Passively Addressable Ultra-Low Volume Sweat Chloride Sensor

Wearable sweat chloride sensors: materials, fabrication and their applications

Chloride is a crucial anion required for multiple functions in the human body including maintaining acid-base balance, fluid balance, electrical neutrality and supporting muscles and nerve cells. Low-chloride levels can cause nausea, diarrhoea, etc. Chloride levels are measured in different body fluids such as urine, serum, sweat and saliva. Sweat chloride measurements are used for multiple applications including disease diagnosis, sports monitoring, and geriatric care. For instance, a sweat chloride test is performed for cystic fibrosis screening. Further, sweat also offers continuous non-invasive access to body fluids for real-time monitoring of chloride that could be used for sports and geriatric care. This review focuses on wearable chloride sensors that are used for periodic and continuous chloride monitoring. The multiple sections in the paper discuss the clinical significance of chloride, detection methods, sensor fabrication methods and their application in cystic fibrosis screening, sports and geriatric care. Finally, the last section discusses the limitation of current sensors and future directions for wearable chloride sensors.

Passive sweat wearable: A new paradigm in the wearable landscape toward enabling "detect to treat" opportunities

Growing interest over recent years in personalized health monitoring coupled with the skyrocketing popularity of wearable smart devices has led to the increased relevance of wearable sweat-based sensors for biomarker detection. From optimizing workouts to risk management of cardiovascular diseases and monitoring prediabetes, the ability of sweat sensors to continuously and noninvasively measure biomarkers in real-time has a wide range of applications. Conventional sweat sensors utilize external stimulation of sweat glands to obtain samples, however; this stimulation influences the expression profile of the biomarkers and reduces the accuracy of the detection method. To address this limitation, our laboratory pioneered the development of the passive sweat sensor subfield, which allowed for our progress in developing a sweat chemistry panel. Passive sweat sensors utilize nanoporous structures to confine and detect biomarkers in ultra-low sweat volumes. The ability of passive sweat sensors to use smaller samples than conventional sensors enable users with sedentary lifestyles who perspire less to benefit from sweat sensor technology not previously afforded to them. Herein, the mechanisms and strategies of current sweat sensors are summarized with an emphasis on the emerging subfield of passive sweat-based diagnostics. Prospects for this technology include discovering new biomarkers expressed in sweat and expanding the list of relevant detectable biomarkers. Moreover, the accuracy of biomarker detection can be enhanced with machine learning using prediction algorithms trained on clinical data. Applying this machine learning in conjunction with multiplex biomarker detection will allow for a more holistic approach to trend predictions. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Biosensing.

Electrochemical Sensing of Urinary Chloride Ion Concentration for Near Real-Time Monitoring

Urinary chloride concentration is a valuable health metric that can aid in the early detection of serious conditions, such as acid base disorders, acute heart failure, and incidences of acute renal failure in the intensive care unit. Physiologically, urinary chloride levels frequently change and are difficult to measure, involving time-consuming and inconvenient lab testing. Thus, near real-time simple sensors are needed to quickly provide actionable data to inform diagnostic and treatment decisions that affect health outcomes. Here, we introduce a chronopotentiometric sensor that utilizes commercially available screen-printed electrodes to accurately quantify clinically relevant chloride concentrations (5-250 mM) in seconds, with no added reagents or electrode surface modification. Initially, the sensor's performance was optimized through the proper selection of current density at a specific chloride concentration, using electrical response data in conjunction with scanning electron microscopy. We developed a unique swept current density algorithm to resolve the entire clinically relevant chloride concentration range, and the chloride sensors can be reliably reused for chloride concentrations less than 50 mM. Lastly, we explored the impact of pH, temperature, conductivity, and additional ions (i.e., artificial urine) on the sensor signal, in order to determine sensor feasibility in complex biological samples. This study provides a path for further development of a portable, near real-time sensor for the quantification of urinary chloride.

Flexible Sweat Sensors: From Films to Textiles

Flexible sweat sensors have found widespread potential applications for long-term wear and tracking and real-time monitoring of human health. However, the main substrate currently used in common flexible sweat sensors is thin film, which has disadvantages such as poor air permeability and the need for additional wearables. In this Review, the recent progress of sweat sensors has been systematically summarized by the types of monitoring methods of sweat sensors. In addition, this Review introduces and compares the performance of sweat sensors based on thin film and textile substrates such as fiber/yarn. Finally, opportunities and suggestions for the development of flexible sweat sensors are presented by summarizing the integration methods of sensors and human body monitoring sites.

Flexible biochemical sensors for point-of-care management of diseases: a review

Health problems have been widely concerned by all mankind. Real-time monitoring of disease-related biomarkers can feedback the physiological status of human body in time, which is very helpful to the diseases management of healthcare. However, conventional non-flexible/rigid biochemical sensors possess low fit and comfort with the human body, hence hindering the accurate and comfortable long-time health monitoring. Flexible and stretchable materials make it possible for sensors to be continuously attached to the human body with good fit, and more precise and higher quality results can be obtained. Thus, tremendous attention has been paid to flexible biochemical sensors in point-of-care (POC) for real-time monitoring the entire disease process. Here, recent progress on flexible biochemical sensors for management of various diseases, focusing on chronic and communicable diseases, is reviewed, and the detection principle and performance of these flexible biochemical sensors are discussed. Finally, some directions and challenges are proposed for further development of flexible biochemical sensors.

Label-Free, Novel Electrofluidic Capacitor Biosensor for Prostaglandin E2 Detection toward Early and Rapid Urinary Tract Infection Diagnosis

Urine Prostaglandin E2 (PGE2) has been identified as an attractive diagnostic and prognostic biomarker for urinary tract infection (UTI). This work demonstrates the use of PGE2 as a biomarker for rapid and label-free testing for UTI. In this work, we have developed a novel electrofluidic capacitor-based biosensor that can used for home-based UTI management with high accuracy in less than 5 min for small volume urine samples (<60 μL). The PGE2 biosensor works on the principle of affinity capture using highly specific monoclonal PGE2 antibody and relies on non-faradaic electrical impedance spectroscopy (EIS) and Mott-Schottky (MS) for quantifying subtle variations in PGE2 levels expressed in human urine (pH 5-8). Dynamic light scattering experiments were performed to characterize surface charge properties and the impact of bulk interferents on the interfacial modulation of electrical properties due to binding and urine pH variations. Binding chemistry between the key elements of the immunosensor stack was validated using attenuated total reflectance-Fourier transform infrared spectroscopy and surface plasmon resonance studies. Linear calibration dose responses were obtained for PGE2 for both EIS and MS. The sensor reliably distinguished between UTI negative and UTI positive cases for both artificial (pH 5-8) and pooled human urine samples. The sensor was not found to cross-react with Prostaglandin D2, a structurally similar interferent, and other abundant urine interferents (urea and creatinine). Human subject studies confirmed the validity of the sensor for robust and accurate UTI diagnosis. This work can be extended to achieve easy, reliable, and rapid home-based UTI management, which can consequently help physicians with timely and appropriate administration of therapy to improve patient outcomes and treatment success.

Label Free, Lateral Flow Prostaglandin E2 Electrochemical Immunosensor for Urinary Tract Infection Diagnosis

A label-free, rapid, and easy-to-use lateral flow electrochemical biosensor was developed for urinary tract infection (UTI) diagnosis in resource challenged areas. The sensor operates in non-faradaic mode and utilizes Electrochemical Impedance Spectroscopy for quantification of Prostaglandin E2, a diagnostic and prognostic urinary biomarker for UTI and recurrent UTI. To achieve high sensitivity in low microliter volumes of neat, unprocessed urine, nanoconfinement of assay biomolecules was achieved by developing a three-electrode planar gold microelectrode system on top of a lateral flow nanoporous membrane. The sensor is capable of giving readouts within 5 min and has a wide dynamic range of 100–4000 pg/mL for urinary PGE2. The sensor is capable of discriminating between low and high levels of PGE2 and hence is capable of threshold classification of urine samples as UTI positive and UTI negative. The sensor through its immunological response (directly related to host immune response) is superior to the commercially available point-of-care UTI dipsticks which are qualitative, have poor specificity for UTI, and have high false-positive rates. The developed sensor shows promise for rapid, easy and cost-effective UTI diagnosis for both clinical and home-based settings. More accurate point-of-care UTI diagnosis will improve patient outcomes and allow for timely and appropriate prescription of antibiotics which can subsequently increase treatment success rates and reduce costs.

Tracking metabolic responses based on macronutrient consumption: A comprehensive study to continuously monitor and quantify dual markers (cortisol and glucose) in human sweat using WATCH sensor

Wearable Awareness Through Continuous Hidrosis (WATCH) sensor is a sweat based monitoring platform that tracks cortisol and glucose for the purpose of understanding metabolic responses related to macronutrient consumption. In this research article, we have demonstrated the ability of tracking these two biomarkers in passive human sweat over a workday period (8 h) for 10 human subjects in conjunction with their macronutrient consumption. The validation of the WATCH sensor performance was carried out via standard reference methods such as Luminex and ELISA This is a first demonstration of a passive sweat sensing technology that can detect interrelated dual metabolites, cortisol, and glucose, on a single sensing platform. The significance of detecting the two biomarkers simultaneously is that capturing the body's metabolic and endocrinal responses to dietary triggers can lead to improved lifestyle management. For sweat cortisol, we achieved a detection limit of 1 ng/ml (range ∼1-12.5 ng/ml) with Pearson's "r" of 0.897 in reference studies and 0.868 in WATCH studies. Similarly, for sweat glucose, we achieved a detection limit of 1 mg/dl (range ∼ 1-11 mg/dl) with Pearson's "r" of 0.968 in reference studies and 0.947 in WATCH studies, respectively. The statistical robustness of the WATCH sensor was established through the Bland-Altman analysis, whereby the sweat cortisol and sweat glucose levels are comparable to the standard reference method. The probability distribution (t-test), power analysis (power 0.82-0.87), α = 0.05. Mean absolute relative difference (MARD) outcome of ˷5.10-5.15% further confirmed the statistical robustness of the sweat sensing WATCH device output.

Label-Free Protein Glycosylation Analysis Using NanoMonitor-An Ultrasensitive Electrochemical Biosensor

Glycans (oligosaccharide chains attached to glycoproteins) are a promising class of biomarkers, found in body fluids such as serum, saliva, urine, etc., that can be used for the diagnosis of disease conditions. Subtle changes in glycans resulting from altered glycosylation machinery have been reported during various diseases, including carcinogenesis. In this article, we detail protocols for the rapid, label-free analysis of glycans using a previously developed highly sensitive and selective electrochemical impedance spectroscopy-based biosensing diagnostic platform called "NanoMonitor." The glycosensor operation is based on the specific affinity capture of the target glycans on the sensor surface by glycan-binding proteins known as lectins. This glycan-lectin binding activity modulates the impedance of the electrical double layer at the buffer-electrode interface. Protocols for the preparation of glycoprotein samples and glycosylation analysis using NanoMonitor and lectin-based ELISA are described here. The data obtained using these protocols show that NanoMonitor is capable of distinguishing between glycoform variants of the glycoprotein fetuin and glycoproteins derived from cultured human pancreatic cancer cells with high sensitivity (orders of magnitude higher than lectin-based ELISA) and selectivity. The results obtained indicate that NanoMonitor protocols can be further developed to enable use of NanoMonitor as a handheld electronic biosensor device for routine multiplexed detection of glycan biomarkers from clinical samples. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Preparing the NanoMonitor surface for glycan biosensing Support Protocol: Synthesis of glycoform variants of fetuin Basic Protocol 2: Performing Electrochemical Impedance Spectroscopy (EIS) for analyzing glycoprotein structures.

Monitoring Body Fluids in Textiles: Combining Impedance and Thermal Principles in a Printed, Wearable, and Washable Sensor

This work explores the feasibility of coupling two different techniques, the impedance and the transient plane source (TPS) principle, to quantify the moisture content and its compositional parameters simultaneously. The sensor is realized directly on textiles with the use of printing and coating technology. Impedance measurements use the fluid's electrical properties, while the TPS measurements are based on the thermal effusivity of the liquid. Impedance and TPS measurements show equal competency in measuring the fluid volume with a lowest measurable quantity of 0.5 μL, enabling ultralow volume passive measurements for sweat analysis. Both sensor principles were tested by monitoring the drying of a wet cloth and the measurements show perfect repeatability and accuracy. Nevertheless, when the biofluid property changes, the TPS sensor does not reflect this information on its readings, whereas, on the other hand, impedance can provide information on compositional changes. However, since the volume of the fluid changes simultaneously, one cannot differentiate between a volume change and a compositional change from impedance measurements alone. Therefore, we show in this work that we can apply impedance to measure the compositional properties; meanwhile, the TPS measurements accurately carry out volume measurements irrespective of the interferences from its compositional variations. To prove this, both of these techniques are applied for the quantification and composition monitoring of sweat, showing the capability to measure moisture content and compositional parameters simultaneously. TPS measurements can also be an indicator of the local temperature of the medium confined by the sensor, and it does not influence the fluid parameters. Compiling both impedance and thermal sensors in a single platform triggers smart wearable prospects of metering the liquid volume and simultaneously analyzing other compositional changes and body temperature. Finally, the repeatability and stability of the sensor readings and the washability of the device are tested. This device could be a potential sensing tool in real-life applications, such as wound monitoring and sweat analysis, and could be a promising addition toward future smart wearable sensors.

Sweating Out the Circadian Rhythm: A Technical Review

Circadian dysfunction or dysregulation is associated with many chronic morbidities. Current state-of-art technologies do not provide an accurate estimation of the extent of disease affliction. Recent advances call for using wearables for improving management and diagnosis of circadian related disorders. Sweat contains an abundance of relevant biomarkers like cortisol, DHEA, and so forth, which could be leveraged toward tracking the user's chronobiology. In this article, we provide a review of the key developments in the field of wearable sensors for circadian technologies. We highlight the value of using sweat along with portable electronics toward developing state-of-the-art platforms for efficient diagnosis and management of chronic conditions. Finally, we discuss challenges and opportunities for using wearable sweat sensors for circadian diagnosis and disease management.

Next-Generation Continuous Metabolite Sensing toward Emerging Sensor Needs

This article discusses the emergent biosensor technology focused on continuous biosensing of metabolites by non-invasive sampling of body fluids emphasized on physiological monitoring in mobility-constrained populations, resource-challenged settings, and harsh environments. The boom of innovative ideas and endless opportunities in healthcare technologies has transformed traditional medicine into a sustainable link between medical practitioners and patients to provide solutions for faster disease diagnosis. The future of healthcare is focused on empowering users to manage their own health. The confluence of big data and predictive analysis and the internet of things (IoT) technology have shown the potential of converting the abundant health profile data amassed from medical diagnosis of patients into useable information, whilst allowing caregivers to provide suitable treatment plans. The implementation of the IoT technology has opened up advanced approaches in real-time, continuous, remote monitoring of patients. Wearable, point-of-care biosensors are the future roadmap to providing direct, real-time information of health status to the user and medical professionals in this digitized era.

ElectrochemSENSE: A platform towards field deployable direct on-produce glyphosate detection

Glyphosate is an organophosphorus herbicide that is applied to the leaves of plants and crops to kill broadleaf plants and grasses. In this paper, for the first time, a field deployable, user-friendly, portable and rapid electrochemical pesticide sensing system is presented that can screen for glyphosate in produce run-off/extract. ElectrochemSENSE comprises the following parts: A polymer based disposable substrate with metallized electrodes that are surface treated with polyclonal antibodies of glyphosate and a custom electronic reader capable of reporting pesticide contamination. Utilizing the principles of capacitive current changes due to selective binding of glyphosate to its capture probe, reporting was achieved rapidly (in under 5 min). ElectrochemSENSE was tested to screen for glyphosate concentrations on produce samples above or below the globally accepted metric criterion, otherwise known as the Maximum Residue Level (MRL). Experiments were conducted on 4 produce types-apples (MRL: 0.2 ppm), strawberries (MRL: 0.2 ppm), bell peppers (MRL: 0.1 ppm) and carrots (MRL: 5 ppm). To further add functionality and increase prediction accuracy- a machine learning binary classifier was integrated with the device as a proof-of-concept so that sensor's response can be trained and characterized to perform with high accuracy, thereby serving as an analytics medium which minimizes error rate. Utilizing this system-the sensor's limit of detection has been determined to be 0.01 ppm (10 ng/mL) considering the permissible Field Operating Range (FOR) for glyphosate residue in various tested produce.