Electrochemical Aptasensing for Lifestyle and Chronic Disease Management.

Over the past decade, researchers have investigated electrochemical sensing for the purpose of fabricating wearable point-of-use platforms. These wearable platforms have the ability to non-invasively track biomarkers that are clinically relevant and provide a comprehensive evaluation of the user's health. Due to many significant operational advantages, aptamer-based sensing is gaining traction.Aptamer-based sensors have properties like long-term stability, resistance to denaturation, and high sensitivity. Using electrochemical sensing with aptamer-based biorecognition is advantageous because it provides significant benefits like lower detection limits, a wider range of operations, and, most importantly, the ability to detect using a label-free approach. This paper provides an outlook into the current state of electrochemical aptasensing. This review looks into the significance of the detection of biomarkers like glucose, cortisol etc., for the purpose of lifestyle and chronic disease monitoring. Moreover, this review will also provide a comprehensive evaluation of the current challenges and prospects in this field.

A machine learning-based on-demand sweat glucose reporting platform.

Diabetes is a chronic endocrine disease that occurs due to an imbalance in glucose levels and altering carbohydrate metabolism. It is a leading cause of morbidity, resulting in a reduced quality of life even in developed societies, primarily affected by a sedentary lifestyle and often leading to mortality. Keeping track of blood glucose levels noninvasively has been made possible due to diverse breakthroughs in wearable sensor technology coupled with holistic digital healthcare. Efficient glucose management has been revolutionized by the development of continuous glucose monitoring sensors and wearable, non/minimally invasive devices that measure glucose concentration by exploiting different physical principles, e.g., glucose oxidase, fluorescence, or skin dielectric properties, and provide real-time measurements every 1-5 min. This paper presents a highly novel and completely non-invasive sweat sensor platform technology that can measure and report glucose concentrations from passively expressed human eccrine sweat using electrochemical impedance spectroscopy and affinity capture probe functionalized sensor surfaces. The sensor samples 1-5 µL of sweat from the wearer every 1-5 min and reports sweat glucose from a machine learning algorithm that samples the analytical reference values from the electrochemical sweat sensor. These values are then converted to continuous time-varying signals using the interpolation methodology. Supervised machine learning, the decision tree regression algorithm, shows the goodness of fit R2 of 0.94 was achieved with an RMSE value of 0.1 mg/dL. The output of the model was tested on three human subject datasets. The results were able to capture the glucose progression trend correctly. Sweet sensor platform technology demonstrates a dynamic response over the physiological sweat glucose range of 1-4 mg/dL measured from 3 human subjects. The technology described in the manuscript shows promise for real-time biomarkers such as glucose reporting from passively expressed human eccrine sweat.

Temporal profiling of cytokines in passively expressed sweat for detection of infection using wearable device.

This work presents the viability of passive eccrine sweat as a functional biofluid toward tracking the human body's inflammatory response. Cytokines are biomarkers that orchestrate the manifestation and progression of an infection/inflammatory event. Hence, noninvasive, real-time monitoring of cytokines can be pivotal in assessing the progression of infection/inflammatory event, which may be feasible through monitoring of host immune markers in eccrine sweat. This work is the first experimental proof demonstrating the ability to detect inflammation/infection such as fever, FLU directly from passively expressed sweat in human subjects using a wearable "SWEATSENSER" device. The developed SWEATSENSER device demonstrates stable, real-time monitoring of inflammatory cytokines in passive sweat. An accuracy of >90% and specificity >95% was achieved using SWEATSENSER for a panel of cytokines (interleukin-6, interleukin-8, interleukin-10, and tumor necrosis factor-α) over an analytical range of 0.2-200 pg mL-1. The SWEATSENSER demonstrated a correlation of Pearson's r > 0.98 for the study biomarkers in a cohort of 26 subjects when correlated with standard reference method. Comparable IL-8 levels (2-15 pg mL-1) between systemic circulation (serum) and eccrine sweat through clinical studies in a cohort of 15 subjects, and the ability to distinguish healthy and sick (infection) cohort using inflammatory cytokines in sweat provides pioneering evidence of the SWEATSENSER technology for noninvasive tracking of host immune response biomarkers. Such a wearable device can offer significant strides in improving prognosis and provide personalized therapeutic treatment for several inflammatory/infectious diseases.

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 Ë·5.10-5.15% further confirmed the statistical robustness of the sweat sensing WATCH device output.

Electrochemical impedimetric biosensors, featuring the use of Room Temperature Ionic Liquids (RTILs): Special focus on non-faradaic sensing.

Over the last decade, significant advancements have been made in the field of biosensing technology. With the rising demand for personalized healthcare and health management tools, electrochemical sensors are proving to be reliable solutions; specifically, impedimetric sensors are gaining considerable attention primarily due to their ability to perform label-free sensing. The novel approach of using Room Temperature Ionic Liquids (RTILs) to improve the sensitivity and stability of these detection systems makes long-term continuous sensing feasible towards a wide range of sensing applications, predominantly biosensing. Through this review, we aim to provide an update on current scientific progress in using impedimetric biosensing combined with RTILs for the development of sensitive biosensing platforms. This review also summarizes the latest trends in the field of biosensing and provides an update on the current challenges that remain unsolved.

A Sweat-based Wearable Enabling Technology for Real-time Monitoring of IL-1ß and CRP as Potential Markers for Inflammatory Bowel Disease.

BACKGROUND: More than 1.2 million people in the United States are affected by inflammatory bowel disease (IBD). Inflammatory bowel disease has a natural course characterized by alternating periods of remission and relapse. Currently, disease flares are unpredictable as they occur in a random way. Further, current testing methods and practices lack the ability for real-time tracking of flares. There exists no technology that can be utilized for continuous monitoring of biomarkers, as most of these rely on samples such as blood, feces, and testing methods by which continuous monitoring is not feasible. Cytokines play a key role in IBD; the development, recurrence, and exacerbation of the inflammatory process are orchestrated by their levels in time and space. Cytokines are also present in sweat. We hypothesize that demonstrating real-time continuous monitoring of interleukin-1ß (IL-1ß) and C-reactive protein (CRP) may help create an enabling technology to track inflammation in IBD patients and identify flare-ups and assess efficacy of therapy. METHODS: A multiplexed SWEATSENSER was used for noninvasive continuous monitoring of interleukin-1ß and C-reactive protein in human eccrine sweat. Impedance spectroscopy was used to measure the sensor response. Sweat was collected using an FDA-approved PharmChek patch from 26 healthy human subjects to determine the levels of the 2 study inflammatory markers. Correlation analysis was performed for preclinical validation of the SWEATSENSER with ELISA as the reference method. On-body continuous monitoring measurements were performed on 20 human subjects using EnLiSense's SWEATSENSER wearable device for real-time monitoring studies. RESULTS: The sensor device can detect interleukin-1ß and C-reactive protein in sweat over a dynamic range of 3 log orders. Pearson correlation of r = 0.99 and r = 0.95 was achieved for IL-1ß and CRP, respectively, for the SWEATSENSER with ELISA. Bland-Altman results further confirmed a good agreement (mean bias of -0.25 and -3.9 pg/mL for IL-1ß and CRP, respectively) of the device with the reference method, demonstrating applicability of the device for real-time monitoring. Continuous on-body measurements were performed in 20 healthy human subjects for the detection of IL-1ß to establish the preclinical utility of the sensor device. The continuous on-body measurements in healthy cohort reported a mean IL-1ß concentration of ~28 pg/mL. Stable measurements for over continuous 30 hours was reported by the device. CONCLUSION: This work demonstrates the first proof-of-feasibility of multiplexed cytokine and inflammatory marker detection in passively expressed eccrine sweat in a wearable form-factor that can be utilized toward better management of inflammatory bowel disease. This is a first step toward demonstrating a noninvasive enabling technology that can enable baseline tracking of an inflammatory response. Furthermore, this is the first study to report and quantify the presence of CRP in human eccrine sweat.

CLIP: Carbon Dioxide testing suitable for Low power microelectronics and IOT interfaces using Room temperature Ionic Liquid Platform.

Health and safety considerations of room occupants in enclosed spaces is crucial for building management which entails control and stringent monitoring of CO2 levels to maintain acceptable air quality standards and improve energy efficiency. Smart building management systems equipped with portable, low-power, non-invasive CO2 sensing techniques can predict room occupancy detection based on CO2 levels exhaled by humans. In this work, we have demonstrated the development and proof-of-feasibility working of an electrochemical RTIL- based sensor prototype for CO2 detection in exhaled human breath. The portability, small form factor, embedded RTIL sensing element, integrability with low-power microelectronic and IOT interfaces makes this CO2 sensor prototype a potential application for passive room occupancy monitoring. This prototype exhibits a wide dynamic range of 400-8000 ppm, a short response time of ~10 secs, and a reset time of ~6 secs in comparison to commercial standards. The calibration response of the prototype exhibits an R2 of 0.956. With RTIL as the sensing element, we have achieved a sensitivity of 29 pF/ppm towards CO2 at ambient environmental conditions and a three times greater selectivity towards CO2 in the presence of N2 and O2. CO2 detection is accomplished by quantifying the capacitance modulations arising within the electrical double layer from the RTIL- CO2 interactions through AC- based electrochemical impedance spectroscopy and DC- based chronoamperometry.

CortiWatch: watch-based cortisol tracker.

Sweat-based analytics have recently caught the attention of researchers and medical professionals alike because they do not require professionally trained personnel or invasive collection techniques to obtain a sample. The following presents a small form-factor biosensor for reporting physiological ranges of cortisol present in ambient sweat (8-151 ng/ml). This device obtains cortisol measurements through low volumes of unstimulated sweat from the user's wrist. We designed a potentiostatic circuit on a printed circuit board to perform electrochemical testing techniques. The detection modality developed for quantifying sensor response to varying cortisol concentrations is a current based electrochemical technique, chronoamperometry (CA). From the results, the sensor can detect cortisol in the physiologically relevant ranges of cortisol; thus, the sensor is a noninvasive, label free, cost-effective solution for tracking cortisol levels for circadian diagnostics.

Non-faradaic electrochemical impedimetric profiling of procalcitonin and C-reactive protein as a dual marker biosensor for early sepsis detection.

In this work, we demonstrate a robust, dual marker, biosensing strategy for specific and sensitive electrochemical response of Procalcitonin and C-reactive protein in complex body fluids such as human serum and whole blood for the detection of sepsis. Enhanced sensitivity is achieved by leveraging the physicochemical properties of zinc oxide at the electrode-solution interface. Characterization techniques such as SEM, EDAX, AFM, FTIR and fluorescence microscopy were performed to ensure a suitable biosensing surface. The characteristic biomolecular interactions between the target analyte and specific capture probe is quantified through unique frequency signatures using non-faradaic electrochemical impedance spectroscopy (EIS). The developed biosensor demonstrated a detection limit of 0.10 ng mL-1 for PCT in human serum and whole blood with an R2 of 0.99 and 0.98 respectively. CRP demonstrated a detection limit of 0.10 µg mL-1 in human serum and whole blood with an R2 of 0.90 and 0.98 respectively. Cross-reactivity analysis demonstrated robust selectivity to PCT and CRP with negligible interaction to non-specific biomolecules. The novel aspect of this technology is the ability to fine-tune individual biomarkers response owing to the optimal frequency tuning capability. The developed biosensor requires an ultra-low sample volume of 10 µL without the need for sample dilution for rapid analysis. We envision the developed dual marker biosensor to be useful as a sepsis-screening device for prognostic monitoring.

Development of ultra-low volume, multi-bio fluid, cortisol sensing platform.

The development of a non-faradaic electrochemical sensor for screening across multiple bio-fluids that demonstrate the expression of cortisol using a gold microelectrode-based sensor is reported in this paper. Room temperature ionic liquid (RTIL), BMIM[BF4] was used as the buffer to modulate the electrical double layer (EDL) to enhance the electrochemical signal response of the sensor. The sensor design and the surface chemistry was optimized using COMSOL Multiphysics software simulations and FTIR respectively. The sensor was designed so that it uses ultra-low volumes between 3-5 µL of bio-fluid for detection. Cortisol detection was achieved in the physiologically relevant ranges when tested in serum, blood, sweat, and, saliva using non-faradaic Electrochemical Impedance Spectroscopy (EIS) and performance parameters of the sensor were determined. Sensor's response was tested against the only commercially available salivary cortisol point-of-care kit using regression analysis. Cross-reactive studies using prednisone indicated that the sensor is specific for cortisol. The sensor displayed a correlation value i.e. R2 > 0.95 between the signal response and the concentration of cortisol present in the system. Dynamic range of the sensor was across the physiologically relevant range of cortisol i.e. 50-200 ng/ml for serum/blood, 1-40 ng/ml for saliva, and 10-150 ng/ml for sweat. Limit of detection for serum and sweat was 10 ng/ml and 1 ng/ml for saliva.

Fully electronic urine dipstick probe for combinatorial detection of inflammatory biomarkers.

AIM: An electrochemical urine dipstick probe biosensor has been demonstrated using molybdenum electrodes on nanoporous polyamide substrate for the quantitative detection of two inflammatory protein biomarkers, CRP and IL-6. MATERIALS & METHODS: The electrode interface was characterized using ζ-potential and Fourier transform infrared spectroscopy. Detection of biomarkers was demonstrated by measuring impedance changes associated with the dose concentrations of the two biomarkers. A proof of feasibility of point-of-care implementation of the biosensor was demonstrated using a portable electronics platform. RESULTS & CONCLUSION: Limit of detection of 1 pg/ml was achieved for CRP and IL-6 in human urine and synthetic urine buffers. The developed portable hardware demonstrated close correlation with benchtop equipment results.

Electrical double layer modulation of hybrid room temperature ionic liquid/aqueous buffer interface for enhanced sweat based biosensing.

We have investigated the role of kosmotropic anionic moieties and chaotropic cationic moieties of room temperature hydrophilic ionic liquids in enhancing the biosensing performance of affinity based immunochemical biosensors in human sweat. Two ionic liquids, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM[BF4]) and choline dihydrogen phosphate (Choline[DHP]) were investigated in this study with Choline[DHP] being more kosmotropic in nature having a more protein stabilizing effect based on the hofmeister series. Non-faradaic interfacial charge transfer has been employed as the mechanism for evaluating the formation and the biosensing of capture probe antibodies in room temperature ionic liquids (RTILs)/aqueous human sweat interface. The charge of the ionic moieties were utilized to form compact electrical double layers around the antibodies for enhancing the stability of the antibody capture probes, which was evaluated through zeta potential measurements. The zeta potential measurements indicated stability of antibodies due to electrostatic repulsion of the RTIL charged moieties encompassing the antibodies, thus preventing any aggregation. Here, we report for the first time of non-faradaic electrochemical impedance spectroscopy equivalent circuit model analysis for analyzing and interpreting affinity based biosensing at hybrid electrode/ionic liquid-aqueous sweat buffer interface guided by the choice of the ionic liquid. Interleukin-6 (IL-6) and cortisol two commonly occurring biomarkers in human sweat were evaluated using this method. The limit of detection (LOD) obtained using both ionic liquids for IL-6 was 0.2 pg mL-1 with cross-reactivity studies indicating better performance of IL-6 detection using Choline[DHP] and no response to cross-reactive molecule. The LOD of 0.1 ng/mL was achieved for cortisol and the cross-reactivity studies indicated that cortisol antibody in BMIM[BF4] did not show any signal response to cross-reactive molecules. Furthermore, improved sensitivity and LOD was achieved using ionic liquids as compared to capture probes in aqueous buffer.

Sub-picomolar label-free detection of thrombin using electrochemical impedance spectroscopy of aptamer-functionalized MoS2.

An ultrasensitive aptasensor for the label free non-faradaic detection of thrombin has been demonstrated on molybdenum disulphide (MoS2) nanosheets. These nanosheets were physiochemically immobilized onto a silicon micro-electrode platform. Thrombin detection was achieved through the charge modulation of the electrical double layer due to the specific and dose dependent binding of thrombin to the surface of thiol terminated ssDNA aptamer functionalized MoS2 nanosheets. Electrical double layer charge modulation associated with thrombin binding was characterized using electrochemical impedance spectroscopy. Dynamic light scattering was also used to confirm the dose dependent behavior. ATR-FTIR spectroscopy and XPS analysis were independently used to validate the functionalization of the ssDNA aptamer onto MoS2 nanosheets. ssDNA aptamer functionalized molybdenum disulfide (MoS2) for selective and specific capture of thrombin was demonstrated both in phosphate buffered saline (PBS) and human serum. The optimized immunoassay enabled the detection of thrombin ranging from 267 fM to 267 pM in phosphate buffer. The limit of detection of 53 pM and the linear dynamic range of detection of thrombin ranged from 53 to 854 pM in human serum. The rapid response time for the electrochemical impedance spectroscopy signal makes it an attractive option for the real-time detection of thrombin based point-of-care diagnostic devices.

A new paradigm in sweat based wearable diagnostics biosensors using Room Temperature Ionic Liquids (RTILs).

Successful commercialization of wearable diagnostic sensors necessitates stability in detection of analytes over prolonged and continuous exposure to sweat. Challenges are primarily in ensuring target disease specific small analytes (i.e. metabolites, proteins, etc.) stability in complex sweat buffer with varying pH levels and composition over time. We present a facile approach to address these challenges using RTILs with antibody functionalized sensors on nanoporous, flexible polymer membranes. Temporal studies were performed using both infrared spectroscopic, dynamic light scattering, and impedimetric spectroscopy to demonstrate stability in detection of analytes, Interleukin-6 (IL-6) and Cortisol, from human sweat in RTILs. Temporal stability in sensor performance was performed as follows: (a) detection of target analytes after 0, 24, 48, 96, and 168 hours post-antibody sensor functionalization; and (b) continuous detection of target analytes post-antibody sensor functionalization. Limit of detection of IL-6 in human sweat was 0.2 pg/mL for 0-24 hours and 2 pg/mL for 24-48 hours post-antibody sensor functionalization. Continuous detection of IL-6 over 0.2-200 pg/mL in human sweat was demonstrated for a period of 10 hours post-antibody sensor functionalization. Furthermore, combinatorial detection of IL-6 and Cortisol in human sweat was established with minimal cross-talk for 0-48 hours post-antibody sensor functionalization.