electrophoresis device and accompanying setup that enables the continuous separation and purification of unlabeled organic synthesis products. The system is applied to the separation and purification of triarylmethanes. For imaging of the unlabeled analytes on-chip a novel setup for large area (3.6 cm2) deep ultra violet excitation fluorescence detection was developed. Suitable separation conditions based on low conductivity electrophoresis buffers were devised to purify the product. With the optimized conditions, starting materials and product of the synthesis were well separated (R > 1.2). The separation was found to be very stable with relative standard deviations of the peak positions smaller than 3.5% over 15 min. The stable conditions enabled collection of the separated compounds, and purity of the product fraction was confirmed using capillary electrophoresis and mass spectrometry. This result demonstrates the great potential of free-flow electrophoresis as a technique for product purification or continuous clean-up in flow synthesis. Graphical Abstract Micro free-flow electrophoresis (µFFE) allows continuous separation and purification of small organic synthesis products. Enabled by a novel deep-UV imaging setup starting materials and product of a recently developed synthesis for triarylmethanes could be purified. Thereby demonstrating the potential of µFFE as continuous purification technique for micro flow synthesis.

Microfluidic Free-Flow Electrophoresis Based Solvent Exchanger for Continuously Operating Lab-on-Chip Applications.

For miniaturization and integration of chemical synthesis and analytics on small length scales, the development of complex lab-on-chip (LOC) systems is in the focus of many current research projects. While application specific synthesis and analytic modules and LOC devices are widely described, the combination and integration of different modules is intensively investigated. Problems for in-line processes such as solvent incompatibilities, e.g., for a multistep synthesis or the combination of an organic drug synthesis with a cell-based biological activity testing system, require a solvent exchange between serialized modules. Here, we present a continuously operating microfluidic solvent exchanger based on the principle of free-flow electrophoresis for miscible organic/aqueous fluids. We highlight a proof-of-principle and describe the working principle for the model compound fluorescein, where the organic solvent DMSO is exchanged against an aqueous buffer. The DMSO removal performance could be significantly increased to 95% by optimization of the microfluidic layout. Moreover, the optimization of the inlet flow ratio resulted in a minimized dilution factor of 5, and we were able to demonstrate that a reduction of the supporting instrumentation is possible without a significant decrease of the DMSO removal performance. Finally, the compatibility of the developed solvent exchanger for cell based downstream applications was proven. The impedimetric monitoring of HEK293A cells in a continuously operating microfluidic setup revealed no adverse effects of the residual DMSO after the solvent replacement. Our solvent exchanger device demonstrates the power of micro-free-flow electrophoresis not only as a powerful technique for separation and purification of compound mixtures but also for solvent replacement.

In vitro field potential monitoring on a multi-microelectrode array for the electrophysiological long-term screening of neural stem cell maturation.

Due to the lack of appropriate cell models as well as automated electrophysiology monitoring technologies, the standardized identification of neurotoxic or protective effects in vitro remains a major problem in today's pharmaceutical ingredient development. Over the past few years, in vivo-like human pluripotent stem cell-derived neuronal networks have turned out to be a promising physiological cell source, if the establishment of robust and time-saving functional maturation strategies based on stable and expandable neural progenitor populations can be achieved. Here, we describe a multi-microelectrode array (MMEA)-based bioelectronics platform that was optimized for long-term electrophysiological activity monitoring of neuronal networks via field potential measurements. Differentiation of small molecule-based neuronal progenitors on MMEAs led to functional neurons within 15 days. More strikingly, these functional neuronal cultures could remain electrophysiologically stable on the MMEAs for more than four weeks. The observed electrophysiological properties correlated with the expression of typical neuron subtype markers and were further validated by specific neurotransmitter applications. With our established monitoring platform, we could show for the first time the long-term stability of the neural stem cell-like progenitor population to differentiate to electrophysiologically active dopaminergic neuronal networks for more than 80 passages. In conclusion, we provide a comprehensive long-term stable field potential monitoring platform based on stem cell-derived human neuronal networks that can be automated and up-scaled for standardized high-content screening applications e.g. in the field of neurotoxic and neuroprotective therapeutics identification.

Peptide-Mediated Specific Immobilization of Catalytically Active Cytochrome P450 BM3 Variant.

Cytochrome P450 BM3 (CYP102A1) from Bacillus megaterium is an interesting target for biotechnological applications, because of its vast substrate variety combined with high P450 monooxygenase activity. The low stability in vitro could be overcome by immobilization on surfaces. Here we describe a novel method for immobilization on metal surfaces by using selectively binding peptides. A P450 BM3 triple mutant (3M-P450BM3: A74G, F87V, L188Q) was purified as protein thioester and ligated to indium tin oxide or gold binding peptides (BP) named HighSP-BP and Cys-BP, respectively. The ligation products were characterized by Western Blot and tryptic digestion combined with mass spectrometry, and displayed high affinity binding on the depicted surfaces. Next, we could demonstrate by benzyloxyresorufin O-dealkylation assay (BROD assay) that the activity of immobilized ligation products is higher than for the soluble form. The study provides a new tool for selective modification and immobilization of P450 variants.

Quantitative characterization of capsaicin-induced TRPV1 ion channel activation in HEK293 cells by impedance spectroscopy.

The analysis of receptor activity, especially in its native cellular environment, has always been of great interest to evaluate its intrinsic but also downstream biological activity. An important group of cellular receptors are ion channels. Since they are involved in a broad range of crucial cell functions, they represent important therapeutic targets. Thus, novel analytical techniques for the quantitative monitoring and screening of biological receptor activity are of great interest. In this context, we developed an impedance spectroscopy-based label-free and non-invasive monitoring system that enabled us to analyze the activation of the transient receptor potential channel Vanilloid 1 (TRPV1) in detail. TRPV1 channel activation by capsaicin resulted in a reproducible impedance decrease. Moreover, concentration response curves with an EC50 value of 0.9 µM could be determined. Control experiments with non TRPV1 channel expressing HEK cells as well as experiments with the TRPV1 channel blocker ruthenium red validated the specificity of the observed impedance decrease. More strikingly, through correlative studies with a cytoskeleton restructuring inhibitor mixture and equivalent circuit analysis of the acquired impedance spectra, we could quantitatively discriminate between the direct TRPV1 channel activation and downstream-induced biological effects. In summary, we developed a quantitative impedimetric monitoring system for the analysis of TRPV1 channel activity as well as downstream-induced biological activity in living cells. It has the capabilities to identify novel ion channel activators as well as inhibitors for the TRPV1 channel but could also easily be applied to other ion channel-based receptors.

Novel Multiparametric Bioelectronic Measurement System for Monitoring Virus-Induced Alterations in Functional Neuronal Networks.

Development and optimisation of bioelectronic monitoring techniques like microelectrode array-based field potential measurement and impedance spectroscopy for the functional, label-free and non-invasive monitoring of in vitro neuronal networks is widely investigated in the field of biosensors. Thus, these techniques were individually used to demonstrate the capabilities of, e.g., detecting compound-induced toxicity in neuronal culture models. In contrast, extended application for investigating the effects of central nervous system infecting viruses are rarely described. In this context, we wanted to analyse the effect of herpesviruses on functional neuronal networks. Therefore, we developed a unique hybrid bioelectronic monitoring platform that allows for performing field potential monitoring and impedance spectroscopy on the same microelectrode. In the first step, a neuronal culture model based on primary hippocampal cells from neonatal rats was established with reproducible and stable synchronised electrophysiological network activity after 21 days of cultivation on microelectrode arrays. For a proof of concept, the pseudorabies model virus PrV Kaplan-ΔgG-GFP was applied and the effect on the neuronal networks was monitored by impedance spectroscopy and field potential measurement for 72 h in a multiparametric mode. Analysis of several bioelectronic parameters revealed a virus concentration-dependent degeneration of the neuronal network within 24-48 h, with a significant early change in electrophysiological activity, subsequently leading to a loss of activity and network synchronicity. In conclusion, we successfully developed a microelectrode array-based hybrid bioelectronic measurement platform for quantitative monitoring of pathologic effects of a herpesvirus on electrophysiological active neuronal networks.

Multielectrode biosensor chip for spatial resolution screening of 3D cell models based on microcavity arrays.

Three-dimensional cell models represent the native in vivo situation more closely than two-dimensional cultures and are therefore preferred today for in vitro studies. In this context, there is a great demand for fast, non-invasive, real-time, and label-free methods that are capable for detailed analyses of three-dimensional cultures. To characterize heterogeneous cultures or to detect localized drug effects, a measurement method such as impedance spectroscopy in combination with microcavity arrays (MCAs) is desirable, which additionally offers spatial resolution. To overcome these limitations of the previously described MCA based on opaque silicon substrates and a square shape with four measurement electrodes imposed by the crystal structure, we used the selective laser etching (SLE) method to fabricate microcavities in fused silica and borosilicate glass without geometric constraints. We successfully developed MCAs with variable base including up to eight measurement electrodes in one cavity, which allows the increase in the number of electrode combinations to improve spatial resolution. In addition, we integrated a central cone electrode at the cavity bottom to extend the spatial resolution on the z-axis. To demonstrate the capability of the MCAs, we used MDA-HB-231 spheroids with an enclosed glass sphere to show that the heterogeneity of the model is evident in the relative impedance spectra. Analyses on various cell spheroids highlight the broad applicability of glass MCAs. In conclusion, our SLE-fabricated MCA clearly improve bioelectronic analyses of cellular changes in heterogeneous 3D models. Thus, bioelectronic analysis of electrophysiologically active cells and tumor biopsy samples could significantly benefit from our development.

Novel PMMA based 96-well microelectrode arrays for bioelectronic high throughput monitoring of cells in a live mode.

Microelectrode arrays (MEA) are widely used for bioelectronic monitoring of alterations in cells and tissues. MEAs are based on a substrate that is structured with electrodes and conducting paths. While cheap substrates like printed circuit board materials offers easy production and flexible contacting, there are limitations regarding microstructure resolution, optical transparency and biocompatibility. In contrast, glass substrates are favored due to its biocompatibility, chemical resistance and optical transparency. Drawbacks are high substrate costs and limited flexibility for routing of conducting paths. To overcome these limitations, we wanted to use optical transparent polymer-based substrates. Therefore, we identified the polymer poly-methyl-methacrylate (PMMA) as a promising substrate material, due to its good optical and mechanical properties as well as biocompatibility. To achieve sufficient chemical resistance for high resolution photolithographic structuring a novel process had to be developed involving a protection coating. After optimization of the structuring process, we achieved a comparable resolution and thus, microelectrodes with diameter of less than 100 µm. Moreover, the use of PMMA allowed the simple integration of more than 400 vias directly into the substrate for contacting of the microelectrode array from the bottom without the need of complex and error prone redirecting adapters with hundreds of additional bonding sides. In order to show that the PMMA based MEA is comparable to glass based MEA in terms of signal quality and sensitivity as well as optical and surface properties, we cultivated different cell models on the MEAs and validated our 96-well PMMA MEAs by different bioelectronic monitoring techniques.

Integration of Impedimetric Sensors for In Situ Electrochemical Impedance Spectroscopy in Free-Flow Electrophoresis Applications in Lab-on-Chip Systems.

Miniaturization and integration of chemical reactions into fluidic systems in combination with product purification or buffer exchange can reduce the amount of solvents and reactants required while increasing synthesis efficiency. A critical step is the regulation of flow rates to realize optimal synthesis conditions and high purification rates, so real-time, label-free monitoring is required in methods such as free-flow electrophoresis. Optical detection methods are widely used, but they often have complex excitation and detection setups that are disadvantageous for point-of-care applications. The method we have chosen is electrochemical impedance spectroscopy for detecting charged compounds in aqueous buffers with low ionic strength. Propranolol was selected for proof of concept and was separated from the organic solvent and the precursor oxirane by free-flow electrophoresis. For this purpose, electrode structures were fabricated in microfluidic channels by photolithographic lift-off technique and optimized in terms of positioning, electrode size and distance for sensitive detection, and quantification of propranolol in the nanomolar range. It is also noteworthy that the organic solvent dimethyl sulfoxide (DMSO) could be detected and quantified by an increased impedance magnitude. Subsequently, the optimized interdigital electrode structures were integrated into the outlet channels of the electrophoretic separation chamber to monitor the various outgoing fluidic streams and provide in-line control of the fluidic flows for the purification step. In conclusion, we can provide a microfluidic chip to monitor the separation efficiency of a substance mixture during free-flow electrophoresis without the need of complex analytical techniques using electrochemical impedance spectroscopy.

Reactive Sputtered Silicon Nitride as an Alternative Passivation Layer for Microelectrode Arrays in Sensitive Bioimpedimetric Cell Monitoring.

Microelectrode arrays (MEAs) are widely used to study the behavior of cells noninvasively and in real time. While the design of MEAs focuses mainly on the electrode material or its application-dependent modification, the passivation layer, which is crucial to define the electrode area and to insulate the conducting paths, remains largely unnoticed. Because often most cells are in direct contact with the passivation layer rather than the electrode material, biocompatible photoresists such as SU-8 are almost exclusively used. However, SU-8 is not without limitations in terms of optical transmission, optimal cell support, or compatibility within polymer-based microfluidic lab on chip systems. Here, we established a silicon nitride (SiN) passivation by physical vapor deposition (PVD), which was optimized and evaluated for impedance spectroscopy-based monitoring of cells. Surface characteristics, biocompatibility, and electrical insulation capability were investigated and compared to SU8 in detail. To investigate the influence of the SiN passivation on the impedimetric analysis of cells, HEK-293 A and MCF-7 were chosen as adherent cell models and measured on microelectrodes of 50-200 µm in diameter. The results clearly revealed an overall suitability of SiN as alternative passivation. While for the smallest electrode size a cell line dependent comparable or slightly decreased cell signal could be observed in comparison with SU-8, a significant higher cell signal was observed for microelectrodes larger than 50 µm in diameter. Furthermore, a high suitability for the bonding of PEGDA and PDMS microfluidic structures on the SiN passivation layer without any leakage could be demonstrated.

Real-time monitoring of relaxation and contractility of smooth muscle cells on a novel biohybrid chip.

Cardiovascular diseases represent the most common cause of death in industrialized countries. In this context vascular smooth muscle cells (SMCs) are a major key player that is involved in pathological processes like hypertension and atherosclerosis. Therefore the pharmaceutical industry is intensively investigated in developing non-destructive and label-free monitoring techniques for a quantitative detection of SMC characteristics in the field of active pharmaceutical development as well as clinical diagnostics. Hence, we developed a novel multiwell interdigital electrode sensor-array in standardized ANSI 96-well layout. Through optimization of electrode geometry and material as well as passivation/adhesion-layer we obtained a novel biohybrid chip for the sensitive and quantitative detection of SMC contractility as well as relaxation via impedance spectroscopy. For the validation of our multiwell sensor-array we established a SMC culture model derived from primary cells that is switchable from a non-contractile pathological to a functional contractile phenotype. Using the reference compounds acetylcholine (ACh) and amlodipine, we could quantify SMC contraction by an impedance decrease to 40% while SMC relaxation was detectable by an impedance increase to 110%. More strikingly we could monitor aging of the isolated SMC which arose by an attenuated contractility over successive passaging. Demonstrating the performance of our self-developed multiwell sensor-array based impedance measurement setup we provide a suitable sensor-array coupled cell model to study the mechanisms that activated SMCs undergo in response to inflammatory mediators or vessel injury.

Biosensing and drug delivery at the microscale : novel devices for controlled and responsive drug delivery.

An overall objective of pharmaceutical research is the controlled release or delivery of drugs at the biological target site in a therapeutically and pharmacodynamically optimal amount. In relation to "intelligent" drug delivery, several basic aspects are important, i.e., release of active pharmaceutical ingredients from the formulation, transport to and penetration across biological barriers, and subsequent biotransformation depending on a controlled release process. Future development of advanced and/or controlled drug releasing systems, e.g. polymeric or particulate drug targeting systems, nano-carbon tube related and/or nano-pillar based drug release, or electronically mediated molecule delivery, is expected to take advantage of progress in molecular cell biology, cell and tissue engineering, membrane nano-biophysics, and bioelectronic properties (Bramstedt et al. 2005; Gardner et al. 2006). In this chapter novel aspects of the development of innovative drug delivery systems described and are categorized into polymeric, lipid-based or electronically mediated delivery systems (De la Heras et al. 2004).

Spheroids of granulosa cells provide an in vitro model for programmed cell death coupled to steroidogenesis.

UNLABELLED: We describe the use of rotary cultures (72 rpm) as an excellent method for generating spheroids from dispersed bovine granulosa cells (GC). The GC spheroids were symmetrical (diameter between 100 and 200 microm), easily accessible, and could be obtained at high yields. On day one, the spheroids showed a two-layered outer zone of cells that stained lighter than the inner zone in semi-thin sections. Bromodeoxyuridine (BrdU) uptake was frequent and randomly distributed. By day two, a striking decrease in BrdU uptake was noted. Apoptotic bodies appeared up to day four, as did TUNEL and propidium iodide labelled dead cells. At that time, the inner zone contained cells with large-sized vacuoles and the core was amorphous. The large-sized vacuoles were identified at the ultrastructural level and represented autophagosomes and autophagolysosomes that were in different stages of development. Surprisingly, conspicuous signs of cell death were accompanied by an increase in spontaneous luteinization compared to conventional stationary cultures. We detected high levels of progesterone (immunoassay) accompanied by high levels of the proteins and enzymes relevant for steroidogenesis (StAR, P450scc, 3beta-HSD by immunoblot and immunohistochemistry, respectively). CONCLUSIONS: Concomitant to cell death, GC spheroids augment progesterone synthesis. The GC spheroids provide an ideal model for studying steroidogenesis coupled to programmed cell death at the level of the mitochondria.

Advanced 96-microtiter plate based bioelectrochemical platform reveals molecular short cut of electron flow in cytochrome P450 enzyme.

In bioelectrocatalysis, immobilised redox enzymes are activated in a bioelectronic interface without redox equivalents such as NADPH, thus enabling heterogeneous flow chemistry. The functional contact between enzyme and electrode requires a high degree of optimisation regarding choice of electrode material, electrode pre-treatment, enzyme immobilisation and reaction conditions. So far, however, there are no systems that can easily enable an optimisation procedure at a higher throughput. Here, we present an advanced platform with a vertical divided cell architecture in conjunction with a developed 96-multipotentiostat to be able to drive redox enzymes in 96 well microtiter plate based multielectrode arrays. This platform controls 96 independent three-electrode setups with arbitrary working electrode materials. We demonstrate its applicability in a mutation study of cytochrome P450 BM3 using indium tin oxide as electrode material and the 7-ethoxycoumarin product quantification assay. We show that the bioelectrocatalytic activity of P450 BM3 can be amplified when the cofactor FAD is erased from the enzyme by a single point mutation, so that FMN becomes the first electron entry point. Bioelectrocatalysis thus offers an approach to enzyme simplification as a remedy for the inherent instability of self-sufficient cytochrome P450 enzymes. In addition, we examined native and artificial enzyme activation with respect to ionic strength and buffer composition. The optimal conditions of the activation types differ substantially from each other and exhibit a new molecular facet in enzyme characteristics. In a proof-of-principle we demonstrate that the platform is also compatible with raw cell extracts, thus opening the door for random mutagenesis screenings.

Multifunctional coatings combining bioactive peptides and affinity-based cytokine delivery for enhanced integration of degradable vascular grafts.

Insufficient endothelialization of cardiovascular devices is a high-risk factor for implant failure. Presentation of extracellular matrix (ECM)-derived coatings is a well-known strategy to improve implant integration. However, the complexity of the system is challenging and strategies for applying multifunctionality are required. Here, we engineered mussel-derived surface-binding peptides equipped with integrin (c[RGDfK]) and proteoglycan binding sites (FHRRIKA) for enhanced endothelialization. Surface-binding properties of the platform containing l-3,4-dihydroxyphenylalanine (DOPA) residues were confirmed for hydrophilized polycaprolactone-co-lactide scaffolds as well as for glass and polystyrene. Further, heparin and the heparin-binding angiogenic factors VEGF, FGF-2 and CXCL12 were immobilized onto the peptide in a modular assembly. Presentation of bioactive peptides greatly enhanced human umbilical vein endothelial cell (HUVEC) adhesion and survival under static and fluidic conditions. In subsequent investigations, peptide-heparin-complexes loaded with CXCL12 or VEGF had an additional increasing effect on cell viability, differentiation and migration. Finally, hemocompatibility of the coatings was ensured. This study demonstrates that coatings combining adhesion peptides, glycosaminoglycans and modulators are a versatile tool to convey ECM-inspired multifunctionality to biomaterials and efficiently promote their integration.

An impedimetric microelectrode-based array sensor for label-free detection of tau hyperphosphorylation in human cells.

Tauopathies such as Alzheimer's disease (AD) belong to the group of neurodegenerative diseases that are characterised by hyperphosphorylation of the protein tau. Hyperphosphorylation of tau is one of the salient events leading to neuronal cytotoxicity and cognitive impairments. In this context, inhibition of tau hyperphosphorylation by specific tau kinase inhibitors can provide an excellent drug target for the treatment of AD and other tau-related neurodegenerative diseases. To improve the identification, optimisation and validation during the high-cost hit-to-lead cycle of AD drugs, we established a fast and sensitive label-free technique for testing the efficacy of tau kinase inhibitors in vitro. Here, we report for the first time that microelectrode-based impedance spectroscopy can be used to detect the pathological risk potential of hyperphosphorylated tau in the human neuroblastoma cell line SH-SY5Y. Our findings provide a novel real-time recording technique for testing the efficiency of tau kinase inhibitors or other lead structures directed to tau hyperphosphorylation on differentiated SH-SY5Y cells.

FEM-based design of optical transparent indium tin oxide multielectrode arrays for multiparametric, high sensitive cell based assays.

Multielectrode array (MEA) technology is widely used for the bioelectronic monitoring of cellular alterations. In general, noble metal based MEAs are preferred e.g. for impedance spectroscopy because of their high conductivity and biocompatibility. Today's research focuses on combining different readout methods in a single measurement setup, such as sensitive electronic and optical readouts, where noble metal-based electrodes are excluded and transparent electrodes and optimized MEAs are required. In this context, we used optical transparent indium tin oxide (ITO) as electrode material. As a drawback, the decreased conductivity can lead to drastically decreased cell signals and it is hardly to predict which layout changes lead to a substantial signal increase. To overcome this limitation, we introduce an approach where equivalent circuit modelling (ECM) on reference multielectrode arrays is used to determine cell type specific electrical parameters, which then are used in finite element method (FEM) simulations to predict achievable cell signals and signal-noise-ratios (SNR) and thus use simulation to efficiently optimize multielectrode arrays. To evaluate our approach, MEAs with a wide range of electrode sizes were fabricated with ITO and gold. HEK-A cells were used to compare achievable cell signals for impedimetric monitoring. Our study revealed that especially for large ITO electrodes, the sensitivity drastically decreases. To overcome this drawback, we designed an optimized dual layer ITO MEA with gold support structures and more strikingly, successfully predict the cell signal increase by using our combined ECM and FEM simulation based approach.