Paper-Based Analytical Biosensor Chip Designed from Graphene-Nanoplatelet-Amphiphilic-diblock-co-Polymer Composite for Cortisol Detection in Human Saliva

Biosensors for psychiatric biomarkers in mental health monitoring

Psychiatric disorders are associated with serve disturbances in cognition, emotional control, and/or behavior regulation, yet few routine clinical tools are available for the real-time evaluation and early-stage diagnosis of mental health. Abnormal levels of relevant biomarkers may imply biological, neurological, and developmental dysfunctions of psychiatric patients. Exploring biosensors that can provide rapid, in-situ, and real-time monitoring of psychiatric biomarkers is therefore vital for prevention, diagnosis, treatment, and prognosis of mental disorders. Recently, psychiatric biosensors with high sensitivity, selectivity, and reproducibility have been widely developed, which are mainly based on electrochemical and optical sensing technologies. This review presented psychiatric disorders with high morbidity, disability, and mortality, followed by describing pathophysiology in a biomarker-implying manner. The latest biosensors developed for the detection of representative psychiatric biomarkers (e.g., cortisol, dopamine, and serotonin) were comprehensively summarized and compared in their sensitivities, sensing technologies, applicable biological platforms, and integrative readouts. These well-developed biosensors are promising for facilitating the clinical utility and commercialization of point-of-care diagnostics. It is anticipated that mental healthcare could be gradually improved in multiple perspectives, ranging from innovations in psychiatric biosensors in terms of biometric elements, transducing principles, and flexible readouts, to the construction of 'Big-Data' networks utilized for sharing intractable psychiatric indicators and cases.

Noninvasive and Multiplex Self-Test of Kidney Disease Biomarkers with Graphene-Based Lab-on-a-Chip (G-LOC): Toward Digital Diagnostics in the Hands of Patients

Chronic kidney disease is one of the major health issues worldwide. However, diagnosis is now highly centralized in large laboratories, resulting in low access to patient monitoring and poor personalized treatments. This work reports the development of a graphene-based lab-on-a-chip (G-LOC) for the digital testing of renal function biomarkers in serum and saliva samples. G-LOC integrates multiple bioelectronic sensors with a microfluidic system that enables multiplex self-testing of urea, potassium, sodium, and chloride. The linearity, limit of detection (LOD), accuracy, and coefficient of variability (CV) were studied. Accuracy values higher than 95.5% and CV lower than 9% were obtained for all of the biomarkers. The analytical performance was compared against three reference lab benchtop analyzers by measuring healthy- and renal-failure-level samples of serum. From receiver operating characteristic (ROC) plots, sensitivities (%) of 99.7, 97.6, 99.1, and 89.0 were obtained for urea, potassium, sodium, and chloride, respectively. Then, the test was evaluated in noninvasive saliva samples and compared against reference methods. Correlation and Bland-Altman plots showed good correlation and agreement of the G-LOC with the reference methods. It is noteworthy that the precision of G-LOC was similar to better than benchtop lab analyzers, with the advantage of being highly portable. Finally, a user testing study was conducted. The analytical performance obtained with untrained volunteers was similar to that obtained with trained chemists. Additionally, based on a user experience survey, G-LOC was found to have very simple usability and would be suitable for at-home diagnostics.

Designed and tailor-made double hydrophilic block copolymer-graphene nanoplatelet hybrids for reinforcing epoxy thermosets

Because of their propensity to build micellar nanostructures, amphiphilic block copolymers (ABCs) are an appropriate and unique toughening agent for epoxy systems individually on their own and in grafted form. The presence of epoxiphilic and phobic ends in ABCs is responsible for the self-assembly and the micellar structure. Nanofiller-grafted ABCs can effectively enhance the toughness of epoxy via the synergistic interaction of nanofillers and the ABCs. Even though there is sound literature supporting the effect of ABCs in epoxy, the action of double hydrophilic block copolymers (DHBC) in the epoxy matrix is less handled. Hence, the grafting of nanofillers in DHBCs and their subsequent role in tuning the properties of epoxy is a new concept. Hence this paper tries to bridge the gap via studying the effect of grafted fillers based on DHBCs in epoxy matrix. As a result, the current study focuses on the synthesis of double hydrophilic graphene nanoplatelets (rGO-g-DHBC) via nitrogen oxide-mediated polymerization for epoxy toughening application. The prepared rGO-g-DHBC was effectively utilized for epoxy toughening applications, resulting in a 457% improvement in toughness without compromising its inherent tensile strength. The mechanism behind the improved toughness was elucidated with the help of a scanning electron microscope, and the thermal, and rheological characteristics were studied.

Recent developments and future perspectives of microfluidics and smart technologies in wearable devices

Wearable devices are gaining popularity in the fields of health monitoring, diagnosis, and drug delivery. Recent advances in wearable technology have enabled real-time analysis of biofluids such as sweat, interstitial fluid, tears, saliva, wound fluid, and urine. The integration of microfluidics and emerging smart technologies, such as artificial intelligence (AI), machine learning (ML), and Internet of Things (IoT), into wearable devices offers great potential for accurate and non-invasive monitoring and diagnosis. This paper provides an overview of current trends and developments in microfluidics and smart technologies in wearable devices for analyzing body fluids. The paper discusses common microfluidic technologies in wearable devices and the challenges associated with analyzing each type of biofluid. The paper emphasizes the importance of combining smart technologies with microfluidics in wearable devices, and how they can aid diagnosis and therapy. Finally, the paper covers recent applications, trends, and future developments in the context of intelligent microfluidic wearable devices.

Ultrasensitive electrochemical sensor for detection of salivary cortisol in stress conditions

A natural stress response induces elevated cortisol levels in biological fluids, such as saliva. While current sensor technologies can detect cortisol in real time, their sensitivity and reliability for human subjects have not been assured. This is due to relatively low concentrations of salivary cortisol, which fluctuate throughout the day and vary significantly between individuals. To address these challenges, we present an improved electrochemical biosensor leveraging graphene's exceptional conductivity and physicochemical properties. A 1-pyrenebutyric acid N-hydroxysuccinimide ester (PBASE-NHS)-modified commercial graphene foam (GF) electrode is presented to realize an ultra-sensitive biosensor for cortisol detection directly in human saliva. The biosensor fabrication process entails the attachment of anti-cortisol monoclonal antibodies (mAb-cort) onto a PBASE-NHS/GF electrode through noncovalent immobilization on the vertically stratified graphene foam electrode surface. This unique immobilization strategy preserves graphene's structural integrity and electrical conductivity while facilitating antibody immobilization. The binding of cortisol to immobilized mAb-cort is read out via differential pulse voltammetry using ferri/ferro redox reactions. The immunosensor demonstrates an exceptional dynamic range of 1.0 fg mL-1 to 10,000 pg mL-1 (R2 = 0.9914) with a detection limit of 0.24 fg mL-1 (n = 3) for cortisol. Furthermore, we have established the reliability of cortisol sensors in monitoring human saliva. We have also performed multiple modes of validation, one against the established enzyme-linked immunosorbent assay (ELISA) and a second by a third-party service Salimetric on 16 student volunteers exposed to different stress levels, showing excellent correlation (r = 0.9961). These findings suggest the potential for using mAb-cort/PBASE-NHS/GF-based cortisol electrodes for monitoring salivary cortisol in the general population.

Electrochemical sensors for cortisol detection: Principles, designs, fabrication, and characterisation

Psychological stress is a major factor contributing to health discrepancies among individuals. Sustained exposure to stress triggers signalling pathways in the brain, which leading to the release of stress hormones in the body. Cortisol, a steroid hormone, is a significant biomarker for stress management due to its responsibility in the body's reply to stress. The release of cortisol in bloodstream prepares the body for a "fight or flight" response by increasing heart rate, blood pressure, metabolism, and suppressing the immune system. Detecting cortisol in biological samples is crucial for understanding its role in stress and personalized healthcare. Traditional techniques for cortisol detection have limitations, prompting researchers to explore alternative strategies. Electrochemical sensing has emerged as a reliable method for point-of-care (POC) cortisol detection. This review focuses on the progress made in electrochemical sensors for cortisol detection, covering their design, principle, and electroanalytical methodologies. The analytical performance of these sensors is also analysed and summarized. Despite significant advancements, the development of electrochemical cortisol sensors faces challenges such as biofouling, sample preparation, sensitivity, flexibility, stability, and recognition layer performance. Therefore, the need to develop more sensitive electrodes and materials is emphasized. Finally, we discussed the potential strategies for electrode design and provides examples of sensing approaches. Moreover, the encounters of translating research into real world applications are addressed.

Reviewing the state of biosensors and lab-on-a- chip technologies: opportunities for extreme environments and space exploration

The space race is entering a new era of exploration, in which the number of robotic and human missions to various places in our solar system is rapidly increasing. Despite the recent advances in propulsion and life support technologies, there is a growing need to perform analytical measurements and laboratory experiments across diverse domains of science, while keeping low payload requirements. In this context, lab-on-a-chip nanobiosensors appear to be an emerging technology capable of revolutionizing space exploration, given their low footprint, high accuracy, and low payload requirements. To date, only some approaches for monitoring astronaut health in spacecraft environments have been reported. Although non-invasive molecular diagnostics, like lab-on-a-chip technology, are expected to improve the quality of long-term space missions, their application to monitor microbiological and environmental variables is rarely reported, even for analogous extreme environments on Earth. The possibility of evaluating the occurrence of unknown or unexpected species, identifying redox gradients relevant to microbial metabolism, or testing for specific possible biosignatures, will play a key role in the future of space microbiology. In this review, we will examine the current and potential roles of lab-on-a-chip technology in space exploration and in extreme environment investigation, reporting what has been tested so far, and clarifying the direction toward which the newly developed technologies of portable lab-on-a-chip sensors are heading for exploration in extreme environments and in space.

Recent developments in wearable & non-wearable point-of-care biosensors for cortisol detection

INTRODUCTION

Cortisol is one of the most prominent biomarkers used for the detection of psychological stress and related disorders. It plays an important role in many physiological processes including immunomodulation and fat metabolism. Thus, monitoring of cortisol levels can be used to indicate different pathological conditions including stress disorders. There has been a gradual rise in the development of point of care (PoC) biosensors for continuous cortisol monitoring.

AREAS COVERED

This review discusses recent breakthroughs toward the development of PoC sensors (wearable and non wearable) for cortisol monitoring. Challenges associated with them have also been summarized.

EXPERT OPINION

Electrochemical PoC devices have recently emerged as a powerful tools for continuous monitoring of cortisol that can be utilized for stress management and treatment of related disorders. However, there are many challenges that should be addressed before such devices can be deployed at mass level, such as inter-individual variability, changing the device calibration with the circadian rhythm, interference from other endocrine moieties, etc. [Figure: see text].

Paper-based optical sensors paired with smartphones for biomedical analysis

The traditional analytical methods used for biomedical analysis are expensive and not easy to handle and require sophisticated instruments, thus their application is limited in resource-limited settings. Due to their portability, low cost, and ability to be applied to different analytical techniques, paper-based analytical devices are becoming valuable tools for biomedical analysis. The integration of smartphones into analytical devices has provided the ability to build portable, cost-effective, straightforward analytical devices for biomedical analysis and mobile health. The key aim of this review is to emphasize the recent applications of PADs combined with a smartphone for the optical analysis of biomedical species. We started this review by highlighting the type of papers and their modifications with different materials to prepare the PADs. After that, this review presents various detection methods including colorimetry, fluorescence, and luminescence where the smartphone is used for read-out. In the end, we provided the recent applications of the analysis of different biomedical compounds such as cancer and cardiovascular biomarkers, metal ions, glucose, viruses, etc. We believe that the present review will attract a wide scientific community in the areas of analytical chemistry, sensors, and clinical testing.

Nanostructured Cyclodextrin-Mediated Surface for Capacitive Determination of Cortisol in Multiple Biofluids

The aim of this work is to develop a reusable polypropylene glycol (PPG):β-cyclodextrin (βCD) biosensor for cortisol detection. To achieve the most stable support for βCD, we developed two PPG surfaces. The first surface is based on a gold surface modified with SAM of 3-mercaptopropionic acid (3MPA), and the second surface is based on a glassy carbon surface grafted with 4-carboxyphenyl diazonium salt. We characterized both surfaces by EIS, XPS, and ATR-FTIR and evaluated the stability and reusability of each surface. We found the GC-carboxyphenyl-PPG:βCD is stable for at least 1 month. We have also demonstrated the reusability of the surface up to 10 times. In detecting cortisol, we used a nonfaradaic electrochemical impedance capacitive model to interpret the surface confirmation changes. We achieved sensitive detection of cortisol in PBS buffer, urine, and saliva with limit of detection of 2.13, 1.29, and 1.33 nM, respectively.

Simple, Skin-Attachable, and Multifunctional Colorimetric Sweat Sensor

In situ analysis of sweat provides a simple, convenient, cost-effective, and noninvasive approach for the early diagnosis of physical illness in humans and is particularly useful in family care. In this study, a flexible and skin-attachable colorimetric sweat sensor for multiplexed analysis is developed using a simple, cost-effective, and convenient method. The obtained sweat sensor can be used to simultaneously detect glucose, lactate, urea, and pH value in sweat, as well as sweat loss and skin temperature. Only 2.5 μL of sweat is enough for the whole test, and the sweat loss and chemical-sensing results can be read out conveniently by naked eyes or a smartphone. In addition, body temperature can also be detected with an additional electrical circuit. Our sweat sensor provides a new, cost-effective, and convenient approach for in vitro diagnosis of multiple components in sweat, and the easy fabrication and cost-effectiveness make our sensor commercializable in the near future.

Nano-Scaled Materials and Polymer Integration in Biosensing Tools

The evolution of biosensors and diagnostic devices has been thriving in its ability to provide reliable tools with simplified operation steps. These evolutions have paved the way for further advances in sensing materials, strategies, and device structures. Polymeric composite materials can be formed into nanostructures and networks of different types, including hydrogels, vesicles, dendrimers, molecularly imprinted polymers (MIP), etc. Due to their biocompatibility, flexibility, and low prices, they are promising tools for future lab-on-chip devices as both manufacturing materials and immobilization surfaces. Polymers can also allow the construction of scaffold materials and 3D structures that further elevate the sensing capabilities of traditional 2D biosensors. This review discusses the latest developments in nano-scaled materials and synthesis techniques for polymer structures and their integration into sensing applications by highlighting their various structural advantages in producing highly sensitive tools that rival bench-top instruments. The developments in material design open a new door for decentralized medicine and public protection that allows effective onsite and point-of-care diagnostics.

A Portable 3D Microfluidic Origami Biosensor for Cortisol Detection in Human Sweat

Analysis of cortisol levels in human sweat is increasingly important as it can be a "stress biomarker" in stress-related disorders, giving real-time information about human health status. In this study, a portable 3D microfluidic origami biosensor based on a smartphone was developed for cortisol-level detection in human sweat. Molybdenum disulfide (MoS₂) nanosheet-mediated fluorescence resonance energy transfer (FRET) and fluorescently labeled aptamers were employed in the biosensing process. A multilayer-structured 3D origami microfluidic chip was fabricated and functionalized to facilitate low-volume perspired human sweat collection, transportation, and detection. The translatability of the biosensor was exhibited by the fluorescence analysis in a smartphone mounted in a custom-designed holder. The critical design parameters of the microfluidic origami biosensor, including the characterization of various paper substrates, the concentration of MoS₂ nanosheets, and the incubation/reaction time, were adjusted to obtain an acceptable range for the assay dynamic range and limit of detection (LOD). Under optimum conditions, various doses of cortisol within the physiologically relevant range of 10-1000 ng/mL reported in human sweat were tested to evaluate the performance of the proposed biosensor. It displayed an LOD of 6.76 ng/mL at 3σ in artificial sweat, an analysis time of 25 min, and high selectivity. The performance of the proposed cortisol sensor was compared with an enzyme-linked immunosorbent assay (ELISA) for a spiked artificial sweat sample, and a correlation coefficient of 0.988 was found. The proposed biosensor also presented satisfactory results in the determination of the cortisol levels in a real human sweat sample. The resulting portable biosensor provides a rapid, low-cost, convenient, and non-invasive sensing solution for the point-of-care analysis of cortisol levels in sweat.

Wearable Cortisol Aptasensor for Simple and Rapid Real-Time Monitoring

The necessity of managing stress levels is becoming increasingly apparent as the world suffers from different kinds of stresses including the extent of pandemic, the corona virus disease 2019 (COVID-19). Cortisol, a clinically confirmed stress hormone related to depression and anxiety, affects individuals mentally and physically. However, current cortisol monitoring methods require expert personnel, large and complex machines, and long time for data analysis. Here, we present a flexible and wearable cortisol aptasensor for simple and rapid cortisol real-time monitoring. The sensing channel was produced by electrospinning conducting polyacrylonitrile (PAN) nanofibers (NFs) and subsequent vapor deposition of carboxylated poly(3,4-ethylenedioxythiophene) (PEDOT). The conjugation of the cortisol aptamer on the PEDOT-PAN NFs provided the critical sensing mechanism for the target molecule. The sensing test was performed with a liquid-ion gated field-effect transistor (FET) on a polyester (polyethylene terepthalate). The sensor performance showed a detection limit of 10 pM (<5 s) and high selectivity in the presence of interference materials at 100 times higher concentrations. The practical usage and real-time monitoring of the cortisol aptasensor with a liquid-ion gated FET system was demonstrated by successful transfer to the swab and the skin. In addition, the real-time monitoring of actual sweat by applying the cortisol aptasensor was also successful since the aptasensor was able to detect cortisol approximately 1 nM from actual sweat in a few minutes. This wearable biosensor platform supports the possibility of further application and on-site monitoring for changes of other numerous biomarkers.

Graphene Oxide Functionalized Biosensor for Detection of Stress-Related Biomarkers

A graphene oxide (GO)-based cortisol biosensor was developed to accurately detect cortisol concentrations from sweat samples at point-of-care (POC) sites. A reference electrode, counter electrode, and working electrode make up the biosensor, and the working electrode was functionalized using multiple layers consisting of GO and antibodies, including Protein A, IgG, and anti-Cab. Sweat samples contact the anti-Cab antibodies to transport electrons to the electrode, resulting in an electrochemical current response. The sensor was tested at each additional functionalization layer and at cortisol concentrations between 0.1 and 150 ng/mL to determine how the current response differed. A potentiostat galvanostat device was used to measure and quantify the electrochemical response in the GO-based biosensor. In both tests, the electrochemical responses were reduced in magnitude with the addition of antibody layers and with increased cortisol concentrations. The proposed cortisol biosensor has increased accuracy with each additional functionalization layer, and the proposed device has the capability to accurately measure cortisol concentrations for diagnostic purposes.

Graphene Biodevices for Early Disease Diagnosis Based on Biomarker Detection

The early diagnosis of diseases plays a vital role in healthcare and the extension of human life. Graphene-based biosensors have boosted the early diagnosis of diseases by detecting and monitoring related biomarkers, providing a better understanding of various physiological and pathological processes. They have generated tremendous interest, made significant advances, and offered promising application prospects. In this paper, we discuss the background of graphene and biosensors, including the properties and functionalization of graphene and biosensors. Second, the significant technologies adopted by biosensors are discussed, such as field-effect transistors and electrochemical and optical methods. Subsequently, we highlight biosensors for detecting various biomarkers, including ions, small molecules, macromolecules, viruses, bacteria, and living human cells. Finally, the opportunities and challenges of graphene-based biosensors and related broad research interests are discussed.

Preparation of nanostructured PDMS film as flexible immunosensor for cortisol analysis in human sweat

This work proposed a novel and flexible immunosensor for highly selective and sensitive determination of cortisol in sweat. The flexible electrode was developed by transferring multi-walled carbon nanotubes (MWCNTs) film on polydimethylsiloxane (PDMS) substrate and subsequent electrochemical deposition of Au nanoparticles (AuNPs) on the MWCNTs surface. The obtained AuNPs/MWCNTs/PDMS electrode was then covalently immobilized with anti-cortisol monoclonal antibody (Anti-C_mab) and blocked with BSA. Scanning electron microscope confirmed that MWCNTs have been firmly combined with PDMS and AuNPs distributed uniformly on the surface of MWCNTs. The PDMS-based sensor possesses a good mechanical stability against stretching, bending and twisting, displaying stable electrochemical performance under deformation. After optimizing the analytical parameters, the developed immunosensor allowed a facile quantification of cortisol in the range of 1 fg/mL-1 μg/mL with a detection limit of 0.3 fg/mL. The cortisol immunosensor was further used to evaluate cortisol levels in human sweat, and the results corresponded closely with commercially available chemiluminescence immunoassay (CLIA) method. Results indicated that the new cortisol immunosensor could provide an effective tool for the noninvasive, point of care measurement of sweat cortisol levels and is promise to be a wearable biosensor for the healthy monitoring.

A Disposable Printed Liquid Gate Graphene Field Effect Transistor for a Salivary Cortisol Test

Circadian rhythm of salivary cortisol is of clinical significance, tracking salivary cortisol in domicile is welcomed by both doctor and patient, due to its merits of noninvasion, ease of sampling, and free-of-stress response. Here, we present a portable salivary cortisol test setup based on a liquid gate graphene field effect transistor (Lg-GFET) for the first time. In this work, the Lg-GFET was prepared by the printing technology and exploited as a sensitive material. In the procedures of device preparation, the modified liquid exfoliation method and direct-ink-write technology were utilized for synthesizing the graphene ink and printing Lg-GFETs; then, the as-prepared Lg-GFETs were decorated and functionalized by tetrakis(4-carboxyphenyl) porphyrin and the cortisol aptamer, successively. Their sensitivity, selectivity, and robustness are seriously examined. The test results indicate that the sensors have good linear sensitivities over a seven-log analyte concentration range (0.01 to 10⁴ nM) and the anti-interference ability to distinguish from the substancess with similar chemical structures. Moreover, the conceptual application for tracking circadian rhythm was carried out successfully. Conclusively, the proposed flexible Lg-GFET-based salivary cortisol detection platform can satisfy the requirements of the salivary cortisol's assay for instant detection. Additionally, it also provides an alternative solution for developing similar household medical appliances.

Facile Functionalization Strategy for Ultrasensitive Organic Protein Biochips in Multi-Biomarker Determination

In recent years, organic field-effect transistors (OFETs) have shown great potential for advanced protein biochips due to their inherent biocompatibility and high-throughput detectability. However, the development of OFET-based protein biochips is still at an early stage. On the one hand, single-biomarker determination is not sufficient for the diagnosis of cancer; thus, simultaneous monitoring of electrical signals toward multi-biomarkers is widely concerned and explored. On the other hand, an optimized functionalization strategy for efficient protein immobilization is another key to make OFET-based protein biochips accessible with improved detection performance. Herein, a facile functionalization strategy is developed for excellent charge-transport thin films by suppressing the gelation of diketopyrrolopyrrole (DPP)-based polymer semiconductors with the addition of the glutaraldehyde cross-linking agent. Besides, functional groups are introduced on the device surface for efficient attachment of antibodies as receptors via a condensation reaction, enabling simultaneous determination of α-fetoprotein biomarker and carcinoembryonic antigen biomarker with improved sensitivity and reliability. Therefore, the proposed high-throughput OFET-based protein biochip has the potential to be widely utilized in early liver cancer diagnosis.

RNA-extraction-free nano-amplified colorimetric test for point-of-care clinical diagnosis of COVID-19

The global pandemic of coronavirus disease 2019 (COVID-19) highlights the shortcomings of the current testing paradigm for viral disease diagnostics. Here, we report a stepwise protocol for an RNA-extraction-free nano-amplified colorimetric test for rapid and naked-eye molecular diagnosis of COVID-19. The test employs a unique dual-prong approach that integrates nucleic acid (NA) amplification and plasmonic sensing for point-of-care detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with a sample-to-assay response time of <1 h. The RNA-extraction-free nano-amplified colorimetric test utilizes plasmonic gold nanoparticles capped with antisense oligonucleotides (ASOs) as a colorimetric reporter to detect the amplified nucleic acid from the COVID-19 causative virus, SARS-CoV-2. The ASOs are specific for the SARS-CoV-2 N-gene, and binding of the ASOs to their target sequence results in the aggregation of the plasmonic gold nanoparticles. This highly specific agglomeration step leads to a change in the plasmonic response of the nanoparticles. Furthermore, when tested using clinical samples, the accuracy, sensitivity and specificity of the test were found to be >98.4%, >96.6% and 100%, respectively, with a detection limit of 10 copies/μL. The test can easily be adapted to diagnose other viral infections with a simple modification of the ASOs and primer sequences. It also provides a low-cost, rapid approach requiring minimal instrumentation that can be used as a screening tool for the diagnosis of COVID-19 at point-of-care settings in resource-poor situations. The colorimetric readout of the test can even be monitored using a handheld optical reader to obtain a quantitative response. Therefore, we anticipate that this protocol will be widely useful for the development of biosensors for the molecular diagnostics of COVID-19 and other infectious diseases.

UV-trained and metal-enhanced fluorescence of biliverdin and biliverdin nanoparticles

Increasing the fluorescence quantum yield of fluorophores is of great interest for in vitro and in vivo biomedical imaging applications. At the same time, photobleaching and photodegradation resulting from continuous exposure to light are major considerations in the translation of fluorophores from research applications to industrial or healthcare applications. A number of tetrapyrrolic compounds, such as heme and its derivatives, are known to provide fluorescence contrast. In this work, we found that biliverdin (BV), a naturally-occurring tetrapyrrolic fluorophore, exhibits an increase in fluorescence quantum yield, without exhibiting photobleaching or degradation, in response to continuous ultraviolet (UV) irradiation. We attribute this increased fluorescence quantum yield to photoisomerization and conformational changes in BV in response to UV irradiation. This enhanced fluorescence can be further altered by chelating BV with metals. UV irradiation of BV led to an approximately 10-fold increase in its 365 nm fluorescence quantum yield, and the most favorable combination of UV irradiation and metal chelation led to an approximately 18.5-fold increase in its 365 nm fluorescence quantum yield. We also evaluated these stimuli-responsive behaviors in biliverdin nanoparticles (BVNPs) at the bulk-state and single-particle level. We determined that UV irradiation led to an approximately 2.4-fold increase in BVNP 365 nm quantum yield, and the combination of UV irradiation and metal chelation led to up to a 6.75-fold increase in BVNP 365 nm quantum yield. Altogether, these findings suggest that UV irradiation and metal chelation can be utilized alone or in combination to tailor the fluorescence behavior of imaging probes such as BV and BVNPs at selected wavelengths.

Research progress on the applications of paper chips

Due to the modern pursuit of the quality of life, science and technology have rapidly developed, resulting in higher requirements for various detection methods based on analytical technology. Herein, the development, fabrication, detection and application of paper-based microfluidic chips (μPAD) are summarized. We aim to provide a comprehensive understanding of paper chips, and then discuss challenges and future prospects in this field.

Molecularly imprinted polymer-enhanced biomimetic paper-based analytical devices: A review

The popularization of paper-based analytical devices (PADs) in analytical science has fostered research on enhancing their analytical performance for accurate and sensitive assays. With their superb recognition capability and structural stability, molecularly imprinted polymers (MIPs) have been extensively employed as biomimetic receptors for capturing target analytes in various complex matrices. The integration of MIPs as recognition elements with PADs (MIP-PADs) has opened new opportunities for advanced analytical devices with elevated selectivity and sensitivity, as well as a shorter assay time and a lower cost. This review covers recent advances in MIP-PAD fabrication and engineering based on multifarious signal transduction systems such as colorimetry, fluorescence, electrochemistry, photoelectrochemistry, and chemiluminescence. The application of MIP-PADs in the fields of biomedical diagnostics, environmental analysis, and food safety monitoring is also reviewed. Further, the advantages, challenges, and perspectives of MIP-PADs are discussed.

Bio-inspired wettability patterns for biomedical applications

Benefiting from the remarkable wettability heterogeneity, bio-inspired wettability patterns present a progressive and versatile platform for manipulating and patterning liquids, which provides an emerging strategy for operating liquid samples with crucial values in biomedical applications. In this review, we present a general summary of bio-inspired wettability patterns. After a compendious introduction of natural wettability phenomena and their underlying mechanisms, we summarize the general design principles and fabrication methods for preparing artificial wettability materials. Next, we shift to patterned surface wettability with an emphasis on the fabrication approaches. Then, we discuss in detail the various practical applications of wettability patterns in the biomedical field, including cell culture, drug screening and biosensors. Critical thinking about the current challenges and future outlook is also provided. We believe that this review would propel the prosperous development of bio-inspired wettability patterns to flourish in the field of biomedical engineering.

Recent advances in graphene-based nanobiosensors for salivary biomarker detection

As biosensing research is rapidly advancing due to significant developments in materials, chemistry, and electronics, researchers strive to build cutting-edge biomedical devices capable of detecting health-monitoring biomarkers with high sensitivity and specificity. Biosensors using nanomaterials are highly promising because of the wide detection range, fast response time, system miniaturization, and enhanced sensitivity. In the recent development of biosensors and electronics, graphene has rapidly gained popularity due to its superior electrical, biochemical, and mechanical properties. For biomarker detection, human saliva offers easy access with a large variety of analytes, making it a promising candidate for its use in point-of-care (POC) devices. Here, we report a comprehensive review that summarizes the most recent graphene-based nanobiosensors and oral bioelectronics for salivary biomarker detection. We discuss the details of structural designs of graphene electronics, use cases of salivary biomarkers, the performance of existing sensors, and applications in health monitoring. This review also describes current challenges in materials and systems and future directions of the graphene bioelectronics for clinical POC applications. Collectively, the main contribution of this paper is to deliver an extensive review of the graphene-enabled biosensors and oral electronics and their successful applications in human salivary biomarker detection.

Rapid, Ultrasensitive, and Quantitative Detection of SARS-CoV-2 Using Antisense Oligonucleotides Directed Electrochemical Biosensor Chip

A large-scale diagnosis of the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) is essential to downregulate its spread within as well as across communities and mitigate the current outbreak of the pandemic novel coronavirus disease 2019 (COVID-19). Herein, we report the development of a rapid (less than 5 min), low-cost, easy-to-implement, and quantitative paper-based electrochemical sensor chip to enable the digital detection of SARS-CoV-2 genetic material. The biosensor uses gold nanoparticles (AuNPs), capped with highly specific antisense oligonucleotides (ssDNA) targeting viral nucleocapsid phosphoprotein (N-gene). The sensing probes are immobilized on a paper-based electrochemical platform to yield a nucleic-acid-testing device with a readout that can be recorded with a simple hand-held reader. The biosensor chip has been tested using samples collected from Vero cells infected with SARS-CoV-2 virus and clinical samples. The sensor provides a significant improvement in output signal only in the presence of its target-SARS-CoV-2 RNA-within less than 5 min of incubation time, with a sensitivity of 231 (copies μL-1)-1 and limit of detection of 6.9 copies/μL without the need for any further amplification. The sensor chip performance has been tested using clinical samples from 22 COVID-19 positive patients and 26 healthy asymptomatic subjects confirmed using the FDA-approved RT-PCR COVID-19 diagnostic kit. The sensor successfully distinguishes the positive COVID-19 samples from the negative ones with almost 100% accuracy, sensitivity, and specificity and exhibits an insignificant change in output signal for the samples lacking a SARS-CoV-2 viral target segment (e.g., SARS-CoV, MERS-CoV, or negative COVID-19 samples collected from healthy subjects). The feasibility of the sensor even during the genomic mutation of the virus is also ensured from the design of the ssDNA-conjugated AuNPs that simultaneously target two separate regions of the same SARS-CoV-2 N-gene.

Advances in Sweat Wearables: Sample Extraction, Real-Time Biosensing, and Flexible Platforms

Wearable biosensors for sweat-based analysis are gaining wide attention due to their potential use in personal health monitoring. Flexible wearable devices enable sweat analysis at the molecular level, facilitating noninvasive monitoring of physiological states via real-time monitoring of chemical biomarkers. Advances in sweat extraction technology, real-time biosensors, stretchable materials, device integration, and wireless digital technologies have led to the development of wearable sweat-biosensing devices that are light, flexible, comfortable, aesthetic, affordable, and informative. Herein, we summarize recent advances of sweat wearables from the aspects of sweat extraction, fabrication of stretchable biomaterials, and design of biosensing modules to enable continuous biochemical monitoring, which are essential for a biosensing device. Key chemical components of sweat, sweat capture methodologies, and considerations of flexible substrates for integrating real-time biosensors with electronics to bring innovations in the art of wearables are elaborated. The strategies and challenges involved in improving the wearable biosensing performance and the perspectives for designing sweat-based wearable biosensing devices are discussed.

Biocompatible and flexible paper-based metal electrode for potentiometric wearable wireless biosensing

A paper-based electrode is a very attractive component for a disposable, nontoxic, and flexible biosensor. In particular, wearable biosensors, which have recently been attracting interest, not only require these characteristics of paper-based electrodes but must also be able to detect various ions and biomolecules in biological fluids. In this paper, we demonstrate the detection ability of paper-based metal electrodes for wearable biosensors as part of a wireless potentiometric measurement system, focusing on the detection of pH and sodium ions. The paper-based metal electrodes were obtained by simply coating a silicone-rubber-coated paper sheet with a Au (/Cr) thin film by sputtering then modifying it with different functional membranes such as an oxide membrane (Ta₂O₅) and a fluoropolysilicone (FPS)-based Na⁺-sensitive membrane, corresponding to the targeted ions. Satisfactory and stable detection sensitivities of the modified paper-based Au electrodes were obtained over several weeks even when they were bent to a radius of curvature in the range of 6.5 to 25 mm, assuming use in a flexible body patch biosensor. Moreover, the Na⁺ concentration in a sweat sample was evaluated using the paper-based Au electrode with the FPS-based Na⁺-sensitive membrane in a wireless and real-time manner while the electrode was bent. Thus, owing to their complex mesh structure, flexible paper sheets should be suitable for use as potentiometric electrodes for wearable wireless biosensors.

Ultrasensitive Stress Biomarker Detection Using Polypyrrole Nanotube Coupled to a Field-Effect Transistor

Stress biomarkers such as hormones and neurotransmitters in bodily fluids can indicate an individual’s physical and mental state, as well as influence their quality of life and health. Thus, sensitive and rapid detection of stress biomarkers (e.g., cortisol) is important for management of various diseases with harmful symptoms, including post-traumatic stress disorder and depression. Here, we describe rapid and sensitive cortisol detection based on a conducting polymer (CP) nanotube (NT) field-effect transistor (FET) platform. The synthesized polypyrrole (PPy) NT was functionalized with the cortisol antibody immunoglobulin G (IgG) for the sensitive and specific detection of cortisol hormone. The anti-cortisol IgG was covalently attached to a basal plane of PPy NT through an amide bond between the carboxyl group of PPy NT and the amino group of anti-cortisol IgG. The resulting field-effect transistor-type biosensor was utilized to evaluate various cortisol concentrations. Cortisol was sensitively measured to a detection limit of 2.7 × 10⁻¹⁰ M (100 pg/mL), with a dynamic range of 2.7 × 10⁻¹⁰ to 10⁻⁷ M; it exhibited rapid responses (<5 s). We believe that our approach can serve as an alternative to time-consuming and labor-intensive health questionnaires; it can also be used for diagnosis of underlying stress-related disorders.

Investigation of cortisol dynamics in human sweat using a graphene-based wireless mHealth system

Understanding and assessing endocrine response to stress is crucial to human performance analysis, stress-related disorder diagnosis, and mental health monitoring. Current approaches for stress monitoring are largely based on questionnaires, which could be very subjective. To avoid stress-inducing blood sampling and to realize continuous, non-invasive, and real-time stress analysis at the molecular levels, we investigate the dynamics of a stress hormone, cortisol, in human sweat using an integrated wireless sensing device. Highly sensitive, selective, and efficient cortisol sensing is enabled by a flexible sensor array that exploits the exceptional performance of laser-induced graphene for electrochemical sensing. Herein, we report the first cortisol diurnal cycle and the dynamic stress response profile constructed from human sweat. Our pilot study demonstrates a strong empirical correlation between serum and sweat cortisol, revealing exciting opportunities offered by sweat analysis toward non-invasive dynamic stress monitoring via wearable and portable sensing platforms.

Electrochemical Paper-Based Biosensor Devices for Rapid Detection of Biomarkers

In healthcare, new diagnostic tools that help in the diagnosis, prognosis, and monitoring of diseases rapidly and accurately are in high demand. For in-situ measurement of disease or infection biomarkers, point-of-care devices provide a dramatic speed advantage over conventional techniques, thus aiding clinicians in decision-making. During the last decade, paper-based analytical devices, combining paper substrates and electrochemical detection components, have emerged as important point-of-need diagnostic tools. This review highlights significant works on this topic over the last five years, from 2015 to 2019. The most relevant articles published in 2018 and 2019 are examined in detail, focusing on device fabrication techniques and materials applied to the production of paper fluidic and electrochemical cell architectures as well as on the final device assembly. Two main approaches were identified, that are, on one hand, those ones where the fabrication of the electrochemical cell is done on the paper substrate, where the fluidic structures are also defined, and, on the other hand, the fabrication of those ones where the electrochemical cell and liquid-driving paper component are defined on different substrates and then heterogeneously assembled. The main limitations of the current technologies are outlined and an outlook on the current technology status and future prospects is given.

The review of Lab-on-PCB for biomedical application

Prevention of infectious diseases, diagnosis of diseases, and determination of treatment options all rely on biosensors to detect and analyze biomarkers, which are usually divided into four parts: cell analysis, biochemical analysis, immunoassay, and molecular diagnosis. However, traditional biosensing devices are expensive, bulky, and require a lot of time to detect, which also limited its application in resource-limited areas. In recent years, Lab-on-PCB, which combines biosensing technology and PCB technology, has been widely used in biomedical applications due to its high integration, personalized design, and easy mass production. Among these Lab-on-PCB sensing devices, the PCB circuit plays an important role. It can be directly used as a resistance sensor to count cells, and also used as a control device to automatically control the detection device. Flexible PCBs can be used to make wearable medical biosensors. In addition, due to the high degree of integration of the PCB circuit, Lab-on-PCB can perform multiple inspections on the same platform, which reduces the inspection time equivalently. Therefore, in this review paper, we discuss the application of Lab-on-PCB in four analysis methods of cell analysis, biochemical analysis, immunoassay, and molecular diagnosis, and give some suggestions for improvement and future development trends at the end.

One-Step Biotinylation of Cellulose Paper by Polymer Coating to Prepare a Paper-Based Analytical Device

Cellulose paper has strong potential as an analytical platform owing to its unique characteristics. In the present study, we investigated a procedure for functionalizing the surface of cellulose paper by dip-coating a mixture of a functional polymer and a perfluoroalkylated surfactant (surfactant 1). The functional polymer comprised a mixture of methyl methacrylate and poly(ethylene glycol) methacrylate monomers. The monomer ratio in the functional polymer affected the hydrophilicity and water absorbance of the cellulose paper after dip-coating. Furthermore, the presence of surfactant 1 during dip-coating promoted the surface segregation of poly(ethylene glycol) (PEG) moieties in the polymer, which enhanced the hydrophilicity, prevented nonspecific protein adsorption, and maintained the water absorbance of the dip-coated cellulose paper. Dip-coating with another functional polymer containing biotin groups produced a cellulose paper with a biotin-decorated surface in a one-step procedure. The displayed biotin groups immobilized avidin on the surface, and the PEG moieties in the polymer prevented nonspecific protein adsorption. We then immobilized a thrombin-binding DNA aptamer on the avidin-immobilized cellulose paper to prepare a paper-based analytical device. It is possible to visualize thrombin in model solutions and serum using the paper-based analytical device.

Electrochemical-digital immunosensor with enhanced sensitivity for detecting human salivary glucocorticoid hormone

In this work, an ultra-sensitive electrochemical-digital sensor chip is devised for potential use as a digital stress analyzer for point-of-care testing (POCT) and preventive on-site recording of the hormone 'cortisol', a glucocorticoid class of steroid hormone present in the human saliva. The sensor was interfaced and re-configured with a high precision impedance converter system (AD5933) and used for electrochemical impedance spectroscopy (EIS) to evaluate the cortisol levels in seven saliva samples. To obtain enhanced biological (cortisol) recognition and achieve a lower limit of detection 0.87 ± 0.12 pg mL-1 (2.4 ± 0.38 pmol mL-1) with a wide range from 1 pg mL-1 to 10 ng mL-1 (2.75 pmol mL-1 to 27.58 pmol mL-1; R2 = 0.9831), bovine serum albumin (1% BSA) was utilized as an effective sensitivity enhancer in addition to optimizing the other two parameters: (i) anti-cortisol antibody (anti-CAb) covalently attached to micro-Au electrodes and (ii) saliva sample incubation time on the sensor chip. The results obtained in this work were corroborated with the gold standard ELISA test with an accuracy of 96.3% and other previously reported biosensors. We envisage that the conceivable standpoint of this study can be a practice towards new development in cortisol biosensing, which will be pertinent to POCT targeted for in vitro psychobiological study on patient cortisol in saliva, and finally an implantable sensor chip in the future.

Pushing the limits of electrochemistry toward challenging applications in clinical diagnosis, prognosis, and therapeutic action

Constant progress in the identification of biomarkers at different molecular levels in samples of different natures, and the need to conduct routine analyses, even in limited-resource settings involving simple and short protocols, are examples of the growing current clinical demands not satisfied by conventional available techniques. In this context, the unique features offered by electrochemical biosensors, including affordability, real-time and reagentless monitoring, simple handling and portability, and versatility, make them especially interesting for adaptation to the increasingly challenging requirements of current clinical and point-of-care (POC) diagnostics. This has allowed the continuous development of strategies with improved performance in the clinical field that were unthinkable just a few years ago. After a brief introduction to the types and characteristics of clinically relevant biomarkers/samples, requirements for their analysis, and currently available methodologies, this review article provides a critical discussion of the most important developments and relevant applications involving electrochemical biosensors reported in the last five years in response to the demands of current diagnostic, prognostic, and therapeutic actions related to high prevalence and high mortality diseases and disorders. Special attention is paid to the rational design of surface chemistry and the use/modification of state-of-the-art nanomaterials to construct electrochemical bioscaffolds with antifouling properties that can be applied to the single or multiplex determination of biomarkers of accepted or emerging clinical relevance in particularly complex clinical samples, such as undiluted liquid biopsies, whole cells, and paraffin-embedded tissues, which have scarcely been explored using conventional techniques or electrochemical biosensing. Key points guiding future development, challenges to be addressed to further push the limits of electrochemical biosensors towards new challenging applications, and their introduction to the market are also discussed.

Detection of prostate specific antigen (PSA) in human saliva using an ultra-sensitive nanocomposite of graphene nanoplatelets with diblock-co-polymers and Au electrodes

Prostate-specific antigen (PSA) is a commonly used biomarker for the detection of prostate cancer (PCa) and there are numerous data available for its invasive detection in the serum and whole blood. In this work, an electrochemical sensing method was devised to detect traces of PSA in human saliva using a hybrid nanocomposite of graphene nanoplatelets with diblock co-polymers and Au electrodes (GRP-PS₆₇-b-PAA₂₇-Au). The pure graphitic composition on filter paper provides significantly high electrical and thermal conductivity while PS₆₇-b-PAA₂₇ makes an amphiphilic bridge between GRP units. The sensor utilizes the binding of an anti-PSA antibody with an antigen-PSA to act as a resistor in a circuit providing an impedance change that in turn allows for the detection and quantification of PSA in saliva samples. A miniaturized electrical impedance analyzer was interfaced with a sensor chip and the data were recorded in real-time using a Bluetooth-enabled module. This fully integrated and optimized sensing device exhibited a wide PSA range of detection from 0.1 pg mL^-1 to 100 ng mL^-1 (R² = 0.963) with a lower limit of detection of 40 fg mL^-1. The performance of the biosensor chip was validated with an enzyme-linked immunosorbent assay technique with a regression coefficient as high as 0.940. The advantages of the newly developed saliva-PSA electrical biosensor over previously reported serum-PSA electrochemical biosensors include a faster response time (3-5 min) to achieve a stable electrical signal for PSA detection, high selectivity, improved sensitivity, no additional requirement of a redox electrolyte for electron exchange and excellent shelf life. The presented sensor is aimed for clinical commercialization to detect PSA in human saliva.