High throughput on-chip amperometric detection of neurotransmitter release

Transfer of information between single neurons and networks is the cornerstone of the central nervous system. Many diseases are linked to the malfunction of the electrical and chemical mechanisms lying behind this communication. Parkinson’s disease, for example, is related to the deterioration of the chemical signal transduction at the synapses of dopaminergic neurons1. Due to the electroactive nature of the neurotransmitter dopamine released in these neurons, the contents of the vesicles released into the synaptic cleft can be detected by means of electrochemical techniques. State of the art monitoring of neurotransmitter release in vitro, is performed using carbon fiber electrodes on single cells2,3. This approach is particularly powerful for single-cell analysis. However, manual positioning of individual microelectrodes is labor intensive and cost-ineffective making it difficult to screen many cells simultaneously and provide enough statistically significant pharmacological data on the effects of various drugs4.We present a novel 64-channel current amplifier system consisting of a pre-amplifying headstage and a main amplifier capable of simultaneous multichannel recordings at pA level required for the detection of exocytotic events (see figure). The system allows on-chip measurement of in vitro cultures using specially developed microelectrode arrays (MEAs). Each MEA contains 4 wells with 16 microelectrodes of 6 µm diameter (see figure) allowing to screen up to three different drugs and one control in a single experiment. Cells are grown on the same chip but can be separated during the experiment to allow independent testing on identical cellular subpopulations. Results of initial experiments on pharmaceutical screening with a catecholamine-containing rat pheochromocytoma PC12 cell line and statistical data analysis are demonstrated

Towards low-cost scalable technologies for bioelectronics applications and diagnostic sensors

Quality of life in third world countries around the world is mostly dependent on the availability of food and water, sanitation, and affordable healthcare. Hence, easy access to fresh clean water and health diagnostics is crucial for leveraging these communities out of poverty. In light of these challenges, the recent decade has brought marked advances in the field of bio- and chemical sensors for detection of various infectious diseases and assessment of water quality. Investigations exploiting novel materials, such as graphene, carbon nanotubes, conductive polymers, and metal nanoparticles have shown the feasibility of miniaturization of diagnostic sensors. Furthermore, instruments for promising detection techniques such as quartz micro-balance, surface acoustic waves, and electrochemical impedance spectroscopy have been shown to be miniaturizable, truly opening the way for field-use of biosensors outside the standard lab settings. At the same time, numerous microfluidic platforms were introduced. These are crucial when handling complex fluids such as blood or urine, and generally integrating sensor into lab-on-a-chip devices. The aspect that is gaining more attention recently is the cost when trying to bring these sensors out of the lab to the market. Commercialization requires the use of scalable technologies that are easily accessible for mass production. Usually, in fundamental research, silicon or glass substrates are used, and the chips are produced in expensive clean-room facilities. Although standard clean room techniques are also scalable if produced in vast amounts, they are often too expensive to allow lower volume market entry for new products. Therefore, a lot of effort has been directed introduce low-cost technologies such as roll-to-roll printing, hot embossing, and injection molding. We have recently demonstrated a low-cost approach using simple printed devices for the electrochemical real-time detection of neurotransmitter release.1 Now we are looking forward to apply high-precision ink-jet printing for the fabrication of microelectrode-based electrochemical sensors. Various conducting materials are available for printing as ink formulations, such as gold or silver nanoparticle-based inks as well as carbon-based materials that are not readily available for most standard clean-room processes such as carbon nanotubes. Features down to approximately 20 µm, are achievable via careful adjustment of substrate surface chemistry and ink viscosity as well as surface tension. Moreover, ink-jet nanoinks can be applied to any surface, either hydrophobic or hydrophilic, owing to the availability of both water-based and hydrocarbon-based inks. We would like to utilize these unique properties and print the microelectrodes directly into the microfluidic devices. The latter also need to be produced in a cost-effective way, and preferably be roll-to-roll scalable. That is why we are testing such widespread materials as polyethylene or polycarbonate, with structures being applied via hot-embossing. We believe, that the transfer of existing sensing methods from clean-room to printing technologies will allow significant cost reduction of devices. In addition to that, availability of novel materials and substrates, only available for printing methods, will open up new sensing approaches and offer further technology development. At last, reduction of reagents used throughout the fabrication and almost waste-free processes enable sustainable manufacturing of sensing devices, the benefits of which can spread into point-of-care diagnostics and water treatment

Parallel On-Chip Analysis of Single Vesicle Neurotransmitter Release

Real-time investigations of neurotransmitter release provide a direct insight on the mechanisms involved in synaptic communication. Carbon fiber microelectrodes are state-of-the-art tools for electrochemical measurements of single vesicle neurotransmitter release. Yet, they lack high-throughput capabilities that are required for collecting robust statistically significant data across multiple samples. Here, we present a chip-based recording system enabling parallel in vitro measurements of individual neurotransmitter release events from cells, cultured directly on planar multielectrode arrays. The applicability of this cell-based platform to pharmacological screening is demonstrated by resolving minute concentration-dependent effects of the dopamine reuptake inhibitor nomifensine on recorded single-vesicle release events from PC12 cells. The experimental results, showing an increased half-time of the recorded events, are complemented by an analytical model for the verification of drug action

2D gradient formation for on-chip detection of neurotransmitter release using microfluidics

The redox-active nature of certain neurotransmitters released from cells, such as catecholamines, allows investigation of interneuronal communication by means of electrochemical methods. Many diseases of the central nervous system are linked to the malfunction of chemical mechanisms lying behind this communication. Parkinson’s disease, for example, is associated with the dysfunction in the chemical signal transduction of dopaminergic neurons. Most of such diseases develop over large timescales of months to years. As a consequence, long term in vitro studies of days to months are of special interest to find clues for the mechanisms underlying these conditions. State of the art monitoring of neurotransmitter release in vitro, is performed using carbon fiber electrodes. This approach is powerful for single-cell analysis. However, manually positioned individual microelectrodes are difficult to maintain close to the cell for more than several hours. Performing multiple experiments for statistically significant drug screening using this approach is, therefore, very labor intensive and ineffective. We present a novel 64-channel current amplifier capable of simultaneous multichannel recordings at pA level coupled to an on-chip microfluidic system for long-term cell culture under concentration gradients. The system allows development of diversified on-chip cell cultures for days or weeks upon exposure to various growth factors or chemicals with in-line recordings using microelectrode arrays (MEAs). Each MEA contains 64 microelectrodes with 6 µm diameter facilitating parallel screening in a single experiment. We demonstrate on-chip gradient formation and show preliminary results of long term neurotransmitter release recordings with a catecholamine-containing rat pheochromocytoma PC12 cell line

Stochastic On-Chip Detection of Subpicomolar Concentrations of Silver Nanoparticles

We introduce the stochastic amperometric detection of silver nanoparticles on-chip using a microelectrode array. The technique combines the advantages of parallel and low-noise recordings at individually addressable microelectrodes. We demonstrate the detection of subpicomolar concentrations of silver nanoparticles with a diameter of 10 nm at sampling rates in the kilohertz regime for each channel. By comparison to random walk simulations, we show that the sensitivity of a single measurement is mainly limited by adsorption of nanoparticles at the surface of the chips and the measurement time