A Review on the Electrochemical Sensors and Biosensors Composed of Nanowires as Sensing Material

Advances in graphene-based 2D materials for tendon, nerve, bone/cartilage regeneration and biomedicine

Two-dimensional (2D) materials, especially graphene-based materials, have important implications for tissue regeneration and biomedicine due to their large surface area, transport properties, ease of functionalization, biocompatibility, and adsorption capacity. Despite remarkable progress in the field of tissue regeneration and biomedicine, there are still problems such as unclear long-term stability, lack of in vivo experimental data, and detection accuracy. This paper reviews recent applications of graphene-based materials in tissue regeneration and biomedicine and discusses current issues and prospects for the development of graphene-based materials with respect to promoting the regeneration of tendons, neuronal cells, bone, chondrocytes, blood vessels, and skin, as well as applications in sensing, detection, anti-microbial activity, and targeted drug delivery.

Advancements in Chemical and Biosensors for Point-of-Care Detection of Acrylamide

Acrylamide (AA), an odorless and colorless organic small-molecule compound found generally in thermally processed foods, possesses potential carcinogenic, neurotoxic, reproductive, and developmental toxicity. Compared with conventional methods for AA detection, bio/chemical sensors have attracted much interest in recent years owing to their reliability, sensitivity, selectivity, convenience, and low cost. This paper provides a comprehensive review of bio/chemical sensors utilized for the detection of AA over the past decade. Specifically, the content is concluded and systematically organized from the perspective of the sensing mechanism, state of selectivity, linear range, detection limits, and robustness. Subsequently, an analysis of the strengths and limitations of diverse analytical technologies ensues, contributing to a thorough discussion about the potential developments in point-of-care (POC) for AA detection in thermally processed foods at the conclusion of this review.

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.

Recent Advances in Gas Detection Methodologies with a Special Focus on Environmental Sensing and Health Monitoring Applications─A Critical Review

With the expansion of the Internet-of-Things (IoT), the use of gas sensors in the field of wearable technology, smart devices, and smart homes has increased manifold. These gas sensors have two key applications─one is the detection of gases present in the environment and the other is the detection of Volatile Organic Compounds (VOCs) that are found in the breath. In this review, we focus systematically on the advancements in the field of various spectroscopic methods such as mass spectrometry-based analysis and point-of-care approach to detect VOCs and gases for environmental monitoring and disease diagnosis. Additionally, we highlight the development of smart sensors that work on the principle of electrochemical detection and provide examples of the same through an extensive literature review. At the end of this review, we highlight various challenges and future perspectives.

Biofunctionalisation of Polypyrrole Nanowires Array with Sulfite Oxidase Coupled with the Integration of Platinum Nanoparticles for Ultrasensitive Amperometric Detection of Sulfite

Sulfite determination in foods and alcoholic beverages is a common requirement by food and drug administration organisations in most countries. In this study, the enzyme, sulfite oxidase (SOx), is used to biofunctionalise a platinum-nanoparticle-modified polypyrrole nanowire array (PPyNWA) for the ultrasensitive amperometric detection of sulfite. A dual-step anodisation method was used to prepare the anodic aluminum oxide membrane used as a template for the initial fabrication of the PPyNWA. PtNPs were subsequently deposited on the PPyNWA by potential cycling in a platinum solution. The resulting PPyNWA-PtNP electrode was then biofuntionalised by adsorption of SOx onto the surface. The confirmation of the adsorption of SOx and the presence of PtNPs in the PPyNWA-PtNPs-SOx biosensor was verified by scanning electron microscopy and electron dispersive X-ray spectroscopy. Cyclic voltammetry and amperometric measurements were used to investigate the properties of the nanobiosensor and to optimise its use for sulfite detection. Ultrasensitive detection of sulfite with the PPyNWA-PtNPs-SOx nanobiosensor was accomplished by use of 0.3 M pyrrole, 10 U mL^-1 of SOx, adsorption time of 8 h, a polymerisation period of 900 s, and an applied current density of 0.7 mA cm^-2. The response time of the nanobiosensor was 2 s, and its excellent analytical performance was substantiated with a sensitivity of 57.33 μA cm^-2 mM^-1, a limit of detection of 12.35 nM, and a linear response range from 0.12 to 1200 μM. Application of the nanobiosensor to sulfite determination in beer and wine samples was achieved with a recovery efficiency of 97-103%.

Smart Mask as Wearable for Post-Pandemic Personal Healthcare

A mask serves as a simple external barrier that protects humans from infectious particles from poor air conditions in the surrounding environment. As an important personal protective equipment (PPE) to protect our respiratory system, masks are able not only to filter pathogens and dust particles but also to sense, reflect or even respond to environmental conditions. This smartness is of particular interest among academia and industries due to its potential in disease detection, health monitoring and caring aspects. In this review, we provide an overlook of the current air filtration strategies used in masks, from structural designs to integrated functional modules that empower the mask's ability to sense and transfer physiological or environmental information to become smart. Specifically, we discussed recent developments in masks designed to detect macroscopic physiological signals from the wearer and mask-based disease diagnoses, such as COVID-19. Further, we propose the concept of next-generation smart masks and the requirements from material selection and function design perspectives that enable masks to interact and play crucial roles in health-caring wearables.

Electrochemical Biosensors for Pathogen Detection: An Updated Review

Electrochemical biosensors are a family of biosensors that use an electrochemical transducer to perform their functions. In recent decades, many electrochemical biosensors have been created for pathogen detection. These biosensors for detecting infections have been comprehensively studied in terms of transduction elements, biorecognition components, and electrochemical methods. This review discusses the biorecognition components that may be used to identify pathogens. These include antibodies and aptamers. The integration of transducers and electrode changes in biosensor design is a major discussion topic. Pathogen detection methods can be categorized by sample preparation and secondary binding processes. Diagnostics in medicine, environmental monitoring, and biothreat detection can benefit from electrochemical biosensors to ensure food and water safety. Disposable and reusable biosensors for process monitoring, as well as multiplexed and conformal pathogen detection, are all included in this review. It is now possible to identify a wide range of diseases using biosensors that may be applied to food, bodily fluids, and even objects' surfaces. The sensitivity of optical techniques may be superior to electrochemical approaches, but optical methods are prohibitively expensive and challenging for most end users to utilize. On the other hand, electrochemical approaches are simpler to use, but their efficacy in identifying infections is still far from satisfactory.

Selection and Functionalization of Germanium Nanowires for Bio-Sensing

In this paper, we investigate the use of dielectrophoresis to align germanium nanowire arrays to realize nanowire-based diodes and their subsequent use for bio-sensing. After establishing that dielectrophoresis is a controllable and repeatable fabrication method to create devices from germanium nanowires, we use the optimum process conditions to form a series of diodes. These are subsequently functionalized with an aptamer, which is able to bind specifically to the spike protein of SARS-Cov2 and investigated as a potential sensor. We observe a linear increase in the source to drain current as the concentration of spike protein is increased from 100 fM/L to 1 nM/L.

Electrochemical Sensing Platform Based on Functionalized Multi-Walled Carbon Nanotubes and Metal Oxide for the Detection and Degradation Studies of Orange II Dye

Textile industry effluents are heavily contaminated with dyes. The discharge of these toxic dyes into waterbodies poses a serious threat to aquatic flora and fauna. The ultimate entrance of these toxins from thereon into the food chain affects the primary and secondary consumers. Therefore, the adoption of a sustainable solution for protection against the detrimental effects associated with adulterated water is an immediate need of the hour. To address the severity of the issue, the present work aims to design an electrochemical sensing platform by modifying the glassy carbon electrode (GCE) with zinc oxide nanoparticles and amino group-functionalized multi-walled carbon nanotubes (NH₂-fMWCNTs) for the detection of Orange II, which is a toxic azo dye. Zinc oxide nanoparticles facilitate electron transfer between the transducer and the analyte. While, the positively charged NH₂-fMWCNTs in acidic medium help in preconcentration of negatively charged analyte molecules at the electrode/electrolyte interface. The modification of the GCE catalyzed the oxidation of Orange II, as evidenced by the negative shift of the oxidation potential and enhancement in peak current intensity. Square wave voltammetry was used to optimize various experimental conditions, such as the supporting electrolyte, pH of the electrolyte, deposition potential, and deposition time for the best performance of the designed sensor. Under the optimized conditions, the detection limit and quantification of the designed sensor were found to be 0.57 and 1.92 nM, respectively. The catalytic degradation studies of Orange II was shown to be facilitated by titanium dioxide, which acted as a photocatalyst. The addition of hydrogen peroxide further promoted the extent and rate of degradation of dye. The breakdown of Orange II was probed by the designed sensing platform electrochemically and also by UV-visible spectroscopy. The dye degraded up to 92% by following pseudo-first-order kinetics.

Functionalization of 2D MoS2 Nanosheets with Various Metal and Metal Oxide Nanostructures: Their Properties and Application in Electrochemical Sensors

Two-dimensional transition metal dichalcogenides (2D TMDs) have gained considerable attention due to their distinctive properties and broad range of possible applications. One of the most widely studied transition metal dichalcogenides is molybdenum disulfide (MoS₂). The 2D MoS₂ nanosheets have unique and complementary properties to those of graphene, rendering them ideal electrode materials that could potentially lead to significant benefits in many electrochemical applications. These properties include tunable bandgaps, large surface areas, relatively high electron mobilities, and good optical and catalytic characteristics. Although the use of 2D MoS₂ nanosheets offers several advantages and excellent properties, surface functionalization of 2D MoS₂ is a potential route for further enhancing their properties and adding extra functionalities to the surface of the fabricated sensor. The functionalization of the material with various metal and metal oxide nanostructures has a significant impact on its overall electrochemical performance, improving various sensing parameters, such as selectivity, sensitivity, and stability. In this review, different methods of preparing 2D-layered MoS₂ nanomaterials, followed by different surface functionalization methods of these nanomaterials, are explored and discussed. Finally, the structure-properties relationship and electrochemical sensor applications over the last ten years are discussed. Emphasis is placed on the performance of 2D MoS₂ with respect to the performance of electrochemical sensors, thereby giving new insights into this unique material and providing a foundation for researchers of different disciplines who are interested in advancing the development of MoS₂-based sensors.

A Study of Ta2O5 Nanopillars with Ni Tips Prepared by Porous Anodic Alumina Through-Mask Anodization

The paper discusses the formation of Ta₂O₅ pillars with Ni tips during thin porous anodic alumina through-mask anodization on Si/SiO₂ substrates. The tantalum nanopillars were formed through porous masks in electrolytes of phosphoric and oxalic acid. The Ni tips on the Ta₂O₅ pillars were formed via vacuum evaporation through the porous mask. The morphology, structure, and magnetic properties at 4.2 and 300 K of the Ta₂O₅ nanopillars with Ni tips have been studied using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometry. The main mechanism of the formation of the Ta₂O₅ pillars during through-mask anodization was revealed. The superparamagnetic behavior of the magnetic hysteresis loop of the Ta₂O₅ nanopillars with Ni tips was observed. Such nanostructures can be used to develop novel functional nanomaterials for magnetic, electronic, biomedical, and optical nano-scale devices.

Integration of Different Graphene Nanostructures with PDMS to Form Wearable Sensors

This paper presents a substantial review of the fabrication and implementation of graphene-PDMS-based composites for wearable sensing applications. Graphene is a pivotal nanomaterial which is increasingly being used to develop multifunctional sensors due to their enhanced electrical, mechanical, and thermal characteristics. It has been able to generate devices with excellent performances in terms of sensitivity and longevity. Among the polymers, polydimethylsiloxane (PDMS) has been one of the most common ones that has been used in biomedical applications. Certain attributes, such as biocompatibility and the hydrophobic nature of PDMS, have led the researchers to conjugate it in graphene sensors as substrates or a polymer matrix. The use of these graphene/PDMS-based sensors for wearable sensing applications has been highlighted here. Different kinds of electrochemical and strain-sensing applications have been carried out to detect the physiological signals and parameters of the human body. These prototypes have been classified based on the physical nature of graphene used to formulate the sensors. Finally, the current challenges and future perspectives of these graphene/PDMS-based wearable sensors are explained in the final part of the paper.

Nanowire-based sensor electronics for chemical and biological applications

Detection and recognition of chemical and biological species via sensor electronics are important not only for various sensing applications but also for fundamental scientific understanding. In the past two decades, sensor devices using one-dimensional (1D) nanowires have emerged as promising and powerful platforms for electrical detection of chemical species and biologically relevant molecules due to their superior sensing performance, long-term stability, and ultra-low power consumption. This paper presents a comprehensive overview of the recent progress and achievements in 1D nanowire synthesis, working principles of nanowire-based sensors, and the applications of nanowire-based sensor electronics in chemical and biological analytes detection and recognition. In addition, some critical issues that hinder the practical applications of 1D nanowire-based sensor electronics, including device reproducibility and selectivity, stability, and power consumption, will be highlighted. Finally, challenges, perspectives, and opportunities for developing advanced and innovative nanowire-based sensor electronics in chemical and biological applications are featured.

The Interaction between DNA and Three Intercalating Anthracyclines Using Electrochemical DNA Nanobiosensor Based on Metal Nanoparticles Modified Screen-Printed Electrode

The screen-printed electrodes have gained increasing importance due to their advantages, such as robustness, portability, and easy handling. The manuscript presents the investigation of the interaction between double-strand deoxyribonucleic acid (dsDNA) and three anthracyclines: epirubicin (EPI), idarubicin (IDA), and doxorubicin (DOX) by differential pulse voltammetry on metal nanoparticles modified by screen-printed electrodes. In order to investigate the interaction, the voltammetric signals of dsDNA electroactive bases were used as an indicator. The effect of various metal nanomaterials on the signals of guanine and adenine was evaluated. Moreover, dsDNA/PtNPs/AgNPs/SPE (platinum nanoparticles/silver nanoparticles/screen-printed electrodes) was designed for anthracyclines–dsDNA interaction studies since the layer-by-layer modification strategy of metal nanoparticles increases the surface area. Using the signal of multi-layer calf thymus (ct)-dsDNA, the within-day reproducibility results (RSD%) for guanine and adenine peak currents were found as 0.58% and 0.73%, respectively, and the between-day reproducibility results (RSD%) for guanine and adenine peak currents were found as 1.04% and 1.26%, respectively. The effect of binding time and concentration of three anthracyclines on voltammetric signals of dsDNA bases were also evaluated. The response was examined in the range of 0.3–1.3 ppm EPI, 0.1–1.0 ppm IDA and DOX concentration on dsDNA/PtNPs/AgNPs/SPE. Electrochemical studies proposed that the interaction mechanism between three anthracyclines and dsDNA was an intercalation mode.

Fabrication strategies and surface tuning of hierarchical gold nanostructures for electrochemical detection and removal of toxic pollutants

The intensive research on the synthesis and characterization of gold (Au) nanostructures has been extensively documented over the last decades. These investigations allow the researchers to understand the relationships between the intrinsic properties of Au nanostructures such as particle size, shape, morphology, and composition to synthesize the Au nano/hybrid nanostructures with novel physicochemical properties. By tuning the properties above, these nanostructures are extensively employed to detect and remove trace amounts of toxic pollutants from the environment. This review attempts to document the achievements and current progress in Au-based nanostructures, general synthetic and fabrication strategies and their utilization in electrochemical sensing and environmental remediation applications. Additionally, the applications of Au nanostructures (e.g., as adsorbents, sensing platforms, catalysts, and electrodes) and advancements in the field of electrochemical sensing of different target analytes (e.g., proteins, nucleic acids, heavy metals, small molecules, and antigens) are summarized. The literature survey concludes the existing methods for the detection of toxic contaminants at various concentration levels. Finally, the existing challenges and future research directions on electrochemical sensing and degradation of toxic contaminants using Au nanostructures are defined.

Carbon Dots: Classification, Properties, Synthesis, Characterization, and Applications in Health Care-An Updated Review (2018-2021)

Carbon dots (CDs) are usually smaller than 10 nm in size, and are meticulously formulated and recently introduced nanomaterials, among the other types of carbon-based nanomaterials. They have gained significant attention and an incredible interest in the field of nanotechnology and biomedical science, which is merely due to their considerable and exclusive attributes; including their enhanced electron transferability, photobleaching and photo-blinking effects, high photoluminescent quantum yield, fluorescence property, resistance to photo-decomposition, increased electrocatalytic activity, good aqueous solubility, excellent biocompatibility, long-term chemical stability, cost-effectiveness, negligible toxicity, and acquaintance of large effective surface area-to-volume ratio. CDs can be readily functionalized owing to the abundant functional groups on their surfaces, and they also exhibit remarkable sensing features such as specific, selective, and multiplex detectability. In addition, the physico-chemical characteristics of CDs can be easily tunable based on their intended usage or application. In this comprehensive review article, we mainly discuss the classification of CDs, their ideal properties, their general synthesis approaches, and primary characterization techniques. More importantly, we update the readers about the recent trends of CDs in health care applications (viz., their substantial and prominent role in the area of electrochemical and optical biosensing, bioimaging, drug/gene delivery, as well as in photodynamic/photothermal therapy).

Biosensors based on aptamer-conjugated gold nanoparticles: A review

Simply synthetized gold nanoparticles have been highly used in medicine and biotechnology as a result of their biocompatibility, conductivity, and being easily functionalized with biomolecules such as aptamer. Aptamer-conjugated gold nanoparticle structures synergically possess characteristics of both aptamer and gold nanoparticles including high binding affinity, high biocompatibility, enhanced target selectivity, and long circulatory half-life. Aptamer-conjugated gold nanoparticles have extensively gained considerable attention for designing of biosensing systems due to their interesting optical and electrochemical features. Moreover, biosensors based on aptamer-gold nanoparticles are easy to use, with fast response, and inexpensive which make them ideal in individualized medicine, disease markers detection, food safety, and so forth. Moreover, due to high selectivity and biocompatibility of aptamer-gold nanoparticles, these biosensing platforms are ideal tools for targeted drug delivery systems. The application of this nanostructure as diagnostic and therapeutic tool has been developed for detection of cancer in the early stage by detecting cancer biomarkers, pathogens, proteins, toxins, antibiotics, adenosine triphosphate, and other small molecules. This review obviously demonstrates that this nanostructure effectively is applicable in the field of biomedicine and possesses potential of commercialization aims.

A Generalized Potentiostat Adaptor for Multiplexed Electroanalysis

Electrochemical measurements over an array of electrodes may be accomplished with one of three potentiostat architectures: a single-channel device which averages the signal from a number of interconnected electrodes, a multichannel device with dedicated circuits for each electrode, or a single-channel device with a multiplexer interface to isolate the signal from specific electrodes. Of these three architectures, the use of a multiplexer interface is best suited to facilitate measurements over individual electrodes without the need for large numbers of dedicated potentiostat channels. We present a versatile strategy for the development of flexible printed circuit (FPC) electrode arrays with accompanying multiplexing hardware to interface with single-channel potentiostats. The FPC array was fabricated with 78 individually addressable 0.3 mm diameter gold working electrodes and characterized using optical and scanning electron microscopy, energy dispersive spectroscopy, profilometry, impedance spectroscopy, and cyclic voltammetry to investigate the morphology, elemental composition, height profile, impedance characteristics, and electrochemical response, respectively. Interfacing the FPC array via a simple connector with three 32-channel ADG731 multiplexers permitted electrochemical measurements using single-channel commercial potentiostats. Voltammetric experiments were conducted to demonstrate the reliability, stability, and reproducibility of the FPC array and interfacing hardware. The combination of these devices represents an accessible hardware platform with robust, functionalizable electrodes, a simple connection interface with commercial potentiostats, and a low cost through the use of off-the-shelf components. Our reported strategy holds great promise to facilitate multiplexed electroanalysis in next-generation sensors to increase statistical sample size and multianalyte detection capabilities.

Wafer-scalable chemical modification of amino groups on graphene biosensors

Graphene's remarkable attributes make it suitable for application to biosensors for biomolecular recognition. Specific and precise target detection is realized by designing robust methods for immobilization of probe molecules, such as oligonucleotides, antibodies, receptors, and sugar chains, to a device surface. In this research, we developed a chemical modification method with a plasma treatment of amino groups on natural defects of graphene, which is compatible with a wafer-scalable semiconductor process, to prevent deterioration of the carrier mobility. The plasma treatment was optimized in terms of the efficiency of the amino radical generation, length of the mean free path, and reaction energy on graphene. The density of the modified amino groups on graphene was approximately 0.065 groups/nm², and the change in the ΔI_d/ΔV_g characteristic of the graphene field-effect transistor (FET) was negligible. DNA probes were then attached to the amino groups on the graphene FET. The target complementary DNA was detected at 1 nM after hybridization using the graphene FET devices. The plasma-assisted modification of the amino groups on the graphene surface was developed for immobilization of the DNA probes, and hybridization with the target DNA was demonstrated without deterioration of the carrier mobility.

Reactant/polymer hybrid films on p-n junction photodetectors for self-powered, non-invasive glucose biosensors

The portability of electronic-based biosensors is limited because of the use of batteries and/or solutions containing reactants such as enzymes for assay, which limits the utility of such biosensors in point-of-care (POC) testing. In this study, we report on the development of a self-powered biosensor composed of only portable components: a reactant-containing poly (ethylene glycol) (PEG) film for the colorimetric assay, and a self-powered n-InGaZnO/p-Si photodetector. The PEG film containing enzymes and color-developing agents was formed on a glass slide by spin coating. The self-powered biosensor was fabricated by placing the hybrid film on the p-n junction photodetector, and applied in non-invasive glucose detection (salivary glucose). Injection of the target-containing solution dissolved the PEG that led to the release of enzymes and color-developing agents, resulting in a colorimetric assay. The colorimetric assay could attenuate the light reaching the photodetector, thus facilitating target concentration verification by measuring the photocurrent. Our self-powered biosensor has two main advantages: (i) all components of the biosensor are portable and (ii) dilution of target concentration is avoided as the reagents are in the PEG film. Therefore, the self-powered biosensor, without solution-phase components, could be highly beneficial for creating portable, sensitive biosensors for POC testing.

Germanium Nanowires as Sensing Devices: Modelization of Electrical Properties

In this paper, we model the electrical properties of germanium nanowires with a particular focus on physical mechanisms of electrical molecular sensing. We use the Tibercad software to solve the drift-diffusion equations in 3D and we validate the model against experimental data, considering a p-doped nanowire with surface traps. We simulate three different types of interactions: (1) Passivation of surface traps; (2) Additional surface charges; (3) Charge transfer from molecules to nanowires. By analyzing simulated I–V characteristics, we observe that: (i) the largest change in current occurs with negative charges on the surfaces; (ii) charge transfer provides relevant current changes only for very high values of additional doping; (iii) for certain values of additional n-doping ambipolar currents could be obtained. The results of these simulations highlight the complexity of the molecular sensing mechanism in nanowires, that depends not only on the NW parameters but also on the properties of the molecules. We expect that these findings will be valuable to extend the knowledge of molecular sensing by germanium nanowires, a fundamental step to develop novel sensors based on these nanostructures.

Silver Nanowires as Electron Transfer Mediators in Electrochemical Catechol Biosensors

The integration of nanomaterials as electron mediators in electrochemical biosensors is taking on an essential role. Due to their high surface-to-volume ratio and high conductivity, metallic nanowires are an interesting option. In this paper, silver nanowires (AgNWs) were exploited to design a novel catechol electrochemical biosensor, and the benefits of increasing the aspect ratio of the electron mediator (nanowires vs. nanoparticles) were analyzed. Atomic force microscopy (AFM) studies have shown a homogeneous distribution of the enzyme along the silver nanowires, maximizing the contact surface. The large contact area promotes electron transfer between the enzyme and the electrode surface, resulting in a Limit of Detection (LOD) of 2.7 × 10⁻⁶ M for tyrosinase immobilized onto AgNWs (AgNWs-Tyr), which is one order of magnitude lower than the LOD of 3.2 × 10⁻⁵ M) obtained using tyrosinase immobilized onto silver nanoparticles (AgNPs-Tyr). The calculated K_M constant was 122 mM. The simultaneous use of electrochemistry and AFM has demonstrated a limited electrochemical fouling that facilitates stable and reproducible detection. Finally, the biosensor showed excellent anti-interference characteristics toward the main phenols present in wines including vanillin, pyrogallol, quercetin and catechin. The biosensor was able to successfully detect the presence of catechol in real wine samples. These results make AgNWs promising elements in nanowired biosensors for the sensitive, stable and rapid voltammetric detection of phenols in real applications.

Plant-derived silica nanoparticles and composites for biosensors, bioimaging, drug delivery and supercapacitors: a review

Silica nanoparticles have rapidly found applications in medicine, supercapacitors, batteries, optical fibers and concrete materials, because silica nanoparticles have tunable physical, chemical, optical and mechanical properties. In most applications, high-purity silica comes from synthetic organic precursors, yet this approach could be costly, polluting and non-biocompatible. Alternatively, natural silica sources from biomass are often cheap and abundant, yet they contain impurities. Silica can be extracted from corn cob, coffee husk, rice husk, sugarcane bagasse and wheat husk wastes, which are often disposed of in rivers, lands and ponds. These wastes can be used to prepare homogenous silica nanoparticles. Here we review properties, preparation and applications of silica nanoparticles. Preparation includes chemical and biomass methods. Applications include biosensors, bioimaging, drug delivery and supercapacitors. In particular, to fight the COVID-19 pandemic, recent research has shown that silver nanocluster/silica deposited on a mask reduces SARS-Cov-2 infectivity to zero.

Controlled Fabrication of DNA Molecular Templates for In Situ Formation and Measurement of Ultrathin Metal Nanostructures

Fabrication of ultrathin metal nanostructures usually requires some combination of high-vacuum deposition and postgrowth processing, which precludes access to nanostructures of ultrasmall cross sections for most materials. DNA nanowires (NWs) are versatile insulating templates with intrinsic sub-10 nm line width. Here, we demonstrate a method of DNA template fabrication with precise control over the location and orientation of the DNA NWs. We further demonstrate that this template can be used to support formation of ultrathin metal NWs for derivative nanodevices: a metal is incrementally deposited, and electrical transport measurement is performed in situ at each step. The results show a homogeneous metal NW is obtained at a thickness as small as 0.9 nm with a cross-section of only a few nm². The high degree of control in the location, separation, and orientation of the DNA NWs affords this method great promise in fabricating complex nanodevices based on metal NWs.

Nanoarchitectonics for Wide Bandgap Semiconductor Nanowires: Toward the Next Generation of Nanoelectromechanical Systems for Environmental Monitoring

Semiconductor nanowires are widely considered as the building blocks that revolutionized many areas of nanosciences and nanotechnologies. The unique features in nanowires, including high electron transport, excellent mechanical robustness, large surface area, and capability to engineer their intrinsic properties, enable new classes of nanoelectromechanical systems (NEMS). Wide bandgap (WBG) semiconductors in the form of nanowires are a hot spot of research owing to the tremendous possibilities in NEMS, particularly for environmental monitoring and energy harvesting. This article presents a comprehensive overview of the recent progress on the growth, properties and applications of silicon carbide (SiC), group III-nitrides, and diamond nanowires as the materials of choice for NEMS. It begins with a snapshot on material developments and fabrication technologies, covering both bottom-up and top-down approaches. A discussion on the mechanical, electrical, optical, and thermal properties is provided detailing the fundamental physics of WBG nanowires along with their potential for NEMS. A series of sensing and electronic devices particularly for environmental monitoring is reviewed, which further extend the capability in industrial applications. The article concludes with the merits and shortcomings of environmental monitoring applications based on these classes of nanowires, providing a roadmap for future development in this fast-emerging research field.

Current progress on COVID-19 related to biosensing technologies: New opportunity for detection and monitoring of viruses

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COVID-19 infection poses a serious risk to human life by causing acute lung damage.

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Various techniques used to identify and quantify COVID-19 infection.

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Major challenges for containing the spread of COVID-19 is the ability to identify asymptomatic cases.

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Currently available diagnostic methods, biosensing technology developed during COVID-19 infection.

The technologies used for coronavirus testing consist of a pre-existing device developed to examine different pathologies, such as bacterial infections, or cancer biomarkers. However, for the 2019 pandemic, researchers knew that their technology could be modified to detect a low viral load at an early stage. Today, countries around the world are working to control the new coronavirus disease (n-SARS-CoV-2). From this perspective, laboratories, universities, and companies around the world have embarked on a race to develop and produce much-needed test kits. This review has been developed to provide an overview of current trends and strategies in n-SARS-CoV-2 diagnostics based on traditional and new emerging assessment technologies, to continuous innovation. It focuses on recent trends in biosensors to build a fast, reliable, more sensitive, accessible, user-friendly system and easily adaptable technology n-SARS-CoV-2 detection and monitoring. On the whole, we have addressed and identified research evidence supporting the use of biosensors on the premise that screening people for n-SARS-CoV-2 is the best way to contain its spread.

Direct growth of germanium nanowires on glass

We report a detailed characterization of Ge NWs directly grown on glass by a MOVPE system, showing how different growth parameters can affect the final outcome and comparing NWs grown on a monocrystalline Ge(111) substrate with NWs grown on amorphous glass. Our experimental results indicate that the choice of the substrate does not affect any of the relevant morphological, crystallographic or electrical properties of Ge NWs. Lengths are in the 20-30 micrometer range with minimal tapering, while growth rates are very similar to to NWs grown on Ge(111); TEM and Raman characterization show a very good crystallinity of measured nanostructures. We have also analyzed the growth process on glass and we were able to reach a conclusion on the specific growth mechanism for Ge NWs on amorphous substrates. Our findings demonstrate that glass is a valid option as cheap substrate for the mass production of these nanostructures.

Unique Host Matrix to Disperse Pd Nanoparticles for Electrochemical Sensing of Morin: Sustainable Engineering Approach

Biomass-based carbon nanospheres derived from Mimosa pudica (commonly called "Touch-me-not") smeared on carbon fiber paper have been used as a host matrix for electrochemical deposition of palladium nanoparticles. The physicochemical characterization of modified electrodes was performed by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. Cyclic voltammetry and electrochemical impedance spectroscopy were used to study the electroanalytical properties of the electrodes. The modified electrode demostrated an excellent electrocatalytic activity for the oxidation of a flavonoid, morin, which gave a sensitive anodic peak at -0.30 V (vs SCE). An ultralow-level detection limit of 572 fM with a linear dynamic range of 37.50-130 pM was achieved. The proposed electrochemical sensor was successfully employed for the analysis of morin in mulberry and guava leaves. This is a sustainable engineering approach where a perfect unique host matrix is created using carbon nanospheres from biomass.

Copper nanowire array as highly selective electrochemical sensor of nitrate ions in water

Contamination of water with nitrate ions is a significant problem that affects many areas of the world. For this reason, European legislation has set the maximum permissible concentration of nitrates in drinking water at 44 mg/L. Thus, it is clear that a continuous monitoring of nitrate ions is of high technological interest but it must be rapid, easy to perform and directly performable in situ. In this work we have developed a nanostructured sensor based on array of copper nanowires obtained with the simple method of galvanic deposition. The nanostructured sensors have a very short response time with a detection limit less than 10 μM. Different interfering species were tested finding a negligible effect except for the chloride ions. However, this problem has been solved by removing chloride ions from the water through a simple precipitation of chloride compounds with low solubility. Nanostructured sensors were also used to analyze real water samples (rain, river and drinking water). In the case of drinking water, we have measured a concentration of nitrate ions very close to the that measured by conventional laboratory techniques.

Nano-porous anodic alumina: fundamentals and applications in tissue engineering

Recently, nanomaterials have been widely utilized in tissue engineering applications due to their unique properties such as the high surface to volume ratio and diversity of morphology and structure. However, most methods used for the fabrication of nanomaterials are rather complicated and costly. Among different nanomaterials, anodic aluminum oxide (AAO) is a great example of nanoporous structures that can easily be engineered by changing the electrolyte type, anodizing potential, current density, temperature, acid concentration and anodizing time. Nanoporous anodic alumina has often been used for mammalian cell culture, biofunctionalization, drug delivery, and biosensing by coating its surface with biocompatible materials. Despite its wide application in tissue engineering, thorough in vivo and in vitro studies of AAO are still required to enhance its biocompatibility and thereby pave the way for its application in tissue replacements. Recognizing this gap, this review article aims to highlight the biomedical potentials of AAO for applications in tissue replacements along with the mechanism of porous structure formation and pore characteristics in terms of fabrication parameters.

Electrochemical biosensors for pathogen detection

Recent advances in electrochemical biosensors for pathogen detection are reviewed. Electrochemical biosensors for pathogen detection are broadly reviewed in terms of transduction elements, biorecognition elements, electrochemical techniques, and biosensor performance. Transduction elements are discussed in terms of electrode material and form factor. Biorecognition elements for pathogen detection, including antibodies, aptamers, and imprinted polymers, are discussed in terms of availability, production, and immobilization approach. Emerging areas of electrochemical biosensor design are reviewed, including electrode modification and transducer integration. Measurement formats for pathogen detection are classified in terms of sample preparation and secondary binding steps. Applications of electrochemical biosensors for the detection of pathogens in food and water safety, medical diagnostics, environmental monitoring, and bio-threat applications are highlighted. Future directions and challenges of electrochemical biosensors for pathogen detection are discussed, including wearable and conformal biosensors, detection of plant pathogens, multiplexed detection, reusable biosensors for process monitoring applications, and low-cost, disposable biosensors.

Carbon Allotrope-Based Optical Fibers for Environmental and Biological Sensing: A Review

Recently, carbon allotropes have received tremendous research interest and paved a new avenue for optical fiber sensing technology. Carbon allotropes exhibit unique sensing properties such as large surface to volume ratios, biocompatibility, and they can serve as molecule enrichers. Meanwhile, optical fibers possess a high degree of surface modification versatility that enables the incorporation of carbon allotropes as the functional coating for a wide range of detection tasks. Moreover, the combination of carbon allotropes and optical fibers also yields high sensitivity and specificity to monitor target molecules in the vicinity of the nanocoating surface. In this review, the development of carbon allotropes-based optical fiber sensors is studied. The first section provides an overview of four different types of carbon allotropes, including carbon nanotubes, carbon dots, graphene, and nanodiamonds. The second section discusses the synthesis approaches used to prepare these carbon allotropes, followed by some deposition techniques to functionalize the surface of the optical fiber, and the associated sensing mechanisms. Numerous applications that have benefitted from carbon allotrope-based optical fiber sensors such as temperature, strain, volatile organic compounds and biosensing applications are reviewed and summarized. Finally, a concluding section highlighting the technological deficiencies, challenges, and suggestions to overcome them is presented.

Organic field-effect transistor-based flexible sensors

Flexible transistors are the next generation sensing technology, due to multiparametric analysis, reduced complexity, biocompatibility, lightweight with tunable optoelectronic properties. We summarize multitude of applications realized with OFETs.

Electrochemical sensory detection of Sus scrofa mtDNA for food adulteration using hybrid ferrocenylnaphthalene diimide intercalator as a hybridization indicator

In this study, an electrochemical DNA biosensor was developed based on the fabrication of silicon nanowires/platinum nanoparticles (SiNWs/PtNPs) on a screen-printed carbon electrode (SPCE) for the detection of Sus scrofa mitochondrial DNA (mtDNA) in food utilizing a new hybrid indicator, ferrocenylnaphthalene diimide (FND). The morphology and elemental composition of the SiNWs/PtNPs-modified SPCE was analyzed by field emission scanning electron microscopy (FESEM) combined with energy dispersive X-ray spectroscopy (EDX). Cyclic voltammetry (CV) was used to study the electrical contact between the PtNPs and the screen-printed working electrode through SiNWs, while electrochemical impedance spectroscopy (EIS) was used to measure the charge transfer resistance of the modified electrode. The results clearly showed that the SiNWs/PtNPs were successfully coated onto the electrode and the effective surface area for the SiNWs/PtNPs-modified SPCE was increased 16.8 times as compared with that of the bare SPCE. Differential pulse voltammetry used for the detection of porcine DNA with FND as an intercalator confirmed its specific binding to the double-stranded DNA (dsDNA) sequences. The developed biosensor showed a selective response towards complementary target DNA and was able to distinguish non-complementary and mismatched DNA oligonucleotides. The SiNWs/PtNPs-modified SPCE that was fortified with DNA hybridization demonstrated good linearity in the range of 3 × 10⁻⁹ M to 3 × 10⁻⁵ M (R² = 0.96) with a detection limit of 2.4 × 10⁻⁹ M. A cross-reactivity study against various types of meat and processed food showed good reliability for porcine samples.

An electrochemical DNA biosensor was developed based on the fabrication of silicon nanowires/platinum nanoparticles on a screen-printed carbon electrode for the detection of Sus scrofa mitochondrial DNA in food.

Cantilever Nanobiosensor Functionalized with Tyrosinase for Detection of Estrone and β-estradiol in Water

This work aimed to develop cantilever nanobiosensor functionalized with tyrosinase enzyme to detect 17β-estradiol and estrone hormones. In this system, the tyrosinase enzyme was covalently immobilized by self-assembled monolayer onto the cantilever sensor surface. It was possible to verify that the high hormone concentration investigated resulted in high voltage response. The nanobiosensor presented a distinction between the concentrations evaluated and was verified sensitivities of 0.497 and 0.101 V/μg, limit of detection of 0.1 and 0.4 ng/L for the hormones 17β-estradiol and estrone, respectively. The device showed good reversibility and during 30 days of storage maintained about 99% of the original signal. The cantilever nanobiosensor applied in different water samples (ultrapure, river, tap, and mineral) showed good performance, so could be readily extended toward the on-site monitoring of the other trace small molecular pollutants in environmental water matrices.

Thermal transports of one-dimensional ultrathin carbon structures

Carbon atomic chain, linear benzene polymers, and carbon nanothreads are all one-dimensional (1D) ultrathin carbon structures. They possess excellent electronic and mechanical properties; however, their thermal transport properties have been rarely explored. Here, we systematically study their thermal conductance by combining the nonequilibrium Green's function and force field methods. The thermal conductance varies from 0.24 to 1.00 nW K^-1 at 300 K, and phonon transport in the linear benzene polymers and carbon nanothreads is strongly dependent on the connectivity styles between the benzene rings. We propose a simple 1D model, namely force-constant model, that explains the complicated transport processes in these structures. Our study not only reveals intrinsic mechanisms of phonon transport in these carbon structures, but also provides an effective method to analyze thermal properties of other 1D ultrathin structures made of only several atomic chains.