Toward Intraoperative Detection of Disseminated Tumor Cells in Lymph Nodes with Silicon Nanowire Field Effect Transistors

Sybodies as Novel Bioreceptors toward Field-Effect Transistor-Based Detection of SARS-CoV-2 Antigens

The SARS-CoV-2 pandemic has increased the demand for low-cost, portable, and rapid biosensors, driving huge research efforts toward new nanomaterial-based approaches with high sensitivity. Many of them employ antibodies as bioreceptors, which have a costly development process that requires animal facilities. Recently, sybodies emerged as a new alternative class of synthetic binders and receptors with high antigen binding efficiency, improved chemical stability, and lower production costs via animal-free methods. Their smaller size is an important asset to consider in combination with ultrasensitive field-effect transistors (FETs) as transducers, which respond more intensely when biorecognition occurs near their surface. This work demonstrates the immobilization of sybodies against the spike protein of the virus on silicon surfaces, which are often integral parts of the semiconducting channel of FETs. Immobilized sybodies maintain the capability to capture antigens, even at low concentrations in the femtomolar range, as observed by fluorescence microscopy. Finally, the first proof of concept of sybody-modified FET sensing is provided using a nanoscopic silicon net as the sensitive area where the sybodies are immobilized. The future development of further sybodies against other biomarkers and their generalization in biosensors could be critical to decrease the cost of biodetection platforms in future pandemics.

Metal-Oxide FET Biosensor for Point-of-Care Testing: Overview and Perspective

Metal-oxide semiconducting materials are promising for building high-performance field-effect transistor (FET) based biochemical sensors. The existence of well-established top-down scalable manufacturing processes enables the reliable production of cost-effective yet high-performance sensors, two key considerations toward the translation of such devices in real-life applications. Metal-oxide semiconductor FET biochemical sensors are especially well-suited to the development of Point-of-Care testing (PoCT) devices, as illustrated by the rapidly growing body of reports in the field. Yet, metal-oxide semiconductor FET sensors remain confined to date, mainly in academia. Toward accelerating the real-life translation of this exciting technology, we review the current literature and discuss the critical features underpinning the successful development of metal-oxide semiconductor FET-based PoCT devices that meet the stringent performance, manufacturing, and regulatory requirements of PoCT.

Nanomaterials for Cortisol Sensing

Space represents one of the most dangerous environments for humans, which can be affected by high stress levels. This can lead to severe physiological problems, such as headaches, gastrointestinal disorders, anxiety, hypertension, depression, and coronary heart diseases. During a stress condition, the human body produces specific hormones, such as dopamine, adrenaline, noradrenaline, and cortisol. In particular, the control of cortisol levels can be related to the stress level of an astronaut, particularly during a long-term space mission. The common analytical methods (HPLC, GC-MS) cannot be used in an extreme environment, such as a space station, due to the steric hindrance of the instruments and the absence of gravity. For these reasons, the development of smart sensing devices with a facile and fast analytical protocol can be extremely useful for space applications. This review summarizes the recent (from 2011) miniaturized sensoristic devices based on nanomaterials (gold and carbon nanoparticles, nanotubes, nanowires, nano-electrodes), which allow rapid and real-time analyses of cortisol levels in biological samples (such as saliva, urine, sweat, and plasma), to monitor the health conditions of humans under extreme stress conditions.

Application of nanotechnology in the early diagnosis and comprehensive treatment of gastrointestinal cancer

Gastrointestinal cancer (GIC) is a common malignant tumour of the digestive system that seriously threatens human health. Due to the unique organ structure of the gastrointestinal tract, endoscopic and MRI diagnoses of GIC in the clinic share the problem of low sensitivity. The ineffectiveness of drugs and high recurrence rates in surgical and drug therapies are the main factors that impact the curative effect in GIC patients. Therefore, there is an urgent need to improve diagnostic accuracies and treatment efficiencies. Nanotechnology is widely used in the diagnosis and treatment of GIC by virtue of its unique size advantages and extensive modifiability. In the diagnosis and treatment of clinical GIC, surface-enhanced Raman scattering (SERS) nanoparticles, electrochemical nanobiosensors and magnetic nanoparticles, intraoperative imaging nanoparticles, drug delivery systems and other multifunctional nanoparticles have successfully improved the diagnosis and treatment of GIC. It is important to further improve the coordinated development of nanotechnology and GIC diagnosis and treatment. Herein, starting from the clinical diagnosis and treatment of GIC, this review summarizes which nanotechnologies have been applied in clinical diagnosis and treatment of GIC in recent years, and which cannot be applied in clinical practice. We also point out which challenges must be overcome by nanotechnology in the development of the clinical diagnosis and treatment of GIC and discuss how to quickly and safely combine the latest nanotechnology developed in the laboratory with clinical applications. Finally, we hope that this review can provide valuable reference information for researchers who are conducting cross-research on GIC and nanotechnology.

An Aptamer-Functionalised Schottky-Field Effect Transistor for the Detection of Proteins

The outbreak of the coronavirus disease 2019 (COVID-19) in December 2019 has highlighted the need for a flexible sensing system that can quickly and accurately determine the presence of biomarkers associated with the disease. This sensing system also needs to be easily adaptable to incorporate both novel diseases as well as changes in the existing ones. Here we report the feasibility of using a simple, low-cost silicon field-effect transistor functionalised with aptamers and designed to attach to the spike protein of SARS-CoV2. It is shown that a linear response can be obtained in a concentration range of 100 fM to 10 pM. Furthermore, by using a larger range of source-drain potentials compared with other FET based sensors, it is possible to look at a wider range of device parameters to optimise the response.

Nanosensors in clinical development of CAR-T cell immunotherapy

Immunotherapy using CAR-T cells is a new technological paradigm for cancer treatment. To avoid severe side effects and tumor escape variants observed for conventional CAR-T cells approach, adaptor CAR technologies are under development, where intermediate target modules redirect immune cells against cancer. In this work, silicon nanowire field-effect transistors are used to develop target modules for an optimized CAR-T cell operation. Focusing on a library of seven variants of E5B9 peptide that is used as CAR targeting epitope, we performed multiplexed binding tests using nanosensor chips. These peptides had been immobilized onto the sensor to compare the transistor signals upon titration with anti-La 5B9 antibodies. The correlation of binding affinities and sensor sensitivities enabled a selection of candidates for the interaction between CAR and target modules. An extremely low detection limit was observed for the sensor, down to femtomolar concentration, outperforming the current assay of the same purpose. Finally, the CAR T-cells redirection capability of selected peptides in target modules was proven successful in an in-vitro cytotoxicity assay. Our results open the perspective for the nanosensors to go beyond the early diagnostics in clinical cancer research towards developing and monitoring immunotherapeutic treatment, where the quantitative analysis with the standard techniques is limited.

A simplified point-of-care testing approach for preeclampsia blood biomarkers based on nanoscale field effect transistors

Rapid diagnosis of preeclampsia is necessary to ensure timely administration of appropriate care and prevent the potentially catastrophic complications of the condition affecting both mothers and babies. While the diagnostic superiority of angiogenic blood biomarkers such as placental growth factor has recently been demonstrated, there is an urgent need to develop point-of-care (PoC) technologies that allow rapid, quantitative, and accurate testing for these markers within local communities. Towards addressing this need, here we report on a fully integrated biodiagnostic platform based on nanoscale indium oxide field effect transistor (FET) sensors. The high-performance FET sensors are integrated with blood sample processing cartridges that minimize the need for operator intervention during the assay and eliminate the need for analytical equipment. Within 40 minutes and from 30 μL of blood, the FET platform could reliably measure PlGF with a limit of detection of 0.06 pg mL^-1 and a five order of magnitudes dynamic range. Pilot clinical validation in four preeclamptic pregnancies confirmed that the accuracy and reliability of the FET platform, paving the way for further development to a much-needed point-of-care preeclampsia testing.

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.

Nanowire-Enabled Bioelectronics

Bioelectronics explores the use of electronic devices for applications in signal transduction at their interfaces with biological systems. The miniaturization of the bioelectronic systems has enabled seamless integration at these interfaces and is providing new scientific and technological opportunities. In particular, nanowire-based devices can yield smaller sized and unique geometry detectors that are difficult to access with standard techniques, and thereby can provide advantages in sensitivity with reduced invasiveness. In this review, we focus on nanowire-enabled bioelectronics. First, we provide an overview of synthetic studies for designed growth of semiconductor nanowires of which structure and composition are controlled to enable key elements for bioelectronic devices. Second, we review nanowire field-effect transistor sensors for highly sensitive detection of biomolecules, their applications in diagnosis and drug discovery, and methods for sensitivity enhancement. We then turn to recent progress in nanowire-enabled studies of electrogenic cells, including cardiomyocytes and neurons. Representative advances in electrical recording using nanowire electronic devices for single cell measurements, cell network mapping, and three-dimensional recordings of synthetic and natural tissues, and in vivo brain mapping are highlighted. Finally, we overview the key challenges and opportunities of nanowires for fundamental research and translational applications.

Biosensing platforms based on silicon nanostructures: A critical review

Biosensors are revolutionizing the health-care systems worldwide, permitting to survey several diseases, even at their early stage, by using different biomolecules such as proteins, DNA, and other biomarkers. However, these sensing approaches are still scarcely diffused outside the specialized medical and research facilities. Silicon is the undiscussed leader of the whole microelectronics industry, and novel sensors based on this material may completely change the health-care scenario. In this review, we will show how novel sensing platforms based on Si nanostructures may have a disruptive impact on applications with a real commercial transfer. A critical study for the main Si-based biosensors is herein presented with a comparison of their advantages and drawbacks. The most appealing sensing devices are discussed, starting from electronic transducers, with Si nanowires field-effect transistor (FET) and porous Si, to their optical alternatives, such as effective optical thickness porous silicon, photonic crystals, luminescent Si quantum dots, and finally luminescent Si NWs. All these sensors are investigated in terms of working principle, sensitivity, and selectivity with a specific focus on the possibility of their industrial transfer, and which ones may be preferred for a medical device.

Comprehensive Understanding of Silicon-Nanowire Field-Effect Transistor Impedimetric Readout for Biomolecular Sensing

Impedance sensing with silicon nanowire field-effect transistors (SiNW-FETs) shows considerable potential for label-free detection of biomolecules. With this technique, it might be possible to overcome the Debye-screening limitation, a major problem of the classical potentiometric readout. We employed an electronic circuit model in Simulation Program with Integrated Circuit Emphasis (SPICE) for SiNW-FETs to perform impedimetric measurements through SPICE simulations and quantitatively evaluate influences of various device parameters to the transfer function of the devices. Furthermore, we investigated how biomolecule binding to the surface of SiNW-FETs is influencing the impedance spectra. Based on mathematical analysis and simulation results, we proposed methods that could improve the impedimetric readout of SiNW-FET biosensors and make it more explicable.

Nanosensor-Based Real-Time Monitoring of Stress Biomarkers in Human Saliva Using a Portable Measurement System

Small molecules with no or little charge are considered to have minimal impact on signals measured by field effect transistor (FET) sensors. This fact typically excludes steroids from the family of analytes, detected by FETs. We present a portable multiplexed platform based on an array of nanowire sensors for label-free monitoring of daytime levels of the stress hormone cortisol in saliva samples, obtained from multiple donors. To achieve an effective quantification of the cortisol with FETs, we rely on the specific DNA aptamer sequences as receptors, bringing the complex "target-receptor" closer to the nanowire surface. Upon binding, cortisol induces conformational changes of negatively charged aptamers, wrapping it into a close proximity to the silicon nanowires, to efficiently modulate their surface potential. Thus, the sensors allow for a real-time assessment of the steroid biomarkers at low nanomolar concentration. The measurement platform is designed in a building-block concept, consisting of a modular measuring unit and a customizable biochip board, and operates using a complementary metal-oxide-semiconductor-integrated multiplexer. The platform is capable of continuous and simultaneous measurement of samples from multiple patients. Cortisol levels detected with the presented platform agreed well with the results obtained with a commercial high-sensitivity immunoassay.

Biosensing based on field-effect transistors (FET): Recent progress and challenges

The use of field-Effect-Transistor (FET) type biosensing arrangements has been highlighted by researchers in the field of early biomarker detection and drug screening. Their non-metalized gate dielectrics that are exposed to an electrolyte solution cover the semiconductor material and actively transduce the biological changes on the surface. The efficiency of these novel devices in detecting different biomolecular analytes in a real-time, highly precise, specific, and label-free manner has been validated by numerous research studies. Considerable progress has been attained in designing FET devices, especially for biomedical diagnosis and cell-based assays in the past few decades. The exceptional electronic properties, compactness, and scalability of these novel tools are very desirable for designing rapid, label-free, and mass detection of biomolecules. With the incorporation of nanotechnology, the performance of biosensors based on FET boosts significantly, particularly, employment of nanomaterials such as graphene, metal nanoparticles, single and multi-walled carbon nanotubes, nanorods, and nanowires. Besides, their commercial availability, and high-quality production on a large-scale, turn them to be one of the most preferred sensing and screening platforms. This review presents the basic structural setup and working principle of different types of FET devices. We also focused on the latest progression regarding the use of FET biosensors for the recognition of viruses such as, recently emerged COVID-19, Influenza, Hepatitis B Virus, protein biomarkers, nucleic acids, bacteria, cells, and various ions. Additionally, an outline of the development of FET sensors for investigations related to drug development and the cellular investigation is also presented. Some technical strategies for enhancing the sensitivity and selectivity of detection in these devices are addressed as well. However, there are still certain challenges which are remained unaddressed concerning the performance and clinical use of transistor-based point-of-care (POC) instruments; accordingly, expectations about their future improvement for biosensing and cellular studies are argued at the end of this review.

High performance indium oxide nanoribbon FETs: mitigating devices signal variation from batch fabrication

Nanostructured field effect transistor (FET) based sensors have emerged as a powerful bioanalytical technology. However, performance variations across multiple devices and between fabrication batches inevitably exist and present a significant challenge holding back the translation of this cutting-edge technology. We report an optimized and cost-effective fabrication process for high-performance indium oxide nanoribbon FET with a steep subthreshold swing of 80 mV per decade. Through systematic electrical characterizations of 57 indium oxide nanoribbon FETs from different batches, we demonstrate an optimal operation point within the subthreshold regime that mitigates the issue of device-to-device performance variation. A non-linear pH sensing of the fabricated indium oxide nanoribbon FETs is also presented.

Catalytic Growth of Gallium Nitride Nanowires on Wet Chemically Etched Substrates by Chemical Vapor Deposition

Growth of gallium nitride nanowires on etched sapphire and GaN substrates using binary catalytic alloy were investigated by manipulating the growth time and precursor-to-substrate distance. The variations in behavior at different growth conditions were observed using X-ray diffractometer, Raman spectroscopy, X-ray photoelectron spectroscopy, cathodoluminescence spectroscopy, optical microscopy, atomic force microscopy, and scanning electron microscopy. It was noticed that, in respect of both the substrates, when growth time and/or precursor-to-substrate distance is increased, thickness of the nanowires around the etch pits remains unaltered, but there is variation in the density of nanowires. In addition, formation of gallium nitride microwires within the etch pits was also observed on etched sapphire substrates. Similarly, the thickness and density of the microwires were found to increase with increase in growth time and decrease with increase in precursor-to-substrate distance. The dimensionality scaling of gallium nitride was found to have a positive effect in improving the luminescence property and band gap of the grown nanowires. This method of nanowire growth can be helpful in increasing the probability of multiple reflections in the materials which makes them a suitable candidate for optoelectronic devices.

Silicon Nanowires Field Effect Transistors: A Comparative Sensing Performance between Electrical Impedance and Potentiometric Measurement Paradigms

Potentiometric sensors based on silicon nanowire field effect transistors (SiNW FETs) typically display exquisite sensitivities, but their bioanalytical implementation is limited due to the need for stringent measurement conditions and high-precision readout units. An alternative operation principle where SiNW FETs are operated in a frequency-domain electrical impedimetric approach is promising. However, to date only limited data is available in regard to the sensing performance and translational relevance of this novel approach in comparison to the standard charge detection paradigm. We demonstrate the feasibility of conducting electrical impedimetric FET measurements with a portable unit for the ultrasensitive detection of cancer biomarkers in biospecimens. Compared to standard potentiometric measurements, electrical impedimetric FET measurements yielded significant improvements in biosensing performances, including the limit of detection, sensing resolution, and dynamic range.

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.

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.

The identification and isolation of CTCs: A biological Rubik's cube

Liquid biopsy represents an alternative to conventional biopsies for the evaluation of tumors mainly due to its easy sampling. One of the main applications is the enumeration of Circulating Tumor Cells (CTCs) to evaluate tumor progression or response to treatment. The analysis of the functional characteristics of CTCs could give us much more information about their role in order to establish a more personalized treatment for the patients. The major issue that has to be solved is the isolation of the CTC population. Multiple protocols have been developed, however none of them has demonstrated to be the definitive one. In fact, a combination of these techniques has often been performed in order to obtain a purer and viable population of CTCs. In this review we have summarized for the first time the different combinatorial approaches used in the last years to optimize the isolation of CTCs and their limitations.

Recent advances in nanowires-based field-effect transistors for biological sensor applications

Nanowires (NWs)-based field-effect transistors (FETs) have attracted considerable interest to develop innovative biosensors using NWs of different materials (i.e. semiconductors, polymers, etc.). NWs-based FETs provide significant advantages over the other bulk or non-NWs nanomaterials-based FETs. As the building blocks for FET-based biosensors, one-dimensional NWs offer excellent surface-to-volume ratio and are more suitable and sensitive for sensing applications. During the past decade, FET-based biosensors are smartly designed and used due to their great specificity, sensitivity, and high selectivity. Additionally, they have the advantage of low weight, low cost of mass production, small size and compatible with commercial planar processes for large-scale circuitry. In this respect, we summarize the recent advances of NWs-based FET biosensors for different biomolecule detection i.e. glucose, cholesterol, uric acid, urea, hormone, proteins, nucleotide, biomarkers, etc. A comparative sensing performance, present challenges, and future prospects of NWs-based FET biosensors are discussed in detail.

Nanowire sensors monitor bacterial growth kinetics and response to antibiotics

Miniaturized and cost-efficient methods aiming at high throughput analysis of microbes are of great importance for the surveillance and control of infectious diseases and the related issue of antimicrobial resistance. Here we demonstrate a miniature nanosensor based on a honeycomb-patterned silicon nanowire field effect transistor (FET) capable of detection of bacterial growth and antibiotic response in microbiologically relevant nutrient media. We determine the growth kinetics and metabolic state of Escherichia coli cells in undiluted media via the quantification of changes in the source-drain current caused by varying pH values. Furthermore, by measuring the time dependent profile of pH change for bacterial cultures treated with antibiotics, we demonstrate for the first time the possibility of electrically distinguishing between bacteriostatic and bactericidal drug effects. We believe that the use of such nanoscopic FET devices enables addressing parameters that are not easily accessible by conventional optical methods in a label-free format, i.e. monitoring of microbial metabolic activity or stress response.

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.

Controlled Engineering of Oxide Surfaces for Bioelectronics Applications Using Organic Mixed Monolayers

Modifying the surfaces of oxides using self-assembled monolayers offers an exciting possibility to tailor their surface properties for various applications ranging from organic electronics to bioelectronics applications. The simultaneous use of different molecules in particular can extend this approach because the surface properties can be tuned via the ratio of the chosen molecules. This requires the composition and quality of the monolayers to be controlled on an organic level, that is, on the nanoscale. In this paper, we present a method of modifying the surface and surface properties of silicon oxide by growing self-assembled monolayers comprising various compositions of two different molecules, (3-aminopropyl)-triethoxysilane and (3-glycidyloxypropyl)-trimethoxysilane, by means of in situ controlled gas-phase deposition. The properties of the resulting mixed molecular monolayers (e.g., effective thickness, hydrophobicity, and surface potential) exhibit a perfect linear dependence on the composition of the molecular layer. Finally, coating the mixed layer with poly(l-lysine) proves that the density of proteins can be controlled by the composition as well. This indicates that the method might be an ideal way to optimize inorganic surfaces for bioelectronics applications.

The lab-on-PCB approach: tackling the μTAS commercial upscaling bottleneck

Commercialization of lab-on-a-chip devices is currently the "holy grail" within the μTAS research community. While a wide variety of highly sophisticated chips which could potentially revolutionize healthcare, biology, chemistry and all related disciplines are increasingly being demonstrated, very few chips are or can be adopted by the market and reach the end-users. The major inhibition factor lies in the lack of an established commercial manufacturing technology. The lab-on-printed circuit board (lab-on-PCB) approach, while suggested many years ago, only recently has re-emerged as a very strong candidate, owing to its inherent upscaling potential: the PCB industry is well established all around the world, with standardized fabrication facilities and processes, but commercially exploited currently only for electronics. Owing to these characteristics, complex μTASs integrating microfluidics, sensors, and electronics on the same PCB platform can easily be upscaled, provided more processes and prototypes adapted to the PCB industry are proposed. In this article, we will be reviewing for the first time the PCB-based prototypes presented in the literature to date, highlighting the upscaling potential of this technology. The authors believe that further evolution of this technology has the potential to become a much sought-after standardized industrial fabrication technology for low-cost μTASs, which could in turn trigger the projected exponential market growth of μTASs, in a fashion analogous to the revolution of Si microchips via the CMOS industry establishment.

Ultrasensitive and Highly Selective Photodetections of UV-A Rays Based on Individual Bicrystalline GaN Nanowire

The detection of UV-A rays (wavelength of 320-400 nm) using functional semiconductor nanostructures is of great importance in either fundamental research or technological applications. In this work, we report the catalytic synthesis of peculiar bicrystalline GaN nanowires and their utilization for building high-performance optoelectronic nanodevices. The as-prepared UV-A photodetector based on individual bicrystalline GaN nanowire demonstrates a fast photoresponse time (144 ms), a high wavelength selectivity (UV-A light response only), an ultrahigh photoresponsivity of 1.74 × 10⁷ A/W and EQE of 6.08 × 10⁹%, a sensitivity of 2 × 10⁴%, and a very large on/off ratio of more than two orders, as well as robust photocurrent stability (photocurrent fluctuation of less than 7% among 4000 s), showing predominant advantages in comparison with other peer semiconductor photodetectors. The outstanding optoelectronic performance of the bicrystalline GaN nanowire UV-A photodetector is further analyzed based on a detailed high-resolution transmission electron microscope (HRTEM) study, and the two separated crystal domains within the GaN nanowires are believed to provide separated and rapid carrier transfer channels. This work paves a solid way toward the integration of high-performance optoelectronic nanodevices based on bicrystalline or horizontally aligned one-dimensional semiconductor nanostructures.