Silicon nanowire field-effect-transistor based biosensors: from sensitive to ultra-sensitive

Hydrogel-Gated MXene-Graphene Field-Effect Transistor for Selective Detection and Screening of SARS-CoV-2 and E. coli Bacteria

Field-effect transistor (FET) biosensors have significantly attracted interest across various disciplines because of their high sensitivity, time-saving, and label-free characteristics. However, it remains a grand challenge to interface the FET biosensor with complex liquid media. Unlike standard liquid electrolytes containing purified protein content, directly exposing FET biosensors to complex biological fluids introduces significant sensing noise, which is caused by the abundance of nonspecific proteins, viruses, and bacteria that adsorb to the biosensor surfaces. In this work, we leverage the hydrogel encapsulation on an MXene-graphene-based FET, which selectively allows the permeation of viruses (e.g., SARS-CoV-2) and bacteria (e.g., E. coli), leading to the high-specificity detection of those biomarkers. The results demonstrated that hydrogel encapsulation could successfully detect the SARS-CoV-2 biomarker at 1 fg/mL while preventing the diffusion of E. coli biomarkers, and the obtained signal output amplitude is twice that of sensors without hydrogel encapsulation, demonstrating significant advantages over conventional bare sensors.

A comprehensive review on the biomedical frontiers of nanowire applications

This comprehensive review examines the immense capacity of nanowires, nanostructures characterized by unbounded dimensions, to profoundly transform the field of biomedicine. Nanowires, which are created by combining several materials using techniques such as electrospinning and vapor deposition, possess distinct mechanical, optical, and electrical properties. As a result, they are well-suited for use in nanoscale electronic devices, drug delivery systems, chemical sensors, and other applications. The utilization of techniques such as the vapor-liquid-solid (VLS) approach and template-assisted approaches enables the achievement of precision in synthesis. This precision allows for the customization of characteristics, which in turn enables the capability of intracellular sensing and accurate drug administration. Nanowires exhibit potential in biomedical imaging, neural interfacing, and tissue engineering, despite obstacles related to biocompatibility and scalable manufacturing. They possess multifunctional capabilities that have the potential to greatly influence the intersection of nanotechnology and healthcare. Surmounting present obstacles has the potential to unleash the complete capabilities of nanowires, leading to significant improvements in diagnostics, biosensing, regenerative medicine, and next-generation point-of-care medicines.

Alzheimer's Disease Biomarker Detection Using Field Effect Transistor-Based Biosensor

Alzheimer's disease (AD) is closely related to neurodegeneration, leading to dementia and cognitive impairment, especially in people aged > 65 years old. The detection of biomarkers plays a pivotal role in the diagnosis and treatment of AD, particularly at the onset stage. Field-effect transistor (FET)-based sensors are emerging devices that have drawn considerable attention due to their crucial ability to recognize various biomarkers at ultra-low concentrations. Thus, FET is broadly manipulated for AD biomarker detection. In this review, an overview of typical FET features and their operational mechanisms is described in detail. In addition, a summary of AD biomarker detection and the applicability of FET biosensors in this research field are outlined and discussed. Furthermore, the trends and future prospects of FET devices in AD diagnostic applications are also discussed.

The Study of Performance of a Nanoribbon Biosensor, Sensitized with Aptamers and Antibodies, upon Detection of Core Antigen of Hepatitis C Virus

The development of highly sensitive diagnostic systems for the early revelation of diseases in humans is one of the most important tasks of modern biomedical research, and the detection of the core antigen of the hepatitis C virus (HCVcoreAg)-a protein marker of the hepatitis C virus-is just the case. Our study is aimed at testing the performance of the nanoribbon biosensor in the case of the use of two different types of molecular probes: the antibodies and the aptamers against HCVcoreAg. The nanoribbon sensor chips employed are based on "silicon-on-insulator structures" (SOI-NR). Two different HCVcoreAg preparations are tested: recombinant β-galactosidase-conjugated HCVcoreAg ("Virogen", Watertown, MA, USA) and recombinant HCVcoreAg ("Vector-Best", Novosibirsk, Russia). Upon the detection of either type of antigen preparation, the lowest concentration of the antigen detectable in buffer with pH 5.1 was found to be approximately equal, amounting to ~10-15 M. This value was similar upon the use of either type of molecular probes.

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.

Investigating on sensing mechanism of MoS2-FET biosensors in response to proteins

Field-effect transistor (FET) biosensors based on two-dimensional materials have gained extensive attention due to their high sensitivity, label-free detection capability, and fast response. Molybdenum disulfide (MoS2), with tunable bandgap, high surface-to-volume ratio, and smooth surface without dangling bonds, is a promising material for FET biosensors. Previous reports have demonstrated the fabrication of MoS2-FET biosensors and their high sensitivity detection of proteins. However, most prior research has focused on the realization of MoS2-FETs for detecting different kinds of proteins or molecules, while comprehensive analysis of the sensing mechanism and dominant device factors of MoS2-FETs in response to proteins is yet to investigate. In this study, we first fabricated MoS2-FET biosensor and detected different types of proteins (immunoglobulin G (IgG),β-actin, and prostate-specific antigen (PSA)). Secondly, we built the model of the device and analyzed the sensing mechanism of MoS2-FETs in response to proteins. Experimental and modeling results showed that the induced doping effect and gating effect caused by the target protein binding to the device surface were the major influential factors. Specifically, the channel doping concentration and gate voltage (Vg) offset exhibited monotonic change as the concentration of the protein solution increases. For example, the channel doping concentration increased up to ∼37.9% and theVgoffset was ∼-1.3 V with 10-7μgμl-1IgG. The change was less affected by the device size. We also investigated the effects of proteins with opposite acid-base properties (β-actin and PSA) to IgG on the device sensing mechanism.β-actin and PSA exhibited behavior opposite to that of IgG. Additionally, we studied the response behavior of MoS2-FETs with different dimensions and dielectric materials (channel length, MoS2thickness, dielectric layer thickness, dielectric layer material) to proteins. The underlying mechanisms were discussed in details. This study provides valuable guidelines for the design and application of MoS2-FET biosensors.

Application of Silicon Nanowire Field Effect Transistor (SiNW-FET) Biosensor with High Sensitivity

As a new type of one-dimensional semiconductor nanometer material, silicon nanowires (SiNWs) possess good application prospects in the field of biomedical sensing. SiNWs have excellent electronic properties for improving the detection sensitivity of biosensors. The combination of SiNWs and field effect transistors (FETs) formed one special biosensor with high sensitivity and target selectivity in real-time and label-free. Recently, SiNW-FETs have received more attention in fields of biomedical detection. Here, we give a critical review of the progress of SiNW-FETs, in particular, about the reversible surface modification methods. Moreover, we summarized the applications of SiNW-FETs in DNA, protein, and microbial detection. We also discuss the related working principle and technical approaches. Our review provides an extensive discussion for studying the challenges in the future development of SiNW-FETs.

Ultrasensitive Silicon Nanowire Biosensor with Modulated Threshold Voltages and Ultra-Small Diameter for Early Kidney Failure Biomarker Cystatin C

Acute kidney injury (AKI) is a frequently occurring severe disease with high mortality. Cystatin C (Cys-C), as a biomarker of early kidney failure, can be used to detect and prevent acute renal injury. In this paper, a biosensor based on a silicon nanowire field-effect transistor (SiNW FET) was studied for the quantitative detection of Cys-C. Based on the spacer image transfer (SIT) processes and channel doping optimization for higher sensitivity, a wafer-scale, highly controllable SiNW FET was designed and fabricated with a 13.5 nm SiNW. In order to improve the specificity, Cys-C antibodies were modified on the oxide layer of the SiNW surface by oxygen plasma treatment and silanization. Furthermore, a polydimethylsiloxane (PDMS) microchannel was involved in improving the effectiveness and stability of detection. The experimental results show that the SiNW FET sensors realize the lower limit of detection (LOD) of 0.25 ag/mL and have a good linear correlation in the range of Cys-C concentration from 1 ag/mL to 10 pg/mL, exhibiting its great potential in the future real-time application.

Advances in silicon nanowire applications in energy generation, storage, sensing, and electronics: a review

Nanowire-based technological advancements thrive in various fields, including energy generation and storage, sensors, and electronics. Among the identified nanowires, silicon nanowires (SiNWs) attract much attention as they possess unique features, including high surface-to-volume ratio, high electron mobility, bio-compatibility, anti-reflection, and elasticity. They were tested in domains of energy generation (thermoelectric, photo-voltaic, photoelectrochemical), storage (lithium-ion battery (LIB) anodes, super capacitors), and sensing (bio-molecules, gas, light, etc). These nano-structures were found to improve the performance of the system in terms of efficiency, stability, sensitivity, selectivity, cost, rapidity, and reliability. This review article scans and summarizes the significant developments that occurred in the last decade concerning the application of SiNWs in the fields of thermoelectric, photovoltaic, and photoelectrochemical power generation, storage of energy using LIB anodes, biosensing, and disease diagnostics, gas and pH sensing, photodetection, physical sensing, and electronics. The functionalization of SiNWs with various nanomaterials and the formation of heterostructures for achieving improved characteristics are discussed. This article will be helpful to researchers in the field of nanotechnology about various possible applications and improvements that can be realized using SiNW.

Polyethylene Glycol Functionalized Silicon Nanowire Field-Effect Transistor Biosensor for Glucose Detection

Accurate monitoring of blood glucose levels is crucial for the diagnosis of diabetes patients. In this paper, we proposed a simple "mixed-catalyzer layer" modified silicon nanowire field-effect transistor biosensor that enabled direct detection of glucose with low-charge in high ionic strength solutions. A stable screening system was established to overcome Debye screening effect by forming a porous biopolymer layer with polyethylene glycol (PEG) modified on the surface of SiNW. The experimental results show that when the optimal ratio (APTMS:silane-PEG = 2:1) modified the surface of silicon nanowires, glucose oxidase can detect glucose in the concentration range of 10 nM to 10 mM. The sensitivity of the biosensor is calculated to be 0.47 μAcm^-2mM^-1, its fast response time not exceeding 8 s, and the detection limit is up to 10 nM. This glucose sensor has the advantages of high sensitivity, strong specificity and fast real-time response. Therefore, it has a potential clinical application prospect in disease diagnosis.

"Silicon-On-Insulator"-Based Biosensor for the Detection of MicroRNA Markers of Ovarian Cancer

Ovarian cancer is a gynecological cancer characterized by a high mortality rate and tumor heterogeneity. Its early detection and primary prophylaxis are difficult to perform. Detecting biomarkers for ovarian cancer plays a pivotal role in therapy effectiveness and affects patients' survival. This study demonstrates the detection of microRNAs (miRNAs), which were reported to be associated with ovarian cancer tumorigenesis, with a nanowire biosensor based on silicon-on-insulator structures (SOI-NW biosensor). The advantages of the method proposed for miRNA detection using the SOI-NW biosensor are as follows: (1) no need for additional labeling or amplification reaction during sample preparation, and (2) real-time detection of target biomolecules. The detecting component of the biosensor is a chip with an array of 3 µm wide, 10 µm long silicon nanowires on its surface. The SOI-NW chip was fabricated using the "top-down" method, which is compatible with large-scale CMOS technology. Oligonucleotide probes (oDNA probes) carrying sequences complementary to the target miRNAs were covalently immobilized on the nanowire surface to ensure high-sensitivity biospecific sensing of the target biomolecules. The study involved two experimental series. Detection of model DNA oligonucleotides being synthetic analogs of the target miRNAs was carried out to assess the method's sensitivity. The lowest concentration of the target oligonucleotides detectable in buffer solution was 1.1 × 10^-16 M. In the second experimental series, detection of miRNAs (miRNA-21, miRNA-141, and miRNA-200a) isolated from blood plasma samples collected from patients having a verified diagnosis of ovarian cancer was performed. The results of our present study represent a step towards the development of novel highly sensitive diagnostic systems for the early revelation of ovarian cancer in women.

Fabrication of Silicon Nanowire Sensors for Highly Sensitive pH and DNA Hybridization Detection

A highly sensitive silicon nanowire (SiNW)-based sensor device was developed using electron beam lithography integrated with complementary metal oxide semiconductor (CMOS) technology. The top-down fabrication approach enables the rapid fabrication of device miniaturization with uniform and strictly controlled geometric and surface properties. This study demonstrates that SiNW devices are well-aligned with different widths and numbers for pH sensing. The device consists of a single nanowire with 60 nm width, exhibiting an ideal pH responsivity (18.26 × 10⁶ Ω/pH), with a good linear relation between the electrical response and a pH level range of 4–10. The optimized SiNW device is employed to detect specific single-stranded deoxyribonucleic acid (ssDNA) molecules. To use the sensing area, the sensor surface was chemically modified using (3-aminopropyl) triethoxysilane and glutaraldehyde, yielding covalently linked nanowire ssDNA adducts. Detection of hybridized DNA works by detecting the changes in the electrical current of the ssDNA-functionalized SiNW sensor, interacting with the targeted ssDNA in a label-free way. The developed biosensor shows selectivity for the complementary target ssDNA with linear detection ranging from 1.0 × 10⁻¹² M to 1.0 × 10⁻⁷ M and an attained detection limit of 4.131 × 10⁻¹³ M. This indicates that the use of SiNW devices is a promising approach for the applications of ion detection and biomolecules sensing and could serve as a novel biosensor for future biomedical diagnosis.

A Fast and Label-Free Potentiometric Method for Direct Detection of Glutamine with Silicon Nanowire Biosensors

In this paper, a potentiometric method is used for monitoring the concentration of glutamine in the bioprocess by employing silicon nanowire biosensors. Just one hydrolyzation reaction was used, which is much more convenient compared with the two-stage reactions in the published papers. For the silicon nanowire biosensor, the Al2O3 sensing layer provides a highly sensitive to solution-pH, which has near-Nernstian sensitivity. The sensitive region to detect glutamine is from ≤40 μM to 20 mM. The Sigmoidal function was used to model the pH-signal variation versus the glutamine concentration. Compared with the amperometric methods, a consistent result from different devices could be directly obtained. It is a fast and direct method achieved with our real-time setup. Also, it is a label-free method because just the pH variation of the solution is monitored. The obtained results show the feasibility of the potentiometric method for monitoring the glutamine concentrations in fermentation processes. Our approach in this paper can be applied to various analytes.

Label-free electrical monitoring of nucleic acid amplification with integrated hydrogel ionic diodes

We demonstrate here for the first time the utility of a monolithically integrated hydrogel ionic diode for label-free quantitative DNA detection and real-time monitoring of nucleic acid amplification. The hydrogel ionic diode presented herein, unlike nanomaterial-based field-effect biosensors, features high cost-effectiveness and convenient fabrication. This is realized by patterning a micrometer-sized heterojunction consisting of adjacent segments of polycationic and polyanionic hydrogels on a microfluidic chip through simple photocuring steps. The integrated diode rectifies ionic currents being sensitive to the charge of DNA adsorbed onto the polycationic chains through electrostatic associations. Based on the mechanism, we show that the ionic biosensor can electrically quantify DNA in a dynamic range relevant to typical nucleic acid amplification assays. Utilizing the device, we demonstrate the evaluation of a PCR assay amplifying a 500-bp DNA fragment of E. coli, an infection-causing pathogen, and real-time in situ monitoring of an isothermal assay amplifying E. coli whole genome. We anticipate that the device could potentially pave the way for miniaturized optics-free platforms for quantifying nucleic acid amplification at point-of-care.

Nucleic acid-based electrochemical biosensors for rapid clinical diagnosis: advances, challenges, and opportunities

Clinical diagnostic tests should be quick, reliable, simple to perform, and affordable for diagnosis and treatment of diseases. In this regard, owing to their novel properties, biosensors have attracted the attention of scientists as well as end-users. They are efficient, stable, and relatively cheap. Biosensors have broad applications in medical diagnosis, including point-of-care (POC) monitoring, forensics, and biomedical research. The electrochemical nucleic acid (NA) biosensor, the latest invention in this field, combines the sensitivity of electroanalytical methods with the inherent bioselectivity of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The NA biosensor exploits the affinity of single-stranded DNA/RNA for its complementary strand and is used to detect complementary sequences of NA based on hybridization. After the NA component in the sensor detects the analyte, a catalytic reaction or binding event that generates an electrical signal in the transducer ensues. Since 2000, much progress has been made in this field, but there are still numerous challenges. This critical review describes the advances, challenges, and prospects of NA-based electrochemical biosensors for clinical diagnosis. It includes the basic principles, classification, sensing enhancement strategies, and applications of biosensors as well as their advantages, limitations, and future prospects, and thus it should be useful to academics as well as industry in the improvement and application of EC NA biosensors.

Design and Development of Graphene FET Biosensor for the Detection of SARS-CoV-2

The most affected disease in recent years is Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-COV-2) that is notable as COVID-19. It has been started as a disease in one place and arisen as a pandemic throughout the world. A serious health problem is developed in the lungs due to the effect of this coronavirus. Sometimes it may result in death as a consequence of extensive alveolar damage and progressive respiratory failure. Hence, early detection and appropriate diagnosis of corona virus in patient’s body is very essential to save the lives of affected patients This work evolves a Silicon (Si) based label-free electrical device i.e. the reduced graphene oxide field-effect transistor (rGO FET) for SARS-CoV-2 detection. Firstly rGO FET functionalized with SARS-CoV-2 monoclonal antibodies (mAbs). Then the rGO FET characteristic response is observed to detect the antibody-antigen reaction of SARS-CoV-2 with different molar ranges. The developed GFET shows better performance towards the drain current and limit-of-detection (LoD) up to 2E-18 M. Therefore, we believe that an intense response was observed than the earlier developed devices and signifies impressive capability for subsequent implementation in point-of-care (PoC) diagnostic tests.

Si nanowire Bio-FET for electrical and label-free detection of cancer cell-derived exosomes

Exosomes are highly important in clinical diagnosis due to their high homology with their parental cells. However, conventional exosome detection methods still face the challenges of expensive equipment, low sensitivity, and complex procedures. Field effect transistors (FETs) are not only the most essential electronic component in the modern microelectronics industry but also show great potential for biomolecule detection owing to the advantages of rapid response, high sensitivity, and label-free detection. In this study, we proposed a Si nanowire field-effect transistor (Si-NW Bio-FET) device chemically modified with specific antibodies for the electrical and label-free detection of exosomes. The Si-NW FETs were fabricated by standard microelectronic processes with 45 nm width nanowires and packaged in a polydimethylsiloxane (PDMS) microfluidic channel. The nanowires were further modified with the specific CD63 antibody to form a Si-NW Bio-FET. The use of the developed Si-NW Bio-FET for the electrical and label-free detection of exosomes was successfully demonstrated with a limit of detection (LOD) of 2159 particles/mL. In contrast to other technologies, in this study, Si-NW Bio-FET provides a unique strategy for directly quantifying and real-time detecting exosomes without labeling, indicating its potential as a tool for the early diagnosis of cancer.

Transistor-Based Biomolecule Sensors: Recent Technological Advancements and Future Prospects

Transistor-based sensors have been widely recognized to be highly sensitive and reliable for point-of-care/bed-side diagnosis. In this line, a range of cutting-edge technologies has been generated to elevate the role of transistors for biomolecule detection. Detection of a wide range of clinical biomarkers has been reported using various configurations of transistors. The inordinate sensitivity of transistors to the field-effect imparts high sensitivity toward wide range of biomolecules. This overview has gleaned the present achievements with the technological advancements using high performance transistor-based sensors. This review encloses transistors incorporated with a variety of functional nanomaterials and organic elements for their excellence in selectivity and sensitivity. In addition, the technological advancements in fabrication of these microdevices or nanodevices and functionalization of the sensing elements have also been discussed. The technological gap in the realization of sensors in transistor platforms and the resulted scope for research has been discussed. Finally, foreseen technological advancements and future research perspectives are described.

Silicon Nanowire Field-Effect Transistor as Label-Free Detection of Hepatitis B Virus Proteins with Opposite Net Charges

The prevalence of hepatitis B virus (HBV) is a global healthcare threat, particularly chronic hepatitis B (CHB) that might lead to hepatocellular carcinoma (HCC) should not be neglected. Although many types of HBV diagnosis detection methods are available, some technical challenges, such as the high cost or lack of practical feasibility, need to be overcome. In this study, the polycrystalline silicon nanowire field-effect transistors (pSiNWFETs) were fabricated through commercial process technology and then chemically functionalized for sensing hepatitis B virus surface antigen (HBsAg) and hepatitis B virus X protein (HBx) at the femto-molar level. These two proteins have been suggested to be related to the HCC development, while the former is also the hallmark for HBV diagnosis, and the latter is an RNA-binding protein. Interestingly, these two proteins carried opposite net charges, which could serve as complementary candidates for evaluating the charge-based sensing mechanism in the pSiNWFET. The measurements on the threshold voltage shifts of pSiNWFETs showed a consistent correspondence to the polarity of the charges on the proteins studied. We believe that this report can pave the way towards developing an approachable tool for biomedical applications.

Passively driven microfluidic device with simple operation in the development of nanolitre droplet assay in nucleic acid detection

Since nucleic acid amplification technology has become a vital tool for disease diagnosis, the development of precise applied nucleic acid detection technologies in point-of care testing (POCT) has become more significant. The microfluidic-based nucleic acid detection platform offers a great opportunity for on-site diagnosis efficiency, and the system is aimed at user-friendly access. Herein, we demonstrate a microfluidic system with simple operation that provides reliable nucleic acid results from 18 uniform droplets via LAMP detection. By using only micropipette regulation, users are able to control the nanoliter scale of the droplets in this valve-free and pump-free microfluidic (MF) chip. Based on the oil enclosure method and impermeable fabrication, we successfully preserved the reagent inside the microfluidic system, which significantly reduced the fluid loss and condensation. The relative standard deviation (RSD) of the fluorescence intensity between the droplets and during the heating process was < 5% and 2.0%, respectively. Additionally, for different nucleic acid detection methods, the MF-LAMP chip in this study showed good applicability to both genome detection and gene expression analysis.

Optimizing surface modification of silicon nanowire field-effect transistors by polyethylene glycol for MicroRNA detection

MicroRNA (miRNA) sensing plays an essential role in the diagnosis of several diseases, especially cancers, for appropriate intervention and treatment. However, quantifying miRNA demands highly sensitive and selective assays which can distinguish analogous sequences with low abundance in bio-samples and determine wide range of concentrations. In this report, we present a novel technique satisfying all those requirements by modifying silicon nanowire field-effect transistors (SiNWFETs) with 2-component mixed self-assembled monolayers (mSAMs) of polyethylene glycol (PEG) at different ratios (silane-PEG-NH₂:silane-PEG-OH = 1:1, 1:3, and 1:5) and glutaraldehyde to immobilize DNA probes for miRNA-21 detection, a biomarker in several types of cancers. Empirical results reveal that all the fabricated PEG-SiNWFET DNA biosensors could quantify miRNA-21 within 1 fM - 10 pM. Especially, the ones modified with silane-PEG-NH₂:silane-PEG-OH = 1:3 exhibited an outstanding performance to recognize miRNA-21 at an ultra-low concentration of 10 aM in the dynamic range up to 6 orders of magnitude (10 aM - 10 pM). This approach is more convenient, analytical competitive, and cost-effective in comparison with currently used methods for nucleic acid testing because of label- and amplification-free characteristics. It is therefore not only feasible for miRNA detection by SiNWFET-based biosensors but also potential for clinical applications of disease diagnosis with oligonucleotide biomarkers.

Addressing the Theoretical and Experimental Aspects of Low-Dimensional-Materials-Based FET Immunosensors: A Review

Electrochemical immunosensors (EI) have been widely investigated in the last several years. Among them, immunosensors based on low-dimensional materials (LDM) stand out, as they could provide a substantial gain in fabricating point-of-care devices, paving the way for fast, precise, and sensitive diagnosis of numerous severe illnesses. The high surface area available in LDMs makes it possible to immobilize a high density of bioreceptors, improving the sensitivity in biorecognition events between antibodies and antigens. If on the one hand, many works present promising results in using LDMs as a sensing material in EIs, on the other hand, very few of them discuss the fundamental interactions involved at the interfaces. Understanding the fundamental Chemistry and Physics of the interactions between the surface of LDMs and the bioreceptors, and how the operating conditions and biorecognition events affect those interactions, is vital when proposing new devices. Here, we present a review of recent works on EIs, focusing on devices that use LDMs (1D and 2D) as the sensing substrate. To do so, we highlight both experimental and theoretical aspects, bringing to light the fundamental aspects of the main interactions occurring at the interfaces and the operating mechanisms in which the detections are based.

Recent Advances of Field-Effect Transistor Technology for Infectious Diseases

Field-effect transistor (FET) biosensors have been intensively researched toward label-free biomolecule sensing for different disease screening applications. High sensitivity, incredible miniaturization capability, promising extremely low minimum limit of detection (LoD) at the molecular level, integration with complementary metal oxide semiconductor (CMOS) technology and last but not least label-free operation were amongst the predominant motives for highlighting these sensors in the biosensor community. Although there are various diseases targeted by FET sensors for detection, infectious diseases are still the most demanding sector that needs higher precision in detection and integration for the realization of the diagnosis at the point of care (PoC). The COVID-19 pandemic, nevertheless, was an example of the escalated situation in terms of worldwide desperate need for fast, specific and reliable home test PoC devices for the timely screening of huge numbers of people to restrict the disease from further spread. This need spawned a wave of innovative approaches for early detection of COVID-19 antibodies in human swab or blood amongst which the FET biosensing gained much more attention due to their extraordinary LoD down to femtomolar (fM) with the comparatively faster response time. As the FET sensors are promising novel PoC devices with application in early diagnosis of various diseases and especially infectious diseases, in this research, we have reviewed the recent progress on developing FET sensors for infectious diseases diagnosis accompanied with a thorough discussion on the structure of Chem/BioFET sensors and the readout circuitry for output signal processing. This approach would help engineers and biologists to gain enough knowledge to initiate their design for accelerated innovations in response to the need for more efficient management of infectious diseases like COVID-19.

A supersensitive silicon nanowire array biosensor for quantitating tumor marker ctDNA

Cancer has become one of the major diseases threatening human health and life. Circulating tumor DNA (ctDNA) testing, as a practical liquid biopsy technique, is a promising method for cancer diagnosis, targeted therapy and prognosis. Here, for the first time, a field effect transistor (FET) biosensor based on uniformly sized high-response silicon nanowire (SiNW) array was studied for real-time, label-free, super-sensitive detection of PIK3CA E542K ctDNA. High-response 120-SiNWs array was fabricated on a (111) silicon-on-insulator (SOI) by the complementary metal oxide semiconductor (CMOS)-compatible microfabrication technology. To detecting ctDNA, we modified the DNA probe on the SiNWs array through silanization. The experimental results demonstrated that the as-fabricated biosensor had significant superiority in ctDNA detection, which achieved ultralow detection limit of 10 aM and had a good linearity under the ctDNA concentration range from 0.1 fM to 100 pM. This biosensor can recognize complementary target ctDNA from one/two/full-base mismatched DNA with high selectivity. Furthermore, the fabricated SiNW-array FET biosensor successfully detected target ctDNA in human serum samples, indicating a good potential in clinical applications in the future.

Combination of Aptamer Amplifier and Antigen-Binding Fragment Probe as a Novel Strategy to Improve Detection Limit of Silicon Nanowire Field-Effect Transistor Immunosensors

Detecting proteins at low concentrations in high-ionic-strength conditions by silicon nanowire field-effect transistors (SiNWFETs) is severely hindered due to the weakened signal, primarily caused by screening effects. In this study, aptamer as a signal amplifier, which has already been reported by our group, is integrated into SiNWFET immunosensors employing antigen-binding fragments (Fab) as the receptors to improve its detection limit for the first time. The Fab-SiNWFET immunosensors were developed by immobilizing Fab onto Si surfaces modified with either 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde (GA) (Fab/APTES-SiNWFETs), or mixed self-assembled monolayers (mSAMs) of polyethylene glycol (PEG) and GA (Fab/PEG-SiNWFETs), to detect the rabbit IgG at different concentrations in a high-ionic-strength environment (150 mM Bis-Tris Propane) followed by incubation with R18, an aptamer which can specifically target rabbit IgG, for signal enhancement. Empirical results revealed that the signal produced by the sensors with Fab probes was greatly enhanced compared to the ones with whole antibody (Wab) after detecting similar concentrations of rabbit IgG. The Fab/PEG-SiNWFET immunosensors exhibited an especially improved limit of detection to determine the IgG level down to 1 pg/mL, which has not been achieved by the Wab/PEG-SiNWFET immunosensors.

A Reliable BioFET Immunosensor for Detection of p53 Tumour Suppressor in Physiological-Like Environment

The concentration of wild-type tumour suppressor p53_wt in cells and blood has a clinical significance for early diagnosis of some types of cancer. We developed a disposable, label-free, field-effect transistor-based immunosensor (BioFET), able to detect p53_wt in physiological buffer solutions, over a wide concentration range. Microfabricated, high-purity gold electrodes were used as single-use extended gates (EG), which avoid direct interaction between the transistor gate and the biological solution. Debye screening, which normally hampers target charge effect on the FET gate potential and, consequently, on the registered FET drain-source current, at physiological ionic strength, was overcome by incorporating a biomolecule-permeable polymer layer on the EG electrode surface. Determination of an unknown p53_wt concentration was obtained by calibrating the variation of the FET threshold voltage versus the target molecule concentration in buffer solution, with a sensitivity of 1.5 ± 0.2 mV/decade. The BioFET specificity was assessed by control experiments with proteins that may unspecifically bind at the EG surface, while 100pM p53_wt concentration was established as limit of detection. This work paves the way for fast and highly sensitive tools for p53_wt detection in physiological fluids, which deserve much interest in early cancer diagnosis and prognosis.

Biosensors Based on Mechanical and Electrical Detection Techniques

Biosensors are powerful analytical tools for biology and biomedicine, with applications ranging from drug discovery to medical diagnostics, food safety, and agricultural and environmental monitoring. Typically, biological recognition receptors, such as enzymes, antibodies, and nucleic acids, are immobilized on a surface, and used to interact with one or more specific analytes to produce a physical or chemical change, which can be captured and converted to an optical or electrical signal by a transducer. However, many existing biosensing methods rely on chemical, electrochemical and optical methods of identification and detection of specific targets, and are often: complex, expensive, time consuming, suffer from a lack of portability, or may require centralised testing by qualified personnel. Given the general dependence of most optical and electrochemical techniques on labelling molecules, this review will instead focus on mechanical and electrical detection techniques that can provide information on a broad range of species without the requirement of labelling. These techniques are often able to provide data in real time, with good temporal sensitivity. This review will cover the advances in the development of mechanical and electrical biosensors, highlighting the challenges and opportunities therein.

Construction of the Nickel Oxide Nanocoral Structure on Microscope Slides for Total Self-Assembly-Oriented Probe Immobilization and Signal Enhancement

Proper orientation of probes and the binding capacity of surfaces will determine the performance of bio-applications. It has been reported that immobilizing through bio-/chemical affinity is an efficient but gentle strategy to solve the above-mentioned issue. Herein, we introduce a total self-assembly approach via the strong affinity of nickel oxide (NiO) to the polyhistidine-tag (His-tag). It allows the efficient immobilizing His-tagged proteins with orientation. Furthermore, we find that the nanocoral structure can be formed after applying rapid thermal annealing at 1100 °C, which could increase the His-tagged protein binding capacity efficiently by the enhanced surface-to-volume ratio. Lastly, we demonstrate the NiO thin film with the nanocoral structure, which has great potential for universal biosensing with a wide range of biomolecules, including DNA, protein, and bacteria. Through His-tagged monomer streptavidin (His₆-mSA) or His-tagged protein G (His₆-protein G), the biotinylated DNA or antibody could be immobilized with proper orientation on the surface consequently to complete a sensitive biomolecule detection. Moreover, the NiO nanocoral structure has the advantages of high hydrophilicity, transmittance, and pH stability that are promising to develop into several kinds of bio-applications in the near future.

Enhancement of cortisol measurement sensitivity by laser illumination for AlGaN/GaN transistor biosensor

In this study, high electron mobility transistor (HEMT) device was used as an immuno biosensor to measure concentration of a stress hormone, cortisol, by using selective binding on cortisol monoclonal antibody (c-Mab). Also, the HEMT sensor was enhanced in its sensitivity through light illumination to generate photocurrent. The optical pumping could assist the biosensor to discriminate more detailed change, which could result in an increment of limit of detection (LOD) to 1.0 pM cortisol level. It was the lowest level of detection with semiconductor device-based cortisol biosensors and the enhancement of surface potential sensitivity was induced by laser light (532 nm). Output current amplificated by photocurrent was higher than dark original current at about 3.39% when gate voltage is applied with -3 V. Since the device could be applied to not only standard cortisol solution but also real human salivary sample, it is expected to apply for in vitro direct diagnosis of point-of-care test (POCT).

Ultrasensitive Field-Effect Biosensors Enabled by the Unique Electronic Properties of Graphene

This review provides a critical overview of current developments on nanoelectronic biochemical sensors based on graphene. Composed of a single layer of conjugated carbon atoms, graphene has outstanding high carrier mobility and low intrinsic electrical noise, but a chemically inert surface. Surface functionalization is therefore crucial to unravel graphene sensitivity and selectivity for the detection of targeted analytes. To achieve optimal performance of graphene transistors for biochemical sensing, the tuning of the graphene surface properties via surface functionalization and passivation is highlighted, as well as the tuning of its electrical operation by utilizing multifrequency ambipolar configuration and a high frequency measurement scheme to overcome the Debye screening to achieve low noise and highly sensitive detection. Potential applications and prospectives of ultrasensitive graphene electronic biochemical sensors ranging from environmental monitoring and food safety, healthcare and medical diagnosis, to life science research, are presented as well.

Antifouling strategies in advanced electrochemical sensors and biosensors

A review presented recent development of antifouling strategies in electrochemical sensors and biosensors based on the modification methods.

An antifouling peptide-based biosensor for determination of Streptococcus pneumonia markers in human serum

We report a peptide-based sensor that involves a multivalent interaction with L-ascorbate 6-phosphate lactonase (UlaG), a protein marker of Streptococcus pneumonia. By integrating the antifouling feature of the sensor, we significantly improved the signal-to-noise ratio of UlaG detection. The antifouling surface was fabricated via electrodeposition using an equivalent mixture of 4-amino-N,N,N-trimethylanilinium and 4-aminobenzenesulfonate. This antifouling layer not only effectively reduces the non-specific adsorption on the biosensor but also decreases the charge transfer resistance (R_ct) of the screen-printed carbon electrode. The aniline-modified S7 peptide, an UlaG-binding peptide, was pre-synthesized and further electrochemically modified to bind onto the antifouling layer. Bio-electrochemical analysis confirms that the antifouling S7-peptide sensor binds strongly to the UlaG with a dissociation constant (K_d) = 0.5 nM. This strong interaction can be attributed to a multivalent interaction between the biosensor and the heximeric form of UlaG. To demonstrate the potential for clinical application, further detection of Streptococcus pneumonia from 50 to 5×10⁴ CFU/mL were successfully performed in 25% human serum.

Biosensors for Detection of Human Placental Pathologies: A Review of Emerging Technologies and Current Trends

Substantial growth in the biosensor research has enabled novel, sensitive and point-of-care diagnosis of human diseases in the last decade. This paper presents an overview of the research in the field of biosensors that can potentially predict and diagnosis of common placental pathologies. A survey of biomarkers in maternal circulation and their characterization methods is presented, including markers of oxidative stress, angiogenic factors, placental debris, and inflammatory biomarkers that are associated with various pathophysiological processes in the context of pregnancy complications. Novel biosensors enabled by microfluidics technology and nanomaterials is then reviewed. Representative designs of plasmonic and electrochemical biosensors for highly sensitive and multiplexed detection of biomarkers, as well as on-chip sample preparation and sensing for automatic biomarker detection are illustrated. New trends in organ-on-a-chip based placental disease models are highlighted to illustrate the capability of these in vitro disease models in better understanding the complex pathophysiological processes, including mass transfer across the placental barrier, oxidative stress, inflammation, and malaria infection. Biosensor technologies that can be potentially embedded in the placental models for real time, label-free monitoring of these processes and events are suggested. Merger of cell culture in microfluidics and biosensing can provide significant potential for new developments in advanced placental models, and tools for diagnosis, drug screening and efficacy testing.

Rapid Prototyping of an Open-Surface Microfluidic Platform Using Wettability-Patterned Surfaces Prepared by an Atmospheric-Pressure Plasma Jet

Open-surface microfluidics is promising in terms of enabling economical and rapid biochemical analysis for addressing challenges associated with medical diagnosis and food safety. To this end, we present a simple and economical approach to develop an open-surface microfluidic platform suitable for facile liquid transport and mixing. Customizable patterns with tailored wettability are deposited using a plasma-assisted deposition technique under atmospheric pressure. The flow of the dispensed liquid is driven by gravity, and the tilting angle of the device determines the extent of mixing. First, a hexamethyldisiloxane film was deposited to create hydrophobic patterns on glass, and then, hydrophilic acrylic acid was deposited by a patterned cardboard mask to construct a channel suitable for forming channels to transport aqueous liquids without the need of an external energy input; the liquid can be confined to designated pathways. Several designs including Y-junctions, serpentine-shaped patterns, splitting channels, and concentration gradient generation patterns are presented. The proposed method can spatially pattern a surface with a hydrophobic/hydrophilic area, which can function as a microfluidic channel, and the surface can be applied in microfluidic devices with other types of substrates.

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.

Biomolecular interfaces based on self-assembly and self-recognition form biosensors capable of recording molecular binding and release

This research proposed to create the next generation of versatile electrochemical-based biosensors capable of monitoring target capture and release as dictated by molecular binding or unbinding. The biosensor integrates cellular machines (i.e., microtubules, structural elements of cells and kinesin molecular motors involved in cellular transport) as functional units; its assembly is based on molecular self-assembly and self-recognition. Our results demonstrate that the designed biosensor was capable of allowing detection of binding and unbinding events based on redox reactions at user-controlled electrode interfaces. The analysis also showed that the sensitivity of the designed biosensor or its ability to record such events could be user-controlled at any given time by adjusting the energy source that "fuels" the system.

Thermopneumatic suction integrated microfluidic blood analysis system

Blood tests provide crucial diagnostic information regarding several diseases. A key factor that affects the precision and accuracy of blood tests is the interference of red blood cells; however, the conventional methods of blood separation are often complicated and time consuming. In this study, we devised a simple but high-efficiency blood separation system on a self-strained microfluidic device that separates 99.7 ± 0.3% of the plasma in only 6 min. Parameters, such as flow rate, design of the filter trench, and the relative positions of the filter trench and channel, were optimized through microscopic monitoring. Moreover, this air-difference-driven device uses a cost-effective and easy-to-use heater device that creates a low-pressure environment in the microchannel within minutes. With the aforementioned advantages, this blood separation device could be another platform choice for point-of-care testing.

Effective Construction of a High-Capacity Boronic Acid Layer on a Quartz Crystal Microbalance Chip for High-Density Antibody Immobilization

Boronic acids (BAs) provide strong potential in orientation immobilization of antibody and the modification method is crucial for efficiency optimization. A highly effective method has been developed for rapid antibody immobilization on gold electrodes through the electrodeposition of a BA–containing linker in this study. Aniline-based BA forms a condense layer while antibody could automatically immobilize on the surface of the electrode. Compare to traditional self-assembled monolayer method, the electrodeposition process dramatically reduces the modification time from days to seconds. It also enhances the immobilized efficiency from 95 to 408 (ng/cm²) with a strong preference being exhibited for shorter aniline-based linkers.

Functionalization of Bulk SiO2 Surface with Biomolecules for Sensing Applications: Structural and Functional Characterizations

Biomolecule immobilization on bulk silicon dioxide (SiO2) is an important aspect in the field of Si-based interfaces for biosensing. The approach used for surface preparation should guarantee not only the stable anchoring of biomolecules but also their structural integrity and biological functioning. In this paper, we review our findings on the SiO2 functionalization process to immobilize a variety of biomolecules, including glucose oxidase, horseradish peroxide, metallothionein, and DNA molecules. Morphological and chemical characterization of SiO2 surfaces after biomolecule immobilization using techniques already employed in the microelectronic industry are presented and discussed. Optical and spectrophotometric analysis revealed the preservation of biomolecules’ activity once they are anchored on the biointerface.

Ultrasensitive Electrical Detection of Follicle-Stimulating Hormone Using a Functionalized Silicon Nanowire Transistor Chemosensor

The follicle-stimulating hormone (FSH) is a hormone that belongs to a family of glycoprotein hormones. Determination of FSH can help in interpreting various factors that include physiology of the reproductive system, fertility maintenance, and identification or treatment of reproductive disorders. Sialic acids are derivatives of neuraminic acids with negative charges, present at the end of the sugar chains and further linked to the cell surfaces and glycoproteins. The direct measurement of FSH in a human body can be recorded by developing a sensor probe that responds particularly to sialic acids over the other hormones. However, existing diagnostic methods still suffer from many difficulties in terms of complicated handling techniques, expensive instrumentation, etc. Development of accurate, rapid, and low-cost FSH detection chemosensors is important to meet these demands. Herein, we utilized a novel sensing method for accurate and fast FSH detection using a metal-oxide semiconductor silicon nanowire field effect transistor (SiNW-FET) device. This is the first report to demonstrate the boronic acid-functionalized SiNW-FET device in FSH detection. FSH detection has been successfully determined using an assay buffer solution with 0.72 fM detection limit as well as using 20% serum with 1.1. fM detection limit. We also investigated the specificity with other gonadotropins/glycosylated serum proteins. The current measurements on FSH concentrations at different time intervals were also studied. The sensitive, cheap, and miniaturized SiNW-FET device can serve as an effective sensing approach for rapid screening of FSH and menopause diagnosis.

A signal amplification system constructed by bi-enzymes and bi-nanospheres for sensitive detection of norepinephrine and miRNA

Achieving the enhanced sensitivity and stability is always the pursuit for the fabrication of enzymatic biosensors. However, their sensitivity was still restricted by the fluctuant detection target (e.g. concentration), complex detection environment and limited recognition capability of enzymes. Herein, an effective and facile approach was designed to construct a bi-enzymatic and bi-nanospherical signal amplification system for fabrication of biosensors based on the designed polydopamine(PDA)-laccase@Au-glucose dehydrogenase. Therein, laccase-catalytic polymerized PDA nanoparticles (NPs) provided the supporting matrix for immobilization of laccase and AuNPs. The AuNPs with good conductivity and large surface area were used not only as a platform for enhanced loading capacity of glucose dehydrogenase but also as a conducting medium for electron transfer acceleration between enzymes and electrode. Moreover, the coordinated catalysis of bi-enzymes (laccase and glucose dehydrogenase) could avoid the fluctuated concentration of detection target (e.g. norepinephrine), while the application of bi-nanospheres loaded with large amount of enzymes could effectively amplify the signal of biosensors. Taking advantages of these merits, the as-prepared biosensors showed preeminent reproducibility, larger detection range from 0.5 nM to 0.5 μM, and lower detection limit of 0.07 nM (S/N = 3) for the norepinephrine detection. Besides, the constructed PDA-laccase@Au-glucose dehydrogenase was also successfully applied as the sensing probes for the detection of microRNA (miRNA), especially for single-nucleotide mismatched miRNA via specific recognition.

Multichannel ZnO nanowire field effect transistors by lift-off process

This paper describes a new, low-cost, top-down fabrication process, which makes it possible to define nanowire field effect transistor arrays with different numbers of nanowires simultaneously and systematically comparing their electrical performance. The main feature of this process is a developed bilayer photoresist pattern with a retrograde profile, which enables the modification of the nanowire in width, length, height and the number of transistor channels. The approach is compatible with low-cost manufacture without electron beam lithography, and benefits from process temperatures below 190 °C. Process reliability has been investigated by scanning electron microscopy, transmission electron microscopy and atomic force microscopy. Electrical measurements demonstrate enhancement mode transistors, which show a scalable correlation between the number of nanowires and the electrical characteristics. Devices with 100 nanowires exhibit the best performance with a high field effect mobility of 11.0 cm² Vs^-1, on/off current ratio of 3.97 × 10⁷ and subthreshold swing of 0.66 V dec^-1.

CMOS-Compatible Silicon Nanowire Field-Effect Transistor Biosensor: Technology Development toward Commercialization

Owing to their two-dimensional confinements, silicon nanowires display remarkable optical, magnetic, and electronic properties. Of special interest has been the development of advanced biosensing approaches based on the field effect associated with silicon nanowires (SiNWs). Recent advancements in top-down fabrication technologies have paved the way to large scale production of high density and quality arrays of SiNW field effect transistor (FETs), a critical step towards their integration in real-life biosensing applications. A key requirement toward the fulfilment of SiNW FETs' promises in the bioanalytical field is their efficient integration within functional devices. Aiming to provide a comprehensive roadmap for the development of SiNW FET based sensing platforms, we critically review and discuss the key design and fabrication aspects relevant to their development and integration within complementary metal-oxide-semiconductor (CMOS) technology.