Monolithic integration of a silicon nanowire field-effect transistors array on a complementary metal-oxide semiconductor chip for biochemical sensor applications

Advances in field-effect biosensors towards point-of-use

The future of medical diagnostics calls for portable biosensors at the point of care, aiming to improve healthcare by reducing costs, improving access, and increasing quality-what is called the 'triple aim'. Developing point-of-care sensors that provide high sensitivity, detect multiple analytes, and provide real time measurements can expand access to medical diagnostics for all. Field-effect transistor (FET)-based biosensors have several advantages, including ultrahigh sensitivity, label-free and amplification-free detection, reduced cost and complexity, portability, and large-scale multiplexing. They can also be integrated into wearable or implantable devices and provide continuous, real-time monitoring of analytesin vivo, enabling early detection of biomarkers for disease diagnosis and management. This review analyzes advances in the sensitivity, parallelization, and reusability of FET biosensors, benchmarks the limit of detection of the state of the art, and discusses the challenges and opportunities of FET biosensors for future healthcare applications.

Multisite Dopamine Sensing With Femtomolar Resolution Using a CMOS Enabled Aptasensor Chip

Many biomarkers including neurotransmitters are found in external body fluids, such as sweat or saliva, but at lower titration levels than they are present in blood. Efficient detection of such biomarkers thus requires, on the one hand, to use techniques offering high sensitivity, and, on the other hand, to use a miniaturized format to carry out diagnostics in a minimally invasive way. Here, we present the hybrid integration of bottom-up silicon-nanowire Schottky-junction FETs (SiNW SJ-FETs) with complementary-metal–oxide–semiconductor (CMOS) readout and amplification electronics to establish a robust biosensing platform with 32 × 32 aptasensor measurement sites at a 100 μm pitch. The applied hetero-junctions yield a selective biomolecular detection down to femtomolar concentrations. Selective and multi-site detection of dopamine is demonstrated at an outstanding sensitivity of ∼1 V/fM. The integrated platform offers great potential for detecting biomarkers at high dilution levels and could be applied, for example, to diagnosing neurodegenerative diseases or monitoring therapy progress based on patient samples, such as tear liquid, saliva, or eccrine sweat.

Direct whole blood analysis by the antigen-antibody chemically-delayed dissociation from nanosensors arrays

A wide range of fields, starting from basic research in life sciences and up to medical applications, are highly interested in the investigation and detection of biomarkers in all their forms, including proteins. However, direct analytical detection of specific protein biomarkers from a physiological biosample is still extremely challenging due to the abundant variety and amount of its components. In this work, we apply the chemically-controlled antigen-dissociation detection approach on silicon nanowires-based field-effect transistor arrays, by creating a suitable 'chemical environment' which enabled the clear-cut splitting of the dissociation regime window into two sub-regimes, thus allowing the complete washing of the nonspecifically adsorbed salts and biomolecules, while significantly delaying the dissociation of specific surface-bounded antigen-antibody pairs. This was accomplished by the addition of the water-miscible organic reagent ethylene glycol, which radically alters the properties of the aqueous solvent, by means of dramatically reducing its interactions with the particular protein antigen, and thus allowing for the increase in the antigen-antibody interaction strength. This in turn, deeply reduces the solubility of the surface-bound protein molecules and increases their interaction with the specific receptor antibody units, which brings to a substantial delay in the antibody-antigen dissociation behavior. This phenomenon allows the clear-cut splitting of the dissociation regime window and the quantitative and accurate analysis of proteins in physiological samples. We demonstrated the direct and quantitative detection of protein biomarkers, down to concentrations in the fM range, from unprocessed whole blood minuscule samples of only a few microliters. This work is the first demonstration on the chemically-controlled dissociation kinetics of antibody-antigen pairs by the use of water-miscible organic solvent mixtures, and its application in the direct ultrasensitive detection of protein biomarkers from whole blood samples.

Direct Detection of Uranyl in Urine by Dissociation from Aptamer-Modified Nanosensor Arrays

An ever-growing demand for uranium in various industries raises concern for human health of both occupationally exposed personnel and the general population. Toxicological effects related to uranium (natural, enriched, or depleted uranium) intake involve renal, pulmonary, neurological, skeletal, and hepatic damage. Absorbed uranium is filtered by the kidneys and excreted in the urine, thus making uranium detection in urine a primary indication for exposure and body burden assessment. Therefore, the detection of uranium contamination in bio-samples (urine, blood, saliva, etc.,) is of crucial importance in the field of occupational exposure and human health-related applications, as well as in nuclear forensics. However, the direct determination of uranium in bio-samples is challenging because of "ultra-low" concentrations of uranium, inherent matrix complexity, and sample diversity, which pose a great analytical challenge to existing detection methods. Here, we report on the direct, real-time, sensitive, and selective detection of uranyl ions in unprocessed and undiluted urine samples using a uranyl-binding aptamer-modified silicon nanowire-based field-effect transistor (SiNW-FET) biosensor, with a detection limit in the picomolar concentration range. The aptamer-modified SiNW-FET presented in this work enables the simple and sensitive detection of uranyl in urine samples. The experimental approach has a straight-forward implementation to other metals and toxic elements, given the availability of target-specific aptamers. Combining the high surface-to-volume ratio of SiNWs, the high affinity and selectivity of the uranyl-binding aptamer, and the distinctive sensing methodology gives rise to a practical platform, offering simple and straightforward sensing of uranyl levels in urine, suitable for field deployment and point-of-care applications.

Real-time monitoring of bacterial biofilms metabolic activity by a redox-reactive nanosensors array

BACKGROUND

Bacterial biofilms are communities of surface-associated microorganisms living in cellular clusters or micro-colonies, encapsulated in a complex matrix composed of an extracellular polymeric substance, separated by open water channels that act as a circulatory system that enable better diffusion of nutrients and easier removal of metabolic waste products. The monitoring of biofilms can provide important information on fundamental biofilm-related processes. That information can shed light on the bacterial processes and enable scientists to find ways of preventing future bacterial infections. Various approaches in use for biofilm analysis are based on microscopic, spectrochemical, electrochemical, and piezoelectrical methods. All these methods provide significant progress in understanding the bio-process related to biofilm formation and eradication, nevertheless, the development of novel approaches for the real-time monitoring of biochemical, in particular metabolic activity, of bacterial species during the formation, life and eradication of biofilms is of great potential importance.

RESULTS

Here, detection and monitoring of the metabolic activity of bacterial biofilms in high-ionic-strength solutions were enabled as a result of novel surface modification by an active redox system, composed of 9,10-dihydroxyanthracene/9,10-anthraquinone, on the oxide layer of the SiNW, yielding a chemically-gated FET array. With the use of enzymatic reactions of oxidases, metabolites can be converted to H2O2 and monitored by the nanosensors. Here, the successful detection of glucose metabolites in high-ionic-strength solutions, such as bacterial media, without pre-processing of small volume samples under different conditions and treatments, has been demonstrated. The biofilms were treated with antibiotics differing in their mechanisms of action and were compared to untreated biofilms. Further examination of biofilms under antibiotic treatment with SiNW-FET devices could shed light on the bioprocess that occurs within the biofilm. Moreover, finding proper treatment that eliminates the biofilm could be examined by the novel nanosensor as a monitoring tool.

CONCLUSIONS

To summarize, the combination of redox-reactive SiNW-FET devices with micro-fluidic techniques enables the performance of rapid, automated, and real-time metabolite detection with the use of minimal sample size, noninvasively and label-free. This novel platform can be used as an extremely sensitive tool for detection and establishing medical solutions for bacterial-biofilm eradication and for finding a proper treatment to eliminate biofilm contaminations. Moreover, the sensing system can be used as a research tool for further understanding of the metabolic processes that occur within the bacterial biofilm population.

Redox-Reactive Field-Effect Transistor Nanodevices for the Direct Monitoring of Small Metabolites in Biofluids toward Implantable Nanosensors Arrays

Chemically modified field-effect transistor (FET) nanodevices were shown to be a selective and extremely sensitive detection platform. In FET-based sensors, signal amplification and transduction is based on electrostatic gating of the nanometric semiconductor channel by analyte-receptor interactions, which measurably affect the transconductance of the device. However, chemically modified FETs must overcome several fundamental limitations before they can be effectively deployed as real-time sensors for bioevents occurring on their surface in complex biofluids. Here, we demonstrate the development of amperoFET devices for the real-time continuous monitoring of small molecular metabolites in biofluids. The surface of the nanowires is covalently modified with a redox reversible moiety, which is easily oxidized in the presence of H2O2. The reversible redox transformation of the surface-confined molecules is carried out by a hot electron injection mechanism, conducted simply by the modulation of the source-drain current through the nanoFET sensing device. By this approach, electrons may be injected by the nanowire element into the surface-confined redox moiety and thus maintain a whole-electrically actuated redox system in which the oxidation state is completely controlled by the current applied to the amperoFET system. The modulation of the source-drain current allows the control of the reduced versus oxidized redox moieties population on the nanowire surface, and this, in turn, is applied as the main sensing mechanism. At a given constant source-drain and gate voltage, the chemical perturbation exerted by the presence of chemical oxidants in the tested biofluid will lead to a measurable conductance change. Alteration in the concentration of the specific metabolite will chemically regulate the extent of perturbation applied to the redox system, which can be utilized for the quantification of the molecular metabolite of interest. These 'equilibrium'-type sensors are fully electrically operated and can be further used in implantable sensing applications.

Hybrid Silicon Nanowire Devices and Their Functional Diversity

In the pool of nanostructured materials, silicon nanostructures are known as conventionally used building blocks of commercially available electronic devices. Their application areas span from miniaturized elements of devices and circuits to ultrasensitive biosensors for diagnostics. In this Review, the current trends in the developments of silicon nanowire-based devices are summarized, and their functionalities, novel architectures, and applications are discussed from the point of view of analog electronics, arisen from the ability of (bio)chemical gating of the carrier channel. Hybrid nanowire-based devices are introduced and described as systems decorated by, e.g., organic complexes (biomolecules, polymers, and organic films), aimed to substantially extend their functionality, compared to traditional systems. Their functional diversity is explored considering their architecture as well as areas of their applications, outlining several groups of devices that benefit from the coatings. The first group is the biosensors that are able to represent label-free assays thanks to the attached biological receptors. The second group is represented by devices for optoelectronics that acquire higher optical sensitivity or efficiency due to the specific photosensitive decoration of the nanowires. Finally, the so-called new bioinspired neuromorphic devices are shown, which are aimed to mimic the functions of the biological cells, e.g., neurons and synapses.

An electrochemical troponin T aptasensor based on the use of a macroporous gold nanostructure

A specific troponin T (TnT) binding aptamer was identified and immobilized on an electrodeposited macroporous gold nanostructure using poly(ethylene glycol) 600, to fabricate a novel and ultrasensitive TnT aptasensor. The transducer surface on the gold disk electrode was characterized by field emission scanning electron microscopy, and immobilization of the aptamer was monitored by open circuit potential measurements. Binding of TnT by the aptamer was monitored by differential pulse voltammetry using ferro/ferricyanide as the redox probe. The aptamer has a high affinity and specificity, and the electrode is sensitive and selective. Best operated at a working potential of 0.23 V (vs. Ag/AgCl), the electrode can detected TnT in the 0.05 to 5.0 ng mL^-1 concentration range with a 23 pg mL^-1 detection limit. The method was applied to the determination of TnT in 99 spiked human serum samples, and the diagnostic sensitivity and specificity were 94 and 95%, respectively. Graphical abstract Schematic presentation of an electrochemical troponin T aptasensor. A macroporous gold nanostructure was electrodeposited followed by immobilization of a specific TnT aptamer. Binding of TnT by the aptamer was electrochemically monitored. MCH: mercaptohexanol; TnT: troponin T.

Triple-Junction Optoelectronic Sensor with Nanophotonic Layer Integration for Single-Molecule Level Decoding

Interest in developing a rapid and robust DNA sequencing platform has surged over the past decade. Various next-/third-generation sequencing mechanisms have been employed to replace the traditional Sanger sequencing method. In sequencing by synthesis, a signal is monitored by a scanning charge-coupled device (CCD) to identify thousands to millions of incorporated dNTPs with distinctive fluorophores on a chip. Because one reaction site usually occupies dozens of pixels on a CCD detector, a bottleneck related to the bandwidth of CCD imaging limits the throughputs of the sequencing performance and causes trade-offs among speed, accuracy, read length, and the numbers of reaction sites in parallel. Thus, current research aims to align one reaction site to a few pixels by directly stacking nanophotonic layers onto a CMOS detector to minimize the size of the sequencing platforms and accelerate the processing procedures. This article reports a custom integrated optoelectronic device based on a triple-junction photodiode (TPD) CMOS sensor in conjunction with NPL integration for real-time illumination and detection of fluorescent molecules.

Flexible electrical aptasensor using dielectrophoretic assembly of graphene oxide and its subsequent reduction for cardiac biomarker detection

Cardiac troponin T (cTnT) is considered a clinical standard for its high specificity and sensitivity when diagnosing acute myocardial infarction; however, most studies on the electrical sensors of cardiac troponin biomarkers have focused on cTnI rather than cTnT. This study presents label-free, low-cost, transparent, and flexible aptamer-based immunosensors for the electrical detection of cTnT using reduced graphene oxide (rGO) sheets. GO was first deposited by AC dielectrophoresis between two predefined source and drain electrodes on a 3-aminopropyltriethoxylsilane-modified polyethylene terephthalate substrate. The GO was then reduced using hydrazine vapour without damaging the substrate, resulting in uniform, controlled, and stable deposition of rGO sheets, and demonstrating more stability than those directly deposited by dielectrophoresis. Amine-modified single-strand DNA aptamers against cTnT were immobilized onto the rGO channels. The relative resistance change of this sensor owing to the attachment of cTnT was quantified as the cTnT concentration decreased from 10 ng/mL to 1 pg/mL in phosphate buffered saline (PBS) and 10-fold diluted human serum in PBS, with the limits of detection being 1.2 pg/mL and 1.7 pg/mL, respectively, which is sufficiently sensitive for clinical applications. High-yield and rapid fabrication of the present rGO sensors will have significant influences on scaled-up fabrication of graphene-based sensors.

Development of the Troponin Detection System Based on the Nanostructure

During the last 30 years, the World Health Organization (WHO) reported a gradual increase in the number of patients with cardiovascular disease (CVD), not only in developed but also in developing countries. In particular, acute myocardial infarction (AMI) is one of the severe CVDs because of the high death rate, damage to the body, and various complications. During these harmful effects, rapid diagnosis of AMI is key for saving patients with CVD in an emergency. The prompt diagnosis and proper treatment of patients with AMI are important to increase the survival rate of these patients. To treat patients with AMI quickly, detection of a CVD biomarker at an ultra-low concentration is essential. Cardiac troponins (cTNs), cardiac myoglobin (cMB), and creatine kinase MB are typical biomarkers for AMI detection. An increase in the levels of those biomarkers in blood implies damage to cardiomyocytes and thus is related to AMI progression. In particular, cTNs are regarded as a gold standard biomarker for AMI diagnosis. The conventional TN detection system for detection of AMI requires long measurement time and is labor-intensive and tedious. Therefore, the demand for sensitive and selective TN detection techniques is increasing at present. To meet this demand, several approaches and methods have been applied to develop a TN detection system based on a nanostructure. In the present review, the authors reviewed recent advances in TN biosensors with a focus on four detection systems: (1) An electrochemical (EC) TN nanobiosensor, (2) field effect transistor (FET)-based TN nanobiosensor, (3) surface plasmon resonance (SPR)-based TN nanobiosensor and (4) surface enhanced Raman spectroscopy (SERS)-based TN nanobiosensor.

Monolithic CMOS sensor platform featuring an array of 9'216 carbon-nanotube-sensor elements and low-noise, wide-bandwidth and wide-dynamic-range readout circuitry

We present the design and characterization of a monolithic complementary metal-oxide-semiconductor (CMOS) biosensor platform comprising of a switch-matrix-based array of 9'216 carbon nanotube field-effect transistors (CNTFETs) and associated readout circuitry. The switch-matrix allows for flexible selection and simultaneous routing of 96 sensor elements to the corresponding readout channels. A low-noise, wide-bandwidth, wide-dynamic-range transimpedance continuous-time amplifier architecture has been implemented to facilitate resistance measurements in the range between 50 kΩ and 1 GΩ at a bandwidth of up to 1 MHz. The achieved accuracy of the resistance measurements over the whole range is 4%. The system has been successfully fabricated and tested and shows a noise performance equal to 2.14 pArms at a bandwidth of 1 kHz and 0.84 nArms at a bandwidth of 1 MHz. A batch integration of the CNTFETs has been achieved by using a dielectrophoresis (DEP)-based manipulation technique. The current-voltage curves of CNTFETs have been acquired, and the sensing capabilities of the system have been demonstrated by recording resistance changes of CNTFETs upon exposure to solutions with different pH values and different concentrations of NaCl. The smallest resolvable concentrations for the respective analytes were estimated to amount to 0.025 pH-units and 4 mM NaCl.

Multicolor Spectral-Specific Silicon Nanodetectors based on Molecularly Embedded Nanowires

Silicon-based photodetectors cannot distinguish between different wavelengths. Therefore, these detectors relay on color-specific filters to achieve color separation. Color filters add complexity to color sensitive device fabrication, and hinder miniaturization of such devices. Here, we report an ultrasmall (as small as ∼20 nm by 300 nm), red-green-blue-violet (RGBV) filter-free spectrally gated field effect transistor (SGFET) detectors. These photodetectors are based on organic-silicon nanowire hybrid FET devices, capable of detecting specific visible wavelength spectrum with full width at half-maxima (fwhm) under 100 nm. Each SGFET is controlled by a distinctive RGBV spectral range, according to its specific organic fluorophore functionalization. The spectral-specific RGBV detection is accomplished via covalent attachment of different fluorophores. The fluorophore molecules inject electrons into the nanowire structure as a result of light absorption at the appropriate RGBV spectral range. These photoinduced electrons modify the occupancies of the oxide's surface states, shifting the device threshold voltage, thus changing its conductivity, and functioning as a negative stress bias in a p-type SiNW FETs. A positive biasing can be achieved via UV light-induced ionization, which leads to detrapping and translocation of electrons at the oxide layer. Furthermore, a novel theoretical model on the mechanism of action of these devices was developed. Also, we show that suspended SGFETs can function as nonvolatile memory elements, which unlike fast-relaxing on-surface SGFETs, can store discrete "on" (RGBV illumination) and "off" (UV illumination) states for several days at ambient conditions. We also demonstrate a unique single-nanowire multicolor photodetector, enabling in principle a broad spectral detection over a single silicon nanowire element. These highly compact, spectral-controlled nanodevices have the potential to serve in various future novel optoelectric applications.

Field-Effect Biosensors for On-Site Detection: Recent Advances and Promising Targets

There is an explosive interest in the immediate and cost-effective analysis of field-collected biological samples, as many advanced biodetection tools are highly sensitive, yet immobile. On-site biosensors are portable and convenient sensors that provide detection results at the point of care. They are designed to secure precision in highly ionic and heterogeneous solutions with minimal hardware. Among various methods that are capable of such analysis, field-effect biosensors are promising candidates due to their unique sensitivity, manufacturing scalability, and integrability with computational circuitry. Recent developments in nanotechnological surface modification show promising results in sensing from blood, serum, and urine. This report gives a particular emphasis on the on-site efficacy of recently published field-effect biosensors, specifically, detection limits in physiological solutions, response times, and scalability. The survey of the properties and existing detection methods of four promising biotargets, exosomes, bacteria, viruses, and metabolites, aims at providing a roadmap for future field-effect and other on-site biosensors.

Antigen-Dissociation from Antibody-Modified Nanotransistor Sensor Arrays as a Direct Biomarker Detection Method in Unprocessed Biosamples

The detection of biomolecules is critical for a wide spectrum of applications in life sciences and medical diagnosis. Nonetheless, biosamples are highly complex solutions, which contain an enormous variety of biomolecules, cells, and chemical species. Consequently, the intrinsic chemical complexity of biosamples results in a significant analytical background noise and poses an immense challenge to any analytical measurement, especially when applied without prior efficient separation and purification steps. Here, we demonstrate the application of antigen-dissociation regime, from antibody-modified Si-nanowire sensors, as a simple and effective direct sensing mechanism of biomarkers of interest in complex biosamples, such as serum and untreated blood, which does not require ex situ time-consuming biosample manipulation steps, such as centrifugation, filtering, preconcentration, and desalting, thus overcoming the detrimental Debye screening limitation of nanowire-based biosensors. We found that two key parameters control the capability to perform quantitative biomarkers analysis in biosamples: (i) the affinity strength (k_off rate) of the antibody-antigen recognition pair, which dictates the time length of the high-affinity slow dissociation subregime, and (ii) the "flow rate" applied during the solution exchange dissociation step, which controls the time width of the low-affinity fast-dissociation subregime. Undoubtedly, this is the simplest and most convenient approach for the SiNW FET-based detection of antigens in complex untreated biosamples. The lack of ex situ biosample manipulation time-consuming processes enhances the portability of the sensing platform and reduces to minimum the required volume of tested sample, as it allows the direct detection of untreated biosamples (5-10 μL blood or serum), while readily reducing the detection cycle duration to less than 5 min, factors of great importance in near-future point-of-care medical applications. We believe this is the first ever reported demonstration on the real-time, direct label-free sensing of biomarkers from untreated blood samples, using SiNW-based FET devices, while not compromising the ultrasensitive sensing capabilities inherent to these devices.

On the Use of Scalable NanoISFET Arrays of Silicon with Highly Reproducible Sensor Performance for Biosensor Applications

As a prerequisite to the development of real label-free bioassay applications, a high-throughput top-down nanofabrication process is carried out with a combination of nanoimprint lithography, anisotropic wet-etching, and photolithography methods realizing nanoISFET arrays that are then analyzed for identical sensor characteristics. Here, a newly designed array-based sensor chip exhibits 32 high aspect ratio silicon nanowires (SiNWs) laid out in parallel with 8 unit groups that are connected to a very highly doped, Π-shaped common source and individual drain contacts. Intricately designed contact lines exert equal feed-line resistances and capacitances to homogenize the sensor response as well as to minimize parasitic transport effects and to render easy integration of a fluidic layer on top. The scalable nanofabrication process as outlined in this article casts out a total of 2496 nanowires (NWs) on a 4 inch p-type silicon-on-insulator (SOI) wafer, yielding 78 sensor chips based on nanoISFET arrays. The sensor platform exhibiting high-performance transistor characteristics in buffer solutions is thoroughly characterized using state-of-the-art surface and electrical measurement techniques. Deploying a pH sensor in liquid buffers after high-quality gas-phase silanization, nanoISEFT arrays demonstrate typical pH sensor behavior with sensitivity as high as 43 ± 3 mV·pH^-1 and a device-to-device variation of 7% at the wafer scale. Demonstration of a high-density sensor platform with uniform characteristics such as nanoISFET arrays of silicon (Si) in a routine and refined nanofabrication process may serve as an ideal solution deployable for real assay-based applications.

3D Stretchable Arch Ribbon Array Fabricated via Grayscale Lithography

Microstructures with flexible and stretchable properties display tremendous potential applications including integrated systems, wearable devices and bio-sensor electronics. Hence, it is essential to develop an effective method for fabricating curvilinear and flexural microstructures. Despite significant advances in 2D stretchable inorganic structures, large scale fabrication of unique 3D microstructures at a low cost remains challenging. Here, we demonstrate that the 3D microstructures can be achieved by grayscale lithography to produce a curved photoresist (PR) template, where the PR acts as sacrificial layer to form wavelike arched structures. Using plasma-enhanced chemical vapor deposition (PECVD) process at low temperature, the curved PR topography can be transferred to the silicon dioxide layer. Subsequently, plasma etching can be used to fabricate the arched stripe arrays. The wavelike silicon dioxide arch microstructure exhibits Young modulus and fracture strength of 52 GPa and 300 MPa, respectively. The model of stress distribution inside the microstructure was also established, which compares well with the experimental results. This approach of fabricating a wavelike arch structure may become a promising route to produce a variety of stretchable sensors, actuators and circuits, thus providing unique opportunities for emerging classes of robust 3D integrated systems.