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

Gold nanostructure-enhanced immunosensing: ultra-sensitive detection of VEGF tumor marker for early disease diagnosis

We present an advanced electrochemical immunosensor designed to detect the vascular endothelial growth factor (VEGF) precisely. The sensor is constructed on a modified porous gold electrode through a fabrication process involving the deposition of silver and gold on an FTO substrate. Employing thermal annealing and a de-alloying process, the silver is eliminated from the electrode, producing a reproducible porous gold substrate. Utilizing a well-defined protocol, we immobilize the heavy-chain (VHH) antibody against VEGF on the gold substrate, facilitating VEGF detection through various electrochemical methods. Remarkably, this immunosensor performs well, featuring an impressive detection limit of 0.05 pg/mL and an extensive linear range from 0.1 pg/mL to 0.1 µg/mL. This emphasizes it's to measure biomarkers across a wide concentration spectrum precisely. The robust fabrication methodology in this research underscores its potential for widespread application, offering enhanced precision, reproducibility, and remarkable detection capabilities for the developed immunosensor.

Advances in human reproductive biomarkers

Reproductive biomarkers are important regulators in women, especially during pregnancy and childbirth. Because of their essential role in women's health, the discovery and quantification of reproductive biomarkers is of great clinical importance. Nowadays, there are many detection strategies to detect these biomarkers, including VEGF, human chorionic gonadotropin (hCG), etc. Consider the limitations and problems of conventional diagnostic methods, new methods are being developed, one of the most important being methods based on nanotechnology. This review includes a review of methods for diagnosing reproductive biomarkers, ranging from mainstream to nanotechnology-based methods. The bulk of this article is an in-depth introduction to the latest advances in biosensor and nanosensor research for the detection and quantitative identification of reproductive biomarkers.

Recent trends in aptamer-based nanobiosensors for detection of vascular endothelial growth factors (VEGFs) biomarker: A review

Vascular endothelial growth factor (VEGF) is a remarkable cytokine that plays an important role in regulating vascular formation during the angiogenesis process. Therefore, real-time detection and quantification of VEGF is essential for clinical diagnosis and treatment due to its overexpression in various tumors. Among various sensing strategies, the aptamer-based sensors in combination with biological molecules improve the detection ability VEGFs. Aptamers are suitable biological recognition agents for the preparation of sensitive and reproducible aptasensors (Apt-sensors) due to their low immunogenicity, simple and straightforward chemical modification, and high resistance to denaturation. Here, a summary of the strategies for immobilization of aptamers (e.g., direct or self-assembled monolayer (SAM) attachment, etc.) on different types of electrodes was provided. Moreover, we discussed nanoparticle deposition techniques and surface modification methods used for signal amplification in the detection of VEGF. Furthermore, we are investigating various types of optical and electrochemical Apt-sensors used to improve sensor characterization in the detection of VEGF biomarkers.

VEGF Detection via Impedance Spectroscopy on Surface Functionalized Interdigitated Biosensor

Vascular endothelial growth factor (VEGF), a clinically important biomarker, often plays a key role in angiogenesis, would healing, tumor growth, lung development, and in retinal diseases. Hence, detecting and quantifying VEGF is deemed medically important in clinical diagnosis for many diseases. In this report, a simple yet highly cost-effective platform was proposed for VEGF protein detection using commercially available interdigitated sensors that are surface modified to present DNA optimally for VEGF capture. The dielectric characteristics between the fingers of the sensor were modulated by the negatively charged aptamer-VEGF capture, and the impedance was estimated using an impedance analyzer. Impedance-spectra tests were compared among pristine unmodified surfaces, functionalized monolayer surfaces, and aptamer-grafted surfaces in order to evaluate the efficacy of VEGF detection. From our results, the sensitivity experiments as conducted showed the ability of the interdigitated sensor to detect VEGF at a low concentration of 5 pM (200 pg/mL). The specificity of the functionalized sensor in detecting VEGF was further examined by comparing the impedance to platelet-derived growth factor, and the results confirm the specificity of the sensor. Finally, the Nyquist plot of impedance spectra was also presented to help data visualization and the overall performance of the device was found to be a highly suitable template for a smart biosensor for the detection of VEGF.

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.

Emerging 0D, 1D, 2D, and 3D nanostructures for efficient point-of-care biosensing

The recent COVID-19 infection outbreak has raised the demand for rapid, highly sensitive POC biosensing technology for intelligent health and wellness. In this direction, efforts are being made to explore high-performance nano-systems for developing novel sensing technologies capable of functioning at point-of-care (POC) applications for quick diagnosis, data acquisition, and disease management. A combination of nanostructures [i.e., 0D (nanoparticles & quantum dots), 1D (nanorods, nanofibers, nanopillars, & nanowires), 2D (nanosheets, nanoplates, nanopores) & 3D nanomaterials (nanocomposites and complex hierarchical structures)], biosensing prototype, and micro-electronics makes biosensing suitable for early diagnosis, detection & prevention of life-threatening diseases. However, a knowledge gap associated with the potential of 0D, 1D, 2D, and 3D nanostructures for the design and development of efficient POC sensing is yet to be explored carefully and critically. With this focus, this review highlights the latest engineered 0D, 1D, 2D, and 3D nanomaterials for developing next-generation miniaturized, portable POC biosensors development to achieve high sensitivity with potential integration with the internet of medical things (IoMT, for miniaturization and data collection, security, and sharing), artificial intelligence (AI, for desired analytics), etc. for better diagnosis and disease management at the personalized level.

Competitive Impedance Spectroscopy in a Schottky-Contacted ZnO Nanorod Structure for Ultrasensitive and Specific Biosensing in a Physiological Analyte

To enable detection and discovery of biomarkers, development of label-free, ultrasensitive, and specific sensors is the need of the hour. For addressing this requirement, here, a Schottky-contacted ZnO nanorod biosensor has been demonstrated, which explores the interplay between Schottky junction capacitance and solution resistance, resulting in an interesting sensing principle of competitive impedance spectroscopy. When the transition of dominating impedance occurs from solution resistance to junction capacitance, a notch or a peak appears in the impedance response at a particular frequency (referred to as the corner frequency) depending on the charge of the target molecule. The appearance of the peak or notch acts like an electronic label for selectivity since it is visible only for target molecules even at ultralow concentrations in the physiological analyte, where the magnitude of impedance change overlaps with that for nonspecific molecules. This phenomenon has been successfully applied for the positively charged vascular endothelial growth factor (VEGF) and the negatively charged hepatitis B surface antigen (HBsAg), where the shifts in the higher corner frequencies for 1 aM concentration of the target molecules have been observed to be more than 3 times the changes in the impedance magnitude. Further, the area of the ZnO nanorods was segmented into two zones corresponding to the lower and higher concentration regimes, thereby expanding the dynamic range. To summarize, an ultralow detection limit of 1 aM with a dynamic range up to 1 pM was achieved for VEGF and HBsAg, which is 4 orders of magnitude and 20 times lower than their most sensitive label-free reports, respectively.

Analysis of Electric Field Distribution for SOI-FET Sensors with Dielectrophoretic Control

Silicon-on-insulator (SOI) nanowire or nanoribbon field-effect transistor (FET) biosensors are versatile platforms of electronic detectors for the real-time, label-free, and highly sensitive detection of a wide range of bioparticles. At a low analyte concentration in samples, the target particle diffusion transport to sensor elements is one of the main limitations in their detection. The dielectrophoretic (DEP) manipulation of bioparticles is one of the most successful techniques to overcome this limitation. In this study, TCAD modeling was used to analyze the distribution of the gradient of the electric fields E for the SOI-FET sensors with embedded DEP electrodes to optimize the conditions of the dielectrophoretic delivery of the analyte. Cases with asymmetrical and symmetrical rectangular electrodes with different heights, widths, and distances to the sensor, and with different sensor operation modes were considered. The results showed that the grad E² factor, which determines the DEP force and affects the bioparticle movement, strongly depended on the position of the DEP electrodes and the sensor operation point. The sensor operation point allows one to change the bioparticle movement direction and, as a result, change the efficiency of the delivery of the target particles to the sensor.

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.

Protein biosensor based on Schottky barrier nanowire field effect transistor

A top-down nanofabrication approach involving molecular beam epitaxy and electron beam lithography was used to obtain silicon nanowire-based back gate field-effect transistors with Schottky contacts on silicon-on-insulator (SOI) wafers. The resulting device is applied in biomolecular detection based on the changes in the drain-source current (I_DS). In this context, we have explained the physical mechanisms of charge carrier transport in the nanowire using energy band diagrams and numerical 2D simulations in TCAD. The results of the experiment and numerical modeling matched well and may be used to develop novel types of nanowire-based biosensors.

Sonochemical Reaction of Bifunctional Molecules on Silicon (111) Hydride Surface

While the sonochemical grafting of molecules on silicon hydride surface to form stable Si-C bond via hydrosilylation has been previously described, the susceptibility towards nucleophilic functional groups during the sonochemical reaction process remains unclear. In this work, a competitive study between a well-established thermal reaction and sonochemical reaction of nucleophilic molecules (cyclopropylamine and 3-Butyn-1-ol) was performed on p-type silicon hydride (111) surfaces. The nature of surface grafting from these reactions was examined through contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Cyclopropylamine, being a sensitive radical clock, did not experience any ring-opening events. This suggested that either the Si-H may not have undergone homolysis as reported previously under sonochemical reaction or that the interaction to the surface hydride via a lone-pair electron coordination bond was reversible during the process. On the other hand, silicon back-bond breakage and subsequent surface roughening were observed for 3-Butyn-1-ol at high-temperature grafting (≈150 °C). Interestingly, the sonochemical reaction did not produce appreciable topographical changes to surfaces at the nano scale and the further XPS analysis may suggest Si-C formation. This indicated that while a sonochemical reaction may be indifferent towards nucleophilic groups, the surface was more reactive towards unsaturated carbons. To the best of the author's knowledge, this is the first attempt at elucidating the underlying reactivity mechanisms of nucleophilic groups and unsaturated carbon bonds during sonochemical reaction of silicon hydride surfaces.

Use of Silicon Nanowire Sensors for Early Cancer Diagnosis

The review covers some research conducted in the field of medical and biomedical application of devices based on silicon sensor elements (Si-NW-sensors). The use of Si-NW-sensors is one of the key methods used in a whole range of healthcare fields. Their biomedical use is among the most important ones as they offer opportunities for early diagnosis of oncological pathologies, for monitoring the prescribed therapy and for improving the people's quality of life.