Detection of Interferon gamma using graphene and aptamer based FET-like electrochemical biosensor

Sensitivity-Enhancing Strategies of Graphene Field-Effect Transistor Biosensors for Biomarker Detection

The ultrasensitive recognition of biomarkers plays a crucial role in the precise diagnosis of diseases. Graphene-based field-effect transistors (GFET) are considered the most promising devices among the next generation of biosensors. GFET biosensors possess distinct advantages, including label-free, ease of integration and operation, and the ability to directly detect biomarkers in liquid environments. This review summarized recent advances in GFET biosensors for biomarker detection, with a focus on interface functionalization. Various sensitivity-enhancing strategies have been overviewed for GFET biosensors, from the perspective of optimizing graphene synthesis and transfer methods, refinement of surface functionalization strategies for the channel layer and gate electrode, design of biorecognition elements and reduction of nonspecific adsorption. Further, this review extensively explores GFET biosensors functionalized with antibodies, aptamers, and enzymes. It delves into sensitivity-enhancing strategies employed in the detection of biomarkers for various diseases (such as cancer, cardiovascular diseases, neurodegenerative disorders, infectious viruses, etc.) along with their application in integrated microfluidic systems. Finally, the issues and challenges in strategies for the modulation of biosensing interfaces are faced by GFET biosensors in detecting biomarkers.

2D Materials in Advanced Electronic Biosensors for Point-of-Care Devices

Since two-dimensionalal (2D) materials have distinct chemical and physical properties, they are widely used in various sectors of modern technologies. In the domain of diagnostic biodevices, particularly for point-of-care (PoC) biomedical diagnostics, 2D-based field-effect transistor biosensors (bio-FETs) demonstrate substantial potential. Here, in this review article, the operational mechanisms and detection capabilities of biosensing devices utilizing graphene, transition metal dichalcogenides (TMDCs), black phosphorus, and other 2D materials are addressed in detail. The incorporation of these materials into FET-based biosensors offers significant advantages, including low detection limits (LOD), real-time monitoring, label-free diagnosis, and exceptional selectivity. The review also highlights the diverse applications of these biosensors, ranging from conventional to wearable devices, underscoring the versatility of 2D material-based FET devices. Additionally, the review provides a comprehensive assessment of the limitations and challenges faced by these devices, along with insights into future prospects and advancements. Notably, a detailed comparison of FET-based biosensors is tabulated along with various other biosensing platforms and their working mechanisms. Ultimately, this review aims to stimulate further research and innovation in this field while educating the scientific community about the latest advancements in 2D materials-based biosensors.

Terahertz Liquid Biosensor Based on A Graphene Metasurface for Ultrasensitive Detection with A Quasi-Bound State in the Continuum

The concept of a quasi-bound state in a continuum (QBIC) has garnered significant attention in various fields such as sensing, communication, and optical switching. Within metasurfaces, QBICs offer a reliable platform that enables sensing capabilities through potent interactions between local electric fields and matter. Herein, a novel terahertz (THz) biosensor based on the integration of QBIC with graphene is reported, which enables multidimensional detection. The proposed biosensor is distinctive because of its ability to discern concentrations of ethanol and N-methylpyrrolidone in a wide range from 100% to 0%, by monitoring the changes in the resonance intensity and maximum wavelet coefficient. This approach demonstrates an excellent linear fit, which ensures robust quantitative analysis. The remarkable sensitivity of our biosensor enables it to detect minute changes in low-concentration solutions, with the lowest detection concentration value (LDCV) of 0.21 pg mL-1 . 2D wavelet coefficient intensity cards are effectively constructed through continuous wavelet transforms, which presents a more accurate approach for determining the concentration of the solution. Ultimately, the novel sensing platform offers a host of advantages, including heightened sensitivity and reusability. This pioneering approach establishes a new avenue for liquid-based terahertz biosensing.

CRISPR/Cas12a-based fluorescence aptasensor integrated with two-dimensional cobalt oxyhydroxide nanosheets for IFN-γ detection

Cytokine storm (CS) is a risky immune overreaction accompanied by significant elevations of pro-inflammatory cytokines including interferon-γ (IFN-γ), interleukin and tumor necrosis factor. Sensitive detection of cytokine is conducive to studying CS progress and diagnosing infectious diseases. In this study, we developed a tandem system combining aptamer, strand displacement amplification (SDA), CRISPR/Cas12a, and cobalt oxyhydroxide nanosheets (termed Apt-SCN tandem system) as a signal-amplified platform for IFN-γ detection. Owing to the stronger affinity, target IFN-γ bound specifically to the aptamer from aptamer-complementary DNA (Apt-cDNA) duplex. The cDNA released from the Apt-cDNA duplex initiated SDA, resulting in the generation of double-stranded DNA products that could activate the trans-cleavage activity of CRISPR/Cas12a. The activated CRISPR/Cas12a further cleaved FAM-labeled single-stranded DNA probe, preventing it from adhering to the cobalt oxyhydroxide nanosheets and recovering the fluorescence signal. Sensitive fluorometric analysis of IFN-γ was successfully performed with detection limit as low as 0.37 nM. Unlike traditional protein analysis methods, Apt-SCN tandem system incorporates multiple signal amplification techniques and may also be applicable for other cytokines assay. This study was the initial study to utilize SDA and CRISPR/Cas12a to detect IFN-γ, showing great potential for cytokines clinical assay and CS prevention.

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.

Paper based SERS aptasensor towards dual-modal detection of interferon gamma

Interferon gamma (IFN-γ), can serve as an active diagnostic biomarker of a broad spectrum of diseases such as auto inflammatory disease, viral and bacterial, parasites infections, and tumor control. The low physiological concentration of IFN-γ at pg‧mL-1 level for most diseases such as tuberculosis and lung cancer demand highly sensitive and selective detection methods. To achieve the goal, a novel paper-based SERS aptasensor towards rapid, dual-modal (visual and ultrasensitive) detection of IFN-γ is presented for the first time. A lateral flow platform with low-cost and user-friendly format in this study is adopted. The detection relies on the competition of the specific aptamer sequence of IFN-γ between its complementary DNA in the test line and IFN-γ in the sample solution. The presence of IFN-γ can be easily observed in the test line by naked eye and detected at pg‧mL-1 level by a portable Raman spectrometer. Linear detection range of 10-2000 pg‧mL-1 could be obtained with detection limit of 8.7 pg‧mL-1. In addition, as low as 10 pg/mL of IFN-γ in human serum could be detected, which is comparable with the results from ELISA.Clinical Relevance- This study establishes a simple, rapid, and low-cost assay for dual-modal detection of IFN-γ, which is in urgent demand in clinics especially vitally important in resource-limited areas.

Metasurface-Assisted Terahertz Sensing

Terahertz (THz) waves, which fall between microwaves and infrared bands, possess intriguing electromagnetic properties of non-ionizing radiation, low photon energy, being highly sensitive to weak resonances, and non-polar material penetrability. Therefore, THz waves are extremely suitable for sensing and detecting chemical, pharmaceutical, and biological molecules. However, the relatively long wavelength of THz waves (30~3000 μm) compared to the size of analytes (1~100 nm for biomolecules, <10 μm for microorganisms) constrains the development of THz-based sensors. To circumvent this problem, metasurface technology, by engineering subwavelength periodic resonators, has gained a great deal of attention to enhance the resonance response of THz waves. Those metasurface-based THz sensors exhibit high sensitivity for label-free sensing, making them appealing for a variety of applications in security, medical applications, and detection. The performance of metasurface-based THz sensors is controlled by geometric structure and material parameters. The operating mechanism is divided into two main categories, passive and active. To have a profound understanding of these metasurface-assisted THz sensing technologies, we review and categorize those THz sensors, based on their operating mechanisms, including resonators for frequency shift sensing, nanogaps for enhanced field confinement, chirality for handedness detection, and active elements (such as graphene and MEMS) for advanced tunable sensing. This comprehensive review can serve as a guideline for future metasurfaces design to assist THz sensing and detection.

Review on two-dimensional material-based field-effect transistor biosensors: accomplishments, mechanisms, and perspectives

Field-effect transistor (FET) is regarded as the most promising candidate for the next-generation biosensor, benefiting from the advantages of label-free, easy operation, low cost, easy integration, and direct detection of biomarkers in liquid environments. With the burgeoning advances in nanotechnology and biotechnology, researchers are trying to improve the sensitivity of FET biosensors and broaden their application scenarios from multiple strategies. In order to enable researchers to understand and apply FET biosensors deeply, focusing on the multidisciplinary technical details, the iteration and evolution of FET biosensors are reviewed from exploring the sensing mechanism in detecting biomolecules (research direction 1), the response signal type (research direction 2), the sensing performance optimization (research direction 3), and the integration strategy (research direction 4). Aiming at each research direction, forward perspectives and dialectical evaluations are summarized to enlighten rewarding investigations.

Vertical Graphene-Based Biosensor for Tumor Cell Dielectric Signature Evaluation

The selective and rapid detection of tumor cells is of critical consequence for the theragnostic field of tumorigenesis; conventional methods, such as histopathological diagnostic methods, often require a long analysis time, excessive analytical costs, complex operations, qualified personnel and deliver many false-positive results. We are considering a new approach of an electrochemical biosensor based on graphene, which is evidenced to be a revolutionary nanomaterial enabling the specific and selective capture of tumor cells. In this paper, we report a biosensor fabricated by growing vertically aligned graphene nanosheets on the conductive surface of interdigitated electrodes which is functionalized with anti-EpCAM antibodies. The dielectric signature of the three types of tumor cells is determined by correlating the values from the Nyquist and Bode diagram: charge transfer resistance, electrical double layer capacity, Debye length, characteristic relaxation times of mobile charges, diffusion/adsorption coefficients, and variation in the electrical permittivity complex and of the phase shift with frequency. These characteristics are strongly dependent on the type of membrane molecules and the electromagnetic resonance frequency. We were able to use the fabricated sensor to differentiate between three types of tumor cell lines, HT-29, SW403 and MCF-7, by dielectric signature. The proposed evaluation method showed the permittivity at 1 MHz to be 3.63 nF for SW403 cells, 4.97 nF for HT 29 cells and 6.9 nF for MCF-7 cells.

Graphene-enhanced hybrid terahertz metasurface sensor for ultrasensitive nortriptyline sensing and detection

Graphene is a two-dimensional material with unique physical and chemical properties, whose excellent biocompatibility has also attracted widespread attention in the field of biosensing and medical detection. Graphene provides a novel solution for dramatically improving the sensitivity of terahertz metasurface sensors, since the electrical conductivity can be modified by contact with biomolecules. In this paper, a metal-graphene hybrid metasurface is proposed and demonstrated for high-sensitive nortriptyline sensing based on the plasmon-induced transparency (PIT) resonances. The π-π stacks between nortriptyline and graphene lead to an increase in the Fermi level of graphene and a decrease in the conductivity, thus enhancing the PIT resonance. Experimental results show that the peak-to-peak amplitude magnitude of the PIT window is enhanced up to 3.4-fold with 1 ng nortriptyline analyte, and the minimum detection limit is extended down to 0.1 ng. But no significant change is observed from the samples without graphene as a comparative experiment, which demonstrates that the presence of graphene greatly enhances the bonding to the drug molecules and improves the sensing sensitivity. This metasurface sensor has the advantages of high sensitivity, fast detection speed, label-free and steady properties, which has potential applications in the fields of trace molecular sensing and disease diagnosis.

Graphene-Based Biosensors for Molecular Chronic Inflammatory Disease Biomarker Detection

Chronic inflammatory diseases, such as cancer, diabetes mellitus, stroke, ischemic heart diseases, neurodegenerative conditions, and COVID-19 have had a high number of deaths worldwide in recent years. The accurate detection of the biomarkers for chronic inflammatory diseases can significantly improve diagnosis, as well as therapy and clinical care in patients. Graphene derivative materials (GDMs), such as pristine graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO), have shown tremendous benefits for biosensing and in the development of novel biosensor devices. GDMs exhibit excellent chemical, electrical and mechanical properties, good biocompatibility, and the facility of surface modification for biomolecular recognition, opening new opportunities for simple, accurate, and sensitive detection of biomarkers. This review shows the recent advances, properties, and potentialities of GDMs for developing robust biosensors. We show the main electrochemical and optical-sensing methods based on GDMs, as well as their design and manufacture in order to integrate them into robust, wearable, remote, and smart biosensors devices. We also describe the current application of such methods and technologies for the biosensing of chronic disease biomarkers. We also describe the current application of such methods and technologies for the biosensing of chronic disease biomarkers with improved sensitivity, reaching limits of detection from the nano to atto range concentration.

Interferon-γ detection in point of care diagnostics: Short review

Interferon (IFN)-γ is a cytokine secreted by immune cells. The elevated levels of IFN-γ are an early indicator of multiple diseases such as tuberculosis and autoimmune diseases. This short review focuses on different sensing methods based on optical, electrochemical, and mechanical principles. We explain how specific biorecognition molecules such as antibodies and aptamers are employed in the sensing methods. We also compare different surface functionalization methods and their details. Although the review gives an overview of only IFN-γ sensing, the same strategies can be applied to sensing other analytes with appropriate modifications.

Biosensors for the detection of Mycobacterium tuberculosis: a comprehensive overview

Tuberculosis (TB) infection is one of the leading causes of death in the world. According to WHO reports 2019, the average rate of decrease in global TB incidences was only 1.6% per year from 2000 to 2018, besides that the global decline in TB deaths was just 11%. Therefore, the dire need for early detection of the pathogen for the successful diagnosis of TB seems justified. Mycobacterium tuberculosis secretory proteins have gained more attention as TB biomarkers, for the early diagnosis and treatment of TB. Here in this review, we elaborate on the recent advancements made in the field of piezoelectric, magnetic, optical, and electrochemical biosensors, in addition to listing their merits and setbacks. Additionally, this review also discusses the construction of biosensors through modern integrated technologies, such as combinations of analytical chemistry, molecular biology, and nanotechnology. Integrated technologies enhance the detection for perceiving highly selective, specific, and sensitive signals to detect M. tuberculosis. Furthermore, this review highlights the recent challenges and scope of improvement in numerous biosensors developed for rapid, specific, selective, and sensitive detection of tuberculosis to reduce the TB burden and successful treatment.

2D Materials-Based Aptamer Biosensors: Present Status and Way Forward

Current advances in constructing functional nanomaterials and elegantly designed nanostructures have opened up new possibilities for the fabrication of viable field biosensors. Two-dimensional materials (2DMs) have fascinated much attention due to their chemical, optical, physicochemical, and electronic properties. They are ultrathin nanomaterials with unique properties such as high surface-to-volume ratio, surface charge, shape, high anisotropy, and adjustable chemical functionality. 2DMs such as graphene-based 2D materials, Silicate clays, layered double hydroxides (LDHs), MXenes, transition metal dichalcogenides (TMDs), and transition metal oxides (TMOs) offer intensified physicochemical and biological functionality and have proven to be very promising candidates for biological applications and technologies. 2DMs have a multivalent structure that can easily bind to single-stranded DNA/RNA (aptamers) through covalent, non-covalent, hydrogen bond, and π-stacking interactions, whereas aptamers have a small size, excellent chemical stability, and low immunogenicity with high affinity and specificity. This review discussed the potential of various 2D material-based aptasensor for diagnostic applications, e.g., protein detection, environmental monitoring, pathogens detection, etc.

Recent advances in the detection of interferon-gamma as a TB biomarker

Tuberculosis (TB) is one of the main infectious diseases worldwide and accounts for many deaths. It is caused by Mycobacterium tuberculosis usually affecting the lungs of patients. Early diagnosis and treatment are essential to control the TB epidemic. Interferon-gamma (IFN-γ) is a cytokine that plays a part in the body’s immune response when fighting infection. Current conventional antibody-based TB sensing techniques which are commonly used include enzyme-linked immunosorbent assay (ELISA) and interferon-gamma release assays (IGRAs). However, these methods have major drawbacks, such as being time-consuming, low sensitivity, and inability to distinguish between the different stages of the TB disease. Several electrochemical biosensor systems have been reported for the detection of interferon-gamma with high sensitivity and selectivity. Microfluidic techniques coupled with multiplex analysis in regular format and as lab-on-chip platforms have also been reported for the detection of IFN-γ. This article is a review of the techniques for detection of interferon-gamma as a TB disease biomarker. The objective is to provide a concise assessment of the available IFN-γ detection techniques (including conventional assays, biosensors, microfluidics, and multiplex analysis) and their ability to distinguish the different stages of the TB disease.

Advances in Nanotechnology-Based Biosensing of Immunoregulatory Cytokines

Cytokines are a large group of small proteins secreted by immune and non-immune cells in response to external stimuli. Much attention has been given to the application of cytokines' detection in early disease diagnosis/monitoring and therapeutic response assessment. To date, a wide range of assays are available for cytokines detection. However, in specific applications, multiplexed or continuous measurements of cytokines with wearable biosensing devices are highly desirable. For such efforts, various nanomaterials have been extensively investigated due to their extraordinary properties, such as high surface area and controllable particle size and shape, which leads to their tunable optical emission, electrical, and magnetic properties. Different types of nanomaterials such as noble metal, metal oxide, and carbon nanoparticles have been explored for various biosensing applications. Advances in nanomaterial synthesis and device development have led to significant progress in pushing the limit of cytokine detection. This article reviews currently used methods for cytokines detection and new nanotechnology-based biosensors for ultrasensitive cytokine detection.

An Intelligent Graphene-Based Biosensing Device for Cytokine Storm Syndrome Biomarkers Detection in Human Biofluids

Abnormal elevated levels of cytokines such as interferon (IFN), interleukin (IL), and tumor necrosis factor (TNF), are considered as one of the prognosis biomarkers for indicating the progression to severe or critical COVID-19. Hence, it is of great significance to develop devices for monitoring their levels in COVID-19 patients, and thus enabling detecting COVID-19 patients that are worsening and to treat them before they become critically ill. Here, an intelligent aptameric dual channel graphene-TWEEN 80 field effect transistor (DGTFET) biosensing device for on-site detection of IFN-γ, TNF-α, and IL-6 within 7 min with limits of detection (LODs) of 476 × 10^-15 , 608 × 10^-15 , or 611 × 10^-15 m respectively in biofluids is presented. Using the customized Android App together with this intelligent device, asymptomatic or mild COVID-19 patients can have a preliminary self-detection of cytokines and get a warning reminder while the condition starts to deteriorate. Also, the device can be fabricated on flexible substrates toward wearable applications for moderate or even critical COVID-19 cases for consistently monitoring cytokines under different deformations. Hence, the intelligent aptameric DGTFET biosensing device is promising to be used for point-of-care applications for monitoring conditions of COVID-19 patients who are in different situations.

Label-free terahertz microfluidic biosensor for sensitive DNA detection using graphene-metasurface hybrid structures

Metasurface assisted terahertz (THz) real-time and label-free biosensors have attracted intense attention. However, it is still challenging for specific detection of highly absorptive liquid samples with high sensitivity in the THz range. Here, we incorporated graphene with THz metasurface into a microfluidic cell for sensitive biosensing. The proposed THz graphene-metasurface microfluidic platform can effectively reduce the volume of the sample solution and boost the interaction between biomolecules and THz waves, thus enhancing the sensitivity. As a proof of concept, comparative experiments using other three kinds of microfluidic cells (pure microfluidic cell, metasurface-based microfluidic cell and graphene-based microfluidic cell) were conducted to explore and verify the sensing mechanism, which evidences the high sensitivity of delicate sensing based on the hybrid graphene-metasurface THz microfluidic device. Furthermore, to perform biosensing applications on that basis, specific aptamers were modified on the graphene-metasurface, enabling DNA sequences of foodborne pathogen Escherichia coli O157:H7 to be recognized. Based on the THz microfluidic biosensor, 100 nM DNA short sequences can be successfully detected. The sensing results of antibiotics and DNA based on the graphene-metasurface microfluidic biosensor confirm the superiority of the proposed design and considerable promise in THz biosensing. The novel sensing platform provides the merits of enabling highly sensitive, label-free, low-cost, easy to use, reusable, and real-time biosensing, which opens an exciting prospect for nanomaterial-metasurface hybrid structure assisted THz label-free biosensing in liquid environment.

Point-of-care detection of cytokines in cytokine storm management and beyond: Significance and challenges

Cytokines are signaling molecules between cells in immune system. Cytokine storm, due to the sudden acute increase in levels of pro‐inflammatory circulating cytokines, can result in disease severity and major‐organ damage. Thus, there is urgent need to develop rapid, sensitive, and specific methods for monitoring of cytokines in biology and medicine. Undoubtedly, point‐of‐care testing (POCT) will provide clinical significance in disease early diagnosis, management, and prevention. This review aims to summarize and discuss the latest technologies for detection of cytokines with a focus on POCT. The overview of diseases resulting from imbalanced cytokine levels, such as COVID‐19, sepsis and other cytokine release syndromes are presented. The clinical cut‐off levels of cytokine as biomarkers for different diseases are summarized. The challenges and perspectives on the development of cytokine POCT devices are also proposed and discussed. Cytokine POCT devices are expected to be the ongoing spotlight of disease management and prevention during COVID‐19 pandemic and also the post COVID‐19 pandemic era.

Electrochemical Biosensors for Cytokine Profiling: Recent Advancements and Possibilities in the Near Future

Cytokines are soluble proteins secreted by immune cells that act as molecular messengers relaying instructions and mediating various functions performed by the cellular counterparts of the immune system, by means of a synchronized cascade of signaling pathways. Aberrant expression of cytokines can be indicative of anomalous behavior of the immunoregulatory system, as seen in various illnesses and conditions, such as cancer, autoimmunity, neurodegeneration and other physiological disorders. Cancer and autoimmune diseases are particularly adept at developing mechanisms to escape and modulate the immune system checkpoints, reflected by an altered cytokine profile. Cytokine profiling can provide valuable information for diagnosing such diseases and monitoring their progression, as well as assessing the efficacy of immunotherapeutic regiments. Toward this goal, there has been immense interest in the development of ultrasensitive quantitative detection techniques for cytokines, which involves technologies from various scientific disciplines, such as immunology, electrochemistry, photometry, nanotechnology and electronics. This review focusses on one aspect of this collective effort: electrochemical biosensors. Among the various types of biosensors available, electrochemical biosensors are one of the most reliable, user-friendly, easy to manufacture, cost-effective and versatile technologies that can yield results within a short period of time, making it extremely promising for routine clinical testing.

An apta-aggregation based machine learning assay for rapid quantification of lysozyme through texture parameters

A novel assay technique that involves quantification of lysozyme (Lys) through machine learning is put forward here. This article reports the tendency of the well- documented Ellington group anti-Lys aptamer, to produce aggregates when exposed to Lys. This property of apta-aggregation has been exploited here to develop an assay that quantifies the Lys using texture and area parameters from a photograph of the elliptical aggregate mass through machine learning. Two assay sets were made for the experimental procedure: one with high Lys concentration between 25–100 mM and another with low concentration between 1–20 mM. The high concentration set had a sample volume of 10 μl while the low concentration set had a higher sample volume of 100 μl, in order to obtain the statistical texture values reliably from the aggregate mass. The platform exhibited an experimental limit of detection of 1 mM and a response time of less than 10 seconds. Further, two potential operating modes for the aptamer were hypothesized for this aggregation property and the more accurate mode among the two was ascertained through bioinformatics studies.

Detection of an IL-6 Biomarker Using a GFET Platform Developed with a Facile Organic Solvent-Free Aptamer Immobilization Approach

Aptamer-immobilized graphene field-effect transistors (GFETs) have become a well-known detection platform in the field of biosensing with various biomarkers such as proteins, bacteria, virus, as well as chemicals. A conventional aptamer immobilization technique on graphene involves a two-step crosslinking process. In the first step, a pyrene derivative is anchored onto the surface of graphene and, in the second step, an amine-terminated aptamer is crosslinked to the pyrene backbone with EDC/NHS (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide) chemistry. However, this process often requires the use of organic solvents such as dimethyl formamide (DMF) or dimethyl sulfoxide (DMSO) which are typically polar aprotic solvents and hence dissolves both polar and nonpolar compounds. The use of such solvents can be especially problematic in the fabrication of lab-on-a-chip or point-of-care diagnostic platforms as they can attack vulnerable materials such as polymers, passivation layers and microfluidic tubing leading to device damage and fluid leakage. To remedy such challenges, in this work, we demonstrate the use of pyrene-tagged DNA aptamers (PTDA) for performing a one-step aptamer immobilization technique to implement a GFET-based biosensor for the detection of Interleukin-6 (IL-6) protein biomarker. In this approach, the aptamer terminal is pre-tagged with a pyrene group which becomes soluble in aqueous solution. This obviates the need for using organic solvents, thereby enhancing the device integrity. In addition, an external electric field is applied during the functionalization step to increase the efficiency of aptamer immobilization and hence improved coverage and density. The results from this work could potentially open up new avenues for the use of GFET-based BioMEMS platforms by broadening the choice of materials used for device fabrication and integration.

Electrochemical Aptasensors: Current Status and Future Perspectives

This article reviews the progress of diversity of electrochemical aptasensor for target analytes detection. The immobilization strategies of aptamers on an electrode surface are addressed. The aptasensors are also introduced in compliance with the assay platforms. Many electrochemical aptasensors are nearly identical to conventional immunochemical approaches, sandwich and competition assays using electroactive signaling moieties. Others are "signal-on" and "sign-off" aptasensors credited to the target binding-induced conformational change of aptamers. Label-free aptasensors are also highlighted. Furthermore, the aptasensors applied for clinically important biomarkers are emphasized.

Graphene field-effect transistors as bioanalytical sensors: design, operation and performance

Graphene field-effect transistors (GFETs) are emerging as bioanalytical sensors, in which their responsive electrical conductance is used to perform quantitative analyses of biologically-relevant molecules such as DNA, proteins, ions and small molecules. This review provides a detailed evaluation of reported approaches in the design, operation and performance assessment of GFET biosensors. We first dissect key design elements of these devices, along with most common approaches for their fabrication. We compare possible modes of operation of GFETs as sensors, including transfer curves, output curves and time series as well as their integration in real-time or a posteriori protocols. Finally, we review performance metrics reported for the detection and quantification of bioanalytes, and discuss limitations and best practices to optimize the use of GFETs as bioanalytical sensors.

Modulating the Linker Immobilization Density on Aptameric Graphene Field Effect Transistors Using an Electric Field

Aptameric graphene-based field-effect transistors (A-GFETs) always employ linkers, which could immobilize on graphene through π-π stacking between contained pyrenyl groups and graphene, to anchor aptamers. Aptamer density is closely associated with the A-GFET sensitivity and determined by the linker density. Using known linker immobilization methods, the linker density is random, uncontrollable, and limited. In this work, we propose a novel linker immobilization method which can be used to effectively modulate the linker density using an electric field and further bridge the relationship between the linker density and the A-GFET sensitivity. Here, polar molecule 1-pyrenebutanoic acid succinimidyl ester (PASE) is used as a linker representative. In the electric field, PASE is arranged regularly with the electron-rich pyrenyl group forced toward graphene in the solution due to electrostatic repulsion, thereby making it possible to modulate the quantity of PASE molecules that could interact with graphene by tuning the electric field application and then realizing the regulation of the A-GFET sensitivity. Experimental results indicate that the limits of detection (LODs) of A-GFETs for detecting interleukin-6 (IL-6) and insulin can be significantly improved to be 618 and 766 fM, respectively, by applying an electric field at -0.3 V for 3 h during PASE immobilization.

Espinosa R, Lavín A, Holgado M. A Point-of-Care Based on Label-Free Interferometric Optical Detection Method to Evaluate Interferon Gamma (IFN-γ): A Correlation with the ELISA Technique

Interferon-gamma (IFN-γ) is a cytokine associated with inflammatory diseases, virus, infection, etc. The quantification of interferon-gamma concentration levels is studied to relate the immune system response to the progression of disease. In this work, we used a label-free point-of-care device based on the increase relative optical power (IROP) and a biosensor based on photonic transducers called BICELLs (Biophotonic Sensing Cells) to evaluate interferon-gamma concentrations. The BICELLs' sensing surface size used is 100 μm in diameter. The bioreceptor is attached to the surface by streptavidin-biotin affinity. This label-free IROP-based device can work with a low concentration of reagents and a low sample volume for measurements. Furthermore, this new device was compared with an ELISA technique in the same conditions. A good correlation was achieved between both techniques. This device is easy to use, and it is a cost-effective tool for monitoring an analyte in a disease.

A study on the response of FRET based DNA aptasensors in intracellular environment

This paper presents a study of the response of FRET based DNA aptasensors in the intracellular environment. Herein, we extend previous studies of aptasensors functioning in the extracellular environment to detection of antigens in the intracellular environment. An essential step in this research is the use of a novel means of achieving the endocytosis of aptasensors. Specifically, it is demonstrated that functioning aptasensors are successfully endocytosed by functionalizing the aptasensors with endocytosis—inducing DSS peptides.

A Wearable and Deformable Graphene-Based Affinity Nanosensor for Monitoring of Cytokines in Biofluids

A wearable and deformable graphene-based field-effect transistor biosensor is presented that uses aptamer-modified graphene as the conducting channel, which is capable of the sensitive, consistent and time-resolved detection of cytokines in human biofluids. Based on an ultrathin substrate, the biosensor offers a high level of mechanical durability and consistent sensing responses, while conforming to non-planar surfaces such as the human body and withstanding large deformations (e.g., bending and stretching). Moreover, a nonionic surfactant is employed to minimize the nonspecific adsorption of the biosensor, hence enabling cytokine detection (TNF-α and IFN-γ, significant inflammatory cytokines, are used as representatives) in artificial tears (used as a biofluid representative). The experimental results demonstrate that the biosensor very consistently and sensitively detects TNF-α and IFN-γ, with limits of detection down to 2.75 and 2.89 pM, respectively. The biosensor, which undergoes large deformations, can thus potentially provide a consistent and sensitive detection of cytokines in the human body.

Ultrasensitive Field-Effect Biosensors Enabled by the Unique Electronic Properties of Graphene

This review provides a critical overview of current developments on nanoelectronic biochemical sensors based on graphene. Composed of a single layer of conjugated carbon atoms, graphene has outstanding high carrier mobility and low intrinsic electrical noise, but a chemically inert surface. Surface functionalization is therefore crucial to unravel graphene sensitivity and selectivity for the detection of targeted analytes. To achieve optimal performance of graphene transistors for biochemical sensing, the tuning of the graphene surface properties via surface functionalization and passivation is highlighted, as well as the tuning of its electrical operation by utilizing multifrequency ambipolar configuration and a high frequency measurement scheme to overcome the Debye screening to achieve low noise and highly sensitive detection. Potential applications and prospectives of ultrasensitive graphene electronic biochemical sensors ranging from environmental monitoring and food safety, healthcare and medical diagnosis, to life science research, are presented as well.

An amplified label-free electrochemical aptasensor of γ-interferon based on target-induced DNA strand transform of hairpin-to-linear conformation enabling simultaneous capture of redox probe and target

In this work, a novel and signal-amplified label-free electrochemical aptasensor was developed and enabled efficient determination of γ-interferon (IFN-γ), based on target-induced DNA strand transform of hairpin-to-linear conformation combining with simultaneous capture of redox probe and target. Gold nanoparticles (AuNPs) were electrodeposited in the matrix of poly(amidoamine) dendrimer (PAMAM), followed by drop-casting addition on MoS₂ nanosheets to prepare AuNPs- PAMAM/MoS₂ composites. HS-terminated hairpin-DNA aptamer of IFN-γ was conjugated with AuNPs to prepare aptamer-AuNPs-PAMAM/MoS₂ onto glassy carbon electrode (GCE), by using bovine serum albumin as the cross-linker and stabilizer. Methylene blue (MB) as a redox probe was absorbed on IFN-γ aptamer. In the presence of IFN-γ, MB electrochemical signal increased gradually. The preparation processes, mechanisms and optimal experiment conditions of aptamer- AuNPs-PAMAM/MoS₂/MB/GCE sensing platform were studied by electron microscope imaging technologies, spectral curves and electrochemical measurements. There is a well plotting linear relationship between the peak current intensities of MB and IFN-γ contents in the range of 0.01-1000 pg mL^-1, showing a low detection limit of 2 fg mL^-1. Experimental results testified that the aptasensor had highly sensitive and selective responses toward IFN-γ, over potential interferents. In real biological samples, the aptasensor of IFN-γ had superior detection recoveries, indicating its high detection performance and feasibility for practicability.

Graphene-based biosensors for the detection of prostate cancer protein biomarkers: a review

Prostate cancer (PC) is the sixth most common cancer type in the world, which causes approximately 10% of total cancer fatalities. The detection of protein biomarkers in body fluids is the key topic for the diagnosis and prognosis of PC. Highly sensitive screening of PC is the most effective approach for reducing mortality. Thus, there are a growing number of literature that recognizes the importance of new technologies for early diagnosis of PC. Graphene is playing an important role in the biosensor field with remarkable physical, optical, electrochemical and magnetic properties. Many recent studies demonstrated the potential of graphene materials for sensitive detection of protein biomarkers. In this review, the graphene-based biosensors toward PC analysis are mainly discussed in two groups: Firstly, novel biosensor interfaces were constructed through the modification of graphene materials onto sensor surfaces. Secondly, ingenious signal amplification strategies were developed using graphene materials as catalysts or carriers. Graphene-based biosensors have exhibited remarkable performance with high sensitivities, wide detection ranges, and long-term stabilities.

A novel label-free electrochemical impedance aptasensor for highly sensitive detection of human interferon-gamma based on target-induced exonuclease inhibition

In this paper, a novel label-free electrochemical impedance aptasensor for highly sensitive detection of IFN-γ based on target-induced exonuclease inhibition was constructed. For this purpose, we designed a DNA hairpin modified on the gold electrode whose loop was the aptamer of the IFN-γ, and the stem was 5'-thiol-modified. In the absence of IFN-γ, Exonuclease III (Exo III) and Exonuclease I (Exo I) digested the double-stranded and single-stranded strands of the hairpin DNA, respectively, causing smaller impedance value on the surface of the electrode. In the presence of IFN-γ, the function of Exo III was greatly inhibited by the binding of the aptamer with the target, and it stopped after cutting three bases of the hairpin DNA. Forming a major target-bound aptamer digestion product, it could not be digested by Exo I, so there was larger impedance on the electrode surface. The calibration curve for IFN-γ was linear in the range of 1 pM-50 nM with the detection limit (LOD) of 0.7 pM_. The proposed aptasensor proved good selectivity and reproducibility, and low cost. In addition, the biosensor was able to detect IFN-γ in serum samples successfully, which is expected to provide an efficient method for TB diagnosis at early stages.

A versatile fluorometric aptasensing scheme based on the use of a hybrid material composed of polypyrrole nanoparticles and DNA-silver nanoclusters: application to the determination of adenosine, thrombin, or interferon-gamma

The authors describe a versatile aptasensing scheme based on the use of polypyrrole nanoparticles (PPyNPs) and DNA-silver nanoclusters (DNA-AgNCs) for multiple target detection. The DNA-AgNCs consist of two functional domains, viz. (a) a nucleation domain for attaching the metal core of the nanoclusters, and (b) a recognition domain which consists of a single-stranded aptamer. In the absence of analytes, the single-strand recognition domain will be absorbed onto the surface of the PPyNPs through π stacking and hydrophobic interactions. As a result, the red fluorescence of the DNA-AgNCs (with excitation/emission peaks at 535/625 nm) is quenched by the PPyNPs. On introducing the analytes, the DNA-AgNCs will bind them. This leads to the desorption of DNA-AgNCs and the recovery of the red fluorescence. Based on the above strategy, a versatile, sensitive and selective aptasensor was established for detection of adenosine, thrombin and interferon-gamma. The method was applied to the detection of the above targets in (spiked) serum samples and gave satisfactory results, with detection limit of 0.58 nM for IFN-γ, 0.39 nM for adenosine, and 2.2 nM for thrombin. The use of PPyNPs results in uniquely low non-specific absorption and in improved analytical results in case of real-sample analysis when compared to previously reported methods. Graphical abstract Schematic illustration of DNA-silver nanoclusters and polypyrrole nanoparticles in an aptasensor for detection of multiple targets.

Aptamer based nanobiosensors: Promising healthcare devices

Nanobiosensors based on aptamer are extensively being studied as potent analytical tools in clinical analysis. These biosensors provide high sensitivity, fast response, specificity and desired portability in addition to simplicity and decreased cost compared to conventional methods. The purpose of this manuscript is to provide readers with an overview of current advances about electrochemical, electrochemiluminescent and photoelectrochemical aptasensors from the sea of available literature. These are mainly used for determination of protein-based biomarkers, especially for cancer diagnosis. Here in we have given special emphasis on nanosize-based aptasensors which have been reported to show considerable improvement in the analytical performance.

Tactile Chemomechanical Transduction Based on an Elastic Microstructured Array to Enhance the Sensitivity of Portable Biosensors

Tactile sensors capable of perceiving biophysical signals such as force, pressure, or strain have attracted extensive interest for versatile applications in electronic skin, noninvasive healthcare, and biomimetic prostheses. Despite these great achievements, they are still incapable of detecting bio/chemical signals that provide even more meaningful and precise health information due to the lack of efficient transduction principles. Herein, a tactile chemomechanical transduction strategy that enables the tactile sensor to perceive bio/chemical signals is proposed. In this methodology, pyramidal tactile sensors are linked with biomarker-induced gas-producing reactions, which transduce biomarker signals to electrical signals in real time. The method is advantageous as it enhances electrical signals by more than tenfold based on a triple-step signal amplification strategy, as compared to traditional electrical biosensors. It also constitutes a portable and general platform capable of quantifying a wide spectrum of targets including carcinoembryonic antigen, interferon-γ, and adenosine. Such tactile chemomechanical transduction would greatly broaden the application of tactile sensors toward bio/chemical signals perception which can be used in ultrasensitive portable biosensors and chemical-responsive chemomechanical systems.

Measurement of cytokine biomarkers using an aptamer-based affinity graphene nanosensor on a flexible substrate toward wearable applications

We present an approach for the label-free detection of cytokine biomarkers using an aptamer-functionalized, graphene-based field effect transistor (GFET) nanosensor on a flexible, SiO2-coated substrate of the polymer polyethylene naphthalate (PEN). The nanosensor conforms to the underlying nonplanar surface and performs GFET-based rapid transduction of the aptamer-biomarker binding, thereby potentially allowing the detection of cytokine biomarkers that are sampled reliably from human bodily fluids (e.g., sweat) in wearable sensing applications. In characterizing the suitability of the nanosensor for wearable applications, we investigate the effects of substrate bending on the equilibrium dissociation constant between the aptamer and the biomarker as well as the graphene transconductance. The utility of the nanosensor is demonstrated by the detection of tumor necrosis factor-α (TNF-α), an inflammatory cytokine biomarker. Experimental results show that the flexible nanosensor can specifically respond to changes in the TNF-α concentration within 5 minutes with a limit of detection as low as 26 pM in a repeatable manner.

Ultratrace antibiotic sensing using aptamer/graphene-based field-effect transistors

Antibiotic residue, as emerging pollution resulting from antibiotic abuse, poses a serious threat on ecosystem and human health. Conventional methods for antibiotic detection, e.g., liquid/gas chromatography, are based on complicated instruments and time-consuming; therefore, efforts have been made to realize in situ and real-time monitoring of antibiotics. Here, a miniaturized and integratable electronic antibiotic sensor based on field-effect transistor (FET) is reported. The reduced graphene oxide (rGO) nanosheet is used as the channel material and the aptamer RNA for tobramycin is modified onto rGO as the probe. A novel sensor design with 6-mercapto-1-hexanol (MCH)/1-pyrenebutanol (PBA) blocking layer (BL) for structure optimization is applied to enhance the sensor reliability and specificity. This rGO/aptamer/BL sensor shows an ultra-sensitivity to tobramycin with a lower detection limit of 0.3 nM and a quick response within 5 s, as well as a high specificity over other antibiotics such as kanamycin, streptomycin, ciprofloxacin, and tetracycline. The sensing mechanism based on the deformation of the charged aptamer probe is proposed via an in-depth analysis of the interactions between aptamer, tobramycin and rGO. In addition, sensing test performed under controlled microfluidic flow conditions demonstrates a great potential of the sensors in practical applications.

Dual-aptamer-based voltammetric biosensor for the Mycobacterium tuberculosis antigen MPT64 by using a gold electrode modified with a peroxidase loaded composite consisting of gold nanoparticles and a Zr(IV)/terephthalate metal-organic framework

An ultrasensitive aptasensor is described for the voltammetric determination of the Mycobacterium tuberculosis antigen MPT64 in human serum. Firstly, an amino-modified Zr(IV) based metal-organic framework (MOF; type UiO-66-NH₂; made up from Zr₆O₃₂ units and 2-amino-terephthalate linkers) with a high specific surface was synthesized and used as the carrier of the gold nanoparticles and the aptamers. Then the signalling nanoprobe was fabricated after the horseradish peroxidase was cast on the nanomaterials. The two aptamers with synergistic effect on binding MPT64 were anchored on the gold electrode. Differential pulse voltammetry indicated that the peak current is highest if the ratio of the two aptamers is 1:1. The assay has a wide linear response range (0.02 to 1000 pg·mL^-1 of MPT64) and a 10 fg·mL^-1 detection limit at a working potential of around -96 mV (vs Ag/AgCl). The results show this biosensor to be a viable tool for detection of tuberculosis at an early stage. Graphical abstract Schematic presentation of the construction of the nanoprobe and biosensor. Firstly, the surface of UiO-66-NH₂ was anchored to gold nanoparticles (AuNPs). A dual-aptamer and HRP were added to form the signalling nanoprobe (Aptamer/HRP/AuNPs/UiO-66-NH₂). Then, the aptamers I and II were attached on the surface of gold electrode and 6-mercapto-1-hexanol was used to block the uncovered active site of the gold electrode. Finally, after incubation with MPT64, the signalling nanoprobe was dropped on the modified electrode and the DPV measurements was used for the analysis of Mycobacterium tuberculosis antigen MPT64. (PVP: poly(vinyl pyrrolidone); HRP: horseradish peroxidase; MCH: 6-Mercapto-1-hexanol; HQ: hydroquinone; BQ: benzoquinone).

Rapid Detection of Tumor Necrosis Factor-Alpha Using Quantum Dot-Based Optical Aptasensor

This paper reports an optical "TURN OFF" aptasensor, which is comprised of a deoxyribonucleic acid aptamer attached to a quantum dot on the terminus and gold nanoparticle on the terminus. The photoluminescence intensity is observed to decrease upon progressive addition of the target protein tumor necrosis factor-alpha (TNF- ) to the sensor. For PBS-based TNF- samples, the beacon exhibited 19%-20% quenching at around 22 nM concentration. The photoluminescence intensity and the quenching efficiency showed a linear decrease and a linear increase, respectively, between 0 to 22.3 nM TNF- . The detection limit of the sensor was found to be 97.2 pM. Specificity test results determined that the sensor has higher selectivity toward TNF- than other control proteins such as C-reactive protein, albumin, and transferrin. The beacon successfully detected different concentrations of TNF- in human serum-based samples exhibiting around 10% quenching efficiency at 12.5 nM of the protein.

Nano-biosensing approaches on tuberculosis: Defy of aptamers

Tuberculosis is a major global health problem caused by the bacterium Mycobacterium tuberculosis (Mtb) complex. According to WHO reports, 53 million TB patients died from 2000 to 2016. Therefore, early diagnosis of the disease is of great importance for global health care programs. The restrictions of traditional methods have encouraged the development of innovative methods for rapid, reliable, and cost-effective diagnosis of tuberculosis. In recent years, aptamer-based biosensors or aptasensors have drawn great attention to sensitive and accessible detection of tuberculosis. Aptamers are small short single-stranded molecules of DNA or RNA that fold to a unique form and bind to targets. Once combined with nanomaterials, nano-scale aptasensors provide powerful analytical platforms for diagnosing of tuberculosis. Various groups designed and studied aptamers specific for the whole cells of M. tuberculosis, mycobacterial proteins and IFN-γ for early diagnosis of TB. Advantages such as high specificity and strong affinity, potential for binding to a larger variety of targets, increased stability, lower costs of synthesis and storage requirements, and lower probability of contamination make aptasensors pivotal alternatives for future TB diagnostics. In recent years, the concept of SOMAmer has opened new horizons in high precision detection of tuberculosis biomarkers. This review article provides a description of the research progresses of aptamer-based and SOMAmer-based biosensors and nanobiosensors for the detection of tuberculosis.