A Multi-Modality CMOS Sensor Array for Cell-Based Assay and Drug Screening

Opportunities in optical and electrical single-cell technologies to study microbial ecosystems

New techniques are revolutionizing single-cell research, allowing us to study microbes at unprecedented scales and in unparalleled depth. This review highlights the state-of-the-art technologies in single-cell analysis in microbial ecology applications, with particular attention to both optical tools, i.e., specialized use of flow cytometry and Raman spectroscopy and emerging electrical techniques. The objectives of this review include showcasing the diversity of single-cell optical approaches for studying microbiological phenomena, highlighting successful applications in understanding microbial systems, discussing emerging techniques, and encouraging the combination of established and novel approaches to address research questions. The review aims to answer key questions such as how single-cell approaches have advanced our understanding of individual and interacting cells, how they have been used to study uncultured microbes, which new analysis tools will become widespread, and how they contribute to our knowledge of ecological interactions.

The next generation of hybrid microfluidic/integrated circuit chips: recent and upcoming advances in high-speed, high-throughput, and multifunctional lab-on-IC systems

Since the field's inception, pioneers in microfluidics have made significant progress towards realizing complete lab-on-chip systems capable of sophisticated sample analysis and processing. One avenue towards this goal has been to join forces with the related field of microelectronics, using integrated circuits (ICs) to perform on-chip actuation and sensing. While early demonstrations focused on using microfluidic-IC hybrid chips to miniaturize benchtop instruments, steady advancements in the field have enabled a new generation of devices that expand past miniaturization into high-performance applications that would not be possible without IC hybrid integration. In this review, we identify recent examples of labs-on-chip that use high-resolution, high-speed, and multifunctional electronic and photonic chips to expand the capabilities of conventional sample analysis. We focus on three particularly active areas: a) high-throughput integrated flow cytometers; b) large-scale microelectrode arrays for stimulation and multimodal sensing of cells over a wide field of view; c) high-speed biosensors for studying molecules with high temporal resolution. We also discuss recent advancements in IC technology, including on-chip data processing techniques and lens-free optics based on integrated photonics, that are poised to further advance microfluidic-IC hybrid chips.

A Multimodal and Multifunctional CMOS Cellular Interfacing Array for Digital Physiology and Pathology Featuring an Ultra Dense Pixel Array and Reconfigurable Sampling Rate

The article presents a fully integrated multimodal and multifunctional CMOS biosensing/actuating array chip and system for multi-dimensional cellular/tissue characterization. The CMOS chip supports up to 1,568 simultaneous parallel readout channels across 21,952 individually addressable multimodal pixels with 13 μm × 13 μm 2-D pixel pitch along with 1,568 Pt reference electrodes. These features allow the CMOS array chip to perform multimodal physiological measurements on living cell/tissue samples with both high throughput and single-cell resolution. Each pixel supports three sensing and one actuating modalities, each reconfigurable for different functionalities, in the form of full array (FA) or fast scan (FS) voltage recording schemes, bright/dim optical detection, 2-/4-point impedance sensing (ZS), and biphasic current stimulation (BCS) with adjustable stimulation area for single-cell or tissue-level stimulation. Each multi-modal pixel contains an 8.84 μm × 11 μm Pt electrode, 4.16 μm × 7.2 μm photodiode (PD), and in-pixel circuits for PD measurements and pixel selection. The chip is fabricated in a standard 130nm BiCMOS process as a proof of concept. The on-chip electrodes are constructed by unique design and in-house post-CMOS fabrication processes, including a critical Al shorting of all pixels during fabrication and Al etching after fabrication that ensures a high-yield planar electrode array on CMOS with high biocompatibility and long-term measurement reliability. For demonstration, extensive biological testing is performed with human and mouse progenitor cells, in which multidimensional biophysiological data are acquired for comprehensive cellular characterization.

Programmable Electrochemical Stimulation on a Large-Scale CMOS Microelectrode Array

In this paper we present spatio-temporally controlled electrochemical stimulation of aqueous samples using an integrated CMOS microelectrode array with 131,072 pixels. We demonstrate programmable gold electrodeposition in arbitrary spatial patterns, controllable electrolysis to produce microscale hydrogen bubbles, and spatially targeted electrochemical pH modulation. Dense spatially-addressable electrochemical stimulation is important for a wide range of bioelectronics applications.

Advances in non-invasive biosensing measures to monitor wound healing progression

Impaired wound healing is a significant financial and medical burden. The synthesis and deposition of extracellular matrix (ECM) in a new wound is a dynamic process that is constantly changing and adapting to the biochemical and biomechanical signaling from the extracellular microenvironments of the wound. This drives either a regenerative or fibrotic and scar-forming healing outcome. Disruptions in ECM deposition, structure, and composition lead to impaired healing in diseased states, such as in diabetes. Valid measures of the principal determinants of successful ECM deposition and wound healing include lack of bacterial contamination, good tissue perfusion, and reduced mechanical injury and strain. These measures are used by wound-care providers to intervene upon the healing wound to steer healing toward a more functional phenotype with improved structural integrity and healing outcomes and to prevent adverse wound developments. In this review, we discuss bioengineering advances in 1) non-invasive detection of biologic and physiologic factors of the healing wound, 2) visualizing and modeling the ECM, and 3) computational tools that efficiently evaluate the complex data acquired from the wounds based on basic science, preclinical, translational and clinical studies, that would allow us to prognosticate healing outcomes and intervene effectively. We focus on bioelectronics and biologic interfaces of the sensors and actuators for real time biosensing and actuation of the tissues. We also discuss high-resolution, advanced imaging techniques, which go beyond traditional confocal and fluorescence microscopy to visualize microscopic details of the composition of the wound matrix, linearity of collagen, and live tracking of components within the wound microenvironment. Computational modeling of the wound matrix, including partial differential equation datasets as well as machine learning models that can serve as powerful tools for physicians to guide their decision-making process are discussed.

A 26.5 pArms Neurotransmitter Front-End With Class-AB Background Subtraction

This paper presents an analog front-end (AFE) for fast-scan cyclic voltammetry (FSCV) with analog background subtraction using a pseudo-differential sensing scheme to cancel the large non-faradaic current before seeing the front-end. As a result, the AFE can be compact and low-power compared to conventional FSCV AFEs with dedicated digital back-ends to digitize and subtract the background from subsequent recordings. The reported AFE, fabricated in a 0.18- μ m CMOS process, consists of a class-AB common-mode rejection circuit, a low-input-impedance current conveyor, and a 1^st-order current-mode delta-sigma (ΔΣ) modulator with an infinite impulse response quantizer. This AFE achieves an effective dynamic range of 83 dB with a state-of-the-art 39.2 pA_rms input-referred noise when loaded with a 1 nF input capacitance (26.5 pA_rms open-circuit) across a 5 kHz bandwidth while consuming an average power of 3.7 μW. This design was tested with carbon-fiber microelectrodes scanned at 300 V/s using flow-injection of dopamine, a key neurotransmitter.

Impedance Imaging of Cells and Tissues: Design and Applications

Due to their label-free and noninvasive nature, impedance measurements have attracted increasing interest in biological research. Advances in microfabrication and integrated-circuit technology have opened a route to using large-scale microelectrode arrays for real-time, high-spatiotemporal-resolution impedance measurements of biological samples. In this review, we discuss different methods and applications of measuring impedance for cell and tissue analysis with a focus on impedance imaging with microelectrode arrays in in vitro applications. We first introduce how electrode configurations and the frequency range of the impedance analysis determine the information that can be extracted. We then delve into relevant circuit topologies that can be used to implement impedance measurements and their characteristic features, such as resolution and data-acquisition time. Afterwards, we detail design considerations for the implementation of new impedance-imaging devices. We conclude by discussing future fields of application of impedance imaging in biomedical research, in particular applications where optical imaging is not possible, such as monitoring of ex vivo tissue slices or microelectrode-based brain implants.

Multi-parametric functional imaging of cell cultures and tissues with a CMOS microelectrode array

Electrode-based impedance and electrochemical measurements can provide cell-biology information that is difficult to obtain using optical-microscopy techniques. Such electrical methods are non-invasive, label-free, and continuous, eliminating the need for fluorescence reporters and overcoming optical imaging's throughput/temporal resolution limitations. Nonetheless, electrode-based techniques have not been heavily employed because devices typically contain few electrodes per well, resulting in noisy aggregate readouts. Complementary metal-oxide-semiconductor (CMOS) microelectrode arrays (MEAs) have sometimes been used for electrophysiological measurements with thousands of electrodes per well at sub-cellular pitches, but only basic impedance mappings of cell attachment have been performed outside of electrophysiology. Here, we report on new field-based impedance mapping and electrochemical mapping/patterning techniques to expand CMOS-MEA cell-biology applications. The methods enable accurate measurement of cell attachment, growth/wound healing, cell-cell adhesion, metabolic state, and redox properties with single-cell spatial resolution (20 μm electrode pitch). These measurements allow the quantification of adhesion and metabolic differences of cells expressing oncogenes versus wild-type controls. The multi-parametric, cell-population statistics captured by the chip-scale integrated device opens up new avenues for fully electronic high-throughput live-cell assays for phenotypic screening and drug discovery applications.

An Integrated Microheater Array With Closed-Loop Temperature Regulation Based on Ferromagnetic Resonance of Magnetic Nanoparticles

Magnetic nanoparticles (MNP) can generate localized heat in response to an external alternating magnetic field, a unique capability that has enabled a wide range of biomedical applications. Compared with other heating mechanisms such as dielectric heating and ohmic heating, MNP-based magnetic heating offers superior material specificity and minimal damage to the surrounding environment since most biological systems are non-magnetic. This paper presents a first-of-its-kind fully integrated magnetic microheater array based on the ferromagnetic resonance of MNP at Gigahertz (GHz) microwave frequencies. Each microheater pixel consists of a stacked oscillator to actuate MNP with a high magnetic field intensity and an electro-thermal feedback loop for precise temperature regulation. The four-stacked/five-stacked oscillator achieves >19.5/26.5 V_pp measured RF output swing from 1.18 to 2.62 GHz while only occupying a single inductor footprint, which eliminates the need for additional RF power amplifiers for compact pixel size (0.6 mm × 0.7 mm) and high dc-to-RF energy efficiency (45%). The electro-thermal feedback loop senses the local temperature and enables closed-loop temperature regulation by controlling the biasing voltage of the stacked oscillator, achieving a measured maximum/RMS temperature error of 0.53/0.29 °C. In the localized heating demonstration, two PDMS membranes mixed with and without MNP are attached to the microheater array chip, respectively, and their surface temperatures are monitored by an infrared (IR) camera. Only the area above the inductor (∼0.03 mm²) is efficiently heated up to 43 °C for the MNP-PDMS membrane, while the baseline temperature stays <37.8 °C for the PDMS membrane without MNP.

CMOS-Based Electrokinetic Microfluidics With Multi-Modal Cellular and Bio-Molecular Sensing for End-to-End Point-of-Care System

The importance of point-of-care (POC) bio-molecular diagnostics capable of rapid analysis has become abundantly evident after the outbreak of the Covid-19 pandemic. While sensing interfaces for both protein and nucleic-acid based assays have been demonstrated with chip-scale systems, sample preparation in compact form factor has often been a major bottleneck in enabling end-to-end POC diagnostics. Miniaturization of an end-to-end system requires addressing the front-end sample processing, without which, the goal for low-cost POC diagnostics remain elusive. In this paper, we address bulk fluid processing with AC-osmotic based electrokinetic fluid flows that can be fully controlled, processed and automated by CMOS ICs, fabricated in TSMC 65 nm LP process. Here, we combine bulk fluid flow control with bio-molecular sensing, cell manipulation, cytometry, and separation-all of which are controlled with silicon chips for an all-in-one bio-sensing device. We show CMOS controlled pneumatic-free bulk fluid flow with fluid velocities reaching up to 160 μm/s within a microfluidic channel of 100 × 50 μm ² of cross-sectional area. We incorporate electrode arrays to allow precise control and focused cell flows ( ±2 μm precision) for robust cytometry, and for subsequent separation. We also incorporate a 16-element impedance spectroscopy receiver array for cell and label-free protein sensing. The massive scalability of CMOS-driven microfluidics, manipulation, and sensing can lead to a new design space and a new class of miniaturized sensing technologies.

Hardware for cell culture electrical impedance tomography: A critical review

Human cell cultures are powerful laboratory tools for biological models of diseases, drug development, and tissue engineering. However, the success of biological experiments often depends on real-time monitoring of the culture state. Conventional culture evaluation methods consist of end-point laborious techniques, not capable of real-time operation and not suitable for three-dimensional cultures. Electrical Impedance Tomography (EIT) is a non-invasive imaging technique with high potential to be used in cell culture monitoring due to its biocompatibility, non-invasiveness, high temporal resolution, compact hardware, automatic operation, and high throughput. This review approaches the different hardware strategies for cell culture EIT that are presented in the literature, discussing the main components of the measurement system: excitation circuit, voltage/current sensing, switching stage, signal specifications, electrode configurations, measurement protocols, and calibration strategies. The different approaches are qualitatively discussed and compared, and design guidelines are proposed.

Review of wearable technologies and machine learning methodologies for systematic detection of mild traumatic brain injuries

Mild traumatic brain injuries (mTBIs) are the most common type of brain injury. Timely diagnosis of mTBI is crucial in making 'go/no-go' decision in order to prevent repeated injury, avoid strenuous activities which may prolong recovery, and assure capabilities of high-level performance of the subject. If undiagnosed, mTBI may lead to various short- and long-term abnormalities, which include, but are not limited to impaired cognitive function, fatigue, depression, irritability, and headaches. Existing screening and diagnostic tools to detect acute andearly-stagemTBIs have insufficient sensitivity and specificity. This results in uncertainty in clinical decision-making regarding diagnosis and returning to activity or requiring further medical treatment. Therefore, it is important to identify relevant physiological biomarkers that can be integrated into a mutually complementary set and provide a combination of data modalities for improved on-site diagnostic sensitivity of mTBI. In recent years, the processing power, signal fidelity, and the number of recording channels and modalities of wearable healthcare devices have improved tremendously and generated an enormous amount of data. During the same period, there have been incredible advances in machine learning tools and data processing methodologies. These achievements are enabling clinicians and engineers to develop and implement multiparametric high-precision diagnostic tools for mTBI. In this review, we first assess clinical challenges in the diagnosis of acute mTBI, and then consider recording modalities and hardware implementation of various sensing technologies used to assess physiological biomarkers that may be related to mTBI. Finally, we discuss the state of the art in machine learning-based detection of mTBI and consider how a more diverse list of quantitative physiological biomarker features may improve current data-driven approaches in providing mTBI patients timely diagnosis and treatment.

An Ultra-High Frame Rate Ion Imaging Platform Using ISFET Arrays With Real-Time Compression

In this paper, a Lab-on-Chip platform with ultra-high throughput and real-time image compression for high speed ion imaging is presented. The sensing front-end comprises of a CMOS ISFET array with sensors biased in velocity saturation for a linear pH-to-current conversion and high spatial and temporal resolution. An array of 128 × 128 pixels is designed with a pixel size of 13.5 μm × 10.5 μm. In-pixel reset switches are applied for offset compensation, by asynchronously resetting the floating gate of the ISFET to a known fixed potential. Additionally, each row of pixels is processed by a current mode signal pipeline with auto zeroing functionality to remove fixed pattern noise, followed by an on-chip 1 MS/s 8-bit row-parallel single slope ADC. Fabricated in standard TSMC 180 nm BCD process, the entire system-on-chip occupies a silicon area of 2 mm × 2 mm, and achieves a frame rate of 6100 fps (7800 fps from simulation). A high speed 25 ms-latency readout platform based on a USB 3.0 interface and standard JPEG is presented for real-time ion imaging and image compression respectively, while an optimised JPEG algorithm is also designed and verified for a higher compression ratio without sacrificing image quality. We demonstrate real-time ion image visualisation by sensing high speed ion diffusion at 6100 fps, which is more than two times faster than the current state-of-the-art.

Electrophysiology Read-Out Tools for Brain-on-Chip Biotechnology

Brain-on-Chip (BoC) biotechnology is emerging as a promising tool for biomedical and pharmaceutical research applied to the neurosciences. At the convergence between lab-on-chip and cell biology, BoC couples in vitro three-dimensional brain-like systems to an engineered microfluidics platform designed to provide an in vivo-like extrinsic microenvironment with the aim of replicating tissue- or organ-level physiological functions. BoC therefore offers the advantage of an in vitro reproduction of brain structures that is more faithful to the native correlate than what is obtained with conventional cell culture techniques. As brain function ultimately results in the generation of electrical signals, electrophysiology techniques are paramount for studying brain activity in health and disease. However, as BoC is still in its infancy, the availability of combined BoC-electrophysiology platforms is still limited. Here, we summarize the available biological substrates for BoC, starting with a historical perspective. We then describe the available tools enabling BoC electrophysiology studies, detailing their fabrication process and technical features, along with their advantages and limitations. We discuss the current and future applications of BoC electrophysiology, also expanding to complementary approaches. We conclude with an evaluation of the potential translational applications and prospective technology developments.

TFT sensor array for real-time cellular characterization, stimulation, impedance measurement and optical imaging of in-vitro neural cells

Real-time in-vitro multi-modality characterization of neuronal cell ensemble involves highly complex interdependent phenomena and processes. Although a variety of microelectrode arrays (MEAs) have been reported, diagnosis techniques are limited in term of sensing area, optical transparency, resolution and number of modalities. This paper presents an optically transparent thin-film-transistor (TFT) array biosensor chip for neuronal ensemble investigation, in which TFT electrodes are used for six modalities including extracellular voltage recording of both action potential (AP) and local field potential (LFP), current or voltage stimulation, chemical stimulation, electrical impedance measurement, and optical imaging. The sensor incorporates a large sensing area (15.6 mm × 15.6 mm) with a 200 × 150 array of indium-tin-oxide (ITO) electrodes placed at a 50 μm or 100 μm pixel pitch and with 10 ms temporal resolution; these performances are comparable to the state-of-the-art MEA devices. The TFT electrode array is designed based on the switch matrix architecture. The reliability and stability of TFTs are examined by measuring their electrical characteristics. Impedance spectroscopy function is verified by mapping the neuron position and the status (cells alive or dead, contamination) on the electrodes, which facilitates the biochemical studies in electrical domain that adds quantitative views to visual observation of cells through the optical microscopy. An in-vitro neuron culture is studied using electrophysiological, electrochemical, and optical characterization. Detailed signal analysis is demonstrated to prove the capability of bioassay.

A Dual-Sensing Thermo-Chemical ISFET Array for DNA-Based Diagnostics

This paper presents a 32 × 32 ISFET array with in-pixel dual-sensing and programmability targeted for on-chip DNA amplification detection. The pixel architecture provides thermal and chemical sensing by encoding temperature and ion activity in a single output PWM, modulating its frequency and its duty cycle respectively. Each pixel is composed of an ISFET-based differential linear OTA and a 2-stage sawtooth oscillator. The operating point and characteristic response of the pixel can be programmed, enabling trapped charge compensation and enhancing the versatility and adaptability of the architecture. Fabricated in 0.18  μm standard CMOS process, the system demonstrates a quadratic thermal response and a highly linear pH sensitivity, with a trapped charge compensation scheme able to calibrate 99.5% of the pixels in the target range, achieving a homogeneous response across the array. Furthermore, the sensing scheme is robust against process variations and can operate under various supply conditions. Finally, the architecture suitability for on-chip DNA amplification detection is proven by performing Loop-mediated Isothermal Amplification (LAMP) of phage lambda DNA, obtaining a time-to-positive of 7.71 minutes with results comparable to commercial qPCR instruments. This architecture represents the first in-pixel dual thermo-chemical sensing in ISFET arrays for Lab-on-a-Chip diagnostics.

An Integrated Biosensor System With a High-Density Microelectrode Array for Real-Time Electrochemical Imaging

Electrochemical methods have been shown to be advantageous to life sciences by supporting studies and discoveries in metabolism activities, DNA analysis, and neurotransmitter signaling. Meanwhile, the integration of Microelectrode Array (MEA) and the accessibility of CMOS technology permit high-density electrochemical sensing method. This paper describes an electrochemical imaging system equipped with a custom CMOS microchip. The microchip holds a 3.6 mm × 3.6 mm sensing area containing 16,064 Pt MEA, the associated 16,064 integrated read channels, and digital control circuits. The novel three-electrode system geometry with a 27.5 μm spatial pitch enables cellular level chemical gradient imaging of bio-samples. The noise level of the on-chip read channel array allows amperometric detection of neurotransmitters such as norepinephrine (NE) with concentrations from 4 μM to 512 μM with 4.7 pA/μM sensitivity (R² = 0.98). Electrochemical response to dissolved oxygen (DO) concentration was also characterized by deoxygenated deionized water containing 5% to 80% of the ambient oxygen concentrations with 86 pA/mg/L sensitivity (R² = 0.89). The system also demonstrated selectivity to different target analytes using cyclic voltammetry method to simultaneously detect NE and uric acid. Also, a custom indium tin oxide with deposited Au glass electrode was integrated into the microfluidic system to enable pH measurement, ensuring the viability of bio-samples during experiments. Electrochemical images confirm the spatiotemporal performance at four frames per second while maintaining the sensitivity to target analytes. Finally, the overall system is controlled and continuously monitored by a MATLAB-based custom user interface, which is optimized for real-time high spatiotemporal resolution chemical imaging.

Correlation of Capacitance and Microscopy Measurements Using Image Processing for a Lab-on-CMOS Microsystem

We present a capacitance sensor chip developed in a 0.35-μm complementary metal-oxide-semiconductor process for monitoring biological cell viability and proliferation. The chip measures the cell-to-substrate binding through capacitance-to-frequency conversion with a sensitivity of 590 kHz/fF. In vitro experiments with two human ovarian cancer cell lines (CP70 and A2780) were performed and showed the ability to track cell viability in realtime over three days. An imaging platform was developed to provide time-lapse images of the sensor surface, which allowed for concurrent visual and capacitance observation of the cells. The results showed the ability to detect single-cell binding events and changes in cell morphology. Image processing was performed to estimate the cell coverage of sensor electrodes, showing good linear correlation and providing a sensor gain of 1.28 ± 0.29 aF/μm², which agrees with values reported in the literature. The device is designed for unsupervised operation with minimal packaging requirements. Only a microcontroller is required for readout, making it suitable for applications outside the traditional laboratory setting.

Spatially resolved electrical impedance methods for cell and particle characterization

Electrical impedance is an established technique used for cell and particle characterization. The temporal and spectral resolution of electrical impedance have been used to resolve basic cell characteristics like size and type, as well as to determine cell viability and activity. Such electrical impedance measurements are typically performed across the entire sample volume and can only provide an overall indication concerning the properties and state of that sample. For the study of heterogeneous structures such as cell layers, biological tissue, or polydisperse particle mixtures, an overall measured impedance value can only provide limited information and can lead to data misinterpretation. For the investigation of localized sample properties in complex heterogeneous structures/mixtures, the addition of spatial resolution to impedance measurements is necessary. Several spatially resolved impedance measurement techniques have been developed and applied to cell and particle research, including electrical impedance tomography, scanning electrochemical microscopy, and microelectrode arrays. This review provides an overview of spatially resolved impedance measurement methods and assesses their applicability for cell and particle characterization.

CMOS based whole cell impedance sensing: Challenges and future outlook

With the increasing need for multi-analyte point-of-care diagnosis devices, cell impedance measurement is a promising technique for integration with other sensing modalities. In this comprehensive review, the theory underlying cell impedance sensing, including the history, complementary metal-oxide-semiconductor (CMOS) based implementations, and applications are critically assessed. Whole cell impedance sensing, also known as electric cell-substrate impedance sensing (ECIS) or electrical impedance spectroscopy (EIS), is an approach for studying and diagnosing living cells in in-vitro and in-vivo environments. The technique is popular since it is label-free, non-invasive, and low cost when compared to standard biochemical assays. CMOS cell impedance measurement systems have been focused on expanding their applications to numerous aspects of biological, environmental, and food safety applications. This paper presents and evaluates circuit topologies for whole cell impedance measurement. The presented review compares several existing CMOS designs, including the classification, measurement speed, and sensitivity of varying topologies.

High-Density Electrical Recording and Impedance Imaging With a Multi-Modal CMOS Multi-Electrode Array Chip

Multi-electrode arrays, both active or passive, emerged as ideal technologies to unveil intricated electrophysiological dynamics of cells and tissues. Active MEAs, designed using complementary metal oxide semiconductor technology (CMOS), stand over passive devices thanks to the possibility of achieving single-cell resolution, the reduced electrode size, the reduced crosstalk and the higher functionality and portability. Nevertheless, most of the reported CMOS MEA systems mainly rely on a single operational modality, which strongly hampers the applicability range of a single device. This can be a limiting factor considering that most biological and electrophysiological dynamics are often based on the synergy of multiple and complex mechanisms acting from different angles on the same phenomena. Here, we designed a CMOS MEA chip with 16,384 titanium nitride electrodes, 6 independent operational modalities and 1,024 parallel recording channels for neuro-electrophysiological studies. Sixteen independent active areas are patterned on the chip surface forming a 4 × 4 matrix, each one including 1,024 electrodes. Electrodes of four different sizes are present on the chip surface, ranging from 2.5 × 3.5 μm² up to 11 × 11.0 μm², with 15 μm pitch. In this paper, we exploited the impedance monitoring and voltage recording modalities not only to monitor the growth and development of primary rat hippocampal neurons, but also to assess their electrophysiological activity over time showing a mean spike amplitude of 144.8 ± 84.6 μV. Fixed frequency (1 kHz) and high sampling rate (30 kHz) impedance measurements were used to evaluate the cellular adhesion and growth on the chip surface. Thanks to the high-density configuration of the electrodes, as well as their dimension and pitch, the chip can appreciate the evolutions of the cell culture morphology starting from the moment of the seeding up to mature culture conditions. The measurements were confirmed by fluorescent staining. The effect of the different electrode sizes on the spike amplitudes and noise were also discussed. The multi-modality of the presented CMOS MEA allows for the simultaneous assessment of different physiological properties of the cultured neurons. Therefore, it can pave the way both to answer complex fundamental neuroscience questions as well as to aid the current drug-development paradigm.

Electrode-Electrolyte Interface Impedance Characterization of Ultra-Miniaturized Microelectrode Arrays Over Materials and Geometries for Sub-Cellular and Cellular Sensing and Stimulation

Electrochemical interfaces with low-impedance, high biocompatibility, and long-term stability are of paramount importance for microelectrode arrays (MEAs), that are widely used in numerous cellular sensing/stimulation applications, e.g., brain interface, electroceuticals, neuroprosthetics, drug discovery, chemical screening, and fundamental biological research. It is becoming increasingly critical since sensing/actuations at sub-cellular resolution necessitate ultra-miniaturized electrodes, which exhibit exacerbated electrochemical interfaces, especially on interfacial impedance. This paper reports the first comprehensive characterization and interfacial electrochemical impedance spectroscopy (EIS) of the ultra-miniaturized electrodes for different electrode sizes ( 8×8 μm² , 16×16 μm² , and 32×32 μm² ) and a wide material collection (Au, Pt, TiN, and ITO). Equivalent electrochemical interfacial circuit models with interface capacitance, charge transfer resistance, and solution resistance are obtained for all the electrode designs based on their EIS measurements. The results can potentially guide the designs of ultra-miniaturized MEAs for future bioelectronics systems.

Impedance Spectroscopy and Electrophysiological Imaging of Cells With a High-Density CMOS Microelectrode Array System

A monolithic multi-functional CMOS microelectrode array system was developed that enables label-free electrochemical impedance spectroscopy of cells in vitro at high spatiotemporal resolution. The electrode array includes 59,760 platinum microelectrodes, densely packed within a 4.5 mm × 2.5 mm sensing region at a pitch of 13.5 μm. A total of 32 on-chip lock-in amplifiers can be used to measure the impedance of any arbitrarily chosen subset of electrodes in the array. A sinusoidal voltage, generated by an on-chip waveform generator with a frequency range from 1 Hz to 1 MHz, was applied to the reference electrode. The sensing currents through the selected recording electrodes were amplified, demodulated, filtered, and digitized to obtain the magnitude and phase information of the respective impedances. The circuitry consumes only 412 μW at 3.3 V supply voltage and occupies only 0.1 mm2, for each channel. The system also included 2048 extracellular action-potential recording channels on the same chip. Proof of concept measurements of electrical impedance imaging and electrophysiology recording of cardiac cells and brain slices are demonstrated in this paper. Optical and impedance images showed a strong correlation.

Multi-parametric cell profiling with a CMOS quad-modality cellular interfacing array for label-free fully automated drug screening

Cells are complex systems with concurrent multi-physical responses, and cell physiological signals are often encoded with spatiotemporal dynamics and further coupled with multiple cellular activities. However, most existing electronic sensors are only single-modality and cannot capture multi-parametric cellular responses. In this paper, a 1024-pixel CMOS quad-modality cellular interfacing array that enables multi-parametric cell profiling for drug development is presented. The quad-modality CMOS array features cellular impedance characterization, optical detection, extracellular potential recording, and biphasic current stimulation. The fibroblast transparency and surface adhesion are jointly monitored by cellular impedance and optical sensing modalities for comprehensive cell growth evaluation. Simultaneous current stimulation and opto-mechanical monitoring based on cardiomyocytes are demonstrated without any stimulation/sensing dead-zone. Furthermore, drug dose-dependent multi-parametric feature extractions in cardiomyocytes from their extracellular potentials and opto-mechanical signals are presented. The CMOS array demonstrates great potential for fully automated drug screening and drug safety assessments, which may substantially reduce the drug screening time and cost in future new drug development.

1024-Pixel CMOS Multimodality Joint Cellular Sensor/Stimulator Array for Real-Time Holistic Cellular Characterization and Cell-Based Drug Screening

This paper presents a fully integrated CMOS multimodality joint sensor/stimulator array with 1024 pixels for real-time holistic cellular characterization and drug screening. The proposed system consists of four pixel groups and four parallel signal-conditioning blocks. Every pixel group contains 16 × 16 pixels, and each pixel includes one gold-plated electrode, four photodiodes, and in-pixel circuits, within a pixel footprint. Each pixel supports real-time extracellular potential recording, optical detection, charge-balanced biphasic current stimulation, and cellular impedance measurement for the same cellular sample. The proposed system is fabricated in a standard 130-nm CMOS process. Rat cardiomyocytes are successfully cultured on-chip. Measured high-resolution optical opacity images, extracellular potential recordings, biphasic current stimulations, and cellular impedance images demonstrate the unique advantages of the system for holistic cell characterization and drug screening. Furthermore, this paper demonstrates the use of optical detection on the on-chip cultured cardiomyocytes to real-time track their cyclic beating pattern and beating rate.

A Surface Acoustic Wave Pumped Lensless Microfluidic Imaging System for Flowing Cell Detection and Counting

The future point-of-care diagnostics requires miniaturizing the existing bulky and expensive bioanalysis instruments, where lab-on-CMOS-chip-based technology can provide a promising solution. In this paper, we presented a surface acoustic wave (SAW) pumped lensless microfluidic imaging system for flowing cell detection and counting. Different from the previous lensless systems, which employ external bulky syringe pump for cell driven, the developed system directly integrates the SAW pump on the CMOS image sensor chip to drive the cell-containing microfluid. Moreover, an efficient temporal-differencing-based motion detection algorithm is proposed for continuous flowing cell detection and counting. Experimental results show that the SAW pump can drive the cells to flow at different driven powers, and also can keep the channel temperature below 40 °C so as not to harm the cells. The human bone marrow stromal cells flowing in the microfluidic channel can be automatically detected and counted with a low statistical error rate of -6.53%. The developed system thereby is competitive for point-of-care cell detection and counting application.

A Microfluidic Cytometer for Complete Blood Count With a 3.2-Megapixel, 1.1- μm-Pitch Super-Resolution Image Sensor in 65-nm BSI CMOS

Based on a 3.2-Megapixel 1.1- μm-pitch super-resolution (SR) CMOS image sensor in a 65-nm backside-illumination process, a lens-free microfluidic cytometer for complete blood count (CBC) is demonstrated in this paper. Backside-illumination improves resolution and contrast at the device level with elimination of surface treatment when integrated with microfluidic channels. A single-frame machine-learning-based SR processing is further realized at system level for resolution correction with minimum hardware resources. The demonstrated microfluidic cytometer can detect the platelet cells (< 2 μm) required in CBC, hence is promising for point-of-care diagnostics.

High-Density Mapping of Brain Slices using a Large Multi-Functional High-Density CMOS Microelectrode Array System

We present a CMOS-based high-density microelectrode array (HD-MEA) system that enables high-density mapping of brain slices in-vitro with multiple readout modalities. The 4.48×2.43 mm2 array consists of 59,760 micro-electrodes at 13.5 µm pitch (5487 electrodes/mm2). The overall system features 2048 action-potential, 32 local-field-potential and 32 current recording channels, 32 impedance-measurement and 28 neurotransmitter-detection channels and 16 voltage/current stimulation channels. The system enables real-time and label-free monitoring of position, size, morphology and electrical activity of brain slices.

A Multi-Functional Microelectrode Array Featuring 59760 Electrodes, 2048 Electrophysiology Channels, Stimulation, Impedance Measurement and Neurotransmitter Detection Channels

Biological cells are characterized by highly complex phenomena and processes that are, to a great extent, interdependent. To gain detailed insights, devices designed to study cellular phenomena need to enable tracking and manipulation of multiple cell parameters in parallel; they have to provide high signal quality and high spatiotemporal resolution. To this end, we have developed a CMOS-based microelectrode array system that integrates six measurement and stimulation functions, the largest number to date. Moreover, the system features the largest active electrode array area to date (4.48×2.43 mm2) to accommodate 59,760 electrodes, while its power consumption, noise characteristics, and spatial resolution (13.5 μm electrode pitch) are comparable to the best state-of-the-art devices. The system includes: 2,048 action-potential (AP, bandwidth: 300 Hz to 10 kHz) recording units, 32 local-field-potential (LFP, bandwidth: 1 Hz to 300 Hz) recording units, 32 current recording units, 32 impedance measurement units, and 28 neurotransmitter detection units, in addition to the 16 dual-mode voltage-only or current/voltage-controlled stimulation units. The electrode array architecture is based on a switch matrix, which allows for connecting any measurement/stimulation unit to any electrode in the array and for performing different measurement/stimulation functions in parallel.

High-density CMOS Microelectrode Array System for Impedance Spectroscopy and Imaging of Biological Cells

A monolithic measurement platform was implemented to enable label-free in-vitro electrical impedance spectroscopy measurements of cells on multi-functional CMOS microelectrode array. The array includes 59,760 platinum microelectrodes, densely packed within a 4.5 mm × 2.5 mm sensing region at a pitch of 13.5 μm. The 32 on-chip lock-in amplifiers can be used to measure the impedance of any arbitrarily chosen electrodes on the array by applying a sinusoidal voltage, generated by an on-chip waveform generator with a frequency range from 1 Hz to 1 MHz, and measuring the respective current. Proof-of-concept measurements of impedance sensing and imaging are shown in this paper. Correlations between cell detection through optical microscopy and electrochemical impedance scanning were established.

CMOS biosensors for in vitro diagnosis - transducing mechanisms and applications

Complementary metal oxide semiconductor (CMOS) technology enables low-cost and large-scale integration of transistors and physical sensing materials on tiny chips (e.g., <1 cm²), seamlessly combining the two key functions of biosensors: transducing and signal processing. Recent CMOS biosensors unified different transducing mechanisms (impedance, fluorescence, and nuclear spin) and readout electronics have demonstrated competitive sensitivity for in vitro diagnosis, such as detection of DNA (down to 10 aM), protein (down to 10 fM), or bacteria/cells (single cell). Herein, we detail the recent advances in CMOS biosensors, centering on their key principles, requisites, and applications. Together, these may contribute to the advancement of our healthcare system, which should be decentralized by broadly utilizing point-of-care diagnostic tools.

Wideband Fully-Programmable Dual-Mode CMOS Analogue Front-End for Electrical Impedance Spectroscopy

This paper presents a multi-channel dual-mode CMOS analogue front-end (AFE) for electrochemical and bioimpedance analysis. Current-mode and voltage-mode readouts, integrated on the same chip, can provide an adaptable platform to correlate single-cell biosensor studies with large-scale tissue or organ analysis for real-time cancer detection, imaging and characterization. The chip, implemented in a 180-nm CMOS technology, combines two current-readout (CR) channels and four voltage-readout (VR) channels suitable for both bipolar and tetrapolar electrical impedance spectroscopy (EIS) analysis. Each VR channel occupies an area of 0.48 mm 2 , is capable of an operational bandwidth of 8 MHz and a linear gain in the range between -6 dB and 42 dB. The gain of the CR channel can be set to 10 kΩ, 50 kΩ or 100 kΩ and is capable of 80-dB dynamic range, with a very linear response for input currents between 10 nA and 100 μ A. Each CR channel occupies an area of 0.21 mm 2 . The chip consumes between 530 μ A and 690 μ A per channel and operates from a 1.8-V supply. The chip was used to measure the impedance of capacitive interdigitated electrodes in saline solution. Measurements show close matching with results obtained using a commercial impedance analyser. The chip will be part of a fully flexible and configurable fully-integrated dual-mode EIS system for impedance sensors and bioimpedance analysis.