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The dysregulation of the hormone cortisol is related to several pathological states, and its monitoring could help prevent severe stress, fatigue, and mental diseases. While wearable antibody-based biosensors could allow real-time and simple monitoring of antigens, an accurate and low-cost antibody-based cortisol detection through electro-chemical methods is considerably challenging due to its low concentration and the high ionic strength of real biofluids. Here, a label-free and fast sensor for cortisol detection is proposed based on antibody-coated organic electrochemical transistors. The developed devices show unprecedented high sensitivities of 50 mu A/dec for cortisol sensing in high-ionic-strength solutions with effective cortisol detection demonstrated with real human sweat. The sensing mechanism is analyzed through impedance spectroscopy and confirmed with electrical models. Compared to existing methods requiring bulky and expensive laboratory equipment, these wearable devices enable point-of-care cortisol detection in 5 min with direct sweat collection for personalized well-being monitoring.

We demonstrate fully inkjet-printed graphene-gated organic electrochemical transistors (OECTs) on polymeric foil for the enzymatic-based biosensing of glucose. The graphene-gated transistors exhibit better linearity, repeatability, and sensitivity than the printed silver-gated devices studied in this work and other types of printed devices previously reported in the literature. Their limit of detection is 100 nM with a normalized sensitivity of 20%/dec in the linear range of 30–5000 μM glucose concentrations, hence comparable with state-of-the-art OECT devices made by lithography processes on rigid substrates and with complex multilayer gates. Electrochemical impedance spectroscopy analysis shows that the improved sensitivity of the graphene-gated devices is related to a significant decrease of the charge-transfer resistance at the graphene electrode–electrolyte interface in the presence of glucose. The optimized sensing method and device configuration are also extended to the detection of the metabolite lactate. This study enables the development of fully printed high-performance enzymatic OECTs with graphene-sensing gates for multimetabolite sensing.

The shifting paradigm in clinical practice to remote healthcare underscores the need to develop novel biosensing modalities to rapidly and continuously assess digital and metabolic biomarkers. Sweat is a rich, heterogeneous biofluid that provides broad insights from the underlying dynamic metabolic activity of human physiology and enables new unobtrusive ways to monitor health status continuously. However, eccrine sweat is a relatively unexplored body fluid and has scant use in clinical practices. Here, we introduce a novel, easy-to-fabricate skin-interfaced sweat collection epidermal microfluidics, which enables multimodal analysis coupled with sponta-neous Raman scattering. The introduced wearable optofluidic patch is soft, fully flexible, can robustly interface with the skin without inducing chemical or physical irritation, and has minimal optical interfaces to the spectra of the analytes. The proposed detection approach by Raman scattering provides label-free chemical fingerprint information, enabling quantitative optical biosensing with high sensitivity and selectivity. As a great advantage, the proposed epidermal optofluidics and optical biosensing technique require neither plasmonic surface fabri-cation for surface Raman enhancement nor bulky ultrashort-pulsed lasers for coherent Raman enhancement, which are typically acquired for increasing Raman signal intensity and sensitivity of quantitative Raman analysis. Moreover, the developed system enables simultaneous sweat glucose, lactate, and urea concentration moni-toring. Furthermore, we show that biomolecule concentration monitoring with only one Raman shift simplifies spectroscopies instrumentation complexities and eliminates the requirement of advanced data processing methods to analyze the entire Raman spectra. Therefore, the proposed "single-band Raman analysis" coupled with developed epidermal optofluidics (epioptofluidics) shows accurate, repeatable, and stable sweat biomole-cule analysis and proposes instrument down-scale and miniaturization possibilities.

Solution processing is an attractive alternative to standard vacuum fabrication techniques for the large-area manufacturing of metal oxide (MOx)-based electron devices. Here, we report on thin-film...

Sweat is a body fluid produced by the sweat glands and is mainly composed of water. Sweat has various functions, the two main ones being the evacuation of heat produced by the body, especially during exercise, and the maintenance of skin homeostasis. Its production is highly variable and depends on many individual and environmental factors. Various diseases or conditions affect its proper functioning. This article presents an overview of the characteristics, the main health issues, and the current and potential applications related to sweat.La sueur est un fluide corporel produit par les glandes sudoripares et composé principalement d’eau. La transpiration remplit diverses fonctions, dont les principales sont l’évacuation de la chaleur produite par l’organisme, en particulier durant l’effort physique, et le maintien de l’homéostasie de la peau. Sa production est très variable quantitativement et qualitativement et dépend de multiples facteurs individuels et environnementaux. Différentes pathologies ou conditions altèrent son bon fonctionnement. Cet article présente un aperçu des caractéristiques, des principaux problèmes de santé et des applications actuelles et potentielles en lien avec la sueur.

This work describes a multisensing wearable platform for monitoring biomarkers in sweat during the practice of exercise. Five electrochemical sensors for pH, potassium, sodium, chloride, and lactate were implemented in a flexible patch approach, together with a paper microfluidic component, to continuously measure sweat composition. The sensors are fabricated with silicon technologies: ion selective field effect transistors (ISFETs) for pH and ionic species; and a gold thin-film microelectrode for lactate. The latter includes a polymeric membrane based on an electropolymerized polypyrroled structure, where all the biocomponents required for carrying out the lactate analyses are entrapped. The flexible patch is fabricated using hybrid integration technologies, including printed pads defined on a polyimide (Kapton®) substrate and wire bonding encapsulation of silicon chips. To fix and align the sensors to the flexible substrate, different laminated materials, such as polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), and silicone-based adhesive, were used. The first results show good performance of the sensors—ISFETS sensitivity between 54–59 mV dec−1 for ion ranges in sweat from 2 to 100 mM and lactate sensor sensitivity of −135 × 102 µA M−1 cm−2 for the range of 2–50 mM. The microfluidic platform has been tested in terms of adequate sensor wettability and rapid response during the time span of exercise activity (2 h) showing excellent results.

We report on organic electrochemical transistors (OECTs) with active channels made of hybrid inkjet-printed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and electropolymerized polyaniline (PANI) layers, exhibiting simultaneously improved electrical and pH sensing characteristics. The aniline electropolymerization with an optimum 6-cycles of cyclic voltammetry forms a porous PANI microstructured layer on the PEDOT:PSS film, resulting in high signal linearity and sensitivity of about 100 mV/pH and 20 μA/pH. The electrochemical impedance spectroscopy analysis demonstrates a 9X higher-change of interfacial capacitance when decreasing the pH with the hybrid PANI-PEDOT:PSS layer, in comparison to a bare PEDOT:PSS layer. The simple fabrication process and the high signal amplification pave the way for flexible and higher-performance pH-sensitive OECTs. These scalable devices, combined with ion-selective OECTs, would lead to a novel tool for multi-parametric analysis in different biofluids.

We are reporting a new approach of developing of soft triboelectric devices with improved conformability and scalability. Here, elastomers, namely, polydimethylsiloxane (PDMS), polyurethane (PU), were used as triboelectric layers, and their carbon based conductive elastomeric composites were implemented as electrodes since they offer greater softness and flexibility. Elastomers can also be coupled with the textile. Simple film casting technique, that provides fast and readily scalable route, was used to prepare low-cost multilayer structures. The technology was tested by preparing vertical-contact separation based triboelectric shoe-insole and stretchable triboelectric band. These examples were tested at low frequencies and at different load resistors for different gestures. The shoe-insole generated optimum rms power ( P r m s ) of 0.28 m W for load resistance ( R L ) of 150 M Ω for walking and 1.79 m W for the R L of 110 M Ω for running, respectively. Stretchable band, which can be applied on different body joints, was tested for the arm stretching motion that delivers the optimum P r m s of 9 μ W for the R L of 400 M Ω.

In-situ laser sintering can be used to locally sinter conductive inks in an uninterrupted process, enabling the embedding of printed electronics within 3D printed structures. In this work we apply a laser sintering method to create highly conductive silver features (50–125 $\mu\Omega$ cm) on top of and embedded within thermosensitive polymers printed by fused deposition modelling (FDM). We exploit this method to locally sinter silver inks deposited by direct ink writing (DIW) without external processing. Furthermore, we perform this while thermally preserving the 3D printed thermoplastic polyurethane (TPU) substrate which has a low glass transition temperature. By analyzing the effect of the process for both small and large shapes of conductive features, we show the importance of the transmitted power and sintering time. Lastly, we apply the developed method to produce flexible conductors and sensors. These include pressure and bending sensors that could find their way into cost-effective and customized soft electronic devices.

We report a light, flexible, and low-power poly(ionic liquid)/alumina composite CO2 sensor. We monitor the direct-current resistance changes as a function of CO2 concentration and relative humidity and demonstrate fast and reversible sensing kinetics. Moreover, on the basis of the alternating-current impedance measurements we propose a sensing mechanism related to proton conduction and gas diffusion. The findings presented herein will promote the development of organic/inorganic composite CO2 gas sensors. In the future, such sensors will be useful for numerous practical applications ranging from indoor air quality control to the monitoring of manufacturing processes.

This paper shows for the first time fully printed organic electrochemical transistors (OECTs) on flexible foil with an integrated gold gate. This gate can be selectively functionalized for bio-chemical sensing. The immobilization of antibodies on the printed gold gate for the detection of Escherchia coli (E. coli) cells is demonstrated herein. Concentrations equal to 10e7 CFU/ml and 10e5 CFU/ml have been detected using OECTs. Innovative claims include: (a) the use of inkjetprinted gold electrodes for biosensing; (b) the selective functionalization of the printed gold gate using antibodies; and (c) fast, sensitive detection of bacteria with a costeffective disposable platform.

With the development of our in-situ Laser Processing techniques we provide solutions to both planarize Fused Deposition Modeling (FDM) printed plastics and sintering of inks printed by Direct Ink Writing (DIW). Laser sintering enables fabrication of 3D printed functional and structural layers out of FDM printed thermoplastics and DIW printed conductive inks. As the sintering is in-situ, the sintered conductive layers, produced out of DIW printed silver inks, can be embedded into thermally sensitive FDM printed thermoplastics. In this fashion, vertical stacks out of these materials can be fabricated, in order to achieve capacitive and resistive mechanical transducers.

This paper presents a novel process for screen printed electrode fabrication, functionalization and integration in a polyethylene terephthalate (PET) fluidics system for electrochemical analysis. The innovative components utilized are: 1. 3D Through-Foil Vias (TFVs) for electrode connection, enabling simple liquid tight lamination of micro-fluidic channels; 2. Screen printed carbon and silver/silver chloride (Ag/AgCl) electrodes on 3D vias; and 3. PET fluidics with a fabrication process compatible with large-area manufacturing. A platform integrating an Ag/AgCl pseudo-reference and a glucose oxidase (GOx)-modified working electrode has been used for glucose sensing in the flexible fluidics system. Detection of small glucose concentrations between 100-400 mu M through Cyclic Voltammetry (CV) is shown. The sensor shows linear response and good sensitivity of similar to 0.8 mA/(mM cm(2)). By changing the electrode coatings, the same technology can potentially be used for detecting multiple analytes in biofluids.

In recent years, wearable epidermal sweat sensors have received extensive attention owing to their great potential to provide personalized information on the health status of individuals at the molecular level. For on‐demand medical analysis of sweat in sedentary conditions, a cost‐effective wearable integrated platform combining sweat stimulation, sampling, transport, and analysis is highly desirable. In this work, a printed iontophoretic system integrated into a microfluidic sensing platform, which combines sweat induction, collection, and real‐time analysis of sweat‐ions into a single patch for on‐demand sweat monitoring on human subjects in stationary conditions is reported. The incorporation of microfluidics features facilitates sweat sampling, collection, and guiding through capillary effect. The multisensing sensor array exhibits sensitivity close to Nernstian behavior for sodium, potassium, and pH. The correlation between the concentrations of ions measured with the sweat patch and with ion chromatography analysis demonstrates the applicability of the system for real‐time point‐of‐care monitoring of the health status of individuals. Furthermore, the sweat patch electronic interface with wireless transmission enables real‐time data monitoring and storage over a cloud platform. This printed iontophoretic‐integrated fluidic sweat patch provides a cost‐effective solution for the on‐demand analysis of sweat components for healthcare applications.

In this review paper, we summarise the status and trends in the research and development of printed sensors on foil substrates. Our focus includes sensor technologies that have some of their elements printed with a special interest for fully printed structures. The paper reviews the two large physical and chemical sensor families addressing different transduction principles. The paper concludes with a short notice on status and perspectives in the field with some words on the commercial maturity and trends of printed sensors on foil.

We propose an autonomous battery-less wireless sensor node that combines on a single printed circuit board an ultra-wideband (UWB) transmitter and its printed antenna, together with a piezoelectric cantilever and a solar cell array to harvest vibrations and light energy, respectively. The co-design of the solar cell array with the printed UWB antenna allows a prototype size of only 85x35 mm2, i.e., less than 65% of a credit card size. Low-cost is achieved by using inexpensive FR4 dual-layer substrate, standard-ceramic capacitors, and low-cost harvesters. The vibrational energy scavenger is fabricated at the wafer scale based on commercially available bulk polycrystalline Lead Zirconate Titanate (PZT), and the solar cells are fabricated by depositing amorphous-Si on 0.5 mm thick glass substrate. The cold-startup time of the demonstrator is about 42 min under indoor-ambient light conditions, and about 34 min under 700 mg vibrations at a frequency of 100 Hz. Once started, the sensor requires only 12.6 µW to allow a transmission rate of one temperature sensor readout every 34 s, thanks to the UWB transmitter that consumes only 206 pJ per pulse and a custom protocol with a reduced overhead.

Wearable sensors have garnered significant attention in recent years owing to their great promise in personalized health care and fitness monitoring [1]. Among these, recent advancements in wearable technology have enabled the development of sweat analysing sensors for in situ real-time and continuous monitoring of ions, alcohol and metabolites. Comparison and correlation between sweat and blood samples provided a further demonstration of the medical and physiological relevance of sweat [2]. Continuous monitoring of ions present in sweat (such as Na+, K+, Cl- and H+), can provide multiple information on our health status, such as for dehydration. One of the main requirement for facilitating real-time analysis is the development of a soft and flexible platform integrated with microfluidics that can be easily interfaced with the epidermis. This allows direct extraction of sweat and continuous sampling [3]. In this context, printing technologies emerge as a promising method, over the traditional multi-step photolithography process, for rapid, high throughput and cost-effective fabrication of configurable flexible sensing platforms [4]. Here we present a microfluidics-integrated potentiometric-based chemical sensing patch for multiplexed sweat ions analysis. Potentiometric sensor arrays on flexible foil are fabricated by the screen printing process, and assembled into a polymeric microfluidic platform through vertical stacking of thin adhesive layers. The microfluidic structure, which comprises of sweat sampling inlet, guiding channels and collecting reservoirs, are devised and fabricated by a programmed laser-cutter. The developed sweat patch facilitates simultaneous real-time detection of ions present in sweat, such as sodium (Na+), potassium (K+), chloride (Cl-), and pH. Our patches pave the way for simple and low-cost fabrication of wearable sweat sensors for point-of-care medical applications and personalized fitness monitoring. Figure 1(a) shows the optical image of the devised patch for sweat analysis. Flexible and transparent polymeric sheet was used as a substrate for creating microfluidic features and fabricating electrodes array for ion sensing. The microfluidic design, which includes sweat intake inlet, channel, reservoir and outlet, was fashioned by a software-based programmed laser cutter through 2D patterning of the polymeric film. Ion sensing electrodes array was fabricated by screen printing, which included printing of (i) silver layer for current collector, (ii) carbon layer as working electrode for Na+, K+, and pH sensing, and (iii) silver/silver chloride (Ag/AgCl) layer as both reference electrode and Cl- selective electrode. A polyurethane (PU) layer was screen printed as an insulator to encapsulate the electrodes in aqueous environments. Sodium and potassium ion selective electrodes (ISEs) were obtained by drop-casting Na+ and K+ ion-selective membranes (ISMs) onto their respective electrodes. The Ag/AgCl reference electrode was modified with a PVB membrane to get a stable reference. Polyaniline (PANI) was electrodeposited in order to obtain an ISE for pH sensing. The final 3D architecture of the sweat patch was obtained by stacking the sensing electrodes array layer and the microfluidic layer using laser patterned double-sided adhesive layers. A biocompatible medical-grade adhesive was used to mount the patch on the skin for real-time analysis. To evaluate the performance of microfluidic patch for sweat secretion and collection, the patch (without electrodes array) was attached to subjects forearm and used to collect sweat. Figure 1(b) shows the optical image of the real-time, in situ collection of sweat using our patch during indoor activities. This continuous real-time test on human subjects validates the capability of our fabricated patch for sampling and collecting sweat through capillary effect. The sensing characteristics of the fabricated ISEs were tested. Each ion-selective sensor response was characterized individually with their respective analyte solution. Figure 1(c) and (d) show the open circuit potential (OCP) responses of the potassium and sodium ISEs, measured in 2-32 mM potassium chloride solutions and 10-160 mM sodium chloride solutions, respectively. Both ISEs showed a fast response and exhibited a linear relationship between OCP and analyte concentration in sweat range with a Nernstian behaviour. Figure 1(e) and (f) show the representative OCP responses of the pH and chloride ISEs measured in McIlwaine’s buffer (pH 4-8) and 5-160 mM sodium chloride solutions, respectively. The pH sensor showed a stable output voltage with nearly Nernstian behaviour. However, the chloride sensor exhibited low sensitivity, and is being further improved by incorporating Cl- selective membrane to the Ag/AgCl electrode. Interference studies have shown that the fabricated ISEs are selective in physiologically relevant concentrations, as shown for K+ ISE in Figure 1(g). The performance of the fabricated patch demonstrates the capability for real-time multiplexed monitoring of sweat analytes for health care applications with as next text its sensing validation on people. [1] W. Gao, S. Emaminejad, H.Y. Nyein, S. Challa, K. Chen, A. Peck, H.M. Fahad, H. Ota, H. Shiraki, D. Kiriya, D.H. Lien, G.A. Brooks, R.W. Davis, A. Javay, Nature 529, 509- 514(2016); doi:10.1038/nature16521. [2] H.Y. Nyein, M. Bariya, L. Kivimäki, S. Uusitalo, T.S. Liaw, E. Jansson, C.H. Ahn CH, J.A. Hangasky, J. Zhao, Y. Lin, T. Happonen, M. Chao, C. Liedert, Y. Zhao, L. Tai, J. Hiltunen, A. Javay, Science Advance 5(8), 1-12(2019); DOI: 10.1126/sciadv.aaw9906. [3] J.R. Sempionatto, A. Martin, L. García-Carmona, A. Barfidokht, J.F. Kurniawan, J.R. Moreto, G. Tang,Shin, X. Liu, A. Escarpa, J. Wang, Electroanalysis 31(2), 239- 245(2019); DOI: 10.1002/elan.201800414. [4] M.Bariya, Z.Shahpar, H.Park, J.Sun, Y.Jung, W.Gao, H.Y..Nyein, T.S .Liaw, L.C.Tai , Q.P.Ngo, M.Chao,ACS nano12(7):6978-87(2018); DOI: 10.1021/acsnano.8b02505 Figure 1

International audience; We demonstrate the functionality of a new active thermal microchip dedicated to the temperature calibration of scanning thermal microscopy (SThM) probes. The silicon micromachined device consists in a suspended thin dielectric membrane in which a heating resistor with a circular area of 50 lm in diameter was embedded. A circular calibration target of 10 lm in diameter was patterned at the center and on top of the membrane on which the SThM probe can land. This target is a resistive temperature detector (RTD) that measures the surface temperature of the sample at the level of the contact area. This allows evaluating the ability of any SThM probe to measure a surface temperature in ambient air conditions. Furthermore, by looking at the thermal balance of the device, the heat dissipated through the probe and the different thermal resistances involved at the contact can be estimated. A comparison of the results obtained for two different SThM probes, microthermocouples and probes with a fluorescent particle is presented to validate the functionality of the micromachined device. Based on experiments and simulations, an analysis of the behavior of probes allows pointing out their performances and limits depending on the sample characteristics whose role is always preponderant. Finally, we also show that a smaller area of the temperature sensor would be required to assess the local disturbance at the contact point.