Electronic Biosensing Research Articles

(Invited) Tackling Leakage, Drift, and Variation in Printed Carbon Nanotube-Based Electronic Biosensors

Semiconducting carbon nanotubes (CNTs) have been pursued for use in electronic biosensors for decades. Their all-surface molecular structure, sizeable semiconducting bandgap, and solution-phase compatibility make them highly sensitive and versatile options for transducing target bioelectrical signals. However, amid the thousands of reports on CNT-based electronic biosensors, very little attention has been given to identifying (let alone addressing) the impact of leakage current, signal drift, and device-to-device variation. This talk will present recent results focused on tackling these issues with specific emphasis on printed CNT-based biosensors. For instance, a variety of passivation strategies were studied to determine the role of leakage current for CNT transistor-based biosensors (i.e., bioFETs or ion-sensitive FETs), revealing that a bilayer epoxy/high-k dielectric stack was most effective at minimizing unwanted leakage current. The influence of signal drift will also be demonstrated, likely playing a significant role in many previous reports of CNT-based biosensors characterized by sequential concentration spikes. Finally, strategies for addressing device-to-device variation in these biosensors will be discussed, including the motivation for a printed thin-film device rather than a single-CNT configuration. Two things seem certain about this field: 1) the promise of CNT-based biosensors continues to suggest they are worth ongoing pursuit, and 2) there is much work remaining towards achieving a reproducible, reliable electronic biosensing technology from CNTs.

Mitigation of electronic crosstalk interference in graphene transistor biosensors

The need for higher sensitivity and parallel detection of multiple biological targets drives the research on electronic biosensing platforms based on two-dimensional (2D) materials. However, signal fidelity from individual sensors may be compromised due to the existing nonidealities of 2D electronic devices. Here, we use graphene field effect transistors (gFETs) as a model system to investigate a multisensor device architecture. We identify two potential sources of crosstalk interference between sensors in such a platform: resistive interference through shared gFET channels and capacitive coupling through the shared device substrate. Having illustrated these sources of interference, we offer solutions to mitigate them for ensuring the fidelity of the biosensor signal. This study provides important practical insights for researchers working on 2D biosensor platforms.

Nanoscale-localized multiplexed biological activation of field effect transistors for biosensing applications.

The rise in antibiotic-resistant pathogens, highly infectious viruses, and chronic diseases has prompted the search for rapid and versatile medical tests that can be performed by the patient. Field-effect transistor (FET)-based electronic biosensing platforms are particularly attractive due to their sensitivity, fast turn-around time, potential for parallel detection of multiple pathogens, and compatibility with semiconductor manufacturing. However, an unmet critical need is a scalable, site-selective multiplexed biofunctionalization method with nanoscale precision for immobilizing different types of pathogen-specific bioreceptors on individual FETs, preventing parallel detection of multiple targets. Here, we propose a paradigm shift in FET biofunctionalization using thermal scanning probe lithography (tSPL) with a thermochemically sensitive polymer. This polymer can be spin-coated on fully-fabricated FET chips, making this approach applicable to any FET sensor material and technology. Crucially, we demonstrate the spatially selective multiplexed functionalization capability of this method by immobilizing different types of bioreceptors at prescribed locations on a chip with sub-20 nm resolution, paving the way for massively parallel FET detection of multiple pathogens. Antibody- and aptamer-modified graphene FET sensors are then realized, achieving ultra-sensitive detection of a minimum measured concentrations of 3 aM of SARS-CoV-2 spike proteins and 10 human SARS-CoV-2 infectious live virus particles per ml, and selectivity against human influenza A (H1N1) live virus.

Interface-Engineered Field-Effect Transistor Electronic Devices for Biosensing.

Promising advances in molecular medicine have promoted the urgent requirement for reliable and sensitive diagnostic tools. Electronic biosensing devices based on field-effect transistors (FETs) exhibit a wide range of benefits, including rapid and label-free detection, high sensitivity, easy operation, and capability of integration, possessing significant potential for application in disease screening and health monitoring. In this perspective, the tremendous efforts and achievements in the development of high-performance FET biosensors in the past decade are summarized, with emphasis on the interface engineering of FET-based electrical platforms for biomolecule identification. First, an overview of engineering strategies for interface modulation and recognition element design is discussed in detail. For a further step, the applications of FET-based electrical devices for in vitro detection and real-time monitoring in biological systems are comprehensively reviewed. Finally, the key opportunities and challenges of FET-based electronic devices in biosensing are discussed. It is anticipated that a comprehensive understanding of interface engineering strategies in FET biosensors will inspire additional techniques for developing highly sensitive, specific, and stable FET biosensors as well as emerging designs for next-generation biosensing electronics.

Direct Writing of Aligned Carbon Nanotubes across a Trench.

Aligned and suspended carbon nanotubes can outperform randomly oriented networks in electronic biosensing and thin-film electronics. However, carbon nanotubes tend to bundle and form random networks. Here, we show that carbon nanotubes spontaneously align in an ammonium deoxycholate surfactant gel even under low shear forces, allowing direct writing and printing of nanotubes into electrically conducting wires and aligned thin layers across trenches. To demonstrate its application potential, we directly printed arrays of disposable electrical biosensors, which show femtomolar sensitivity in the detection of DNA and SARS-CoV-2 RNA.

Structural tailoring of semiconducting tetrazine polymers based immobilizing matrix for superior electronic biosensing of carcinoembryonic antigen

AbstractImmobilizing matrix plays a crucial role in anchoring the receptors of target biomolecules and enhancing the sensing capability of biosensor. Howbeit, the immobilization platforms that induce stable molecular interactions with the receptors without the need for harsh reaction conditions (covalent bonding) are rare. Herein, we report the design, development and application of novel semiconducting one‐dimensional (1D) tetrazine polymers (TTz, PhTTz, PhAlkTz) as immobilizing matrices for electronic biosensing of carcinoembryonic antigen (CEA), a cancer biomarker. The polymers are fully loaded with electron‐deficient tetrazine units (nitrogen‐rich), which develop strong hydrogen bonding (H‐bonding) interactions and effectively immobilize the bioreceptor (anti‐CEA). The sensor comprises reduced graphene oxide (rGO) as the base conducting layer and tetrazine polymers as immobilizing matrices for the CEA antibodies. The rGO/TTz/anti‐CEA, rGO/PhTTz/anti‐CEA, rGO/PhAlkTz/anti‐CEA sensors exhibited 3.5 to 34.16 μA, 2.2 to 34.89 μA, 1.1 to 39.27 μA responses, respectively, for 1 pg/ml to 200 ng/ml of CEA. The sensors' (TTz, PhTTz, and PhAlkTz) sensitivities, selectivities and stabilities are found to be better than that of previously reported partially tetrazine loaded polymer (PhPTz). The study discloses the presence of H‐bonding in tetrazine units is highly critical for superior sensing. The concept of utilizing N‐rich tetrazine units in the immobilizing platforms can be generalized to several other hetero‐atom based systems and polymers. Thus, a wide variety of novel immobilizing substrates can be developed to realize superior sensing performance.

Aerosol Jet Printing of SU-8 as a Passivation Layer Against Ionic Solutions.

To ensure stability for low-cost electronics used in direct contact with ionic solutions (such as electronic biosensors), electrodes are frequently passivated to protect against current leakage, which leads to corrosion. The epoxy-based polymer SU-8 yields favorable properties for passivation against ionic solutions. However, it is nearly universally patterned via cleanroom techniques, which increases device cost and fabrication complexity. Printing electronic components has been shown to be a viable approach for decreasing fabrication cost. Previous reports on SU-8 printing focus on the resultant printed structure, with little emphasis on its subsequent use as a passivation layer. Here, we demonstrate the printing of SU-8 with an aerosol jet printer using ultrasonic aerosolization. We show that SU-8 can be printed without reformulation, and that printed SU-8 is a viable passivation layer over conductive silver lines, when tested in ionic solutions. Extending the printed SU-8 film beyond the underlying conductive electrodes by 100 μm produced a six order of magnitude decrease in leakage current and resulted high stability over 20 voltage sweeps. Finally, we optimized post-printing cure time to 15 minutes at 160°C, which further minimized leakage current. While the development of low-cost, electronic biosensing devices has increasingly moved towards printing methods, the lack of a printed passivation strategy has hindered this transition. The advancements made in this study towards an aerosol jet printable SU-8 passivation layer provide useful progress towards a fully printed, stable electronic biosensing device.

Divalent Cation Dependence Enhances Dopamine Aptamer Biosensing.

Oligonucleotide receptors (aptamers), which change conformation upon target recognition, enable electronic biosensing under high ionic-strength conditions when coupled to field-effect transistors (FETs). Because highly negatively charged aptamer backbones are influenced by ion content and concentration, biosensor performance and target sensitivities were evaluated under application conditions. For a recently identified dopamine aptamer, physiological concentrations of Mg2+ and Ca2+ in artificial cerebrospinal fluid produced marked potentiation of dopamine FET-sensor responses. By comparison, divalent cation-associated signal amplification was not observed for FET sensors functionalized with a recently identified serotonin aptamer or a previously reported dopamine aptamer. Circular dichroism spectroscopy revealed Mg2+- and Ca2+-induced changes in target-associated secondary structure for the new dopamine aptamer, but not the serotonin aptamer nor the old dopamine aptamer. Thioflavin T displacement corroborated the Mg2+ dependence of the new dopamine aptamer for target detection. These findings imply allosteric binding interactions between divalent cations and dopamine for the new dopamine aptamer. Developing and testing sensors in ionic environments that reflect intended applications are best practices for identifying aptamer candidates with favorable attributes and elucidating sensing mechanisms.

New Approach for Making Standard the Development of Biosensing Devices by a Modular Multi-Purpose Design.

The fast widening of biosensing applications, such as healthcare, drug delivery, food, and military industries, is increasing the need for generality and compatibility among different sensors. To address this challenge, we present here an innovative approach for the fast development of new electronic biosensing systems, linking a custom-designed front-end with a multi-purpose system. We envision an open tool to help designers to focus on the target molecule and related detection method instead of designing each time a dedicated electronic device. The architecture of the proposed system is based on a modular approach, where only the front-end and the software need to be custom re-designed according to the application. Considering current research and applying a rigorous definition of the technical requirements, the core of the system is designed to fit the highest number of biosensing methods. The flexibility of this approach is successfully demonstrated with three different types of biosensors, i.e., amperometric, ion-sensitive, and memristive.

Harnessing Selectivity and Sensitivity in Electronic Biosensing: A Novel Lab-on-Chip Multigate Organic Transistor.

Electrolyte gated organic transistors can operate as powerful ultrasensitive biosensors, and efforts are currently devoted to devising strategies for reducing the contribution of hardly avoidable, nonspecific interactions to their response, to ultimately harness selectivity in the detection process. We report a novel lab-on-a-chip device integrating a multigate electrolyte gated organic field-effect transistor (EGOFET) with a 6.5 μL microfluidics set up capable to provide an assessment of both the response reproducibility, by enabling measurement in triplicate, and of the device selectivity through the presence of an internal reference electrode. As proof-of-concept, we demonstrate the efficient operation of our pentacene based EGOFET sensing platform through the quantification of tumor necrosis factor alpha with a detection limit as low as 3 pM. Sensing of inflammatory cytokines, which also include TNFα, is of the outmost importance for monitoring a large number of diseases. The multiplexable organic electronic lab-on-chip provides a statistically solid, reliable, and selective response on microliters sample volumes on the minutes time scale, thus matching the relevant key-performance indicators required in point-of-care diagnostics.

In Situ Electrochemical Synthesis of a Conducting Polymer Composite for Multimetabolite Sensing

AbstractElectrochemical polymerization is a versatile method for rapid deposition of conducting polymer (CP) films. The target substrates have, however, been limited to planar, metallic surfaces; hence, the devices that integrate electropolymerized CP films have predominantly been passive electrodes. In this work, it is shown that electrochemical polymerization has a high degree of freedom, which allows growing biofunctionalized CP films in microscale transistor channels. CP films are electrochemically deposited from two monomers, namely, 3,4‐ethylenedioxythiophene (EDOT) and hydroxymethyl EDOT (EDOTOH), inside the channel of an organic electrochemical transistor (OECT). In aqueous electrolytes, the copolymer p(EDOT‐ran‐EDOTOH) shows excellent charging capability and OECT performance. The presence of hydroxyl groups facilitates stable incorporation of catalytic enzymes in the copolymer matrix during electropolymerization, rendering OECT channels biologically functionalized. The transistor channels made of CP films with the entrapped enzyme show output characteristics that change with respect to the concentration of its target metabolite. In the form of a miniaturized, single chip, the multi‐transistor platform simultaneously measures glucose, cholesterol, and lactate concentrations of a given fluid. With the ability to grow and pattern CPs functionalized with biorecognition units on miniaturized areas, this technique promises for the development of multiplexed platforms for electronic biosensing.

Flexible low-voltage paper transistors harnessing ion gel/cellulose fiber composites

Paper transistors are indispensable devices for paper-based electronic biosensing systems. Existing paper transistors mainly use paper as a mechanical support in a passive fashion. By taking advantage of the cellulose fibers in paper, here we report a transistor-in-paper where paper is employed as an essential part to allow for low-voltage operation, which addresses the long-standing challenge of high-voltage operation with existing paper transistors. Such a low-threshold voltage is because of the ion gel/cellulose fiber composite dielectric formed by modifying the paper with ion gels. We further developed paper-based inverters as examples of logic gates and an integrated tactile sensing mat based on a transistor array–enabled multiplexing device. The results collectively indicate that the ion gel–modified paper leads to a class of flexible, low-voltage transistors and integrated electronic devices, which hold promise in many applications.

Tissue Paper as a Substrate for Electronic Biosensing.

In the presented work, we combine a commonplace commodity, tissue paper, with biosensing capabilities to provide on-the-go detection of biomarkers. We developed a simple light-weight sensor using single walled carbon nanotubes (SWCNT) on commercially available tissue paper. As a proof of concept, we show that these sensors can be used to quantify Interleukin-6 protein concentration. Detection is carried out by examining the modulation in electrical properties of the substrate induced by addition of protein on these sensors. Our results show that these sensors can provide the foundation for development of tissue paper based portable sensors for biomarkers relevant to on-the-go testing.

Diamondoid-functionalized nanogaps: from small molecules to electronic biosensing

The potential of reading-out DNA molecules using functionalized electrodes embedded in nanopores is discussed here. Focus is given on functionalization using tiny diamond-like hydrogenated cages, the diamondoids. A derivative known as memantine of the smallest diamondoid is taken. This offers hydrogen bonding possibilities. Based on quantum-mechanical calculations, we first assess the interaction details of memantine with DNA units, the nucleotides. At a next step, nucleotides are placed within the nanogap formed by the diamondoid-functionalized electrodes. Quantum transport calculations are performed and show the high sensitivity of the electrodes in distinguishing among the different nucleotide types. We proceed by qualitatively revealing the influence of the DNA molecules by simply rotating the nucleotide within the nanogap. The effect of an aqueous environment is also included and the dynamic behavior of the conductance across the functionalized electrodes is addressed. In the end, we discuss the relevance of our results in detecting DNA sequences.

A chemodosimeter-modified carbon nanotube-field effect transistor: toward a highly selective and sensitive electrical sensing platform.

We present a carbon nanotube-field effect transistor (CNT-FET) biosensor which first implements the chemodosimeter sensing principle in CNT nanoelectronics. We experimentally illustrate the specific molecular interplay that the cysteine-selective chemodosimeter immobilized on the CNT surface can specifically interact with cysteine, which leads to the chemical transformation of the chemodosimeter. Since the chemical transformation of the chemodosimeter can disrupt the charge distribution in the vicinity of the CNT surface, the carrier equilibrium in CNT might be altered, and manifested by the conductivity change of CNT-FET. The real-time conductance measurements show our biosensor is capable of label-free, rapid, highly selective and ultrasensitive detection of cysteine with a detection limit down to 0.45 fM. These results first verify the signaling principle competency of chemical transformation of the chemodosimeter in CNT electronic sensors. Combined with the advantages of the highly selective chemodosimeter and sensitive CNT-FET, the excellent performance of our sensor indicates its promising prospect as a valuable tool for developing highly sensitive and selective sensing platforms in practical application.

Electronic biosensing with flexible organic transistor devices

In this short review, we summarize the design and implementation of organic semiconducting materials-based field-effect transistors (OFETs) and the fabrication and use of reduced graphene-oxide field-effect transistors (rGO–FETs) as flexible transducers for electronic biosensing. We demonstrate that these platforms allow for the quantitative, in situ, and in real time monitoring of bio-affinity reactions between analytes from solution to the surface-immobilized receptors. The examples given include the binding of anti-bovine serum albumin (BSA) antibodies to their antigen, BSA, covalently attached to the channel of an OFET, or the reverse mode of operation, i.e., the binding of BSA from solution to the antibodies immobilized on a rGO transistor. Finally, we will discuss a few results obtained with odorant binding proteins used as receptors on a rGO–FET transducer for the realization of a biomimetic smell sensor.

Monte Carlo Simulation of Nanowires Array Biosensor With AC Electroosmosis

Critically important for electronic biosensing is to reduce detection time that is necessary to sense the capture of biomolecules. The essential factors to study the detection time are the number of captured biomolecules per unit time and the sensitivity of capturing biomolecules. In this paper, we numerically study how ac electroosmosis (ACEO) improves the performance of biosensor unit comprising 400 nanowires by using a Monte Carlo simulation. Note that the number of captured biomolecules per unit time hardly increases if a depleted fluid layer hides the biosensor unit from biomolecules in electrolyte. However, the Monte Carlo simulation tells us that ACEO removes the depleted fluid layer by circulating the electrolyte. This improves the capture efficiency by 4.4 times and the detection speed by 24.8 times. Furthermore, we discuss the scaling effect of nanowires on the sensitivity. As a result, we can more improve the sensitivity if we bury nanowires in a planar oxide layer than wrapping it by an oxide film.

Electronic Biosensing with Functionalized rGO FETs.

In the following we give a short summary of examples for biosensor concepts in areas in which reduced graphene oxide-based electronic devices can be developed into new classes of biosensors, which are highly sensitive, label-free, disposable and cheap, with electronic signals that are easy to analyze and interpret, suitable for multiplexed operation and for remote control, compatible with NFC technology, etc., and in many cases a clear and promising alternative to optical sensors. The presented areas concern sensing challenges in medical diagnostics with an example for detecting general antibody-antigen interactions, for the monitoring of toxins and pathogens in food and feed stuff, exemplified by the detection of aflatoxins, and the area of smell sensors, which are certainly the most exciting development as there are very few existing examples in which the typically small and hydrophobic odorant molecules can be detected by other means. The example given here concerns the recording of a honey flavor (and a cancer marker for neuroblastoma), homovanillic acid, by the odorant binding protein OBP 14 from the honey bee, immobilized on the reduced graphene oxide gate of an FET sensor.

Electronic desalting for controlling the ionic environment in droplet-based biosensing platforms.

The ability to control the ionic environment in saline waters and aqueous electrolytes is useful for desalination as well as electronic biosensing. We demonstrate a method of electronic desalting at micro-scale through on-chip micro electrodes. We show that, while desalting is limited in bulk solutions with unlimited availability of salts, significant desalting of ≥1 mM solutions can be achieved in sub-nanoliter volume droplets with diameters of ∼250 μm. Within these droplets, by using platinum-black microelectrodes and electrochemical surface treatments, we can enhance the electrode surface area to achieve >99% and 41% salt removal in 1 mM and 10 mM salt concentrations, respectively. Through self-consistent simulations and experimental measurements, we demonstrate that conventional double-layer theory over-predicts the desalting capacity and, hence, cannot be used to model systems that are mass limited or undergoing significant salt removal from the bulk. Our results will provide a better understanding of capacitive desalination, as well as a method for salt manipulation in high-throughput droplet-based microfluidic sensing platforms.

Electrochemical processes and mechanistic aspects of field-effect sensors for biomolecules.

Electronic biosensing is a leading technology for determining concentrations of biomolecules. In some cases, the presence of an analyte molecule induces a measured change in current flow, while in other cases, a new potential difference is established. In the particular case of a field effect biosensor, the potential difference is monitored as a change in conductance elsewhere in the device, such as across a film of an underlying semiconductor. Often, the mechanisms that lead to these responses are not specifically determined. Because improved understanding of these mechanisms will lead to improved performance, it is important to highlight those studies where various mechanistic possibilities are investigated. This review explores a range of possible mechanistic contributions to field-effect biosensor signals. First, we define the field-effect biosensor and the chemical interactions that lead to the field effect, followed by a section on theoretical and mechanistic background. We then discuss materials used in field-effect biosensors and approaches to improving signals from field-effect biosensors. We specifically cover the biomolecule interactions that produce local electric fields, structures and processes at interfaces between bioanalyte solutions and electronic materials, semiconductors used in biochemical sensors, dielectric layers used in top-gated sensors, and mechanisms for converting the surface voltage change to higher signal/noise outputs in circuits.