A 1024-Channel CMOS Microelectrode Array With 26,400 Electrodes for Recording and Stimulation of Electrogenic Cells In Vitro.

To advance our understanding of the functioning of neuronal ensembles, systems are needed to enable simultaneous recording from a large number of individual neurons at high spatiotemporal resolution and good signal-to-noise ratio. Moreover, stimulation capability is highly desirable for investigating, for example, plasticity and learning processes. Here, we present a microelectrode array (MEA) system on a single CMOS die for in vitro recording and stimulation. The system incorporates 26,400 platinum electrodes, fabricated by in-house post-processing, over a large sensing area (3.85 × 2.10 mm2) with sub-cellular spatial resolution (pitch of 17.5 µm). Owing to an area and power efficient implementation, we were able to integrate 1024 readout channels on chip to record extracellular signals from a user-specified selection of electrodes. These channels feature noise values of 2.4 µVrms in the action-potential band (300 Hz-10 kHz) and 5.4 µVrms in the local-field-potential band (1 Hz-300 Hz), and provide programmable gain (up to 78 dB) to accommodate various biological preparations. Amplified and filtered signals are digitized by 10 bit parallel single-slope ADCs at 20 kSamples/s. The system also includes 32 stimulation units, which can elicit neural spikes through either current or voltage pulses. The chip consumes only 75 mW in total, which obviates the need of active cooling even for sensitive cell cultures.

Characterization of a microfluidic dispensing system for localised stimulation of cellular networks.

We present a 3-D microfluidic device designed for localized drug delivery to cellular networks. The device features a flow cell comprising a main channel for nutrient delivery as well as multiple channels for drug delivery. This device is one key component of a larger, fully integrated system now under development, based upon a microelectrode array (MEA) with on-chip CMOS circuitry for recording and stimulation of electrogenic cells (e.g. neurons, cardiomyocytes). As a critical system unit, the microfluidics must be carefully designed and characterized to ensure that candidate drugs are delivered to specific regions of the culture at known concentrations. Furthermore, microfluidic design and functionality is dictated by the size, geometry, and material/electrical characteristics of the CMOS MEA. Therefore, this paper reports on the design considerations and fabrication of the flow cell, including theoretical and experimental analysis of the mass transfer properties of the nutrient and drug flows, which are in good agreement with one another. To demonstrate proof of concept, the flow cell was mounted on a dummy CMOS chip, which had been plated with HL-1 cardiomyocytes. A test chemical compound was delivered to the cell culture in a spatially resolved manner. Envisioned applications of this stand-alone system include simultaneous toxicological testing of multiple compounds and chemical stimulation of natural neural networks for neuroscience investigations.

Characterization of subcellular morphology of single yeast cells using high frequency microfluidic impedance cytometer.

Single-cell impedance cytometry is an electrical analysis method, which has been used to count and discriminate cells on the basis of their dielectric properties. The method has several advantages, such as being label free and requiring minimal sample preparation. So far, however, it has been limited to measuring cell properties that are visible at low frequencies, such as size and membrane capacitance. We demonstrate a microfluidic single cell impedance cytometer capable of dielectric characterization of single cells at frequencies up to 500 MHz. This device features a more than ten-fold increased frequency range compared to other devices and enables the study of both low and high frequency dielectric properties in parallel. The increased frequency range potentially allows for characterization of subcellular features in addition to the properties that are visible at lower frequencies. The capabilities of the cytometer are demonstrated by discriminating wild-type yeast from a mutant, which differs in size and distribution of vacuoles in the intracellular fluid. This discrimination is based on the differences in dielectric properties at frequencies around 250 MHz. The results are compared to a 3D finite-element model of the microfluidic channel accommodating either a wild-type or a mutant yeast cell. The model is used to derive quantitative values to characterize the dielectric properties of the cells.

Resonance-enhanced microfluidic impedance cytometer for detection of single bacteria.

This paper reports on a novel impedance-based cytometer, which can detect and characterize sub-micrometer particles and cells passing through a microfluidic channel. The cytometer incorporates a resonator, which is constructed by means of a discrete inductor in series with the measurement electrodes in the microfluidic channel. The use of a resonator increases the sensitivity of the system in comparison to state-of-the-art devices. We demonstrate the functionality and sensitivity of the cytometer by discriminating E. coli and B. subtilis from beads of similar sizes by means of the resonance-enhanced phase shift of the current through the microfluidic channel. The phase shift can be correlated to size and dielectric properties of the measured objects.

Multisite monitoring of choline using biosensor microprobe arrays in combination with CMOS circuitry.

A miniature device enabling parallel in vivo detection of the neurotransmitter choline in multiple brain regions of freely behaving rodents is presented. This is achieved by combining a biosensor microprobe array with a custom-developed CMOS chip. Each silicon microprobe comprises multiple platinum electrodes that are coated with an enzymatic membrane and a permselective layer for selective detection of choline. The biosensors, based on the principle of amperometric detection, exhibit a sensitivity of 157±35 µA mM(-1) cm(-2), a limit of detection of below 1 µM, and a response time in the range of 1 s. With on-chip digitalization and multiplexing, parallel recordings can be performed at a high signal-to-noise ratio with minimal space requirements and with substantial reduction of external signal interference. The layout of the integrated circuitry allows for versatile configuration of the current range and can, therefore, also be used for functionalization of the electrodes before use. The result is a compact, highly integrated system, very convenient for on-site measurements.

Microfluidics/CMOS orthogonal capabilities for cell biology.

The study of individual cells and cellular networks can greatly benefit from the capabilities of microfabricated devices for the stimulation and the recording of electrical cellular events. In this contribution, we describe the development of a device, which combines capabilities for both electrical and pharmacological cell stimulation, and the subsequent recording of electrical cellular activity. The device combines the unique advantages of integrated circuitry (CMOS technology) for signal processing and microfluidics for drug delivery. Both techniques are ideally suited to study electrogenic mammalian cells, because feature sizes are of the same order as the cell diameter, approximately 50 microm. Despite these attractive features, we observe a size mismatch between microfluidic devices, with bulky fluidic connections to the outside world, and highly miniaturized CMOS chips. To overcome this problem, we developed a microfluidic flow cell that accommodates a small CMOS chip. We simulated the performances of a flow cell based on a 3-D microfluidic system, and then fabricated the device to experimentally verify the nutrient delivery and localized drug delivery performance. The flow-cell has a constant nutrient flow, and six drug inlets that can individually deliver a drug to the cells. The experimental analysis of the nutrient and drug flow mass transfer properties in the flowcell are in good agreement with our simulations. For an experimental proof-of-principle, we successfully delivered, in a spatially resolved manner, a 'drug' to a culture of HL-1 cardiac myocytes.