Wearable wristband-based electrochemical sensor for the detection of phenylalanine in biofluids

Volatile organic compounds (VOCs) detection for the identification of bacterial infections in clinical wound samples

Early detection of wound infections is critical for timely intervention and prevention of possible complications since prompt treatment can help lower pathogen spread and enhance faster healing. Early detection also helps reduce the risk of serious infections requiring extensive medical interventions or life-threatening diseases such as sepsis. Culture-based approaches currently used for bacterial identification have limited sensitivity and specificity. At the same time, they are time-consuming, resulting in delays in therapy and, therefore, having a negative impact on the treatment outcomes. Quantifying the volatile organic compounds (VOCs) released by bacteria residing in wounds is a promising, non-invasive option for detecting infections at early stages. This method allows for continuous monitoring without requiring invasive procedures, thereby reducing patient discomfort and the risk of further complications. Spectroscopy methods and sensors are the primary VOC detection and quantification approaches, but sensors are more rapid, cost-effective, non-invasive, and precise. This review highlights the significance of the early detection of wound infection to enable timely intervention and prevent complications, emphasizing the limitations of culture-based approaches. It also explores the potential of quantifying VOCs using different methods and discusses the correlation between their levels and the rate of bacterial infections in wounds. Additionally, the review evaluates current VOC-based monitoring methods for wound management, identifies gaps in the field, and advocates for further research to advance wound care and enhance patient outcomes.

Recent Advances in Paper-Based Electronics: Emphasis on Field-Effect Transistors and Sensors

Paper-based electronics have emerged as a sustainable, low-cost, and flexible alternative to traditional substrates for electronics, particularly for disposable and wearable applications. This review outlines recent developments in paper-based devices, focusing on sensors and paper-based field-effect transistors (PFETs). Key fabrication techniques such as laser-induced graphene, inkjet printing, and screen printing have enabled the creation of highly sensitive and selective devices on various paper substrates. Material innovations, especially the integration of graphene, carbon-based materials, conductive polymers, and other novel micro- and nano-enabled materials, have significantly enhanced device performance. This review discusses modern applications of paper-based electronics, with a particular emphasis on biosensors, electrochemical and physical sensors, and PFETs designed for flexibility, low power, and high sensitivity. Advances in PFET architectures have further enabled the development of logic gates and memory systems on paper, highlighting the potential for fully integrated circuits. Despite challenges in durability and performance consistency, the field is rapidly evolving, driven by the demand for green electronics and the need for decentralized, point-of-care diagnostic tools. This paper also identifies detection strategies used in paper-based sensors, reviews limitations in the current fabrication methods, and outlines opportunities for the scalable production of multifunctional paper-based systems. This review addresses a critical gap in the literature by linking device-level innovation with real-world sensor applications on paper substrates.

Fully integrated microneedle biosensor array for wearable multiplexed fitness biomarkers monitoring

Fitness monitoring has become increasingly important in modern lifestyles; the current fitness monitoring always relies on physical sensors, making it challenging to detect pertinent issues at a deeper level when exercising. Here, we report a fully integrated wearable microneedle sensor that simultaneously measures fitness related biomarkers (e.g., glucose, lactate, and alcohol) during physical exercise. Such a sensor integrates a biocompatible 3D-printed microneedle array that can comfortably access skin interstitial fluid and a small circuit for signal processing and calibration, and wireless communication. The microneedle array features good biocompatibility and highly sensitive biochemical sensors that can detect even the slightest variations within the biomarkers of this fluid. On-body experimental results indicate that such a sensor can monitor fitness-related biomarkers across multiple subjects and support multi-day monitoring, with results showing a good correlation with commercial devices. The data was transmitted to a smartphone via Bluetooth and uploaded to cloud platforms for further health assessment. This study has the potential to boost intelligent wearable devices in sports health.

Engineering with Biomedical Sciences Changing the Horizon of Healthcare-A Review

In the dynamic realm of healthcare, the convergence of engineering and biomedical sciences has emerged as a pivotal frontier. In this review we go into specific areas of innovation, including medical imaging and diagnosis, developments in biomedical sensors, and drug delivery systems. Wearable biosensors, non-wearable biosensors, and biochips, which include gene chips, protein chips, and cell chips, are all included in the scope of the topic that pertains to biomedical sensors. Extensive research is conducted on drug delivery systems, spanning topics such as the integration of computer modeling, the optimization of drug formulations, and the design of delivery devices. Furthermore, the paper investigates intelligent drug delivery methods, which encompass stimuli-responsive systems such as temperature, redox, pH, light, enzyme, and magnetic responsive systems. In addition to that, the review goes into topics such as tissue engineering, regenerative medicine, biomedical robotics, automation, biomechanics, and the utilization of green biomaterials. The purpose of this analysis is to provide insights that will enhance continuing research and development efforts in engineering-driven biomedical breakthroughs, ultimately contributing to the improvement of healthcare. These insights will be provided by addressing difficulties and highlighting future prospects.

Electrochemical Sensing of Phenylalanine using Polyaniline-Based Molecularly Imprinted Polymers

Polyaniline (PANI)-based molecularly imprinted polymers were investigated for their efficacy in sensing phenylalanine (Phe) when fabricated on both glassy carbon electrode (GCE) and indium tin oxide (ITO) sheets. This study highlights the superior performance of PANI-MIP/ITO over PANI-MIP/GCE for sensing Phe, with clear and distinct redox responses. Molecular computation helps to understand the interaction mechanism between PANI and Phe, where molecular crowding, aggregated clusters, hydrogen bonding, and π-π stacking facilitate stable interactions. We tested the specificity of Phe sensing by PANI-MIP with different amino acids such as cysteine, tryptophan, and tyrosine as well as organic molecules such as ascorbic acid, allantoin, sucrose, and urea, confirming its remarkable electrochemical efficiency. The oxidation response curve yielded a limit of detection of 4.88 μM and a limit of quantification of 16.3 μM, comparable to or better than earlier reported sensors. This work demonstrates the promise of MIP-based electrochemical sensing. It also lays the groundwork for future investigations into optimizing PANI-MIPs with nanocomposites to develop more selective and stable sensors.

Current Advances and Material Innovations in the Search for Novel Treatments of Phenylketonuria

Phenylketonuria (PKU) is a genetically inherited disease caused by a mutation of the gene encoding phenylalanine hydroxylase (PAH) and is the most common inborn error of amino acid metabolism. A deficiency of PAH leads to increased blood and brain levels of phenylalanine (Phe), which may cause permanent neurocognitive symptoms and developmental delays if untreated. Current management strategies for PKU consist of early detection through neonatal screening and implementation of a restrictive diet with minimal amounts of natural protein in combination with Phe-free supplements and low-protein foods to meet nutritional requirements. For milder forms of PKU, oral treatment with synthetic sapropterin (BH4), the cofactor of PAH, may improve metabolic control of Phe and allow for more natural protein to be included in the patient's diet. For more severe forms, daily injections of pegvaliase, a PEGylated variant of phenylalanine ammonia-lyase (PAL), may allow for normalization of blood Phe levels. However, the latter treatment has considerable drawbacks, notably a strong immunogenicity of the exogenous enzyme and the attached polymeric chains. Research for novel therapies of PKU makes use of innovative materials for drug delivery and state-of-the-art protein engineering techniques to develop treatments which are safer, more effective, and potentially permanent.

Recent advancements in non-invasive wearable electrochemical biosensors for biomarker analysis - A review

A biomarker is a molecular indicator that can be used to identify the presence or severity of a disease. It may be produced due to biochemical or molecular changes in normal biological processes. In some cases, the presence of a biomarker itself is an indication of the disease, while in other cases, the elevated or depleted level of a particular protein or chemical substance aids in identifying a disease. Biomarkers indicate the progression of the disease in response to therapeutic interventions. Identifying these biomarkers can assist in diagnosing the disease early and providing proper therapeutic treatment. In recent years, wearable electrochemical (EC) biosensors have emerged as an important tool for early detection due to their excellent selectivity, low cost, ease of fabrication, and improved sensitivity. There are several challenges in developing a fully integrated wearable sensor, such as device miniaturization, high power consumption, incorporation of a power source, and maintaining the integrity and durability of the biomarker for long-term continuous monitoring. This review covers the recent advancements in the fabrication techniques involved in device development, the types of sensing platforms utilized, different materials used, challenges, and future developments in the field of wearable biosensors.

Paper-Based Electrochemical (Bio)Sensors for the Detection of Target Analytes in Liquid, Aerosol, and Solid Samples

The last decade has been incredibly fruitful in proving the multifunctionality of paper for delivering innovative electrochemical (bio)sensors. The paper material exhibits unprecedented versatility to deal with complex liquid matrices and facilitate analytical detection in aerosol and solid phases. Such remarkable capabilities are feasible by exploiting the intrinsic features of paper, including porosity, capillary forces, and its easy modification, which allow for the fine designing of a paper device. In this review, we shed light on the most relevant paper-based electrochemical (bio)sensors published in the literature so far to identify the smart functional roles that paper can play to bridge the gap between academic research and real-world applications in the biomedical, environmental, agrifood, and security fields. Our analysis aims to highlight how paper's multifarious properties can be artfully harnessed for breaking the boundaries of the most classical applications of electrochemical (bio)sensors.

Emerging biosensors in Phenylketonuria

Phenylketonuria (PKU) is an autosomal recessive metabolic disorder resulting from deficient phenylalanine hydroxylase (PAH) enzyme activity, leading to impaired phenylalanine (Phe) metabolism. This condition can lead to intellectual disability, epilepsy, and behavioural issues. Treatment typically involves strict dietary restrictions on natural protein intake, supplemented with chemically manufactured protein substitutes containing amino acids other than Phe. Various approaches, including casein glycomacropeptide (GMP), tetrahydrobiopterin (BH4), phenylalanine ammonia-lyase (PAL) therapy, large neutral amino acid (LNAA) supplementation, enzyme therapy, gene therapy, and medical therapies, aim to prevent Phe transport in the brain to potentially treat PKU. Although newborn screening programs and early dietary interventions have enhanced outcomes of the potential treatment strategies, limitations still persist in this direction. These involve potent accuracy concerns in diagnosis due to the existence of antibiotics in blood of PKU patients, affecting growth of the bacteria in the bacterial inhibition assay. Monitoring involves complex methods for instance, mass spectrometry and high-pressure liquid chromatography, which involve shortcomings such as lengthy protocols and the need for specialized equipment. To address these limitations, adaptable testing formats like bio/nano sensors are emerging with their cost-effectiveness, biodegradability, and rapid, accurate, and sensitive detection capabilities, offering promising alternatives for PKU diagnosis. This review provides insights into current treatment and diagnostic approaches, emphasizing on the potential applications of the diverse sensors intended for PKU diagnosis.

Skin-interfacing wearable biosensors for smart health monitoring of infants and neonates

Health monitoring of infant patients in intensive care can be especially strenuous for both the patient and their caregiver, as testing setups involve a tangle of electrodes, probes, and catheters that keep the patient bedridden. This has typically involved expensive and imposing machines, to track physiological metrics such as heart rate, respiration rate, temperature, blood oxygen saturation, blood pressure, and ion concentrations. However, in the past couple of decades, research advancements have propelled a world of soft, wearable, and non-invasive systems to supersede current practices. This paper summarizes the latest advancements in neonatal wearable systems and the different approaches to each branch of physiological monitoring, with an emphasis on smart skin-interfaced wearables. Weaknesses and shortfalls are also addressed, with some guidelines provided to help drive the further research needed.

Satisfaction with home blood sampling methods and expectations for future point-of-care testing in phenylketonuria: Perspectives from patients and professionals

INTRODUCTION

Phenylketonuria (PKU) requires regular phenylalanine monitoring to ensure optimal outcome. However, home sampling methods used for monitoring suffer high pre-analytical variability, inter-laboratory variability and turn-around-times, highlighting the need for alternative methods of home sampling or monitoring.

METHODS

A survey was distributed through email and social media to (parents of) PKU patients and professionals working in inherited metabolic diseases in Denmark, The Netherlands, and United Kingdom regarding satisfaction with current home sampling methods and expectations for future point-of-care testing (POCT).

RESULTS

210 parents, 156 patients and 95 professionals completed the survey. Countries, and parents and patients were analysed together, in absence of significant group differences for most questions. Important results are: 1) Many patients take less home samples than advised. 2) The majority of (parents of) PKU patients are (somewhat) dissatisfied with their home sampling method, especially with turn-around-times (3-5 days). 3) 37% of professionals are dissatisfied with their home sampling method and 45% with the turn-around-times. 4) All responders are positive towards developments for POCT: 97% (n = 332) of (parents of) patients is willing to use a POC-device and 76% (n = 61) of professionals would recommend their patients to use a POC-device. 5) Concerns from all participants for future POC-devices are costs/reimbursements and accuracy, and to professionals specifically, accessibility to results, over-testing, patient anxiety, and patients adjusting their diet without consultation.

CONCLUSION

The PKU community is (somewhat) dissatisfied with current home sampling methods, highlighting the need for alternatives of Phe monitoring. POCT might be such an alternative and the community is eager for its arrival.

Disease diagnosis and application analysis of molecularly imprinted polymers (MIPs) in saliva detection

Saliva has significantly evolved as a diagnostic fluid in recent years, giving a non-invasive alternative to blood analysis. A high protein concentration in saliva is delivered directly from the bloodstream, making it a "human mirror" that reflects the body's physiological state. It plays an essential role in detecting diseases in biomedical and fitness monitoring. Molecularly imprinted polymers (MIPs) are biomimetic materials with custom-designed synthetic recognition sites that imitate biological counterparts renowned for sensitive analyte detection. This paper reviews the progress made in research about MIP biosensors for detecting saliva biomarkers. Specifically, we investigate the link between saliva biomarkers and various diseases, providing detailed insights into the corresponding biosensors. Furthermore, we discuss the principles of molecular imprinting for disease diagnostics and application analysis, including recent advances in integrated MIP-sensor technologies for high-affinity analyte detection in saliva. Notably, these biosensors exhibit high discrimination, allowing for the detection of saliva biomarkers linked explicitly to chronic stress disorders, diabetes, cancer, bacterial or viral-induced illnesses, and exposure to illicit toxic substances or tobacco smoke. Our findings indicate that MIP-based biosensors match and perhaps surpass their counterparts featuring integrated natural antibodies in terms of stability, signal-to-noise ratios, and detection limits. Additionally, we highlight the design of MIP coatings, strategies for synthesizing polymers, and the integration of advanced biodevices. These tailored biodevices, designed to assess various salivary biomarkers, are emerging as promising screening or diagnostic tools for real-time monitoring and self-health management, improving quality of life.

Interindividual- and blood-correlated sweat phenylalanine multimodal analytical biochips for tracking exercise metabolism

In situ monitoring of endogenous amino acid loss through sweat can provide physiological insights into health and metabolism. However, existing amino acid biosensors are unable to quantitatively assess metabolic status during exercise and are rarely used to establish blood-sweat correlations because they only detect a single concentration indicator and disregard sweat rate. Here, we present a wearable multimodal biochip integrated with advanced electrochemical electrodes and multipurpose microfluidic channels that enables simultaneous quantification of multiple sweat indicators, including phenylalanine and chloride, as well as sweat rate. This combined measurement approach reveals a negative correlation between sweat phenylalanine levels and sweat rates among individuals, which further enables identification of individuals at high metabolic risk. By tracking phenylalanine fluctuations induced by protein intake during exercise and normalizing the concentration indicator by sweat rates to reduce interindividual variability, we demonstrate a reliable method to correlate and analyze sweat-blood phenylalanine levels for personal health monitoring.

A polymer dot-based NADH-sensitive electrochemiluminescence biosensor for analysis of metabolites in serum

Nicotinamide adenine dinucleotide (NADH) plays a pivotal role in metabolism. Convenient detection of NADH and its related metabolites has the pursuit of point-of-care and clinical analysis. Here, we propose a polymer dots (Pdots)-based NADH-sensitive electrochemiluminescence (ECL) biosensor for detection of NADH and three metabolites. Pdots acted as the efficient ECL emitters without additional modification to construct this biosensor. Specially, NADH both acted as the final detection target and at the same time as the bio-coreactants to sensitively influence the ECL intensities, in which NADH was generated or consumed in the presence of the target analyte and their specific enzyme. For glucose and lactic acid detection, NAD+ was reduced to NADH to generate an enhanced ECL signal. Conversely, for pyruvate detection, NADH was consumed to further decrease the ECL. The designed Pdots-based ECL biosensor showed wide detection ranges, high selectivity and low limits of detection of 4.6 μM, 0.7 μM and 0.5 μM for the analysis of three analytes, respectively. This strategy was successfully applied in quantifying the concentrations of glucose, lactic acid and pyruvate in human serum, which also has the potential to be implemented as a powerful and fast tool for ECL sensing of NADH and other related metabolites for point-of-care use and disease monitoring.

Hydrogen Peroxide and Dopamine Sensors Based on Electrodeposition of Reduced Graphene Oxide/Silver Nanoparticles

In this work, silver nanoparticles (AgNPs)/reduced graphene oxide (rGO) nanocomposites were electrodeposited on glassy carbon electrodes (GCE) to construct electrochemical sensors for the detection of hydrogen peroxide (H2O2) and dopamine (DA). The AgNPs were synthesized on graphene oxide (GO) by the hydrothermal method, followed by the reduction of the GO during the electrodeposition process, resulting in the formation of the nanocomposites on the surface of the electrodes. The generation of AgNPs on the graphene sheets was verified by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The AgNPs/rGO/GCE showed a linear response to H2O2 in the range of 5 μM to 620 μM, with a sensitivity of 49 μA mM-1cm-2 and a limit of detection (LOD) of 3.19 μA. The linear response of the AgNPs/rGO/GCE to DA ranged from 1 μM to 276 μM, the sensitivity was 7.86 μA mM-1cm-2, and the LOD was 0.18 μM. Furthermore, DA and H2O2 were detected simultaneously in the same solution without interferences, and the sensors displayed good stability over time. The preparation method for the sensors is relatively eco-friendly, convenient, and efficient, exhibiting great potential for sensitive detection of DA and H2O2.

Fully Integrated Point-of-Care Platform for the Self-Monitoring of Phenylalanine in Finger-Prick Blood

Development of point-of-care platforms combining reliability and ease of use is a challenge for the evolution of sensing in healthcare technologies. Here, we report the development and testing of a fully integrated enzymatic colorimetric assay for the sensing of phenylalanine in blood samples from phenylketonuria patients. The platform works with a customized mobile app for data acquisition and visualization and comprises an electronic system and a disposable sensor. The sensing approach is based on specific enzymatic phenylalanine recognition, and the optical transduction method is based on in situ gold nanostructure formation. The phenylketonuria (PKU) smart sensor platform is conceived to perform self-monitoring on phenylalanine levels and real-time therapy tuning, thanks to the direct connection with clinicians. Validation of the technologies with a population of patients affected by PKU, together with the concurrent validation of the platform through centralized laboratories, has confirmed the good analytical performances in terms of sensitivity and specificity, robustness, and utility for phenylalanine sensing. The self-monitoring of phenylalanine for the daily identification of abnormal health conditions could facilitate rapid therapy tuning, improving the wellness of PKU patients.

Wearable Microneedle-Based Array Patches for Continuous Electrochemical Monitoring and Drug Delivery: Toward a Closed-Loop System for Methotrexate Treatment

Wearable devices based on microneedle (MN) technology have recently emerged as tools for in situ transdermal sensing or delivery in interstitial fluid (ISF). Particularly, MN-based electrochemical sensors allow the continuous monitoring of analytes in a minimally invasive manner through ISF. Exogenous small molecules found in ISF such as therapeutic drugs are ideal candidates for MN sensors due to their correlation with blood levels and their relevance for the optimal management of personalized therapies. Herein, a hollow MN array patch is modified with conductive pastes and functionalized with cross-linked chitosan to develop an MN-based voltammetric sensor for continuous monitoring of methotrexate (MTX). Interestingly, the chitosan coating avoids biofouling while enabling the adsorption of MTX at the electrode's surface for sensitive analysis. The MN sensor exhibits excellent analytical performance in vitro with protein-enriched artificial ISF and ex vivo under a Franz diffusion cell configuration. The MN sensor shows a linear range from 25 to 400 μM, which fits within the therapeutic range of high-dose MTX treatment for cancer patients and an excellent continuous operation for more than two days. Moreover, an iontophoretic hollow MN array patch is developed with the integration of both the anode and cathode in the single MN array patch. The ex vivo characterization demonstrates the transdermal on-demand drug delivery of MTX. Overall, the combination of both MN patches represents impactful progress in closed-loop systems for therapeutic drug management in disorders such as cancer, rheumatoid arthritis, or psoriasis.

Perfluorosulfonic Acid Membranes with Short and Long Side Chains and Their Use in Sensors for the Determination of Markers of Viral Diseases in Saliva

The development of accessible express methods to determine markers of viral diseases in saliva is currently an actual problem. Novel cross-sensitive sensors based on Donnan potential with bio-comparable perfluorosulfonic acid membranes for the determination of salivary viral markers (N-acetyl-L-methionine, L-carnitine, and L-lysine) were proposed. Membranes were formed by casting from dispersions of Nafion or Aquivion in N-methyl-2-pyrollidone or in a mixture of isopropyl alcohol and water. The influence of the polymer equivalent weight and the nature of dispersing liquid on water uptake, ion conductivity, and slope of Donnan potential for the membranes in H+ and Na+ form was investigated. The varying of the sorption and transport properties of perfluorosulfonic acid membranes provided a change in the distribution of the sensor sensitivity to N-acetyl-L-methionine, L-carnitine, and L-lysine ions, which was necessary for multisensory system development. The simultaneous determination of three analytes, and the group analysis of them in artificial saliva solutions, was performed. The errors of N-acetyl-L-methionine and L-carnitine determination were 4-12 and 3-11%, respectively. The determination of L-lysine was complicated by its interaction with Ca2+ ions. The error of the group analysis was no greater than 9%. The reverse character of the viral markers' sorption by the membranes provided long-term sensor operation.

A method for phenylalanine self-monitoring using phenylalanine ammonia-lyase and a pre-existing portable ammonia detection system

Phenylketonuria is an inborn error of phenylalanine metabolism caused by a phenylalanine hydroxylase deficiency. To prevent the occurrence of neurological symptoms and maternal complications resulting from phenylketonuria, patients must adhere to a strict diet therapy, tetrahydrobiopterin supplementation, or pegvaliase injection to maintain blood phenylalanine levels within a recommended range throughout their lives. Therefore, monitoring blood phenylalanine levels is necessary to determine the recent metabolic status of phenylalanine in patients with PKU; however, there are no available instruments for individuals to monitor their own blood phenylalanine levels using whole fingertip blood. We developed a phenylalanine monitoring system (designated as PheCheck) that included a pre-existing portable ammonia detection device and phenylalanine ammonia-lyase, which converts phenylalanine to trans-cinnamic acid and ammonia. This system was able to remove 86.7% ± 0.03% of the ammonia contained in fingertip blood and successfully reduce background ammonia levels. A good correlation was found between the estimated plasma phenylalanine levels detected by PheCheck and plasma phenylalanine levels detected by high-performance liquid chromatography (R² 0.97). The entire PheCheck process for measuring blood phenylalanine takes only 20 min. PheCheck can lay the foundation for home phenylalanine monitoring with high feasibility because all the components are easily accessible. Further studies with a more user-friendly PheCheck optimized for practice are needed to improve blood phenylalanine control, reduce the burden on patients and/or caregivers, and prevent the sequelae associated with phenylketonuria.

Fluid-based wearable sensors: a turning point in personalized healthcare

Nowadays, it has become very popular to develop wearable devices that can monitor biomarkers to analyze the health status of the human body more comprehensively and accurately. Wearable sensors, specially designed for home care services, show great promise with their ease of use, especially during pandemic periods. Scientists have conducted many innovative studies on new wearable sensors that can noninvasively and simultaneously monitor biochemical indicators in body fluids for disease prediction, diagnosis, and management. Using noninvasive electrochemical sensors, biomarkers can be detected in tears, saliva, perspiration, and skin interstitial fluid (ISF). In this review, biofluids used for noninvasive wearable sensor detection under four main headings, saliva, sweat, tears, and ISF-based wearable sensors, were examined in detail. This report analyzes nearly 50 recent articles from 2017 to 2023. Based on current research, this review also discusses the evolution of wearable sensors, potential implementation challenges, and future prospects.

A wearable sensor based on multifunctional conductive hydrogel for simultaneous accurate pH and tyrosine monitoring in sweat

Flexible and wearable sweat sensors have drawn extensive attention by virtue of their continuous and real-time monitoring of molecular level information. However, current sweat-based sensors still pose several challenges, such as low accuracy for analytes detection, susceptibility to microorganism and poor mechanical performance. Herein, we demonstrated a noninvasive wearable sweat sensing patch composed of an electrochemical sensing system, and a pilocarpine-based iontophoretic system to stimulate sweat secretion. The electrochemical sensor based on tannic acid-Ag-carbon nanotube-polyaniline (TA-Ag-CNT-PANI) composite hydrogel was designed for on-body detection of pH and tyrosine (Tyr), a disease marker associated with multiple disorders, such as tyrosinemia and bulimia nervosa. The wearable sweat sensor can not only monitor the pH and Tyr in sweat simultaneously, but also further calibrate Tyr detection results with the measured pH value, so as to eliminate the effect of Tyr response variance at different pH and enhance the accuracy of the sensor. Furthermore, the presence of tannic acid chelated-Ag nanoparticles (TA-Ag NPs) and carbon nanotubes (CNTs) significantly improved the conductivity and flexibility of the hydrogel and endowed the composite hydrogel with antibacterial capability. Of note, the constructed wearable sensor was capable of monitoring Tyr with enhanced accuracy in various sweats.

An electrochemical sensor for direct and sensitive detection of ketamine

Ketamine is an organic drug with weak electrochemical activity, which makes it difficult to directly detect by electrochemical methods. Herein, an electrochemical sensor, with excellent detection sensitivity, is proposed for direct detection of ketamine based on a weakly conductive poly-L-cysteine molecularly imprinted membrane. Poly-L-cysteine molecularly imprinted membrane sensor (poly-L-Cys-KT-MIM/GCE) is obtained using L-cysteine as a functional monomer and ketamine as a template molecule based on electropolymerization. The green and highly active cysteine is selected as a functional monomer during electropolymerization, which cannot only achieve specific recognition but also improve detection sensitivity. Furthermore, the oxidation mechanism and fingerprint of ketamine on the electrode surface are established by analyzing the corresponding oxidation products using high/resolution mass spectrometry, which will help to promote the application of electrochemistry in the rapid detection of drugs. Under optimal conditions, the as-designed sensor demonstrated a linear response to ketamine within the range of 5.0 × 10^-7 to 2.0 × 10^-5 mol L^-1 and a detection limit of 1.6 × 10^-7 mol L^-1. The proposed method exhibited excellent performance from the viewpoints of selectivity, sensitivity and stability. Notably, the sensor rendered excellent reliability and could be used for the detection of target analytes in hair and urine samples with high recovery rates.

A Systematic Review on the Advanced Techniques of Wearable Point-of-Care Devices and Their Futuristic Applications

Personalized point-of-care testing (POCT) devices, such as wearable sensors, enable quick access to health monitoring without the use of complex instruments. Wearable sensors are gaining popularity owing to their ability to offer regular and continuous monitoring of physiological data by dynamic, non-invasive assessments of biomarkers in biofluids such as tear, sweat, interstitial fluid and saliva. Current advancements have concentrated on the development of optical and electrochemical wearable sensors as well as advances in non-invasive measurements of biomarkers such as metabolites, hormones and microbes. For enhanced wearability and ease of operation, microfluidic sampling, multiple sensing, and portable systems have been incorporated with materials that are flexible. Although wearable sensors show promise and improved dependability, they still require more knowledge about interaction between the target sample concentrations in blood and non-invasive biofluids. In this review, we have described the importance of wearable sensors for POCT, their design and types of these devices. Following which, we emphasize on the current breakthroughs in the application of wearable sensors in the realm of wearable integrated POCT devices. Lastly, we discuss the present obstacles and forthcoming potentials including the use of Internet of Things (IoT) for offering self-healthcare using wearable POCT.

Paper-Based Sandwich-Structured Wearable Sensor with Sebum Filtering for Continuous Detection of Sweat pH

Wearable sweat sensors, a product of the development of flexible electronics and microfluidic technologies, can continuously and noninvasively monitor abundant biomarkers in human sweat; however, sweat interferences, such as sebum, can reduce sensor reliability and accuracy. Herein, for the first time, the influence of sebum on the potentiometric response of an all-solid-state pH sensor was studied, and the obtained experimental results show that sebum mixed in sweat can decrease the potential response of the sensor and the slope of its calibration curve. A paper-based sandwich-structured pH sensor that can filter the sebum mixed in sweat was proposed based on commonly used oil-control sheets. Moreover, the hydrophilic properties, microstructure, and microfluidic performance of the sensor were investigated. The detection performance of the paper-based sandwich-structured pH sensor was comprehensively evaluated in terms of calibration in the presence of sebum and potentiometric response upon the addition of sebum. Furthermore, the anti-interference ability of the sensor was evaluated using different analytes under various deformation conditions. On-body trials were conducted to verify the performance, and their results showed that the proposed sensor can filter over 90% of the sebum in sweat, significantly enhancing sensor reliability and accuracy. Additionally, microfluidic channels could be simply fabricated using a scissor and paper, obviating the need for complex micromachining processes, such as photolithography and laser engraving. Overall, this work illustrates the influence of sebum on the detection performance of traditional potentiometric wearable sensors and paves the way for their development for real-world applications.

Novel Wearable Optical Sensors for Vital Health Monitoring Systems-A Review

Wearable sensors are pioneering devices to monitor health issues that allow the constant monitoring of physical and biological parameters. The immunity towards electromagnetic interference, miniaturization, detection of nano-volumes, integration with fiber, high sensitivity, low cost, usable in harsh environments and corrosion-resistant have made optical wearable sensor an emerging sensing technology in the recent year. This review presents the progress made in the development of novel wearable optical sensors for vital health monitoring systems. The details of different substrates, sensing platforms, and biofluids used for the detection of target molecules are discussed in detail. Wearable technologies could increase the quality of health monitoring systems at a nominal cost and enable continuous and early disease diagnosis. Various optical sensing principles, including surface-enhanced Raman scattering, colorimetric, fluorescence, plasmonic, photoplethysmography, and interferometric-based sensors, are discussed in detail for health monitoring applications. The performance of optical wearable sensors utilizing two-dimensional materials is also discussed. Future challenges associated with the development of optical wearable sensors for point-of-care applications and clinical diagnosis have been thoroughly discussed.

A highly sensitive colorimetric approach based on tris (bipyridine) Ruthenium (II/III) mediator for the enzymatic detection of phenylalanine

The accurate monitoring of phenylalanine concentration plays a prominent role in the treatment of phenylketonuria (PKU). In this study, we present an enzymatic assay based on Phenylalanine Dehydrogenase/NAD⁺ and tris (bipyridine) Ruthenium (II/III) as a colorimetric mediator for the detection of Phenylalanine concentration. The amount of amino acid was quantitatively recognized by optical absorption measurements at 452 nm through the conversion of Ru (byp)₃ ³⁺ to Ru (byp)₃ ²⁺, which is induced by the neoformed NADH. A detection limit of 0.33 µM, a limit of quantification of 1.01 µM, and a sensitivity of 36.6 a.u nM^-1 were obtained. The proposed method was successfully tested using biological specimens from patients affected by hyperphenylalaninemia. The proposed enzymatic assay showed a high selectivity, making it a promising alternative for the development of versatile assays for the detection of phenylalanine in diluted serums.

An ECL sensor combined with a paper electrode for the determination of phenylalanine

An electrochemiluminescence (ECL) sensor combined with a paper electrode was developed for the detection of phenylalanine (l-Phe) in blood samples.