Large-scale graphene micropattern nano-biohybrids: high-performance transducers for FET-type flexible fluidic HIV immunoassays

A brief overview of passive microvalves in microfluidics: Mechanism, manufacturing, and applications

Microvalves play a crucial role in manipulating fluid states within a microfluidic system and are finding widespread applications in fields such as biology, medicine, and environmental preservation. Leveraging the characteristics and features of microvalves enables the realization of various complicated microfluidic functions. Continuous advancement in the manufacturing process contributes to more flexible control modes for passive microvalves. As a consequence, these valves are progressively shrinking in size while simultaneously improving in precision and stability. Although active microvalves have the benefits of low leakage, rapid response time, and wide adaptability range, the energy supply system limits the size and even their applicability in integration and miniaturization. In comparison, passive microvalves have the advantage of relying solely on the fluid flow or fluid driving pressure to control the open/close of fluid flow over active microvalves, in spite of having slightly reduced control accuracy. Their self-sustaining feature is highly consistent with the need for assembly and miniaturization in the point-of-care testing technology. Hence, these valves have attracted significant interest for research and application purposes. This review focuses on the recent literature on passive microvalves and details existing passive microvalves from three different aspects: operating principle, processing method, and applications. This work aims to increase the visibility of passive microvalves among researchers and enhance their comprehension by classifying them according to the aforementioned three aspects, facilitating the practical applications and further developments of passive microvalves. Additionally, this paper is expected to serve as a comprehensive and systematic reference for interdisciplinary researchers that intend to design related microfluidic systems.

Synchronous Diagnosis of Respiratory Viruses Variants via Receptonics Based on Modeling Receptor-Ligand Dynamics

The transmission and pathogenesis of highly contagious fatal respiratory viruses are increasing, and the need for an on-site diagnostic platform has arisen as an issue worldwide. Furthermore, as the spread of respiratory viruses continues, different variants have become the dominant circulating strains. To prevent virus transmission, the development of highly sensitive and accurate on-site diagnostic assays is urgently needed. Herein, a facile diagnostic device is presented for multi-detection based on the results of detailed receptor-ligand dynamics simulations for the screening of various viral strains. The novel bioreceptor-treated electronics (receptonics) device consists of a multichannel graphene transistor and cell-entry receptors conjugated to N-heterocyclic carbene (NHC). An ultrasensitive multi-detection performance is achieved without the need for sample pretreatment, which will enable rapid diagnosis and prevent the spread of pathogens. This platform can be applied for the diagnosis of variants of concern in clinical respiratory virus samples and primate models. This multi-screening platform can be used to enhance surveillance and discriminate emerging virus variants before they become a severe threat to public health.

Advances in flexible graphene field-effect transistors for biomolecule sensing

With the increasing demand for biomarker detection in wearable electronic devices, flexible biosensors have garnered significant attention. Additionally, graphene field-effect transistors (GFETs) have emerged as key components for constructing biosensors, owing to their high sensitivity, multifunctionality, rapid response, and low cost. Leveraging the advantages of flexible substrates, such as biocompatibility, adaptability to complex environments, and fabrication flexibility, flexible GFET sensors exhibit promising prospects in detecting various biomarkers. This review provides a concise summary of design strategies for flexible GFET biosensors, including non-encapsulated gate without dielectric layer coverage and external gate designs. Furthermore, notable advancements in sensing applications of biomolecules, such as proteins, glucose, and ions, are highlighted. Finally, we discuss the future challenges and prospects in this field, aiming to inspire researchers to address these issues in their further investigations.

Recent advances in the detection of pathogenic microorganisms and toxins based on field-effect transistor biosensors

In food safety analysis, the detection and control of foodborne pathogens and their toxins are of great importance. Monitoring of virus transmission is equally important, especially in light of recent findings that coronaviruses have been detected in frozen foods and packages during the current global epidemic of coronavirus disease 2019. In recent years, field-effect transistor (FET) biosensors have attracted considerable scholarly attention for pathogenic microorganisms and toxins detection and sensing due to their rapid response time, high sensitivity, wide dynamic range, high specificity, label-free detection, portability, and cost-effectiveness. FET-based biosensors can be modified with specific recognition elements, thus providing real-time qualitative and semiquantitative analysis. Furthermore, with advances in nanotechnology and device design, various high-performance nanomaterials are gradually applied in the detection of FET-based biosensors. In this article, we review specific detection in different biological recognition elements are immobilized on FET biosensors for the detection of pathogenic microorganisms and toxins, and we also discuss nonspecific detection by FET biosensors. In addition, there are still unresolved challenges in the development and application of FET biosensors for achieving efficient, multiplexed, in situ detection of pathogenic microorganisms and toxins. Therefore, directions for future FET biosensor research and applications are discussed.

Discrimination of the H1N1 and H5N2 Variants of Influenza A Virus Using an Isomeric Sialic Acid-Conjugated Graphene Field-Effect Transistor

There has been a continuous effort to fabricate a fast, sensitive, and inexpensive system for influenza virus detection to meet the demand for effective screening in point-of-care testing. Herein, we report a sialic acid (SA)-conjugated graphene field-effect transistor (SA-GFET) sensor designed using α2,3-linked sialic acid (3'-SA) and α2,6-linked sialic acid (6'-SA) for the detection and discrimination of the hemagglutinin (HA) protein of the H5N2 and H1N1 viruses. 3'-SA and 6'-SA specific for H5 and H1 influenza were used in the SA-GFET to capture the HA protein of the influenza virus. The net charge of the captured viral sample led to a change in the electrical current of the SA-GFET platform, which could be correlated to the concentration of the viral sample. This SA-GFET platform exhibited a highly sensitive response in the range of 10¹-10⁶ pfu mL^-1, with a limit of detection (LOD) of 10¹ pfu mL^-1 in buffer solution and a response time of approximately 10 s. The selectivity of the SA-GFET platform for the H1N1 and H5N2 influenza viruses was verified by testing analogous respiratory viruses, i.e., influenza B and the spike protein of SARS-CoV-2 and MERS-CoV, on the SA-GFET. Overall, the results demonstrate that the developed dual-channel SA-GFET platform can potentially serve as a highly efficient and sensitive sensing platform for the rapid detection of infectious diseases.

Wireless portable bioelectronic nose device for multiplex monitoring toward food freshness/spoilage

Monitoring food freshness/spoilage is important to ensure food quality and safety. Current methods of food quality monitoring are mostly time-consuming and labor intensive processes that require massive analytical equipment. In this study, we developed a portable bioelectronic nose (BE-nose) integrated with trace amine-associated receptor (TAAR) nanodiscs (NDs), allowing food quality monitoring via the detection of food spoilage indicators, including the biogenic amines cadaverine (CV) and putrescine (PT). The olfactory receptors TAAR13c and TAAR13d, which have specific affinities for CV and PT, were produced and successfully reconstituted in ND structures. TAAR13 NDs BE-nose-based side-gated field-effect transistor (SG-FET) system was constructed by utilizing a graphene micropattern (GM) into which two types of olfactory NDs (TAAR13c ND and TAAR13d ND) were introduced, and this system showed ultrahigh sensitivity for a limit of detection (LOD) of 1 fM for CV and PT. Moreover, the binding affinities between the TAAR13 NDs and the indicators were confirmed by a tryptophan fluorescence quenching assay and biosimulations, in which the specific binding site was confirmed. Gas-phase indicators were detected by the TAAR13 NDs BE-nose platform, and the LODs for CV and PT were confirmed to be 26.48 and 7.29 ppb, respectively. In addition, TAAR13 NDs BE-nose was fabricated with commercial gas sensors as a portable platform for the measurement of NH₃ and H₂S, multiplexed monitoring was achieved with similar performance, and the change ratio of the indicators was observed in a real sample. The integration of commercial gas sensors on a BE-nose enhanced the accuracy and reliability for the quality monitoring of real food samples. These results indicate that the portable TAAR13 NDs BE-nose can be used to monitor CV and PT over a wide range of concentrations, therefore, the electronic nose platform can be utilized for monitoring the freshness/spoilage step in various foods.

In-situ food spoilage monitoring using a wireless chemical receptor-conjugated graphene electronic nose

Monitoring food spoilage is one of the most effective methods for preventing food poisoning caused by biogenic amines or microbes. Therefore, various analytical techniques have been introduced to detect low concentrations of cadaverine (CV) and putrescine (PT), which are representative biogenic polyamines involved in food spoilage (5-8 ppm at the stage of initial decomposition after storage for 5 days at 5 °C and 17-186 ppm at the stage of advanced decomposition after storage for 7 days at 5 °C). Although previous methods showed selective CV and PT detection even at low concentrations, the use of these methods remains challenging in research areas that require in-situ, real-time, on-site monitoring. In this study, we demonstrated for the first time an in-situ high-performance chemical receptor-conjugated graphene electronic nose (CRGE-nose) whose limits of detection (LODs), 27.04 and 7.29 ppb, for CV and PT are up to 10² times more sensitive than those of conventional biogenic amine sensors. Specifically, the novel chemical receptors 2,7-bis(3-morpholinopropyl)benzo[lmn][3,8] phenanthroline-1,3,6,8(2H,7H)-tetraone (NaPhdiMor (NPM)) and 2,7-bis(2-((3-morpholinopropyl)amino)ethyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NaPhdiEtAmMor (NPEAM)) were designed on the basis of density functional theory (DFT) calculations, and their interaction mechanism was characterized by a DFT 3D simulation. Interestingly, the CRGE-nose was connected on a micro sim chip substrate via wire bonding and then integrated into wireless portable devices, resulting in a cost-effective, high-performance prototype CRGE-nose device capable of on-site detection. The portable CRGE-nose can be used for in-situ monitoring of CV and PT concentration changes as low as 27.04 and 7.29 ppb in real meats such as pork, beef, lamb and chicken.

2D material based field effect transistors and nanoelectromechanical systems for sensing applications

Sensors are ubiquitous in modern society because of their wide applications in healthcare, security, forensic industries as well as environmental protection. Specifically, sensors which can be microfabricated employing very-large-scale-integration (VLSI) compatible microfabrication techniques are particularly desirable. This is because they can provide several advantages: small size, low cost, and possibility of mass fabrication. 2D materials are a promising building block for such sensors. Their atomically thin nature, flat surfaces and ability to form van der Waals hetero junctions opens up the pathway for versatile functionalities. Here, we review 2D material-based field-effect-transistors (FETs) and nano-electro-mechanical systems (NEMs) for applications in detecting different gases, chemicals, and biomolecules. We will provide insights into the unique advantages of these materials for these sensing applications and discuss the fabrication methods, detection schemes and performance pertaining to these technologies. Finally, we will discuss the current challenges and prospects for this field.

A case study of SARS-CoV-2 transmission behavior in a severely air-polluted city (Delhi, India) and the potential usage of graphene based materials for filtering air-pollutants and controlling/monitoring the COVID-19 pandemic

Globally, humanity is facing its most significant challenge in 100 years due to the novel coronavirus, SARS-CoV-2, which is responsible for COVID-19. Under the enormous pressure created by the pandemic, scientists are studying virus transmission mechanisms in order to develop effective mitigation strategies. However, no established methods have been developed to control the spread of this deadly virus. In addition, the ease in lockdown has escalated air pollution which may affect SARS-CoV-2 transmission through attachment to particulates. The present review summarizes the role of graphene nanomaterials, which show antimicrobial behavior and have antiviral efficacy, in reducing the spread of COVID-19. Graphene and its derivatives have excellent antimicrobial efficacy, providing both physical and chemical mechanisms of damage. Coupled with their lightness, optimal properties, and ease of functionalization, they are optimal nanomaterials for coating onto fabrics such as personal protection equipment, face masks and gloves to control the transmission of SARS-CoV-2 effectively. Biosensors using graphene can effectively detect the virus with high accuracy and sensitivity, providing rapid quantification. It is envisioned that the present work will boost the development of graphene-based highly sensitive, accurate and cost-effective diagnostic tools for efficiently monitoring and controlling the spread of COVID-19 and other air-borne viruses.

Development strategies of conducting polymer-based electrochemical biosensors for virus biomarkers: Potential for rapid COVID-19 detection

Rapid, accurate, portable, and large-scale diagnostic technologies for the detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) are crucial for controlling the coronavirus disease (COVID-19). The current standard technologies, i.e., reverse-transcription polymerase chain reaction, serological assays, and computed tomography (CT) exhibit practical limitations and challenges in case of massive and rapid testing. Biosensors, particularly electrochemical conducting polymer (CP)-based biosensors, are considered as potential alternatives owing to their large advantages such as high selectivity and sensitivity, rapid detection, low cost, simplicity, flexibility, long self-life, and ease of use. Therefore, CP-based biosensors can serve as multisensors, mobile biosensors, and wearable biosensors, facilitating the development of point-of-care (POC) systems and home-use biosensors for COVID-19 detection. However, the application of these biosensors for COVID-19 entails several challenges related to their degradation, low crystallinity, charge transport properties, and weak interaction with biomarkers. To overcome these problems, this study provides scientific evidence for the potential applications of CP-based electrochemical biosensors in COVID-19 detection based on their applications for the detection of various biomarkers such as DNA/RNA, proteins, whole viruses, and antigens. We then propose promising strategies for the development of CP-based electrochemical biosensors for COVID-19 detection.

Recent Progress on Biomaterials Fighting against Viruses

Viruses not only pose severe threats to public health, but also influence the development of society. Over the past decade, rapid advances have been seen in the application of nanomaterials to virus research. As an interdisciplinary field, nanotechnology offers powerful functions because the structures of nanomaterials are unique, with remarkable physicochemical properties and excellent biocompatibility. Nanomaterials have been developed for virus detection and tracking and for antiviral strategies, to better understand viruses and reduce viral infections, implying a bright future for this field. Herein, the recent advances are systematically summarized regarding the nanomaterials used in viral studies. Representative applications of nanomaterials to viral detection and tracking are described. The antiviral effects achieved with nanomaterials based on different mechanisms are also described, including entry inhibition, inhibition of viral replication, and immunological enhancement. The current challenges and future opportunities in this promising field are also discussed.

Real-time monitoring of geosmin based on an aptamer-conjugated graphene field-effect transistor

In this paper, we propose a novel field-effect transistor (FET) using graphene, which is a two-dimensional (2D) nanomaterial, capable of evaluating water quality, and immobilizing the surface of a graphene micropatterned transistor with a highly responsive bioprobe for a water contamination indicator, geosmin, with high selectivity. A high-quality bioprobe-immobilized graphene FET (GFET) was fabricated for the real-time monitoring of geosmin using a liquid-gate measurement configuration. Immobilization was confirmed by measuring the change in the electrical characteristics of the platform (slope of the current-voltage (I-V) curve) and fluorescence images. In addition, a selectivity test showed remarkable implementation of the highly sensitive sensing platform with an insignificant signal when a nontarget was added. Using the fabricated device, the linear range for geosmin detection was determined to be from 0.01 nM - 1 μM with a detection limit of 0.01 nM. In addition, geosmin concentrations as low as 10 nM could be determined from river water samples with the sensor platform. This sensor can be utilized to immediately determine the presence of odorous substances by analyzing a water supply source without additional pretreatment. Another advantage is that the sensor device is a promising tool that does not have special equipment that requirs careful maintenance. In addition, the device provides a new platform for detecting harmful substances in various water sources by varying the bioprobes that are empolyed.

Graphene-based field-effect transistor biosensors for the rapid detection and analysis of viruses: A perspective in view of COVID-19

Current situation of COVID-19 demands a rapid, reliable, cost-effective, facile detection strategy to break the transmission chain and biosensor has emerged as a feasible solution for this purpose. Introduction of nanomaterials has undoubtedly improved the performance of biosensor and the addition of graphene enhanced the sensing ability to a peerless level. Amongst different graphene-based biosensing schemes, graphene field-effect transistor marked its unique presence owing to its ability of ultrasensitive and low-noise detection thereby facilitating instantaneous measurements even in the presence of small amounts of analytes. Recently, graphene field-effect transistor type biosensor is even successfully employed in rapid detection of SARS-CoV-2 and this triggers the interest of the scientific community in reviewing the current developments in graphene field-effect transistor. Subsequently, in this article, the recent progress in graphene field-effect transistor type biosensors for the detection of the virus is reviewed and challenges along with their strengths are discussed.

Carbon Nanomaterials for Biomedical Application

The use of carbon-based nanomaterials (CNs) with outstanding properties has been rising in many scientific and industrial application fields. These CNs represent a tunable alternative for applications with biomolecules, which allow interactions in either covalent or noncovalent way. Diverse carbon-derived nanomaterial family exhibits unique features and has been widely exploited in various biomedical applications, including biosensing, diagnosis, cancer therapy, drug delivery, and tissue engineering. In this chapter, we aim to present an overview of CNs with a particular interest in intrinsic structural, electronic, and chemical properties. In particular, the detailed properties and features of CNs and its derivatives, including carbon nanotube (CNT), graphene, graphene oxide (GO), and reduced GO (rGO) are summarized. The interesting biomedical applications are also reviewed in order to offer an overview of the possible fields for scientific and industrial applications of CNs.

High-performance portable graphene field-effect transistor device for detecting Gram-positive and -negative bacteria

Current techniques for Gram-typing and for diagnosing a pathogen at the early infection stage rely on Gram stains, cultures, Enzyme linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and gene microarrays, which are labor-intensive and time-consuming approaches. In addition, a delayed or imprecise diagnosis of clinical pathogenic bacteria leads to a life-threatening emergency or overuse of antibiotics and a high-rate occurrence of antimicrobial-resistance microbes. Herein, we report high-performance antibiotics (as bioprobes) conjugated graphene micropattern field-effect transistors (ABX-GMFETs) to facilitate on-site Gram-typing and help in the detection of the presence or absence of Gram-negative and -positive bacteria in the samples. The ABX-GMFET platform, which consists of recognition probes and GM transistors conjugated with novel interfacing chemical compounds, was integrated into the microfluidics to minimize the required human intervention and facilitate automation. The mechanism of binding of ABX-GMFET was based on a charge or chemical moiety interaction between the bioprobes and target bacteria. Subsequently, ABX-GMFETs exhibited unprecedented high sensitivity with a limit of detection (LOD) of 10⁰ CFU/mL (1-9 CFU/mL), real-time target specificity.

Antimicrobial Mechanisms and Effectiveness of Graphene and Graphene-Functionalized Biomaterials. A Scope Review

Bacterial infections represent nowadays the major reason of biomaterials implant failure, however, most of the available implantable materials do not hold antimicrobial properties, thus requiring antibiotic therapy once the infection occurs. The fast raising of antibiotic-resistant pathogens is making this approach as not more effective, leading to the only solution of device removal and causing devastating consequences for patients. Accordingly, there is a large research about alternative strategies based on the employment of materials holding intrinsic antibacterial properties in order to prevent infections. Between these new strategies, new technologies involving the use of carbon-based materials such as carbon nanotubes, fullerene, graphene and diamond-like carbon shown very promising results. In particular, graphene- and graphene-derived materials (GMs) demonstrated a broad range antibacterial activity toward bacteria, fungi and viruses. These antibacterial activities are attributed mainly to the direct physicochemical interaction between GMs and bacteria that cause a deadly deterioration of cellular components, principally proteins, lipids, and nucleic acids. In fact, GMs hold a high affinity to the membrane proteoglycans where they accumulate leading to membrane damages; similarly, after internalization they can interact with bacteria RNA/DNA hydrogen groups interrupting the replicative stage. Moreover, GMs can indirectly determine bacterial death by activating the inflammatory cascade due to active species generation after entering in the physiological environment. On the opposite, despite these bacteria-targeted activities, GMs have been successfully employed as pro-regenerative materials to favor tissue healing for different tissue engineering purposes. Taken into account these GMs biological properties, this review aims at explaining the antibacterial mechanisms underlying graphene as a promising material applicable in biomedical devices.

Peptide hormone sensors using human hormone receptor-carrying nanovesicles and graphene FETs

Hormones within very low levels regulate and control the activity of specific cells and organs of the human body. Hormone imbalance can cause many diseases. Therefore, hormone detection tools have been developed, particularly over the last decade. Peptide hormones have a short half-life, so it is important to detect them within a short time. In this study, we report two types of peptide hormone sensors using human hormone receptor-carrying nanovesicles and graphene field-effect transistors (FETs). Parathyroid hormone (PTH) and glucagon (GCG) are peptide hormones present in human blood that act as ligands to G protein-coupled receptors (GPCRs). In this paper, the parathyroid hormone receptor (PTHR) and the glucagon receptor (GCGR) were expressed in human embryonic kidney-293 (HEK-293) cells, and were constructed as nanovesicles carrying the respective receptors. They were then immobilized onto graphene-based FETs. The two hormone sensors developed were able to detect each target hormone with high sensitivity (ca. 100 fM of PTH and 1 pM of GCG). Also, the sensors accurately recognized target hormones among different types of peptide hormones. In the development of hormone detection tools, this approach, using human hormone receptor-carrying nanovesicles and graphene FETs, offers the possibility of detecting very low concentrations of hormones in real-time.

Ultrasensitive, Selective, and Highly Stable Bioelectronic Nose That Detects the Liquid and Gaseous Cadaverine

Field-effect transistor (FET) devices based on conductive nanomaterials have been used to develop biosensors. However, development of FET-based biosensors that allow efficient stability, especially in the gas phase, for obtaining reliable and reproducible responses remains a challenge. In this study, we developed a nanodisc (ND)-functionalized bioelectronic nose (NBN) based on a nickel (Ni)-decorated carboxylated polypyrrole nanoparticle (cPPyNP)-FET that offers the detection of liquid and gaseous cadaverine (CV). The TAAR13c, specifically binding to CV, which is an indicator of food spoilage, was successfully constructed in NDs. The NBN was fabricated by the oriented assembly of TAAR13c-embedded NDs (T13NDs) onto the transistor with Ni/cPPyNPs. The NBN showed high performance in selectivity and sensitivity for the detection of CV, with excellent stability in both aqueous and gas phases. Moreover, the NBN allowed efficient measurement of corrupted real-food samples. It demonstrates the ND-based device can allow the practical biosensor that provides high stability in the gas phase.

Attomolar detection of virus by liquid coplanar-gate graphene transistor on plastic

The direct method of detecting a virus with extremely low concentration is recommended for the diagnosis of viral disease. In this study, coplanar-gate graphene field-effect transistors (GFETs) were built on flexible polyethylene terephthalate substrates for the attomolar detection of a virus. The GFETs exhibited a very low detection limit of 47.8 aM with relatively low source/drain voltage due to aqueous dielectric media which stabilizes viruses and antibodies for specific bonding. The antibody as a probe molecule was decorated on a graphene surface using 1-pyrenebutanoic acid succinimidyl ester that had previously been immobilized on a graphene surface. The Dirac point voltage shifted downward after dropping the virus solution, due to the electrostatic gating effect of graphene in the antigen (namely, virus)-antibody complex. The virus detection platform used in this study is expected to be beneficial for direct diagnosis in saline environments, since the performances of GFETs were not significantly affected by the presence of Na⁺ and Cl^-. Furthermore, since our flexible and transparent virus sensors can be used in a wearable device, they provide a simple and fast method for diagnosing viruses.

HIV biosensors for early diagnosis of infection: The intertwine of nanotechnology with sensing strategies

Human immunodeficiency virus (HIV) is a lentivirus that leads to acquired immunodeficiency syndrome (AIDS). With increasing awareness of AIDS emerging as a global public health threat, different HIV testing kits have been developed to detect antibodies (Ab) directed toward different parts of HIV. A great limitation of these tests is that they can not detect HIV antibodies during early virus infection. Therefore, to overcome this challenge, a wide range of biosensors have been developed for early diagnosis of HIV infection. A significant amount of these studies have been focused on the application of nanomaterials for improving the sensitivity and accuracy of the sensing methods. Following an introduction into this field, a first section of this review covers the synthesis and applicability of such nanomaterials as metal nanoparticles (NPs), quantum dots (QDs), carbon-based nanomaterials and metal nanoclusters (NCs). A second larger section covers the latest developments concerning nanomaterial-based biosensors for HIV diagnosis, with paying a special attention to the determination of CD4⁺ cells as a hall mark of HIV infection, HIV gene, HIV p24 core protein, HIV p17 peptide, HIV-1 virus-like particles (VLPs) and HIV related enzymes, particularly those that are passed on from the virus to the CD⁴⁺ T lymphocytes and are necessary for viral reproduction within the host cell. These studies are described in detail along with their diverse principles/mechanisms (e.g. electrochemistry, fluorescence, electromagnetic-piezoelectric, surface plasmon resonance (SPR), surface enhanced Raman spectroscopy (SERS) and colorimetry). Despite the significant progress in HIV biosensing in the last years, there is a great need for the development of point-of-care (POC) technologies which are affordable, robust, easy to use, portable, and possessing sufficient quantitative accuracy to enable clinical decision making. In the final section, the focus is on the portable sensing devices as a new standard of POC and personalized diagnostics.

The design, fabrication, and applications of flexible biosensing devices

Flexible biosensors form part of a rapidly growing research field that take advantage of a multidisciplinary approach involving materials, fabrication and design strategies to be able to function at biological interfaces that may be soft, intrinsically curvy, irregular, or elastic. Numerous exciting advancements are being proposed and developed each year towards applications in healthcare, fundamental biomedical research, food safety and environmental monitoring. In order to place these developments in perspective, this review is intended to present an overview on field of flexible biosensor development. We endeavor to show how this subset of the broader field of flexible and wearable devices presents unique characteristics inherent in their design. Initially, a discussion on the structure of flexible biosensors is presented to address the critical issues specific to their design. We then summarize the different materials as substrates that can resist mechanical deformation while retaining their function of the bioreceptors and active elements. Several examples of flexible biosensors are presented based on the different environments in which they may be deployed or on the basis of targeted biological analytes. Challenges and future perspectives pertinent to the current and future stages of development are presented. Through these summaries and discussion, this review is expected to provide insights towards a systematic and fundamental understanding for the fabrication and utilization of flexible biosensors, as well as inspire and improve designs for smart and effective devices in the future.

A smart nanosensor for the detection of human immunodeficiency virus and associated cardiovascular and arthritis diseases using functionalized graphene-based transistors

Human immunodeficiency virus (HIV), which isa worldwide public health issue, is commonly associated with cardiovascular disorders (CVDs) and rheumatoid arthritis (RA). A smart nanosensor was developed for the detection of HIV and its related diseases (CVDs and RA) using graphene-based field-effect transistors (FETs). In this study, amine-functionalized graphene (afG) was conjugated with antibodies [anti-p24 for HIV, anti-cardiac troponin 1 (anti-cTn1) for CVDs, and anti-cyclic citrullinated peptide (anti-CCP) for RA] to detect various biomarkers. The antibodies were covalently conjugated to afG via carbodiimide activation. The bioconjugate (graphene-antibody) was characterized by various biophysical techniques such as UV-Vis, Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The electrochemical performance of the sensor was evaluated with respect to changes in the resistance of the electrode surface due to the interaction of the antigen with its specific antibody. The developed sensor was highly sensitive and showed a linear response to p24, cTn1, and, CCP from 1 fg/mL to 1 μg/mL. The limit of detection (LOD) was 100 fg/mL for p24 and 10 fg/mL for cTn1 and CCP under standard optimized conditions. The graphene-based smart nanodevice demonstrated excellent performance; thus, it could be used for the on-site detection of HIV, CVD, and RA biomarkers in real samples.

Study on the Sensing Signal Profiles for Determination of Process Window of Flexible Sensors Based on Surface Treated PDMS/CNT Composite Patches

In this study, analysis of sensing signal profiles was conducted focusing on the close relationship between electrical conductivity and signal intensity in surface treated poly(dimethylsiloxane)/carbon nanotube (PDMS/CNT) composite patches for the purpose of their practical application as flexible chemical sensors. The flexible PDMS/CNT composite patches were prepared from a PDMS/CNT mixture with a two-roll apparatus. It was found that the PDMS/CNT pads showed a high electrical conductivity (10⁻¹ S/m) even at low CNT loading (0.6 wt %) and a contact angle range of 105–118°. The surface of the obtained PDMS/CNT composite patches was treated using a simple bio-conjugation method to incorporate beta-cyclodextrin (beta-CD) molecules onto the surface as a sensing medium, in order to detect a model compound (Methyl Paraben, MePRB). FT-IR spectra indicated that beta-cyclodextrin molecules were effectively introduced on the surface of the PDMS/CNT patches. It was shown that the sensor signal intensity was substantially dependent on the base current value, which increased with increasing CNT loading. Accordingly, the base current value was intimately associated with the electrical conductivity of the composite patches. On the other hand, the increase in current over the base current (ΔI/I₀) obtained after the addition of the model compound was inversely proportional to the CNT content. In this way, analysis on the sensing signal profiles of the flexible chemical sensor system was conducted to determine a process window. This study is a very useful springboard for future research activities, as more profound studies are necessary to fully understand sensing signal profiles.

In vivo toxicity evaluation of pristine graphene in developing zebrafish (Danio rerio) embryos

Graphene has been used in several fields covering from electronics to biomedicine, especially exhibiting a widespread variety of promising biological and biomedical applications. In the past decade, the biomedical applications of graphene have attracted much interest. However, the effect of pristine graphene (pG) toxicity in aquatic vertebrates has not been fully studied. Thus, in this study, the toxicity of pG was experimentally evaluated using developing zebrafish embryos as in vivo model system. To determine this, 4-hpf embryos were exposed to different concentrations of pG (1, 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 μg/L) and different early life-stage parameters were observed at 24, 48, 72, and 96 hpf. Through embryogenesis, pG was observed to induce significant embryonic mortality, delayed hatching, heartbeat, several morphological defects, pericardial toxicity, and bradycardia. Yolk sac edema and pericardial edema were induced by pG in developing embryos. These outcomes would provide new insights into the adverse effects of pG on the developing embryonic cardiac defects in vertebrates and highlight the probable natural environment and health hazards of pG flakes.

An overview of an artificial nose system

The present review describes recent advances in the development of an artificial nose system based on olfactory receptors and various sensing platforms. The kind of artificial nose, the production of olfactory receptors, the sensor platform for signal conversion and the application of the artificial nose system based on olfactory receptors and various sensing platforms are presented. The associated transduction modes are also discussed. The paper presents a review of the latest achievements and a critical evaluation of the state of the art in the field of artificial nose systems.

Nozzle-jet printed flexible field-effect transistor biosensor for high performance glucose detection

Printable electronics is a subject of great interest for low-cost, facile and environmentally-friendly large scale device production. But, it still remains challenging for printable biosensor development. Herein, we present the fabrication of nozzle-jet printed flexible field-effect transistor (FET) glucose biosensor. The silver source-drain electrodes and ZnO seed layers were printed on flexible substrate by nozzle-jet printer followed by ZnO nanorods (ZnO NRs) synthesis and glucose oxidase (GOx) immobilization. Utilization of nozzle-jet printing methods resulted in highly reproducible electrodes with well-defined vertical grown ZnO NRs for high GOx loading and enhanced glucose sensing performance in a wide glucose detection range. The stability, anti-interference ability, reproducibility, reusability, and applicability in human serum samples were also assessed. Overall, biosensor fabrication using nozzle-jet printer will not only provide large scale production of highly reproducible electrodes but also reduce the fabrication cost. Additionally, printed electrodes can be modified accordingly for different analyte detection.

Dopamine Receptor D1 Agonism and Antagonism Using a Field-Effect Transistor Assay

The field-effect transistor (FET) has been used in the development of diagnostic tools for several decades, leading to high-performance biosensors. Therefore, the FET platform can provide the foundation for the next generation of analytical methods. A major role of G-protein-coupled receptors (GPCRs) is in the transfer of external signals into the cell and promoting human body functions; thus, their principle application is in the screening of new drugs. The research community uses efficient systems to screen potential GPCR drugs; nevertheless, the need to develop GPCR-conjugated analytical devices remains for next-generation new drug screening. In this study, we proposed an approach for studying receptor agonism and antagonism by combining the roles of FETs and GPCRs in a dopamine receptor D1 (DRD1)-conjugated FET system, which is a suitable substitute for conventional cell-based receptor assays. DRD1 was reconstituted and purified to mimic native binding pockets that have highly discriminative interactions with DRD1 agonists/antagonists. The real-time responses from the DRD1-nanohybrid FET were highly sensitive and selective for dopamine agonists/antagonists, and their maximal response levels were clearly different depending on their DRD1 affinities. Moreover, the equilibrium constants (K) were estimated by fitting the response levels. Each K value indicates the variation in the affinity between DRD1 and the agonists/antagonists; a greater K value corresponds to a stronger DRD1 affinity in agonism, whereas a lower K value in antagonism indicates a stronger dopamine-blocking effect.

A highly sensitive FET-type aptasensor using flower-like MoS2 nanospheres for real-time detection of arsenic(iii)

Arsenic (As) contamination in drinking water is problematic due to its threat to human health. Highly stable, sensitive and selective sensors are needed for As(iii), which is the most toxic of the various forms of arsenic. Herein, we describe the fabrication of field-effect transistor (FET)-type aptasensors for As(iii) detection that is based on carboxylic polypyrrole (CPPy)-coated flower-like MoS₂ nanospheres (CFMNSs). Arsenic-binding aptamer-conjugated CFMNSs were integrated into a liquid-ion gated FET system, leading to extraordinary performance with a rapid response (on a time scale of less than 1 s). Field-induced current changes occurred through the interaction between the aptamer and As(iii), resulting in sensitive discrimination of As(iii) at unprecedentedly low concentrations (ca. 1 pM). Moreover, the CFMNS-based aptasensor selectively recognized As(iii) among numerous other metal ions and accurately detected As(iii) in a mixed solution. The FET aptasensor could also discriminate target analytes in a real sample derived from river water. This MoS₂-based aptasensor is a promising tool for the detection of As(iii) and could be used in a wide range of practical applications.

Diverse Applications of Nanomedicine

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.

Microchemical Pen: An Open Microreactor for Region-Selective Surface Modification

Various micro surface-modification approaches including photolithography, dip-pen lithography and ink-jet systems have been developed and used to extend the functionalities of solid surfaces. While those approaches work in the "open space", push-pull systems which work in solutions have recently drawn considerable attention. However, the confining flows performed by push-pull systems have realized only the dispense process, while microscale, region-selective chemical reactions have remained unattainable. This study reports a microchemical pen that enables region-selective chemical reactions for the micro surface modification/patterning. The chemical pen is based on the principle of microfluidic laminar flows and the resulting mixing of reagents by the mutual diffusion. The tiny diffusion layer performs as the working region. This report represents the first demonstration of an open microreactor in which two different reagents react on a real solid sample. The multifunctional characteristics of the microchemical pen are confirmed by different types of reactions in many research areas, including inorganic chemistry, polymer science, electrochemistry and biological sample treatment.

Duplex Bioelectronic Tongue for Sensing Umami and Sweet Tastes Based on Human Taste Receptor Nanovesicles

For several decades, significant efforts have been made in developing artificial taste sensors to recognize the five basic tastes. So far, the well-established taste sensor is an E-tongue, which is constructed with polymer and lipid membranes. However, the previous artificial taste sensors have limitations in various food, beverage, and cosmetic industries because of their failure to mimic human taste reception. There are many interactions between tastants. Therefore, detecting the interactions in a multiplexing system is required. Herein, we developed a duplex bioelectronic tongue (DBT) based on graphene field-effect transistors that were functionalized with heterodimeric human umami taste and sweet taste receptor nanovesicles. Two types of nanovesicles, which have human T1R1/T1R3 for the umami taste and human T1R2/T1R3 for the sweet taste on their membranes, immobilized on micropatterned graphene surfaces were used for the simultaneous detection of the umami and sweet tastants. The DBT platform led to highly sensitive and selective recognition of target tastants at low concentrations (ca. 100 nM). Moreover, our DBT was able to detect the enhancing effect of taste enhancers as in a human taste sensory system. This technique can be a useful tool for the detection of tastes instead of sensory evaluation and development of new artificial tastants in the food and beverage industry.

Conducting Polymer Based Nanobiosensors

In recent years, conducting polymer (CP) nanomaterials have been used in a variety of fields, such as in energy, environmental, and biomedical applications, owing to their outstanding chemical and physical properties compared to conventional metal materials. In particular, nanobiosensors based on CP nanomaterials exhibit excellent performance sensing target molecules. The performance of CP nanobiosensors varies based on their size, shape, conductivity, and morphology, among other characteristics. Therefore, in this review, we provide an overview of the techniques commonly used to fabricate novel CP nanomaterials and their biosensor applications, including aptasensors, field-effect transistor (FET) biosensors, human sense mimicking biosensors, and immunoassays. We also discuss prospects for state-of-the-art nanobiosensors using CP nanomaterials by focusing on strategies to overcome the current limitations.

Synthesis, toxicity, biocompatibility, and biomedical applications of graphene and graphene-related materials

Graphene is a two-dimensional atomic crystal, and since its development it has been applied in many novel ways in both research and industry. Graphene possesses unique properties, and it has been used in many applications including sensors, batteries, fuel cells, supercapacitors, transistors, components of high-strength machinery, and display screens in mobile devices. In the past decade, the biomedical applications of graphene have attracted much interest. Graphene has been reported to have antibacterial, antiplatelet, and anticancer activities. Several salient features of graphene make it a potential candidate for biological and biomedical applications. The synthesis, toxicity, biocompatibility, and biomedical applications of graphene are fundamental issues that require thorough investigation in any kind of applications related to human welfare. Therefore, this review addresses the various methods available for the synthesis of graphene, with special reference to biological synthesis, and highlights the biological applications of graphene with a focus on cancer therapy, drug delivery, bio-imaging, and tissue engineering, together with a brief discussion of the challenges and future perspectives of graphene. We hope to provide a comprehensive review of the latest progress in research on graphene, from synthesis to applications.

Graphene field-effect transistor array with integrated electrolytic gates scaled to 200 mm

Ten years have passed since the beginning of graphene research. In this period we have witnessed breakthroughs both in fundamental and applied research. However, the development of graphene devices for mass production has not yet reached the same level of progress. The architecture of graphene field-effect transistors (FET) has not significantly changed, and the integration of devices at the wafer scale has generally not been sought. Currently, whenever an electrolyte-gated FET (EGFET) is used, an external, cumbersome, out-of-plane gate electrode is required. Here, an alternative architecture for graphene EGFET is presented. In this architecture, source, drain, and gate are in the same plane, eliminating the need for an external gate electrode and the use of an additional reservoir to confine the electrolyte inside the transistor active zone. This planar structure with an integrated gate allows for wafer-scale fabrication of high-performance graphene EGFETs, with carrier mobility up to 1800 cm(2) V(-1) s(-1). As a proof-of principle, a chemical sensor was achieved. It is shown that the sensor can discriminate between saline solutions of different concentrations. The proposed architecture will facilitate the mass production of graphene sensors, materializing the potential of previous achievements in fundamental and applied graphene research.

Dual-Color Emissive Upconversion Nanocapsules for Differential Cancer Bioimaging In Vivo

Early diagnosis of tumor malignancy is crucial for timely cancer treatment aimed at imparting desired clinical outcomes. The traditional fluorescence-based imaging is unfortunately faced with challenges such as low tissue penetration and background autofluorescence. Upconversion (UC)-based bioimaging can overcome these limitations as their excitation occurs at lower frequencies and the emission at higher frequencies. In this study, multifunctional silica-based nanocapsules were synthesized to encapsulate two distinct triplet-triplet annihilation UC chromophore pairs. Each nanocapsule emits different colors, blue or green, following a red light excitation. These nanocapsules were further conjugated with either antibodies or peptides to selectively target breast or colon cancer cells, respectively. Both in vitro and in vivo experimental results herein demonstrate cancer-specific and differential-color imaging from single wavelength excitation as well as far greater accumulation at targeted tumor sites than that due to the enhanced permeability and retention effect. This approach can be used to host a variety of chromophore pairs for various tumor-specific, color-coding scenarios and can be employed for diagnosis of a wide range of cancer types within the heterogeneous tumor microenvironment.

Nano-Bioelectronics

Nano-bioelectronics represents a rapidly expanding interdisciplinary field that combines nanomaterials with biology and electronics and, in so doing, offers the potential to overcome existing challenges in bioelectronics. In particular, shrinking electronic transducer dimensions to the nanoscale and making their properties appear more biological can yield significant improvements in the sensitivity and biocompatibility and thereby open up opportunities in fundamental biology and healthcare. This review emphasizes recent advances in nano-bioelectronics enabled with semiconductor nanostructures, including silicon nanowires, carbon nanotubes, and graphene. First, the synthesis and electrical properties of these nanomaterials are discussed in the context of bioelectronics. Second, affinity-based nano-bioelectronic sensors for highly sensitive analysis of biomolecules are reviewed. In these studies, semiconductor nanostructures as transistor-based biosensors are discussed from fundamental device behavior through sensing applications and future challenges. Third, the complex interface between nanoelectronics and living biological systems, from single cells to live animals, is reviewed. This discussion focuses on representative advances in electrophysiology enabled using semiconductor nanostructures and their nanoelectronic devices for cellular measurements through emerging work where arrays of nanoelectronic devices are incorporated within three-dimensional cell networks that define synthetic and natural tissues. Last, some challenges and exciting future opportunities are discussed.

One-pot synthesis of multidimensional conducting polymer nanotubes for superior performance field-effect transistor-type carcinoembryonic antigen biosensors

Aptamer FET sensors based on carboxylated polypyrrole multidimensional nanotubes show ultrahigh sensitivity and selectivity toward CEA, and superior lifetimes.