Direct Laser Writing of the Porous Graphene Foam for Multiplexed Electrochemical Sweat Sensors

pH effects on graphene foam capacitance induced by adsorption of 1-pyrenemethylamine

The interfacial capacitance of graphene foam electrodes (Gii-Sens) in contact to aqueous media (determined by electrochemical impedance spectroscopy) is strongly affected by adsorption of 1-pyrenemethylamine (PMA). An order of magnitude increase in capacitance upon adsorption is ascribed predominantly to the quantum capacitance contribution (i.e. changes in the electronic density of states in graphene layers) in response to the cationic adsorbent. A change in capacitance (reversible) is observed as a function of pH. Although likely to be linked to the amine protonation, the change in measured capacitance occurs over a wide range of pH values (approx. linear from pH 2 to pH 12) and could provide a diagnostic capacitance-based tool for pH. Exploratory measurements in pure human serum (with pH adjustment) suggest that the capacitance effect is specific to protons and correlated to pH even in complex sensing media. However, the response of the graphene foam electrode surface is sensitive to the preparation and storage conditions and currently not fully understood.

Wearable MXene-enhanced organic Bio-FET paper patch for glucose detection in sweat with pH and temperature calibration

This paper proposes the design of organic Bio-FET sensors using paper as a substrate. Three different wearable biosensors have been engineered for the non-invasive monitoring of sweat biomarkers. The proposed sensors, which have a field-effect transistor (FET) structure, contribute to an array that is flexible, bendable, affordable, disposable, and biocompatible. The approach of drawing Organic FETs (OFETs) on paper using a paintbrush could successfully make cost-effective sweat biochemical sensors (glucose and pH Sensors) and biophysical sensors (temperature-sensor) which are versatile and sensors for real-time health monitoring. PDMS, PEDOT: PSS, and sensitive materials have been used as the oxide layer, source/drain electrodes, and the FET channel, respectively. The wearable glucose sensor utilizes a composite of copper oxide (CuO), carboxyl-functionalized multiwall carbon nanotubes (MWCNT-COOH), and Ti₃C₂ MXene (Ti₃C₂ MXene/CuO/MWCNT) as the channel material in its FET structure, enhancing its sensitivity and performance. Additionally, Ti3C2 MXene/MWCNT and Ti₃C₂ MXene/rGO/MWCNT composites were employed in the pH and temperature sensors, respectively, to enhance their functionality and performance. The proposed Bio-FETs are fabricated in three different designs: resistive, side-gated and back-gated structures, and their responses are compared and discussed. Continuous health monitoring is achieved through a fully integrated, disposable wireless device that combines glucose, pH, and temperature sensing. The fabricated Bio-FET exhibits high sensitivity and promising reproducibility, stability, and repeatability. To enhance precision, the proposed glucose sensor has been calibrated using real-time temperature and pH measurements.

Tuning Mn-MOF by Incorporating a Phthalocyanine Derivative as an Enzyme Mimic for Efficient EGFET-based Ascorbic Acid Detection

In this study, we present the effect of catalytic performance in Mn-MOF upon incorporating varied concentrations of phthalocyanine derivative (H2PcP8OH16) for ascorbic acid detection in an extended gate field-effect transistor (EGFET) configuration. The fabricated Mn-OM-MOF-2/CP electrode demonstrated notable selectivity toward ascorbic acid in physiological conditions of sweat, with a sensitivity of 71.375 μA·mM-1·cm-2, a response time of less than 6 s, and a linear range from 5 to 240 μM. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.26 and 0.78 μM, respectively. Remarkably, the prepared electrodes followed the Michaelis-Menten kinetics. Among them, the Mn-OM-MOF-2/CP electrode demonstrated the highest affinity for ascorbic acid, with a Km value of 0.142 mM. To gain deeper insights into the charge transfer mechanism during ascorbic acid interaction with Mn-OM-MOF-2/CP, we employed the scanning Kelvin probe (SKP) technique and conducted post-FTIR analysis to understand the sensing mechanism. Additionally, post-UV-visible (UV-vis) measurements were performed to explore how the incorporation of the phthalocyanine derivative enhances affinity. Additional studies using standard artificial sweat have confirmed the Mn-OM-MOF-2/CP electrode's good recovery. Overall, the results of the EGFET method demonstrated the suitability of the Mn-OM-MOF-2/CP electrode for rapid, noninvasive, single-use ascorbic acid detection in 1× phosphate buffer saline (1× PBS).

A surface modified laser-induced graphene based flexible biosensor for multiplexed sweat analysis

The growing popularity of electrochemical sensors featuring non-invasive biosensing technologies has generated significant enthusiasm for continuous monitoring of bodily fluid biomarkers, potentially aiding in the early detection of health issues in individuals. However, detection of multiple biomarkers in complex biofluids often necessitates a high-density array which creates a challenge in achieving cost-effective fabrication methods. To overcome this constraint, this work reports the fabrication of an electrochemical sensor utilizing a NiO-Ti3C2Tx MXene-modified flexible laser-induced graphene (LIG) electrode for the separate and concurrent analysis of ascorbic acid (AA), dopamine (DA), and uric acid (UA) in human sweat and also addresses the deficiencies in the existing state of the art by offering a cost-efficient and high-performance sensor that mitigates the degrading constraints of conventional LIG electrodes. Cyclic voltammetry and differential pulse voltammetry measurements reveals that the electrochemical properties of the modified electrode, attain a low detection limit and great sensitivity for the target biomarkers. The NiO-Ti3C2Tx/LIG sensor demonstrated enhanced electrocatalytic activity for the oxidation of ascorbic acid, dopamine, and uric acid, and proved useful for analysing these biomarkers in synthetic sweat samples. Under the optimized conditions, the LOD values were estimated to be 16, 1.97 and 0.78 μM for AA, DA and UA, respectively. The developed high-efficiency sensor holds significant promise for applications in flexible and wearable electronics for health monitoring.

Porous Core-Shell Yarn in Wearable Electrochemical Sensors for Real-Time Sweat Monitoring

Wearable sweat sensors have garnered substantial attention owing to their actual significance in the noninvasive and real-time monitoring of health conditions. However, it remains significantly challenging to efficiently construct a high-sensitivity sweat sensor with stable long-term sensing capability. Herein, we report an effective methodology based on wet-spinning/acid-etching technology to construct a porous core-shell yarn-based wearable electrochemical sensor. This strategy increases the inductive surface area of the ion concentration and facilitates signal transmission. As a result, the sensor demonstrates high sensitivity for monitoring K+ and pH in sweat (54.89 mV/dec for K+ and 40.2 mV/pH for pH). Furthermore, the sensors exhibit outstanding sensing stability, good long-term stability (>16 h), and satisfactory bending resistance (>1000 cycles). More importantly, the sensing yarns could be prepared at speeds of up to 500 m/h with a continuous preparation strategy, which enabled mass fabrication of the electrochemical sensor. Electrochemical sensors could serve as sweat-sensing systems for real-time health monitoring and hold great potential for the commercialization of health-detection technology.

Role of wearable electrochemical biosensors in monitoring renal function biomarkers in sweat: a review

Real-time detection of renal biomarkers is crucial for immediate and continuous monitoring of kidney function, facilitating early diagnosis and intervention in kidney-related disorders. This proactive approach enables timely adjustments in treatment plans, particularly in critical situations, and enhances overall patient care. Wearable devices emerge as a promising solution, enabling non-invasive and real-time data collection. This comprehensive review investigates numerous types of wearable sensors designed to detect kidney biomarkers in body fluids such as sweat. It critically evaluates the precision, dependability, and user-friendliness of these devices, contemplating their seamless integration into daily life for continuous health tracking. The review highlights the potential influence of wearable technology on individualized renal healthcare and its role in preventative medicine while also addressing challenges and future directions. The review's goal is to provide guidance to academics, healthcare professionals, and technologists working on wearable solutions for renal biomarker detection by compiling the body of current knowledge and advancements.

From Lab to Life: Self-Powered Sweat Sensors and Their Future in Personal Health Monitoring

The rapid development of wearable sweat sensors has demonstrated their potential for continuous, non-invasive disease diagnosis and health monitoring. Emerging energy harvesters capable of converting various environmental energy sources-biomechanical, thermal, biochemical, and solar-into electrical energy are revolutionizing power solutions for wearable devices. Based on self-powered technology, the integration of the energy harvesters with wearable sweat sensors can drive the device for biosensing, signal processing, and data transmission. As a result, self-powered sweat sensors are able to operate continuously without external power or charging, greatly facilitating the development of wearable electronics and personalized healthcare. This review focuses on the recent advances in self-powered sweat sensors for personalized healthcare, covering sweat sensors, energy harvesters, energy management, and applications. The review begins with the foundations of wearable sweat sensors, providing an overview of their detection methods, materials, and wearable devices. Then, the working mechanism, structure, and a characteristic of different types of energy harvesters are discussed. The features and challenges of different energy harvesters in energy supply and energy management of sweat sensors are emphasized. The review concludes with a look at the future prospects of self-powered sweat sensors, outlining the trajectory of the field and its potential to flourish.

Toward Integrated Multifunctional Laser-Induced Graphene-Based Skin-Like Flexible Sensor Systems

The burgeoning demands for health care and human-machine interfaces call for the next generation of multifunctional integrated sensor systems with facile fabrication processes and reliable performances. Laser-induced graphene (LIG) with highly tunable physical and chemical characteristics plays vital roles in developing versatile skin-like flexible or stretchable sensor systems. This Progress Report presents an in-depth overview of the latest advances in LIG-based techniques in the applications of flexible sensors. First, the merits of the LIG technique are highlighted especially as the building blocks for flexible sensors, followed by the description of various fabrication methods of LIG and its variants. Then, the focus is moved to diverse LIG-based flexible sensors, including physical sensors, chemical sensors, and electrophysiological sensors. Mechanisms and advantages of LIG in these scenarios are described in detail. Furthermore, various representative paradigms of integrated LIG-based sensor systems are presented to show the capabilities of LIG technique for multipurpose applications. The signal cross-talk issues are discussed with possible strategies. The LIG technology with versatile functionalities coupled with other fabrication strategies will enable high-performance integrated sensor systems for next-generation skin electronics.

Multifunctional laser-induced graphene circuits and laser-printed nanomaterials toward non-invasive human kidney function monitoring

Faced with the increasing prevalence of chronic kidney disease (CKD), portable monitoring of CKD-related biomarkers such as potassium ion (K+), creatinine (Cre), and lactic acid (Lac) levels in sweat has shown tremendous potential for early diagnosis. However, a rapidly manufacturable portable device integrating multiple CKD-related biomarker sensors for ease of sweat testing use has yet to be reported. Here, a portable electrochemical sensor integrated with multifunctional laser-induced graphene (LIG) circuits and laser-printed nanomaterials based working electrodes fabricated by fully automatic laser manufacturing is proposed for non-invasive human kidney function monitoring. The sensor comprises a two-electrode LIG circuit for K+ sensing, a three-electrode LIG circuit with a Kelvin compensating connection for Cre and Lac sensing, and a printed circuit board based portable electrochemical workstation. The working electrodes containing Cu and Cu2O nanoparticles fabricated by two-step laser printing show good sensitivity and selectivity toward Cre and Lac sensing. The sensor circuits are fabricated by generating a hydrophilic-hydrophobic interface on a patterned LIG through laser. This sensor recruited rapid laser manufacturing and integrated with multifunctional LIG circuits and laser-printed nanomaterials based working electrodes, which is a potential kidney function monitoring solution for healthy people and kidney disease patients.

Electrochemical detection of nitrofurazone using laser-engraved three-electrode graphene array

BACKGROUND

Nitrofurazone (NFZ) is a widely-used antimicrobial agent in aquaculture. The NFZ residue can be transmitted to humans through the food chain, and cause adverse health effects including carcinogenesis and teratogenesis. Until now, a number of modified electrodes have been developed for NFZ detection, however, there are some issues that need to be improved. For example, the reported detection sensitivity is relatively low, the modification procedure is complicated, and conventional three-electrode system is used. Therefore, it is quite important to develop new NFZ detection method with higher sensitivity, simplicity and practicality.

RESULTS

Herein, a kind of integrated three-electrode array consisted with porous graphene is easily prepared through laser engraving of commercial polyimide tape. Five kinds of graphene arrays were prepared at different laser power percentage (i.e. 30 %, 40 %, 50 %, 60 % and 70 %). It is found that their structure, morphology, fluffiness and porosity show great difference, consequently affecting the electrochemical performance of graphene arrays such as conductivity, active area and electron transfer ability. The engraved graphene array at 50 % laser power percentage (LIG-50 array) is superior owing to uniform 3D structure, abundant pores and high stability. More importantly, LIG-50 array is more active for NFZ oxidation, and significantly enhances the detection sensitivity. The linear range of LIG-50 sensor is from 0.2 to 8 μM, and the detection limit is 0.035 μM, which is successfully used in fish meat samples.

SIGNIFICANCE

A sensitive, portable and practical electrochemical sensor has been successfully developed for NFZ using laser-engraved graphene array. The demonstration using fish meat samples manifests this new sensor has good accuracy and great potential in application. This study could provide a new possibility for the design and fabrication of other high-performance electrochemical sensor for various applications in the future.

Ultraconformal Skin-Interfaced Sensing Platform for Motion Artifact-Free Monitoring

Capable of directly capturing various physiological signals from human skin, skin-interfaced bioelectronics has emerged as a promising option for human health monitoring. However, the accuracy and reliability of the measured signals can be greatly affected by body movements or skin deformations (e.g., stretching, wrinkling, and compression). This study presents an ultraconformal, motion artifact-free, and multifunctional skin bioelectronic sensing platform fabricated by a simple and user-friendly laser patterning approach for sensing high-quality human physiological data. The highly conductive membrane based on the room-temperature coalesced Ag/Cu@Cu core-shell nanoparticles in a mixed solution of polymers can partially dissolve and locally deform in the presence of water to form conformal contact with the skin. The resulting sensors to capture improved electrophysiological signals upon various skin deformations and other biophysical signals provide an effective means to monitor health conditions and create human-machine interfaces. The highly conductive and stretchable membrane can also be used as interconnects to connect commercial off-the-shelf chips to allow extended functionalities, and the proof-of-concept demonstration is highlighted in an integrated pulse oximeter. The easy-to-remove feature of the resulting device with water further allows the device to be applied on delicate skin, such as the infant and elderly.

Materials and Structural Designs toward Motion Artifact-Free Bioelectronics

Bioelectronics encompassing electronic components and circuits for accessing human information play a vital role in real-time and continuous monitoring of biophysiological signals of electrophysiology, mechanical physiology, and electrochemical physiology. However, mechanical noise, particularly motion artifacts, poses a significant challenge in accurately detecting and analyzing target signals. While software-based "postprocessing" methods and signal filtering techniques have been widely employed, challenges such as signal distortion, major requirement of accurate models for classification, power consumption, and data delay inevitably persist. This review presents an overview of noise reduction strategies in bioelectronics, focusing on reducing motion artifacts and improving the signal-to-noise ratio through hardware-based approaches such as "preprocessing". One of the main stress-avoiding strategies is reducing elastic mechanical energies applied to bioelectronics to prevent stress-induced motion artifacts. Various approaches including strain-compliance, strain-resistance, and stress-damping techniques using unique materials and structures have been explored. Future research should optimize materials and structure designs, establish stable processes and measurement methods, and develop techniques for selectively separating and processing overlapping noises. Ultimately, these advancements will contribute to the development of more reliable and effective bioelectronics for healthcare monitoring and diagnostics.

Recent advances in smart wearable sensors for continuous human health monitoring

In recent years, the biochemical and biological research areas have shown great interest in a smart wearable sensor because of its increasing prevalence and high potential to monitor human health in a non-invasive manner by continuous screening of biomarkers dispersed throughout the biological analytes, as well as real-time diagnostic tools and time-sensitive information compared to conventional hospital-centered system. These smart wearable sensors offer an innovative option for evaluating and investigating human health by incorporating a portion of recent advances in technology and engineering that can enhance real-time point-of-care-testing capabilities. Smart wearable sensors have emerged progressively with a mixture of multiplexed biosensing, microfluidic sampling, and data acquisition systems incorporated with flexible substrate and bodily attachments for enhanced wearability, portability, and reliability. There is a good chance that smart wearable sensors will be relevant to the early detection and diagnosis of disease management and control. Therefore, pioneering smart wearable sensors into reality seems extremely promising despite possible challenges in this cutting-edge technology for a better future in the healthcare domain. This review presents critical viewpoints on recent developments in wearable sensors in the upcoming smart digital health monitoring in real-time scenarios. In addition, there have been proactive discussions in recent years on materials selection, design optimization, efficient fabrication tools, and data processing units, as well as their continuous monitoring and tracking strategy with system-level integration such as internet-of-things, cyber-physical systems, and machine learning algorithms.

A wearable flexible electrochemical biosensor with CuNi-MOF@rGO modification for simultaneous detection of uric acid and dopamine in sweat

BACKGROUND

In health assessment and personalized medical services, accurate detection of biological markers such as dopamine (DA) and uric acid (UA) in sweat is crucial for providing valuable physiological information. However, there are challenges in detecting sweat biomarkers due to their low concentrations, variations in sweat yield among individuals, and the need for efficient sweat collection.

RESULTS

We synthesized CuNi-MOF@rGO as a high-activity electrocatalyst and investigated its feasibility and electrochemical mechanism for simultaneously detecting low-concentration biomarkers UA and DA. Interaction between the non-coordinating carboxylate group and the sample produces effective separation signals for DA and UA. The wearable biomimetic biosensor has a wide linear range of 1-500 μM, with a detection limit of 9.41 μM and sensitivity of 0.019 μA μM-1 cm-2 for DA, and 10-1000 μM, with a detection limit of 9.09 μM and sensitivity of 0.026 μA μM-1 cm-2 for UA. Thus, our sensor performs excellently in detecting low-concentration biomarkers. To improve sweat collection, we designed a microfluidic-controlled device with hydrophilic modification in the microchannel. Experimental results show optimal ink flow at 2% concentration. Overall, we developed an innovative and highly active electrocatalyst, successfully enabling simultaneous detection of low-concentration biomarkers UA and DA.

SIGNIFICANCE

This study provides a strategy for sweat analysis and health monitoring. Moreover, the sensor also showed good performance in detecting real sweat samples. This study has shown great potential in future advances in sweat analysis and health monitoring.

Porous Laser-Scribed Graphene Electrodes Modified with Zwitterionic Moieties: A Strategy for Antibiofouling and Low-Impedance Interfaces

Laser-scribed graphene electrodes (LSGEs) are promising platforms for the development of electrochemical biosensors for point-of-care settings and continuous monitoring and wearable applications. However, the frequent occurrence of biofouling drastically reduces the sensitivity and selectivity of these devices, hampering their sensing performance. Herein, we describe a versatile, low-impedance, and robust antibiofouling interface based on sulfobetaine-zwitterionic moieties. The interface induces the formation of a hydration layer and exerts electrostatic repulsion, protecting the electrode surface from the nonspecific adsorption of various biofouling agents. We demonstrate through electrochemical and microscopy techniques that the modified electrode exhibits outstanding antifouling properties, preserving more than 90% of the original signal after 24 h of exposure to bovine serum albumin protein, HeLa cells, and Escherichia coli bacteria. The promising performance of this antifouling strategy suggests that it is a viable option for prolonging the lifetime of LSGEs-based sensors when operating on complex biological systems.

A stretchable wearable sensor with dual working electrodes for reliable detection of uric acid in sweat

Wearable sweat sensors with stretch capabilities and robust performances are desired for continuous monitoring of human health, and it remains a challenge for sweat sensors to detect targets reliably in both static and dynamic states. Herein, a flexible sweat sensor was created using a cost-effective approach involving the utilization of three-dimensional graphene foam and polydimethylsiloxane (PDMS). The flexible electrochemical sensor was fabricated based on PDMS and Pt/Pd nanoparticles modified 3D graphene foam for the detection of uric acid in sweat. Pt/Pd nanoparticles were electrodeposited on the graphene foam to markedly enhance the electrocatalytic activity for uric acid detection. The graphene foam with excellent electrical property and high porosity, and PDMS with an ideal mechanical property endow the sensing device with high stretchability (tolerable strain up to 110 %), high sensitivity (0.87 μA μM-1 cm-2), and stability (remaining unchanged for more than 5000 cycles) for daily wear. To eliminate possible interferences, the wearable sensor was designed with dual working electrodes, and their response difference ensured reliable and accurate detection of targets. This strategy of constructing sweat sensors with dual working electrodes based on the flexible composite material represents a promising way for the development of robust wearable sensing devices.