High-Density Redox Amplified Coulostatic Discharge-Based Biosensor Array

A Multichannel Electrochemical Sensor Interface IC for Bioreactor Monitoring

This research article introduces a novel integrated circuit (IC) designed for bioreactor applications catering to multichannel electrochemical sensing. The proposed IC comprises 2x potentiometric, 2x potentiostat, 2x ISFET channels and 1x temperature channel. The potentiostat channel utilizes a current conveyor-based architecture with a programmable mirroring ratio, enabling an extensive measurement range of 114 dB. The potentiometric channel incorporates a customized electrostatic discharge (ESD) protection circuit to achieve ultra-low input leakage in the picoampere range, while the ISFET channel employs a constant-voltage, constant-current topology for accurate pH measurement. Combined with the die temperature sensor, this IC is well-suited for monitoring bioreactions in real-time. Additionally, all channels can be time-multiplexed to a reconfigurable analog backend, facilitating the conversion of input signals into digital codes. The prototype of the IC is fabricated using 0.18 μm standard CMOS technology, and each channel is experimentally characterized. The interface IC demonstrates a peak power consumption of 22 μW.

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 Scalable CMOS Molecular Electronics Chip for Single-Molecule Biosensing

This work reports the first CMOS molecular electronics chip. It is configured as a biosensor, where the primary sensing element is a single molecule "molecular wire" consisting of a ∼100 GΩ, 25 nm long alpha-helical peptide integrated into a current monitoring circuit. The engineered peptide contains a central conjugation site for attachment of various probe molecules, such as DNA, proteins, enzymes, or antibodies, which program the biosensor to detect interactions with a specific target molecule. The current through the molecular wire under a dc applied voltage is monitored with millisecond temporal resolution. The detected signals are millisecond-scale, picoampere current pulses generated by each transient probe-target molecular interaction. Implemented in a 0.18 μm CMOS technology, 16k sensors are arrayed with a 20 μm pitch and read out at a 1 kHz frame rate. The resulting biosensor chip provides direct, real-time observation of the single-molecule interaction kinetics, unlike classical biosensors that measure ensemble averages of such events. This molecular electronics chip provides a platform for putting molecular biosensing "on-chip" to bring the power of semiconductor chips to diverse applications in biological research, diagnostics, sequencing, proteomics, drug discovery, and environmental monitoring.

A 174.7-dB FoM, 2nd-Order VCO-Based ExG-to-Digital Front-End Using a Multi-Phase Gated-Inverted-Ring Oscillator Quantizer

This paper presents a second-order voltage-controlled oscillator (VCO)-based front-end for the direct digitization of biopotential signals. This work addresses the non-linearity of VCO-based ADC architectures with a mismatch resilient, multi-phase quantizer, a gated-inverted-ring oscillator (GIRO), achieving >110-dB SFDR. Leveraging the time-domain encoding of the first integrator, the ADC's power is dynamically scaled with the input amplitude enabling up to 35% power savings in the absence of motion artifacts or interference. An auxiliary input-impedance booster increases the ADC's input impedance to 50 MΩ across the entire bandwidth. Fabricated in a 65-nm CMOS process, this ADC achieves 92.3-dB SNDR in a 1 kHz BW while consuming 5.8 µW for a 174.7 dB Schreier FoM.

A CMOS Multi-Modal Electrochemical and Impedance Cellular Sensing Array for Massively Paralleled Exoelectrogen Screening

The paper presents a 256-pixel CMOS sensor array with in-pixel dual electrochemical and impedance detection modalities for rapid, multi-dimensional characterization of exoelectrogens. The CMOS IC has 16 parallel readout channels, allowing it to perform multiple measurements with a high throughput and enable the chip to handle different samples simultaneously. The chip contains a total of 2 × 256 working electrodes of size 44 μm × 52 μm, along with 16 reference electrodes of dimensions 56 μm × 399 μm and 32 counter electrodes of dimensions 399 μm × 106 μm, which together facilitate the high resolution screening of the test samples. The chip was fabricated in a standard 130nm BiCMOS process. The on-chip electrodes are subjected to additional fabrication processes, including a critical Al-etch step that ensures the excellent biocompatibility and long-term reliability of the CMOS sensor array in bio-environment. The electrochemical sensing modality is verified by detecting the electroactive analyte NaFeEDTA and the exoelectrogenic Shewanella oneidensis MR-1 bacteria, illustrating the chip's ability to quantify the generated electrochemical current and distinguish between different analyte concentrations. The impedance measurements with the HEK-293 cancer cells cultured on-chip successfully capture the cell-to-surface adhesion information between the electrodes and the cancer cells. The reported CMOS sensor array outperforms the conventional discrete setups for exoelectrogen characterization in terms of spatial resolution and speed, which demonstrates the chip's potential to radically accelerate synthetic biology engineering.

Applications of CMOS Devices for the Diagnosis and Control of Infectious Diseases

Emerging infectious diseases such as coronavirus disease of 2019 (COVID-19), Ebola, influenza A, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) in recent years have threatened the health and security of the global community as one of the greatest factors of mortality in the world. Accurate and immediate diagnosis of infectious agents and symptoms is a key to control the outbreak of these diseases. Rapid advances in complementary metal-oxide-semiconductor (CMOS) technology offers great advantages like high accuracy, high throughput and rapid measurements in biomedical research and disease diagnosis. These features as well as low cost, low power and scalability of CMOS technology can pave the way for the development of powerful devices such as point-of-care (PoC) systems, lab-on-chip (LoC) platforms and symptom screening devices for accurate and timely diagnosis of infectious diseases. This paper is an overview of different CMOS-based devices such as optical, electrochemical, magnetic and mechanical sensors developed by researchers to mitigate the problems associated with these diseases.

Design and Analysis of a Sample-and-Hold CMOS Electrochemical Sensor for Aptamer-based Therapeutic Drug Monitoring

In this paper, we present the design and the analysis of an electrochemical circuit for measuring the concentrations of therapeutic drugs using structure-switching aptamers. Aptamers are single-stranded nucleic acids, whose sequence is selected to exhibit high affinity and specificity toward a molecular target, and change its conformation upon binding. This property, when coupled with a redox reporter and electrochemical detection, enables reagent-free biosensing with a sub-minute temporal resolution for in vivo therapeutic drug monitoring. Specifically, we design a chronoamperometry-based electrochemical circuit that measures the direct changes in the electron transfer (ET) kinetics of a methylene blue reporter conjugated at the distal-end of the aptamer. To overcome the high-frequency noise amplification issue when interfacing with a large-size (> 0.25 mm2) implantable electrode, we present a sample-and-hold (S/H) circuit technique in which the desired electrode potentials are held onto noiseless capacitors during the recording of the redox currents. This allows disconnecting the feedback amplifiers to avoid its noise injection while reducing the total power consumption. A prototype circuit implemented in 65-nm CMOS demonstrates a cell-capacitance-insensitive input-referred noise (IRN) current of 15.2 pArms at a 2.5-kHz filtering bandwidth. We tested our system in human whole blood samples and measured the changes in the ET kinetics from the redox-labeled aptamers at different kanamycin concentrations. By employing principal component analysis (PCA) to compensate for the sampling errors, we report a molecular noise floor (at SNR = 1) of 3.1 µM with sub 1-sec acquisition time at 0.22-mW power consumption.

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.

A CMOS Magnetoresistive Sensor Front-End With Mismatch-Tolerance and Sub-ppm Sensitivity for Magnetic Immunoassays

Magnetic biosensing is an emerging technique for ultra-sensitive point-of-care (PoC) biomolecular detection. However, the large baseline-to-signal ratio and sensor-to-sensor mismatch in magnetoresistive (MR) biosensors severely complicates the design of the analog front-end (AFE) due to the high dynamic range (DR) required. The proposed AFE addresses these issues through new architectural and circuit level techniques including fast settling duty-cycle resistors (DCRs) to reduce readout time and a high frequency interference rejection (HFIR) sampling technique embedded in the ADC to relax the DR requirement. The AFE achieves an input-referred noise of 46.4 nT/√Hz, an input-referred baseline of less than 0.235 mT, and a readout time of 11 ms while consuming just 1.39 mW. Implemented in a 0.18 μm CMOS process, this work has state-of-the-art performance with 22.7× faster readout time, >7.8× lower baseline, and 2.3× lower power than previously reported MR sensor AFEs.

DNA Biosensor Based on Double-Layer Discharge for the Detection of HPV Type 16

DNA electrochemical biosensors represent a feasible alternative for the diagnosis of different pathologies. In this work, the development of an electrochemical method for Human Papillomavirus-16 (HPV-16) sensing is reported based on potential relaxation measurements related to the discharge of a complex double layer of a DNA-modified gold electrode. The method used allows us to propose an equivalent circuit (EC) for a DNA/Au electrode, which was corroborated by electrochemical impedance spectroscopy (EIS) measurement. This model differs from the Randles circuit that is commonly used in double-layer simulations. The change in the potential relaxation and associated charge transfer resistance were used for sensing the DNA hybridization by using the redox pair Fe(CN)₆^4-/Fe(CN)₆³⁺ as an electrochemical indicator. In order to determinate only the potential relaxation of the composed double layer, the faradic and double-layer current contributions were separated using a rectifier diode arrangement. A detection limit of 0.38 nM was obtained for the target HPV-16 DNA sequences. The biosensor showed a qualitative discrimination between a single-base mismatched sequence and the fully complementary HPV-16 DNA target. The results indicate that the discharge of the double-layer detection method can be used to develop an HPV DNA biosensor.