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Recently, flexible capacitive pressure sensors have received significant attention in the field of wearable electronics. The high sensitivity over a wide linear range combined with long-term durability is a critical requirement for the fabrication of reliable pressure sensors for versatile applications. Herein, we propose a special approach to enhance the sensitivity and linearity range of a capacitive pressure sensor by fabricating a hybrid ionic nanofibrous membrane as a sensing layer composed of Ti

Advancement of sensing systems, soft robotics, and point-of-care testing requires the development of highly efficient, scalable, and cost-effective physical sensors with competitive and attractive ...

A nature-inspired special structure of bismuth is newly presented as Zn ion sensing layer for high-performance electrochemical heavy metal detection sensor applications. The rime ice-like bismuth (RIBi) has been synthesized using an easy ex situ electrodeposition method on the surface of a flexible graphene-based electrode. The flexible graphene-based electrode was fabricated via simple laser-writing and substrate-transfer techniques. The Zn ion sensing performance of the proposed heavy metal sensor was evaluated by square wave anodic stripping voltammetry after investigating the effects of several parameters, such as preconcentration potential, preconcentration time, and pH of acetate buffer. The proposed RIBi-based heavy metal sensor demonstrated a good linear relationship between concentration and current in the range 100–1600 ppb Zn ions with an acceptable sensitivity of 106 nA/ppb·cm2. The result met the requirements in terms of common human perspiration levels (the average Zn ion concentration in perspiration is 800 ppb). In addition, the heavy metal sensor response to Zn ions was successfully performed in human perspiration samples as well, and the results were consistent with those measured by atomic absorption spectroscopy. Besides, the fabricated Zn ion sensor exhibited excellent selectivity, repeatability, and flexibility. Finally, a PANI-LIG-based pH sensor (measurement range: pH 4–7) was also integrated with the Zn ion sensor to form a single chip hybrid sensor. These results may provide a great possibility for the use of the proposed flexible sensor to realize wearable perspiration-based healthcare systems.

Recent advances in non-invasive epidermal wearable sensors have included various electronic sensors to monitor either physiological signs such as heart rate, skin temperature, and respiration rate, or metabolites. Nevertheless, most of them have focused only on a single electrophysiological measurement at a time, which greatly inhibits the calibration of various biological signals and diagnostic facilities. Herein, we have newly developed an epidermal electrochemical-electrophysiological hybrid patch for precise glucose detecting with pH and temperature correction as well as simultaneously monitoring of electrocardiogram (ECG). The fabricated epidermal hybrid patch has overcome the inconvenience of mandatory attachment of multiple patches on the human body owing to the full integration of various electrochemical and electrophysiological sensors on the same flexible printed circuit board toward advanced glycemic control and continuous ECG monitoring for effective management of chronic diseases.

In this work, a highly conductive treated PEDOT:PSS (poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate)) layer was utilized for the transduction layer of an ion-selective flexible electrode (ISFE) and well-deposited on the carbon paste and polyethylene terephthalate (PET) substrate. The PEDOT:PSS was also treated by a co-solvent of ethylene glycol (EG) using bath-sonication to enhance electrical and electrochemical characteristics and finally coated with Ca2+ selective membrane cocktail. Electrochemical properties exhibited that EG treated PEDOT:PSS drop-casted ISFE achieves improved charge transport with remarkable electric conductivity enhancement. The fabricated Ca2+-ISFE was demonstrated a near-Nernst response of 31.9 mV/decade between 10-4 and 10-1 M with the rapid response (< 20 seconds). Moreover, the EG-treated PEDOT:PSS based ISFE proved significant potential stability with a negligible potential drift of 0.34 mV/min, compared to pristine PEDOT:PSS based ISFE (0.56 mV/min). Based on these analyses, it can be expected that the EG-treated PEDOT:PSS will pave the way for other bio-chemical compounds monitoring.

In this study, an ultra-high sensitive, flexible, wireless, battery-free, and fully integrated (no external analysis equipment) electrochemical sensing patch system, including a microfluidic-sweat collecting unit, was newly developed for the on-site monitoring of the [K+] concentration in human sweat. Multiwalled carbon nanotube (MWCNT) and MXene-Ti3C2TX based hybrid multi-dimensional networks were applied to obtain a high surface activation area and faster charge transfer rate, strongly adsorbing the valinomycin membrane to protect the ionophore for effective transshipment and immobilization of the [K+]. Furthermore, the controllable porosity of carbon-based materials can accelerate the kinetic process of ion diffusion. This hybrid nanonetwork structure effectively enhanced electrochemical stability and sensitivity, addressing the noise and signal drifting problems experienced with low concentration detection. The fabricated sensor exhibited a high ion concentration sensitivity of 63 mV/dec with excellent selectivity, amplified to 173 mV/dec with the integrated amplification system. The Near Field Communication (NFC) is used to transmit measurements to a smartphone wirelessly. A microfluidic channel was integrated with the electrochemical sensor patch to efficiently collect sweat on the human skin surface and mitigate the sensor surface contamination problem. Furthermore, the developed sensing patch can also be applied to other biomarkers on-site detection after modifying the working electrode with the corresponding selective membranes.

In this paper, we have newly designed and fabricated horseshoe-shaped skin attachable minimally invasive wearable patch with implantable microneedle biosensor for continuous glucose monitoring in interstitial fluid (ISF). In order to reduce the effects of skin movement or external stress on the fabricated sensor, we considered both hardness and stretchability of the microneedle and appropriate material. The fabricated microneedle biosensor exhibited an excellent amperometric response to glucose molecules as much as $128.65\ \mu \mathrm{A}/\text{mM}\cdot \text{cm}^{2}$ and ultra-low limit of detection (LOD) as $0.198\ \mu \mathrm{M}$ . Furthermore, the linear range of the sensor was indicated up to 30 mM in two glucose concentration regions.

In this research, we have newly developed a highperformance conductive hydrogel hybrid sensor based on polyacrylamide (PAAm) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) for simultaneous detection of pressure and temperature which applies to artificial neural and skin system. The proposed sensor can detect the pressure through the variation of electrical double layer (EDL) capacitance between two electrodes and hydrogel containing PEDOT:PSS as well as the relative temperature difference between the top and bottom electrodes by measuring the voltage caused by Seebeck effect simultaneously. Especially, the measured sensitivity of the temperatures variation was as much as $603\ \mu \mathrm{V}/\mathrm{K}$ in varying temperature of 0 to 30 K, and it was observed that the ammonium persulfate ions in the hydrogel contributed to the enhancement of Seebeck coefficient. The sensitivity of the pressure was indicated to 0.52 kPa−1 and 0.07 kPa−1 in the low range from 0 to 9.7 kPa and the high range from 15.2 kPa to 97 kPa, respectively.

We report very small shape-factored microstructures developed via a simple and cost-effective approach, enabling a high degree of sensitivity in a low-pressure regime (

Fast advancement of dry biopotential electrode has driven to the reduction of using Ag/AgCl (wet electrode). There is a necessity for development of flexible and eco-friendly micro-structured (MSE) dry biopotential electrode utilizing biodegradable and non-toxic materials for a better life and sustainable future. It is very difficult to create micro-structure without using any solvents or high-end equipment. Here, a novel micro-structured electrode coated with Ti/Au film is fabricated using a sandpaper template and is proposed for biopotential signal monitoring applications. We used sandpaper, which is recyclable and biodegradable. The proposed MSE is a flexible, stretchable, and biocompatible dry micro-structured electrode. The sheet resistance of the proposed MSE is 2.5 Ω/sq. The area of MSE was only 4 cm × 4 cm (l × w), and the sweat of the epidermis layer of human skin could be utilized as the electrolyte for the flexible MSE during the electrocardiography (ECG) and electromyography (EMG) recording. The fabricated MSE was enough thin and flexible to be well attached onto the skin. The contact impedance of the flexible MSE was stable and suitable for long-term biopotential recording. The main advantage of the electrodes is simple fabrication, which can be used in wearable electrode systems to monitor human health. The results of the experiment show that the proposed electrode can operate in dry conditions when the subject is resting, and it shows fewer motion artifacts during movement.

In this paper, a trimetallic Pd@Au@Pt nanocomposites platform on -COOH terminated reduced graphene oxide (COOH-rGO) was newly developed for sensing carcinoembryonic antigen (CEA) and prostate specific antigen (PSA) biomarkers. Trimetallic electro-catalytic surfaces were prepared by the electrodeposition of noble metals (Pd@Au@Pt) nanoparticles on COOH- rGO. After EDC/NHS treatment, the anti-CEA and anti-PSA were immobilized separately on two different platforms. Under optimized conditions, the platforms were analyzed by cyclic voltammetry and differential pulse voltammetry (DPV). The platform shows good electro catalytic activity, high sensitivity, and acceptable stability for sensing CEA and PSA biomarkers. For CEA, we obtained sensitivity of 0.099 ± 0.007 µA ng−1 ml, wide linear range from 12 pg ml−1 to 85 ng ml−1 and a limit of detection (LOD) of 8 pg ml−1, while for PSA sensitivity is 0.267 ± 0.02 µA ng −1 ml, wide linear range from 3 pg ml−1 to 60 ng ml−1 and LOD of 2 pg ml−1. The validation of the platform was observed through standard addition method. Thus, the sensing platform could be used for the point of care detection of CEA and PSA.

Here, an ultrasensitive enzymatic electrochemical L-glutamate sensor was successfully developed and characterized using carboxyl terminated reduce graphene oxide (Crbxl-RGO) and Pt nanoparticles as a supporting and catalyzing medium. Crbxl-RGO was drop casted on the Au substrate and Pt nanoparticles were electrodeposited on Crbxl-RGO/Au modified substrate. L-Glutamate dehydrogenase-chitosan (GLDH-chit) composite was immobilized on the sensing area using EDC/NHS bonding material treatment. The physical characteristic of the sensor matrix was monitored through field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS), Energy dispersive spectroscopy (EDX) and analytical characterization was analyzed by using cyclic voltammetry (CV), electrochemical impedance spectroscopy and differential pulse voltammetry (DPV). Under optimized condition the sensor showed sensitivity of 973 ± 4 μA/mMcm2, wide linear range 0.004–0.9 mM and limit of detection 0.1 μM that indicates promising approach for detecting L-glutamate.

Due to the insufficiency of binding sites for the immobilized recognition biomolecules on the immunosensing platform, cancer detection becomes challenging. Whereas, the degradation of black phosphorene (BP) in the presence of the environmental factors becomes a concerning issue for use in electrochemical sensing. In this study, BP is successfully encapsulated by polyallylamine (PAMI) to increase its stability as well as to enhance its electrochemical performance. The successful encapsulation of BP is ensured through X-ray Photoelectron spectroscopy and Raman spectroscopy, whereas the stability of black phosphorus is ensured by Zeta potential measurements and cyclic voltammetry tests. The developed BP-PAMI composite showed high stability in the ambient environment and exhibited improved electrochemical performances. The impedimetric immunosensor was developed on a BP-PAMI modified laser burned graphene (LBG) to detect interleukin-6 biomarkers using electrochemical impedance spectroscopy (EIS). Under the optimized parameters, the fabricated immunosensor demonstrated a wide linear range of 0.003-75 ng/mL, limit of detection (LOD) of 1 pg/mL. Based on the experimental analysis, the developed sensing strategy can be employed as an easy, disposable, cost-effective and highly selective point-of-care cancer detection. In addition, the developed technique can be applied broadly for detecting other biomarkers after treating with suitable biomolecules.

In this study, a flexible and highly sensitive capacitive pressure sensor has been fabricated by coating a microporous polydimethylsiloxane (PDMS) elastomeric dielectric onto conductive fibers. Conductive fibers were prepared by depositing silver nanoparticles (AgNPs) in poly(styrene-block-butadiene-styrene) (SBS) polymer on the surface of Twaron fibers. The configuration obtained by cross-stacking of two microporous PDMS-coated fibers imitates a capacitive sensor, which responds to compressive stress by increasing the contact area and decreasing the separation between the fiber electrodes. Moreover, the gradual closure of micropores under pressure increases the effective permittivity of the dielectric, thereby enhancing the sensitivity of the sensor. A relatively high sensitivity of 0.278 kPa−1 for a low pressure region (

We propose a strategy for the fabrication of a highly sensitive and reliable strain sensor based on MoS 2 -decorated laser-scribed graphene (MDS-LSG) for flexible and wearable electronics. The laser-thinning of multilayered MoS 2 coated on commercial polyimide (PI) film using a CO 2 infrared laser exhibits three-dimensional hierarchical porous graphene network decorated with MoS 2 enabling superior electrical properties. By exploiting the advantage of high mobility of graphene and strain-dependent property of MoS 2 , the technique offers a rapid route towards a simple, facile and scalable approach for the fabrication of high-performance strain sensor. As fabricated sensor endows high sensitivity (gauge factor, GF ~290), wide working range, fast response time and stability over 7000 cycles. Finally, we successfully apply the sensor’s performance for subtle deformation of the skin (wrist pulse) and various human-motion detections.

Here, we newly proposed laser-induced graphene (LIG) stamp to transfer directly it onto Au substrate from polyimide (PI) substrate. The stamped-LIG was strongly adhered by van der waals force with Au. Unlike conventional transferred LIG electrode composed of totally carbon-based material, the proposed LIG stamp was formed with several layers of carbon on top of highly conductive Au electrode resulting in the improvement electrical and electrochemical properties. In addition, we successfully electrodeposited Pt nanoparticles (PtNPs) as catalytic material on the surface of the stamped LIG for electrochemical biosensor applications, which also resulted in highly improved redox characteristics. We characterized and compared various materials such as Au, Au/PtNPs, Au/stamped-LIG, and Au/stamped-LIG/PtNPs through cyclic voltammetry and amperometric measurement. As a result, the electrical and electrochemical redox properties were much improved. Through amperometric measurement, the developed electrochemical sensor electrode indicated $69.33\ \mu \mathrm{A}/\text{mM}\cdot \text{cm}^{2}$ of the sensitivity at hydrogen peroxide concentration of 10 to $3760\ \mu \mathrm{M}$ and limit of detection of $2.2\ \mu \mathrm{M}$ , respectively.

The rapid development of pressure sensors with distinct functionalities, notably, with increased sensitivity, fast response time, conformability, and a high degree of deformability, has increased the demand for wearable electronics. In particular, pressure sensors with an excellent sensitivity in the low-pressure range (2 kPa) and a large working range simultaneously are strongly demanded for practical applications in wearable electronics. Here, we demonstrate an emerging class of solid polymer electrolyte obtained by incorporating a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with poly(vinylidene fluoride- co-hexafluoropropylene) as a high-capacitance dielectric layer for interfacial capacitive pressure sensing applications. The solid polymer electrolyte exhibits a very high interfacial capacitance by virtue of mobile ions that serve as an electrical double layer in response to an electric field. The randomly distributed microstructures created on the solid electrolyte help the material to elastically deform under pressure. Moreover, the interfacial capacitance is improved by utilizing a highly conductive porous percolated network of silver nanowires reinforced with poly(dimethylsiloxane) as the electrodes. An ultrahigh-pressure sensitivity of 131.5 kPa

Three-dimensional (3D) porous laser-guided graphene (LGG) electrodes on elastomeric substrates are of great significance for developing flexible functional electronics. However, the high sheet resistance and poor mechanical properties of LGG sheets obstruct their full exploitation as electrode materials. Herein, we applied 2D MXene nanosheets to functionalize 3D LGG sheets via a C–O–Ti covalent crosslink to obtain an LGG-MXene hybrid scaffold exhibited high conductivity and improved electrochemistry with fast heterogeneous electron transfer (HET) rate due to the synergistic effect between LGG and MXene. Then we transferred the obtained hybrid scaffold onto PDMS to engineer a smart, flexible, and stretchable multifunctional sensors-integrated wound bandage capable of assessing uric acid (UA), pH, and temperature at the wound site. The integrated UA sensor exhibited a rapid response toward UA in an extended wide range of 50–1200 μM with a high sensitivity of 422.5 μA mM−1 cm−2 and an ultralow detection limit of 50 μM. Additionally, the pH sensor demonstrated a linear Nernstian response (R2 = 0.998) with a high sensitivity of −57.03 mV pH−1 in the wound relevant pH range of 4–9. The temperature sensor exhibited a fast and stable linear resistive response to the temperature variations in the physiological range of 25–50 °C with an excellent sensitivity and correlation coefficient of 0.09% ⁰C−1 and 0.999, respectively. We anticipate that this stretchable and flexible smart bandage could revolutionize wound care management and have profound impacts on the therapeutic outcomes.

We developed a new patch-shaped enzyme free biosensor using a micro-needle array with Pt black sensing electrode layer for painless continuous glucose monitoring applications. We fabricated the micro-needle array using a bulk micromachining technique and commercial stainless steel 316L grade substrate. Pt black and Ag/AgCl were then electroplated on the tip of each micro-needle as working and counter/reference electrodes of the sensor, respectively. The fabricated micro-needle was 650 μm high and 150 μm wide. We used 48 and 24 micro-needles for the working electrode and counter/reference electrode, respectively. The measured sensitivity was 1.62 μA mM −1 with high linearity of 0.9939, and was obtained within 13 sec, in glucose concentrations ranging up to 36 mM. The biosensor also exhibited a low detection limit of 50 μM. We tested the sensor under PBS solution over a period of 6 days. Then we partially inserted the sensor into a rabbit, to monitor the interstitial glucose level. We then induced change of interstitial glucose concentration by oral glucose tolerance test. Although we expected the sensor to perform for more than 6 days, it performed for just 4 days as a sensor, due to bio fouling.

Controlled deposition of 2D multilayered nanomaterials onto different electrodes to design a highly sensitive biosensing platform utilizing their active inherent electrochemistry is extremely challenging. Herein, a green, facile, and cost-effective one-pot deposition mechanism of 2D MXene-Ti3C2Tx nanosheets (MXNSs) onto conductive electrodes within few minutes via electroplating (termed electroMXenition) is reported for the first time. The redox reaction in the colloidal MXNS solution under the effect of a constant applied potential generates an electric field, which drives the nanoparticles toward a specific electrode interface such that they are cathodically electroplated. A task-specific ionic liquid, that is, 4-amino-1-(4-formyl-benzyl) pyridinium bromide (AFBPB), is exploited as a multiplex host arena for the substantial immobilization of MXNSs and covalent binding of antibodies. A miniaturized, single-masked gold dual interdigitated microelectrode (DIDμE) is microfabricated and presented by investigating the benefit of AFBPB coated on MXNSs. The resulting MXNSs-AFBPB-film-modified DIDμE biosensor exhibited a 7× higher redox current than bare electrodes owing to the uniform deposition. Using Apo-A1 and NMP 22 as model bladder cancer analytes, this newly developed dual immunosensor demonstrated precise and large linear ranges over five orders of significance with limit of detection values as low as 0.3 and 0.7 pg mL-1, respectively.

The patterned LIG flakes are generally not interconnected due to the line gap of the laser ray, leading to lower uniform conductivity and fragile graphene. Thus, the fabrication of a highly conductive and mechanically robust LIG-based biosensing platform remains challenging. In this study, the fabrication of a flexible electrochemical biosensor is reported based on poly (3, 4-ethylene dioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) modified 3-dimensional (3D) stable porous laser-induced graphene (LIG) for the detection of glucose and pH. PEDOT:PSS was spray-coated on the LIG to improve electrode robustness and deliver uniform electrical conductivity. The as-prepared PEDOT:PSS modified LIG (PP/LIG) was characterized using field-emission scanning electron microscopy (FESEM), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). Platinum and palladium nanoparticles (Pt@Pd) were successfully electrodeposited on PP/LIG, markedly enhancing the electrocatalytic activity for glucose detection. The fabricated biosensor exhibited an excellent amperometric response to glucose with a wide linear range of 10 μM − 9.2 mM, a high sensitivity of 247.3 μAmM−1cm−2, and a low detection limit (LOD) of 3 μM, with high selectivity. In addition, the pH sensor was functionalized by the polyaniline (PANI) on PP/LIG, and it also exhibited excellent potentiometric response with a high sensitivity of 75.06 mV/pH in the linear range of pH 4 − 7. Ultimately, the feasibility of the biosensor was confirmed by the analysis of human perspiration collected during physical exercise. This approach validates the utility of the novel fabrication procedure, and the potential of the LIG-conductive polymer composite for biosensing applications.

Porous laser-induced graphene (LIG) is an attractive and promising carbon material for electrochemical applications because it can immobilize various proteins, such as enzymes, antibodies, and receptors. However, poor inherent electrical properties caused by low surface conductivity is still a critical drawback for various applications. Here, we have proposed a surface modification method for the LIG electrode using acetic acid treatment via facile and practicable dipping technique. This simple acetic acid treatment dramatically increased the ratio of carbon-carbon bonds which effectively increased conductivity and decreased sheet resistance. In other words, acetic acid additionally reduced carbohydrate functional groups. Importantly, these unique properties also facilitated the stable and uniform dispersion of highly catalytic Pt nanoparticles (PtNPs) on LIG by avoiding the concentration of electric field on nanoparticles that can cause aggregation during electrodeposition. Finally, chitosan-glucose oxidase (GOx) composite was successfully immobilized onto the LIG/PtNPs electrode to fabricate a sweat glucose biosensor. The as-prepared LIG/PtNPs electrode exhibited a high sensitivity of 4.622 μA/mM as well as an ultra-low limit of detection (signal to noise ratio is 3) which was less than 300 nM and dynamic linear range up to 2.1 mM. Furthermore, we tested the variation of blood glucose level before and after meal using the amperometric response of the sensor which demonstrates the commercial potential of this unique sweat glucose biosensor.

Electroplating of nanoporous Pt (nPt) induces an extremely strong tensile stress, which results in the exfoliation of nPt on flexible polymer substrate despite plasma treatment to improve adhesion. Here, we overcame this challenge by modifying flexible stainless-steel, and developed wearable, robust, flexible, and non-enzymatic continuous glucose monitoring system. The flexible stainless-steel was highly effective in improving the adhesion between the metal layer and substrate. The developed wireless system included electrochemical analysis circuits, a microcontroller unit, and a wireless communication module. Finally, we evaluated the continuous glucose monitoring system through two animal testing, by implanting into subcutaneous tissue and measuring interstitial fluid (ISF) glucose values at 5-15-min intervals. Comparison of the measured ISF glucose with blood glucose determined by the Clarke error grid analysis showed that 82.76% of the measured glucose was within zone A. Furthermore, the wearable glucose sensor exhibited bio-compatible to implant through various bio-compatibility tests.

In this paper, semi-implantable and highly miniaturized needle-shaped biosensor was newly developed for painless and continuous glucose monitoring. Three electrochemical electrodes (nanoporous Pt and Ag/AgCl for working, counter, and reference electrodes, respectively) were micro-fabricated on a flexible polyimide film using electroplating technique, diced, and firmly wrapped onto a medical PTFE catheter by using silicone adhesive. The fabricated bio-sensor was much improved in stability and reliability because the PTFE catheter was used as the supporting structure of flexible sensor. The fabricated sensor could also be easily delivered to subcutaneous tissue by using stainless steel guide needle through minimally invasive tool without surgery. In addition, the catheter can also simultaneously be sued as a tool for drug delivery. Diameter and total length of the polyimide/PTFE needle is 900 μm and 500 mm, respectively. The fabricated bio-sensor indicated 415 nA/mM of sensitivity and 0.996 of R-square for glucose and good selectivity for interfering reagents. In addition, in-vivo measurement was successfully demonstrated in the dynamic glucose variation during 2 hours.