Amperometric electrochemical microsystem for a miniaturized protein biosensor array

Design and Evaluation of In-Plane Silicon Microneedles Fabricated with Post-CMOS Compatible Processes

In this paper, a comprehensive study was carried out on in-plane silicon (Si) microneedles, a useful tool for transdermal drug delivery and sample collection. Microneedles with eleven designs were investigated by post-complementary metal-oxide-semiconductor (CMOS) compatible microfabrication processes and characterized via pricking tests by insertion in chicken breast flesh. Mechanical strength of all designs were also evaluated by theoretical calculation and finite element modeling (FEM) for bending and buckling analysis. To efficiently improve the sharpness and insertion, the wedge-shaped needle tips with thickness determined by Si wafer thickness were sharpened by a wet chemical etching process. Insertion forces recorded from pricking tests and bending and buckling from theoretical calculation and FEM analysis before and after etching were compared. The results showed that the insertion force, free bending force and the maximum buckling force were all reduced and the maximum bending stress were improved after tip sharpening. Furthermore, the buckling safety factor of all eleven designs was great than 1 and the maximum bending stress was less than the fracture strength of Si, indicating that our in-plane Si microneedles are robust enough for insertion into human skin.

Design of a photoelectrochemical lab-on-a-chip immunosensor based on enzymatic production of quantum dots in situ

We present a new photoelectrochemical immunoassay based on a microfluidic device. Its operation employs enzymatic generation of CdS quantum dots.

Metallization of Organically Modified Ceramics for Microfluidic Electrochemical Assays

Organically modified ceramic polymers (ORMOCERs) have attracted substantial interest in biomicrofluidic applications owing to their inherent biocompatibility and high optical transparency even in the near-ultraviolet (UV) range. However, the processes for metallization of ORMOCERs as well as for sealing of metallized surfaces have not been fully developed. In this study, we developed metallization processes for a commercial ORMOCER formulation, Ormocomp, covering several commonly used metals, including aluminum, silver, gold, and platinum. The obtained metallizations were systematically characterized with respect to adhesion (with and without adhesion layers), resistivity, and stability during use (in electrochemical assays). In addition to metal adhesion, the possibility for Ormocomp bonding over each metal as well as sufficient step coverage to guarantee conductivity over topographical features (e.g., over microchannel edges) was addressed with a view to the implementation of not only planar, but also three-dimensional on-chip sensing elements. The feasibility of the developed metallization for implementation of microfluidic electrochemical assays was demonstrated by fabricating an electrophoresis separation chip, compatible with a commercial bipotentiostat, and incorporating integrated working, reference, and auxiliary electrodes for amperometric detection of an electrochemically active pharmaceutical, acetaminophen.

CMOS Interfaces for Internet-of-Wearables Electrochemical Sensors: Trends and Challenges

Smart wearables, among immediate future IoT devices, are creating a huge and fast growing market that will encompass all of the next decade by merging the user with the Cloud in a easy and natural way. Biological fluids, such as sweat, tears, saliva and urine offer the possibility to access molecular-level dynamics of the body in a non-invasive way and in real time, disclosing a wide range of applications: from sports tracking to military enhancement, from healthcare to safety at work, from body hacking to augmented social interactions. The term Internet of Wearables (IoW) is coined here to describe IoT devices composed by flexible smart transducers conformed around the human body and able to communicate wirelessly. In addition the biochemical transducer, an IoW-ready sensor must include a paired electronic interface, which should implement specific stimulation/acquisition cycles while being extremely compact and drain power in the microwatts range. Development of an effective readout interface is a key element for the success of an IoW device and application. This review focuses on the latest efforts in the field of Complementary Metal–Oxide–Semiconductor (CMOS) interfaces for electrochemical sensors, and analyses them under the light of the challenges of the IoW: cost, portability, integrability and connectivity.

Integrated Optoelectronic Device for Detection of Fluorescent Molecules

This paper presents the development of a compact optoelectronic device suitable for on-chip detection of fluorescent molecules. In order to obtain a highly integrated device, a long-pass multi-dielectric filter has been integrated with thin-film amorphous silicon photosensors on a single glass substrate. Filter rejects the excitation light, allowing the reduction of the distance between the source and the fluorescent site and avoiding the use of external optical component. The compatibility of the technological processes determined the materials and the temporal sequence of the device fabrication. The developed device has been designed for the fluorescence detection of ruthenium complex based molecules and tested, as a proof of concept, for the detection of double-stranded DNA down to 0.5 ng. Results demonstrate the correct operation of the integrated system in both rejecting the excitation light and in detecting the fluorescent signal, demonstrating the suitability of this optoelectronic platform in practical biomedical applications.

High-Density Redox Amplified Coulostatic Discharge-Based Biosensor Array

High-density biosensor arrays are essential for many cutting-edge biomedical applications including point-of-care vaccination screening to detect multiple highly-contagious diseases. Typical electrochemical biosensing techniques are based on the measurement of sub-pA currents for micron-sized sensors requiring highly-sensitive readout circuits. Such circuits are often too complex to scale down for high-density arrays. In this paper, a high-density 4,096-pixel electrochemical biosensor array in 180 nm CMOS is presented. It uses a coulostatic discharge sensing technique and interdigitated electrode geometry to reduce both the complexity and size of the readout circuitry. Each biopixel contains an interdigitated microelectrode with a 13 aA low-leakage readout circuit directly underneath. Compared to standard planar electrodes, the implemented interdigitated electrodes achieve a maximum amplification factor of 10.5× from redox cycling. The array's sensor density is comparable to state-of-the-art arrays, all without augmenting the sensors with complex post-processing. The detection of anti-Rubella and anti-Mumps antibodies in human serum is demonstrated.

Lab-on-a-chip electrical multiplexing techniques for cellular and molecular biomarker detection

Signal multiplexing is vital to develop lab-on-a-chip devices that can detect and quantify multiple cellular and molecular biomarkers with high throughput, short analysis time, and low cost. Electrical detection of biomarkers has been widely used in lab-on-a-chip devices because it requires less external equipment and simple signal processing and provides higher scalability. Various electrical multiplexing for lab-on-a-chip devices have been developed for comprehensive, high throughput, and rapid analysis of biomarkers. In this paper, we first briefly introduce the widely used electrochemical and electrical impedance sensing methods. Next, we focus on reviewing various electrical multiplexing techniques that had achieved certain successes on rapid cellular and molecular biomarker detection, including direct methods (spatial and time multiplexing), and emerging technologies (frequency, codes, particle-based multiplexing). Lastly, the future opportunities and challenges on electrical multiplexing techniques are also discussed.

Ultracompact Microwatt CMOS Current Readout With Picoampere Noise and Kilohertz Bandwidth for Biosensor Arrays

High-density on-chip electrochemical biosensor arrays are advancing toward a crucial role in health monitoring and development of new medicines and medical treatments. Nanopore and ion channel based sensors especially have great potential but present demanding resolution/speed/power/area requirements on instrumentation circuits. This paper presents a pixel-level current readout circuit and new group-cluster architecture to address the circuit challenges in high-performance biosensor arrays. Fabricated in 0.5 μm CMOS, this electrochemical voltammetry circuit achieves 7.2 pA_rms noise in an 11.5-kHz bandwidth and only consumes 21-μ W power and 0.06 mm² area per readout channel. Cyclic voltammetry experiments in a potassium ferricyanide solution and patch-clamp whole-cell experiments were performed to validate the circuit's feasibility for electrochemical biosensor applications.

Miniaturized FDDA and CMOS Based Potentiostat for Bio-Applications

A novel fully differential difference CMOS potentiostat suitable for neurotransmitter sensing is presented. The described architecture relies on a fully differential difference amplifier (FDDA) circuit to detect a wide range of reduction-oxidation currents, while exhibiting low-power consumption and low-noise operation. This is made possible thanks to the fully differential feature of the FDDA, which allows to increase the source voltage swing without the need for additional dedicated circuitry. The FDDA also reduces the number of amplifiers and passive elements in the potentiostat design, which lowers the overall power consumption and noise. The proposed potentiostat was fabricated in 0.18 µm CMOS, with 1.8 V supply voltage. The device achieved 5 µA sensitivity and 0.99 linearity. The input-referred noise was 6.9 µV rms and the flicker noise was negligible. The total power consumption was under 55 µW. The complete system was assembled on a 20 mm × 20 mm platform that includes the potentiostat chip, the electrode terminals and an instrumentation amplifier for redox current buffering, once converted to a voltage by a series resistor. the chip dimensions were 1 mm × 0.5 mm and the other PCB components were off-chip resistors, capacitors and amplifiers for data acquisition. The system was successfully tested with ferricyanide, a stable electroactive compound, and validated with dopamine, a popular neurotransmitter.

CMOS Electrochemical Instrumentation for Biosensor Microsystems: A Review

Modern biosensors play a critical role in healthcare and have a quickly growing commercial market. Compared to traditional optical-based sensing, electrochemical biosensors are attractive due to superior performance in response time, cost, complexity and potential for miniaturization. To address the shortcomings of traditional benchtop electrochemical instruments, in recent years, many complementary metal oxide semiconductor (CMOS) instrumentation circuits have been reported for electrochemical biosensors. This paper provides a review and analysis of CMOS electrochemical instrumentation circuits. First, important concepts in electrochemical sensing are presented from an instrumentation point of view. Then, electrochemical instrumentation circuits are organized into functional classes, and reported CMOS circuits are reviewed and analyzed to illuminate design options and performance tradeoffs. Finally, recent trends and challenges toward on-CMOS sensor integration that could enable highly miniaturized electrochemical biosensor microsystems are discussed. The information in the paper can guide next generation electrochemical sensor design.

A Glucose Biosensor Using CMOS Potentiostat and Vertically Aligned Carbon Nanofibers

This paper reports a linear, low power, and compact CMOS based potentiostat for vertically aligned carbon nanofibers (VACNF) based amperometric glucose sensors. The CMOS based potentiostat consists of a single-ended potential control unit, a low noise common gate difference-differential pair transimpedance amplifier and a low power VCO. The potentiostat current measuring unit can detect electrochemical current ranging from 500 nA to 7 [Formula: see text] from the VACNF working electrodes with high degree of linearity. This current corresponds to a range of glucose, which depends on the fiber forest density. The potentiostat consumes 71.7 [Formula: see text] of power from a 1.8 V supply and occupies 0.017 [Formula: see text] of chip area realized in a 0.18 [Formula: see text] standard CMOS process.

A CMOS Amperometric System for Multi-Neurotransmitter Detection

In vivo multi-target and selective concentration monitoring of neurotransmitters can help to unravel the brain chemical complex signaling interplay. This paper presents a dedicated integrated potentiostat transducer circuit and its selective electrode interface. A custom 2-electrode time-based potentiostat circuit was fabricated with 0.13 μm CMOS technology and provides a wide dynamic input current range of 20 pA to 600 nA with 56 μ W, for a minimum sampling frequency of 1.25 kHz. A multi-working electrode chip is functionalized with carbon nanotubes (CNT)-based chemical coatings that offer high sensitivity and selectivity towards electroactive dopamine and non-electroactive glutamate. The prototype was experimentally tested with different concentrations levels of both neurotransmitter types, and results were similar to measurements with a commercially available potentiostat. This paper validates the functionality of the proposed biosensor, and demonstrates its potential for the selective detection of a large number of neurochemicals.

A MEMS Interface IC With Low-Power and Wide-Range Frequency-to-Voltage Converter for Biomedical Applications

This paper presents an interface circuit for capacitive and inductive MEMS biosensors using an oscillator and a charge pump based frequency-to-voltage converter. Frequency modulation using a differential crossed coupled oscillator is adopted to sense capacitive and inductive changes. The frequency-to-voltage converter is designed with a negative feedback system and external controlling parameters to adjust the sensitivity, dynamic range, and nominal point for the measurement. The sensitivity of the frequency-to-voltage converter is from 13.28 to 35.96 mV/MHz depending on external voltage and charging current. The sensitivity ranges of the capacitive and inductive interface circuit are 17.08 to 54.4 mV/pF and 32.11 to 82.88 mV/mH, respectively. A capacitive MEMS based pH sensor is also connected with the interface circuit to measure the high acidic gastric acid throughout the digestive tract. The sensitivity for pH from 1 to 3 is 191.4 mV/pH with 550 μV(pp) noise. The readout circuit is designed and fabricated using the UMC 0.18 μm CMOS technology. It occupies an area of 0.18 mm (2) and consumes 11.8 mW.

Methods and approaches of utilizing ionic liquids as gas sensing materials

Gas monitoring is of increasing significance for a broad range of applications in the fields of environmental and civil infrastructures, climate and energy, health and safety, industry and commerce. Even though there are many gas detection devices and systems available, the increasing needs for better detection technologies that not only satisfy the high analytical standards but also meet additional device requirements (e.g., being robust to survive under field conditions, low cost, small, smart, more mobile), demand continuous efforts in developing new methods and approaches for gas detection. Ionic Liquids (ILs) have attracted a tremendous interest as potential sensing materials for the gas sensor development. Being composed entirely of ions and with a broad structural and functional diversity, i.e., bifunctional (organic/inorganic), biphasic (solid/liquid) and dual-property (solvent/electrolyte), they have the complementing attributes and the required variability to allow a systematic design process across many sensing components to enhance sensing capability especially for miniaturized sensor system implementation. The emphasis of this review is to describe molecular design and control of IL interface materials to provide selective and reproducible response and to synergistically integrate IL sensing materials with low cost and low power electrochemical, piezoelectric/QCM and optical transducers to address many gas detection challenges (e.g., sensitivity, selectivity, reproducibility, speed, stability, cost, sensor miniaturization, and robustness). We further show examples to justify the importance of understanding the mechanisms and principles of physicochemical and electrochemical reactions in ILs and then link those concepts to developing new sensing methods and approaches. By doing this, we hope to stimulate further research towards the fundamental understanding of the sensing mechanisms and new sensor system development and integration, using simple sensing designs and flexible sensor structures both in terms of scientific operation and user interface that can be miniaturized and interfaced with modern wireless monitoring technologies to achieve specifications heretofore unavailable on current markets for the next generation of gas sensor applications.

Noise limits of CMOS current interfaces for biosensors: a review

Current sensing readout is one of the most frequent techniques used in biosensing due to the charge-transfer phenomena occurring at solid-liquid interfaces. The development of novel nanodevices for biosensing determines new challenges for electronic interface design based on current sensing, especially when compact and efficient arrays need to be organized, such as in recent trends of rapid label-free electronic detection of DNA synthesis. This paper will review the basic noise limitations of current sensing interfaces with particular emphasis on integrated CMOS technology. Starting from the basic theory, the paper presents, investigates and compares charge-sensitive amplifier architectures used in both continuous-time and discrete-time approaches, along with their design trade-offs involving noise floor, sensitivity to stray capacitance and bandwidth. The ultimate goal of this review is providing analog designers with helpful design rules and analytical tools. Also, in order to present a comprehensive overview of the state-of-the-art, the most relevant papers recently appeared in the literature about this topic are discussed and compared.

A CMOS cantilever-based label-free DNA SoC with improved sensitivity for hepatitis B virus detection

This paper presents a highly-integrated DNA detection SoC, where several kinds of cantilever DNA sensors, a readout circuit, an MCU, voltage regulators, and a wireless transceiver, are integrated monolithically in a 0.35 μm CMOS Bio-MEMS process. The cantilever-based biosensors with embedded piezoresistors aim to transduce DNA hybridization into resistance variation without cumbersome labeling process. To improve detection sensitivity for low DNA concentration use, an oscillator-based self-calibrated readout circuit with high precision is proposed to convert small resistance variation ( of original resistance) of the sensor into adequate frequency variation and further into digital data. Moreover, its wireless capacity enables isolation of the sample solution from electrical wire lines and facilitates data transmission. To demonstrate the effectiveness of full system, it is applied to detect hepatitis B virus (HBV) DNA. The experimental results show that it has the capability to distinguish between one base-pair (1-bp) mismatch DNAs and match DNAs and achieves a limit of detection (LOD) of less than 1 pM.

A 0.18 μm biosensor front-end based on 1/f noise, distortion cancelation and chopper stabilization techniques

This paper presents a novel sensor front-end circuit that addresses the issues of 1/f noise and distortion in a unique way by using canceling techniques. The proposed front-end is a fully differential transimpedance amplifier (TIA) targeted for current mode electrochemical biosensing applications. In this paper, we discuss the architecture of this canceling based front-end and the optimization methods followed for achieving low noise, low distortion performance at minimum current consumption are presented. To validate the employed canceling based front-end, it has been realized in a 0.18 μm CMOS process and the characterization results are presented. The front-end has also been tested as part of a complete wireless sensing system and the cyclic voltammetry (CV) test results from electrochemical sensors are provided. Overall current consumption in the front-end is 50 μA while operating on a 1.8 V supply.

Camera phone-based quantitative analysis of C-reactive protein ELISA

We demonstrate the use of a camera phone as a low-cost optical detector for quantitative analysis of a high-sensitivity C-reactive protein (hs-CRP) enzyme-linked immunosorbent assay (ELISA). The camera phone was used to acquire images of the ELISA carried out in a conventional 96 well plate. Colorimetric analysis of the images was used to determine a standard curve that exhibited excellent agreement with a fitted 4-parameter logistic model (R²=0.998). The limit of detection (LOD) for this approach was determined to be 0.026 ± 0.002 μg/ml (1.035 ± 0.079 μM) CRP. Furthermore, these results were found to be in very close agreement with measurements obtained for the same assay using a laboratory-based instrument. These findings indicate the basic technology to enable low-cost quantitative home-based monitoring of an important clinical biomarker of inflammatory disease may already be present in the patient's home.

A small-area low-power current readout circuit using two-stage conversion method for 64-channel CNT sensor arrays

In this paper, a small-area and low-power current readout circuit with a novel two-stage conversion method is presented for 64-channel CNT (carbon nanotube) sensor arrays. In the first stage, current of each CNT sensor is amplified by 64 active input current mirrors (AICMs). In the second stage, the amplified current is converted to a voltage level through the shared variable gain amplifier (S-VGA). Then the S-VGA output is digitalized by successive approximation register analog-to-digital converter (SAR-ADC). The proposed readout circuit significantly reduces chip area and power consumption, since VGA is shared over 64 channels and passive elements are used only in S-VGA. Fabricated chip area is 0.173 mm(2) in 0.13 μm CMOS technology. Measured power consumption and linearity error are 73.06 μW and 5.3%, respectively, at the input current range of 10 nA-10 μA and conversion rate of 640 samples/s. A prototype real-time CNT sensor system was implemented using the fabricated readout circuit, and successfully detected alcohol reaction.

CMOS neurotransmitter microarray: 96-channel integrated potentiostat with on-die microsensors

A 8 × 12 array of integrated potentiostats for on-CMOS neurotransmitter imaging is presented. Each potentiostat channel measures bidirectional redox currents proportional to the concentration of a neurochemical. By combining the current-to-frequency and the single-slope analog-to-digital converter (ADC) architectures a total linear dynamic range of 95 dB is achieved. A 3.8 mm × 3.1 mm prototype fabricated in a 0.35 μm standard CMOS technology was integrated with flat and 3D on-die gold microelectrodes and an on-chip microfluidic network. It is experimentally validated in in-situ recording of neurotransmitter dopamine.

A protein-based electrochemical biosensor array platform for integrated microsystems

This paper elucidates challenges in integrating different classes of proteins into a microsystem and presents an electrochemical array strategy for heterogeneous protein-based biosensors. The overlapping requirements and limitations imposed by biointerface formation, electrochemical characterization, and microsystem fabrication are identified. A planar electrode array is presented that synergistically resolves these requirements using thin film Au and Ag/AgCl electrodes on a dielectric substrate. Using molecular self-assembly, electrodes were modified by nano-structures of two diverse proteins, alkali ion-channel protein and alcohol dehydrogenase enzyme. Electrochemical impedance spectroscopy and cyclic voltammetry measurements were performed to characterize sensor response to alkali ion and alcohol, respectively. This work demonstrates the viability of the electrochemical microsystem platform for heterogeneous protein-based biosensor interfaces.

16-channel CMOS impedance spectroscopy DNA analyzer with dual-slope multiplying ADCs

We present a 16-channel, mixed-signal CMOS DNA analyzer that utilizes frequency response analysis (FRA) to extract the real and imaginary impedance components of the biosensor. Two computationally intensive operations, the multiplication and integration required by the FRA algorithm, are performed by an in-channel dual-slope multiplying ADC in the mixed-signal domain resulting in minimal area and power consumption. Multiplication of the input current by a digital coefficient is implemented by modulating the counter-controlled duration of the charging phase of the ADC. Integration is implemented by accumulating output digital bits in the ADC counter over multiple input samples. The 1.05 mm×1.6 mm prototype fabricated in a 0.13 μm standard CMOS technology has been validated in prostate cancer DNA detection. Each channel occupies an area of only 0.06 mm² and consumes 42 μW of power from a 1.2 V supply.

CMOS low current measurement system for biomedical applications

We present a micro-chip implementation of a low current measurement system for biomedical applications using capacitive feedback that exhibits 190 fA of RMS noise in a 1 kHz bandwidth. The sampling rate is selectable up to 100 kHz. When measuring the amplifier noise with a 10 GΩ resistor and a 47 pF capacitor at the input, typical of cell membrane capacitance in DNA and patch clamp experiments, the measured RMS noise was 2.44 pA on a 50 pA signal in a 10 kHz bandwidth. Two channels were implemented on 630 × 440 μm² using a 0.5-μm 3-metal 2-poly CMOS process. Each channel consumes 1.5 mW of power from a 3.3 V supply. We measured the characteristics of an artificial lipid bilayer similar to the ones used in DNA sequencing experiments via nanopores.

CMOS Amperometric Instrumentation and Packaging for Biosensor Array Applications

An integrated CMOS amperometric instrument with on-chip electrodes and packaging for biosensor arrays is presented. The mixed-signal integrated circuit supports a variety of electrochemical measurement techniques including linear sweep, constant potential, cyclic and pulse voltammetry. Implemented in 0.5 μm CMOS, the 3 × mm(2) chip dissipates 22.5 mW for a 200 kHz clock. The highly programmable chip provides a wide range of user-controlled stimulus rate and amplitude settings with a maximum scan range of 2 V and scan rates between 1 mV/sec and 400 V/sec. The amperometric readout circuit provides ±500 fA linear resolution and supports inputs up to ±47 μA. A 2 × 2 gold electrode array was fabricated on the surface of the CMOS instrumentation chip. An all-parylene packaging scheme was developed for compatibility with liquid test environments as well as a harsh piranha electrode cleaning process. The chip was tested using cyclic voltammetry of different concentrations of potassium ferricyanide at 100 mV/s and 200 mV/s, and results were identical to measurements using commercial instruments.

Recent advances in neural recording microsystems

The accelerating pace of research in neuroscience has created a considerable demand for neural interfacing microsystems capable of monitoring the activity of large groups of neurons. These emerging tools have revealed a tremendous potential for the advancement of knowledge in brain research and for the development of useful clinical applications. They can extract the relevant control signals directly from the brain enabling individuals with severe disabilities to communicate their intentions to other devices, like computers or various prostheses. Such microsystems are self-contained devices composed of a neural probe attached with an integrated circuit for extracting neural signals from multiple channels, and transferring the data outside the body. The greatest challenge facing development of such emerging devices into viable clinical systems involves addressing their small form factor and low-power consumption constraints, while providing superior resolution. In this paper, we survey the recent progress in the design and the implementation of multi-channel neural recording Microsystems, with particular emphasis on the design of recording and telemetry electronics. An overview of the numerous neural signal modalities is given and the existing microsystem topologies are covered. We present energy-efficient sensory circuits to retrieve weak signals from neural probes and we compare them. We cover data management and smart power scheduling approaches, and we review advances in low-power telemetry. Finally, we conclude by summarizing the remaining challenges and by highlighting the emerging trends in the field.