Silicon Nanowire Field-effect Transistor Biosensor Research Articles

A Calibration Strategy for Silicon Nanowire Field-Effect Transistor Biosensors and Its Application in Ultra-Sensitive, Label-Free Biosensing.

The silicon nanowire field-effect transistor (SiNW FET) has been developed for over two decades as an ultrasensitive, label-free biosensor for biodetection. However, inconsistencies in manufacturing and surface functionalization at the nanoscale have led to poor sensor-to-sensor consistency in performance. Despite extensive efforts to address this issue through process improvements and calibration methods, the outcomes have not been satisfactory. Herein, based on the strong correlation between the saturation response of SiNW FET biosensors and both their feature size and surface functionalization, we propose a calibration strategy that combines the sensing principles of SiNW FET with the Langmuir-Freundlich model. By normalizing the response of the SiNW FET biosensors (ΔI/I0) with their saturation response (ΔI/I0)max, this strategy fundamentally overcomes the issues mentioned above. It has enabled label-free detection of nucleic acids, proteins, and exosomes within 5 min, achieving detection limits as low as attomoles and demonstrating a significant reduction in the coefficient of variation. Notably, the nucleic acid test results exhibit a strong correlation with the ultraviolet-visible (UV-vis) spectrophotometer measurements, with a correlation coefficient reaching 0.933. The proposed saturation response calibration strategy exhibits good universality and practicability in biological detection applications, providing theoretical and experimental support for the transition of mass-manufactured nanosensors from theoretical research to practical application.

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.

Dual-Channel Detection of Breast Cancer Biomarkers CA15-3 and CEA in Human Serum Using Dialysis-Silicon Nanowire Field Effect Transistor.

Breast cancer (BC) is the most common malignant tumors and the leading cause of cancer deaths among women. The early diagnosis and treatment of BC are effective measures that can increase survival rates and reduce mortality. Carbohydrate antigens 15-3 (CA15-3) and carcinoma embryonic antigens (CEA) have been regarded as the most two valuable tumor markers of BC. The combined detection of CA15-3 and CEA could improve the sensitivity and accuracy of early diagnosis for BC. The multi-channel double-gate silicon nanowire field effect transistor (SiNW-FET) biosensors were fabricated by using the top-down semiconductor manufacturing technology. By surface modification of the different SiNW surfaces with monoclonal CA15-3 and CEA antibodies separately, the prepared SiNW-FET was processed into biosensor for dual-channel detection of CA15-3 and CEA. The prepared SiNW-FET biosensors were proved to have high sensitivity and specificity for the dual-channel detection of CA15-3 and CEA, and the detection limit is as low as 0.1U/mL CA15-3 and 0.01 ng/mL CEA. Moreover, the SiNW-FET biosensors were able to detect CA15-3 and CEA in serum by connecting a miniature hemodialyzer. The present study reported a SiNW-FET biosensor for dual-channel detection of breast cancer biomarkers CA15-3 and CEA in serum, which has potential clinical application value for the early diagnosis and curative effect observation of BC.

Silicon Nanowires Length and Numbers Dependence on Sensitivity of the Field-Effect Transistor Sensor for Hepatitis B Virus Surface Antigen Detection.

Silicon nanowire field effect transistor (NWFET) sensors have been demonstrated to have high sensitivity, are label free, and offer specific detection. This study explored the effect of nanowire dimensions on sensors’ sensitivity. We used sidewall spacer etching to fabricate polycrystalline silicon NWFET sensors. This method does not require expensive nanoscale exposure systems and reduces fabrication costs. We designed transistor sensors with nanowires of various lengths and numbers. Hepatitis B surface antigen (HBsAg) was used as the sensing target to explore the relationships of nanowire length and number with biomolecule detection. The experimental results revealed that the sensor with a 3 µm nanowire exhibited high sensitivity in detecting low concentrations of HBsAg. However, the sensor reached saturation when the biomolecule concentration exceeded 800 fg/mL. Sensors with 1.6 and 5 µm nanowires exhibited favorable linear sensing ranges at concentrations from 800 ag/mL to 800 pg/mL. The results regarding the number of nanowires revealed that the use of few nanowires in transistor sensors increases sensitivity. The results demonstrate the effects of nanowire dimensions on the silicon NWFET biosensors.

Rapid and Sensitive Detection of Mycobacterium tuberculosis by an Enhanced Nanobiosensor.

Tuberculosis (TB) mostly spreads from person to person through Mycobacterium tuberculosis (MTB). However, the majority of conventional detection methods for MTB cannot satisfy the requirements for actual TB detection. As one of the most promising powerful platforms, a silicon nanowire field-effect transistor (SiNW-FET) biosensor shows good prospect in TB detection. In this study, an enhanced SiNW-FET biosensor was developed for the rapid and sensitive detection of MTB. The surface functional parameters of the biosensor were explored and optimized. The SiNW-FET biosensor has good sensitivity with a detection limit of 0.01 fg/mL toward protein. The current change value shows a linear upward trend with the increase in protein concentration in the range of 1 fg/mL to 100 μg/mL. One whole test cycle can be accomplished within only 30 s. More importantly, a good distinction was realized in the sputum without pretreatment between normal people and TB patients, which greatly shortened the TB detection time (only 2-5 min, considering the dilution of sputum). Compared with other methods, the SiNW-FET biosensor can detect MTB with a remarkably broad dynamic linear range in a shorter time.

Process Variability in Top-Down Fabrication of Silicon Nanowire-Based Biosensor Arrays.

Silicon nanowire field-effect transistors (SiNW-FET) have been studied as ultra-high sensitive sensors for the detection of biomolecules, metal ions, gas molecules and as an interface for biological systems due to their remarkable electronic properties. “Bottom-up” or “top-down” approaches that are used for the fabrication of SiNW-FET sensors have their respective limitations in terms of technology development. The “bottom-up” approach allows the synthesis of silicon nanowires (SiNW) in the range from a few nm to hundreds of nm in diameter. However, it is technologically challenging to realize reproducible bottom-up devices on a large scale for clinical biosensing applications. The top-down approach involves state-of-the-art lithography and nanofabrication techniques to cast SiNW down to a few 10s of nanometers in diameter out of high-quality Silicon-on-Insulator (SOI) wafers in a controlled environment, enabling the large-scale fabrication of sensors for a myriad of applications. The possibility of their wafer-scale integration in standard semiconductor processes makes SiNW-FETs one of the most promising candidates for the next generation of biosensor platforms for applications in healthcare and medicine. Although advanced fabrication techniques are employed for fabricating SiNW, the sensor-to-sensor variation in the fabrication processes is one of the limiting factors for a large-scale production towards commercial applications. To provide a detailed overview of the technical aspects responsible for this sensor-to-sensor variation, we critically review and discuss the fundamental aspects that could lead to such a sensor-to-sensor variation, focusing on fabrication parameters and processes described in the state-of-the-art literature. Furthermore, we discuss the impact of functionalization aspects, surface modification, and system integration of the SiNW-FET biosensors on post-fabrication-induced sensor-to-sensor variations for biosensing experiments.

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.

Fabrication and Characterization of an Aptamer-Based N-type Silicon Nanowire FET Biosensor for VEGF Detection

Cancer detection is an important part of modern medical diagnosis and many strategies based on nanotechnology had been developed in recent years. Of which, silicon nanowire (SiNW) field-effect transistor (FET) biosensor via DNA aptamer capture is considered as an interesting and viable option. Hence, in this report, we had assembled a n-type triple SiNW FET biosensor for the detection of vascular endothelial growth factor (VEGF) via surface functionalized DNA aptamer for a proof-of-concept. The SiNW FET biosensor was fabricated via "top-down" approach and the physical nature of the nanowire assembly was examined via atomic force microscopy (AFM) as well as scanning electron microscopy (SEM). We had subsequently grafted VEGF specific DNA aptamer via conventional EDC/NHS chemistry and later measured the conductance of the nanowires in a four-point probe detector for VEGF detection. We had demonstrated that the detection of VEGF was possible even at a concentration of 2.59 nM which was highly comparable to the other common biosensors for detection of VEGF protein. In addition to being scalable with complementary metal–oxide–semiconductor (CMOS) technology, the findings as demonstrated from our simple SiNW FET biosensor setup had helped to provide better insights towards optimizing the approach for the development of the next generation of miniature biosensors.

Hepatocellular Carcinoma Diagnosis by Detecting α-Fucosidase with a Silicon Nanowire Field-Effect Transistor Biosensor

Hepatocellular carcinoma (HCC) is one of the most frequent and fatal cancers. However, traditional clinical imaging modalities cannot detect small tumors and are not suitable for the early stage diagnosis of hepatic cancer. In this study, we applied silicon nanowire field-effect transistors (SiNW-FETs) as a biosensor to detect α-fucosidase (AFU), which is a biomarker of high sensitivity and specificity for the HCC diagnosis. Fuconojirimycin (FNJ) is an inhibitor of AFU with very high binding affinity to AFU. By modifying the FNJs of optimized receptor length and number density on SiNW-FET (referred to as FNJ/SiNW-FET), this biosensing device can detect AFU to a very low concentration level with the detection limit of ∼1.3 pM. With the merits of high sensitivity, target specificity, and label-free detection, this FNJ/SiNW-FET can be developed as a powerful biosensor to detect AFU for the early HCC diagnosis.

The application of silicon nanowire field-effect transistor-based biosensors in molecular diagnosis

Cancer, one of the most life-threatening diseases, causes a heavy burden to both the society and family. Timely and efficient early diagnosis of cancer is critical to enable effective treatment and improving survival rate, which also is currently one of the most challenging problems in clinical medicine. Although modern medical imaging is an important tool for cancer diagnosis, detection of molecular biomarkers (such as DNA, RNA, proteins, and metabolites), released from the cancer cells or the organs, is the preferred approach for detecting and tracking cancer due to their unique association with genomic changes in cancer cells, especially for screening and early diagnosis of cancer. Molecular diagnosis can help doctors not only make a precise diagnosis in diseases’ early stage, but also make a judgment in disease staging, classification, curative effect monitoring and prognosis evaluation. A variety of conventional technologies are developed for biomarker detection, such as radio-immunoassay and enzyme-linked immunosorbent assay (ELISA), however, they are label-based, multi-step, time-consuming, and required experienced personnel to conduct the experiment. Silicon nanowire field-effect transistors (SiNW-FETs), as new one-dimensional semiconducting nanostructures, exhibit some unique properties, including high surface-to-volume ratios, fast electron transfer, and biocompatibility. SiNW-FET based biosensors have recently been attracted tremendous attention as a promising tool in biomedical and chemical detection because of their ultrasensitivity, specificity, label-free detection, and rapid and real-time response capabilities, which demonstrate a great potential in the application of medical diagnosis, chemical analysis, environmental monitoring, and food industry. Over the past decade, SiNW-FET biosensors are employed in the detections of DNA sequences, microRNAs, proteins, small molecules, cancer biomarkers, cells, and viruses. Here, we present a comprehensive review which introduces the working principle of SiNW-FETs, the fabrication of SiNWs, influence factors of the sensitivity, as well as the applications of SiNW-FET biosensors in cancers’ molecular diagnosis (including nucleic acid detection, biomarkers detection, and studies of molecule-molecule interactions). The future prospects in this area are also discussed, which can provide a guidance for the further applications in early diagnosis. SiNW-FET biosensors, as a promise tool in molecular diagnosis, held great potential applications in large-scale screening and point-of-care testing for early-stage cancer.

Silicon nanowire biosensor for highly sensitive and multiplexed detection of oral squamous cell carcinoma biomarkers in saliva.

Silicon nanowire (SiNW) field-effect transistor (FET) biosensors have already been used as powerful sensors for the direct detection of disease-related biomarkers. However, the multiplexed detection of biomarkers in real samples is still challenging. Interleukin 8 (IL-8) and tumor necrosis factor α (TNF-α) are two typical biomarkers of oral squamous cell carcinoma (OSCC). In this study, we developed a multiplexed detection methodology for IL-8 and TNF-α detection in saliva using SiNW FET biosensors. We fabricated the SiNW FET sensors using a top-down lithography fabrication technique. Subsequently, we achieved the multiplexed detection of two biomarkers in saliva by specific recognition of the two biomarkers with their corresponding antibodies, which were modified on the SiNW. The established method was found to have a limit of detection as low as 10 fg/mL in 1 × PBS as well as 100 fg/mL in artificial saliva. Because of its advantages, including label-free and multiplexed detection, non-invasive analysis, highly sensitive and specific determination, the proposed method is expected to be widely used for the early diagnosis of OSCC.

(Invited) Nanowire Field-Effect Transistor-Based Biosensors as a Tool for Life Science

Electrical biosensors based on silicon nanowire field-effect transistors (SiNW-FETs) have attracted enormous interest in the biosensing field. SiNW-FETs have proven to be significant and efficient in detecting diverse biomolecular species with the advantages of high probing sensitivity, target selectivity, real-time recording, and label-free detection. In recent years, significant advances in biosensors have been achieved, particularly for cellular investigation and biomedical diagnosis. In this paper, we will report on the recent achievements with SiNW-FET biosensors for the fast screening of protein-protein interaction and sensitive detection of neurotransmitters release from live cells. Despite these remarkable achievements, certain improvements remain necessary in the device performance and clinical applications of FET-based biosensors; thus, several prospects about the future development of nanowire transistor-based instruments for biosensing employments are discussed at the end of this paper.

Invited: Nanowire Field-Effect Transistor-Based Biosensors as a Tool for Life Science

Silicon nanowire field-effect transistors (SiNW-FETs) have been used as a highly sensitive biosensor for label-free, real-time, and target selective detections in biomedical diagnosis and cellular-recording investigation. For practical uses, a reusable SiNW-FET was made possible with a reversible surface functionalization method, allowing for calibratable and quantitative analysis (Figure 1). In recent studies, we have applied SiNW-FETs for probing neurotransmitter release from living neurons, screening protein-protein interactions (Figure 2), detecting influenza virus, and monitoring extracellular K+ flux from stimulated chromaffin cells. In the study of protein-protein interactions, we integrated SiNW-FET with mass spectrometry (MS) for not only fast screening (by NW-FET) but also spectrally identifying (by MS) the unknown interacting proteins that were captured on the probe protein-modified SiNW-FET. To improve the sensitivity of SiNW-FETs, we designed a modification method to immobilize probe molecules only on the SiNW channel without contaminating the surrounding substrate, thus substantially enhancing the detection sensitivity. Recently, we developed an ultrasensitive biosensor for selective dopamine detection by an aptamer-modified multiple-parallel-connected (MPC) SiNW-FET with a detection limit of ~10 pM (Figure 3). This MPC SiNW-FET was applied to monitor the dopamine release under hypoxic stimulation from living PC12 cells. We resolved the controversial pathways that the increase in intracellular Ca2+ to trigger dopamine secretion is dominated by an extracellular Ca2+ influx, rather than the release of intracellular Ca2+ stores.In conclusion, SiNW-FET biosensors have been successfully applied in biological and cellular studies, including the label-free and real-time recordings of neurotransmitter release, protein-protein interaction, virus detection, dopamine release from stimulated excitable cells, and clinical diagnosis. Finally, this novel bio-nano-electronic FET device, which is capable of integrating with living cell systems, provides a promising tool for biological analysis and cellular investigation and adds a new item to the biosensor toolbox for the future studies of cell biology and clinical disease diagnosis.This work is partially supported by the Ministry of Science and Technology of Taiwan under NSC 101-2113-M-002-016-MY2 and NSC 102-2627-M-002-001.Figure 1. Taking advantage of the reversible association-dissociation between glutathione (GSH) and glutathione S-transferase (GST), we built a reusable SiNW-FET biosensor for fast screening protein-protein interactions. The strategy used in the study includes the association of GST-tagged calmodulin (represented by CaM-GST) with a GSH-modified SiNW-FET (referred to as GSH/SiNW-FET) to form CaM/SiNW-FET, the subsequent detection of interacting proteins with CaM, and the removal of bound proteins via the dissociation of GSH-GST with concentrated GSH (³1 mM) washing solution. (PNAS, 107, 1047 (2010))Figure 2. (a) An illustration for the detection of membrane fractions containing N-type voltage-gated Ca2+ channels (VGCCs) utilizing a CaM/SiNW-FET. (b–c) Real-time electrical detections of the binding of N-type VGCCs to the CaM/SiNW-FET in 0.1× PS (phosphate solution, consisting of 0.76 mM Na2HPO4 and 0.24 mM NaH2PO4 at pH 7.4) supplemented with (b) 100 mM Ca2+; (c) 500 mM EDTA. (d) Two control tests were conducted separately. (top graph) Electrical detection of the membrane fraction without the a1b subunit by CaM/SiNW-FET in 0.1× PS supplemented with 100 mM Ca2+. (bottom graph) Electrical detection of N-type VGCCs by GST/SiNW-FET (without CaM) in 0.1× PS supplemented with 100 mM Ca2+. (PNAS, 107, 1047 (2010))Figure 3. (a) Schematics illustrate (top graph) the experimental setup of a DNA-aptamer/MPC SiNW-FET for detecting dopamine exocytosis from living PC12 cells under hypoxic stimulation and (bottom graph) the procedure for immobilization of the DNA-aptamer on the surface of SiNW. (b) An illustration about how the hypoxic condition triggers the dopamine (DA) exocytosis by the escalation of intracellular Ca2+ concentration via the hypothetical pathway of either extracellular Ca2+ influx (solid line) or intracellular Ca2+ store release (dashed line). (c) Real-time recordings for the dopamine exocytosis from living PC12 cells under different hypoxic stimulations: (upper trace) 35% [O2] reduced buffer, (middle trace) 70% [O2] reduced buffer, and (bottom trace) 70% [O2] reduced buffer containing 1 mM CdI2. (JACS, 135, 16034 (2013))

Real-Time and Label-Free Detection of the Prostate-Specific Antigen in Human Serum by a Polycrystalline Silicon Nanowire Field-Effect Transistor Biosensor

In this research, we used a polycrystalline silicon nanowire field-effect transistor (poly-Si NWFET) as a biosensor that employs the sidewall spacer technique instead of an expensive electron beam lithography method. When compared with commercial semiconductor processes, the sidewall spacer technique has the advantages of simplicity and low cost. In this study, we employed a novel poly-Si NWFET device for real-time, label-free, and ultrahigh-sensitivity detection of prostate-specific antigen (PSA) in human serum. Since serum proteome is very complex containing high levels of salts and other interfering compounds, we hereby developed a standard operating procedure for real-sample pretreatment to keep a proper pH value and ionic strength of the desalted serum and also utilized Tween 20 to serve as the passivation agent by surface modification on the NWFET to reduce nonspecific binding for medical diagnostic applications. We first modified 3-aminopropyltriethoxysilane on the surface of a poly-Si nanowire device followed by glutaraldehyde functionalization, and the PSA antibodies were immobilized on the aldehyde terminal. While PSA was prepared in the buffers to maintain an appropriate pH value and ionic strength, the results indicated that the sensor could detect trace PSA at less than 5 fg/mL in a microfluidic channel. The novel poly-Si NWFET is developed as a diagnostic platform for monitoring prostate cancer and predicting the risk of early biochemical relapse.

Nanowire Transistor‐Based Ultrasensitive Virus Detection with Reversible Surface Functionalization

We have applied a reusable silicon nanowire field-effect transistor (SiNW-FET) as a biosensor to conduct ultrasensitive detection of H5N2 avian influenza virus (AIV) in very dilute solution. The reversible surface functionalization of SiNW-FET was made possible using a disulfide linker. In the surface functionalization, 3-mercaptopropyltrimethoxysilane (MPTMS) was first modified on the SiNW-FET (referred to as MPTMS/SiNW-FET), with subsequent dithiothreitol washing to reduce any possible disulfide bonding between the thiol groups of MPTMS. Subsequently, receptor molecules could be immobilized on the MPTMS/SiNW-FET by the formation of a disulfide bond. The success of the reversible surface functionalization was verified with fluorescence examination and electrical measurements. A surface topograph of the SiNW-FET biosensor modified with a monoclonal antibody against H5N2 virus (referred to as mAb(H5)/SiNW-FET) after detecting approximately 10(-17) M H5N2 AIVs was scanned by atomic force microscopy to demonstrate that the SiNW-FET is capable of detecting very few H5N2 AIV particles.

Fabrication of Silicon Nanowire Field-Effect Transistor Biosensor by CMOS Compatible Top-Down Approach with Descum Process

Fabrication of Silicon Nanowire Field-Effect Transistor Biosensor by CMOS Compatible Top-Down Approach with Descum Process