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This article presents a smart bandage with wireless strain and temperature sensors and a batteryless near-field communication (NFC) tag. Both sensors are based on conductive poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) polymer. The highly sensitive strain sensor consists of a microfluidic channel filled with PEDOT:PSS in Polydimethylsiloxane (PDMS) substrate. The strain sensor shows 3 order (~1250) increase in the resistance for 10% strain and considerably high gauge factor (GF) of ~12 500. The sensor was tested for ~30% strain, which is more than typical stretching of human skin or body parts such as chest expansion during respiration. The strain sensor was also tested for different bending and the electrical resolution was ~150% per degree of free bending and ~12k% per percentage of stretching. The resistive temperature sensor, fabricated on a Polyvinyl Chloride (PVC) substrate, showed a ~60% decrease in resistance when the temperature changed from 25 °C to 85 °C and a sensitivity of ~1% per °C. As a proof of concept, the sensors and NFC tag were integrated on wound dressing to obtain wearable systems with smart bandage form factor. The sensors can be operated and read from distance of 25 mm with a user-friendly smartphone application developed for powering the system as well as real-time acquisition of sensors data. Finally, we demonstrate the potential use of smart bandage in healthcare applications such as assessment of wound status or respiratory diseases, such as asthma and COVID-19, where monitoring via wearable strain (e.g., respiratory volume) and temperature sensors is critical.

Herein, a novel tactile sensing device (SensAct) with a soft touch/pressure sensor seamlessly integrated on a flexible actuator is presented. The squishy touch sensor is developed with custom-made graphite paste on a tiny permanent magnet, encapsulated in Sil-Poxy, and the actuator (15 μ-thick coil) is fabricated on polyimide by Lithographie Galvanoformung Abformung (LIGA) micromolding method. The actuator can operate in two modes (expansion and contraction/squeeze) and two states (vibration and nonvibration). The sensor was tested with up to 12 N applied forces and exhibited ≈70% average relative resistance variation (ΔR/Ro), ≈0.346 kPa−1 sensitivity, and ≈49 ms response time with excellent repeatability (≈12.7% coefficient of variation) at 5 N. During simultaneous sensing and actuation, the modulation of coil current, due to ΔR/Ro (≈14% at 2 N force) in the sensor, allows the close loop control (ΔI/Io ≈385%) of expansion/contraction (≈69.8 μm expansion in nonvibration state and ≈111.5 μm peak-to-peak in the vibration state). Finally, the soft sensor is embedded in the 3D-printed fingertip of a robotic hand to demonstrate its use for pressure mapping along with remote vibrotactile stimulation using SensAct device. The self-controllable actuation of SensAct could provide eSkin the ability to tune stiffness and the vibration states could be utilized for controlled haptic feedback.

Several studies have shown that the determination of pH in sweat, which is one of the most accessible body fluids, can be an indicator of health and wellness, and even be used for potential disease diagnosis. On that basis, we present herein a wearable wristband for continuous and wireless monitoring of sweat pH with potential applications in the field of personal health assessment. The developed wristband consists of two main parts: a microfluidic cloth analytical device (μCAD) to collect continuously the sweat from skin with a color-based pH sensing area; and a readout and processing module with a digital color sensor to obtain the pH of sweat from the color changes in the μCAD. In addition, the readout module includes a low-power Bluetooth interface to transmit the measurements in real-time to a custom-designed smartphone application. To allow continuous operation, an absorbent pad was included in the design to retire and store thsweat from the sensing area through a passive pump path. It was found that the Hue parameter (H) in the HSV color space can be related to the sweat pH and fitted to a Boltzmann equation (R2 = 0.997). The range of use of the wristband device goes from 6 to 8, which includes the pH range of sweat, with a precision at different pH values from 3.6 to 6.0 %. Considering the typical human sweat rate, the absorbent pad allows continuous operation up to more than 1000 min.

Disposable and flexible sensors are needed in biomedical and healthcare applications because of hygiene requirements. At the same time, they should provide an affordable solution for point-of-care (POC) testing and large-scale deployment. In this view, herein we report flexible polyimide-based disposable sensor patch for the detection of a-amylase in blood serum. The concentration of a-amylase in blood serum is a potential indicator of health issues such as pancreatitis and pancreatic cancer and an affordable solution to detect its concentration could benefit many. Here, the detection is based on thermal Marangoni circulation inside a microfluidic droplet of starch-FeSO 4 salt solution, which detects the a-amylase concentration upon addition of blood serum. It was observed that the temperature difference between the droplet substrate and ambient sets a thermal Marangoni and natural convections motion inside the droplet. The performance of the microdropletbased sensor was best at temperature difference (~18–20°C). The sensor is capable of detecting 20-110 units/liter concentration of α-amylase with ~80% change in the electrical resistance across the microdroplet (at ~40°C substrate temperature), and with a sensitivity of 0.88% (units/liter) -1 . The response of the sensor was also compared with pathological laboratory results and both were found to be in agreement. The presented sensor has the potential to be used as a POC device for detecting α-amylase in real-time.

Concentration of α-amylase in human serum is a key indicator of various pancreatic ailments and an affordable point-of-care detection of this biomarker can benefit millions suffering from these diseases. In view of this situation, we report the development of a flexible patch-sensor, which simply requires a microdroplet of aqueous starch-FeSO4 solution to detect α-amylase in serum. The detection is achieved through the generation of mixing vortices (~12 rpm) inside the droplet with the help of an imposed thermal gradient. Such vortices due to Marangoni and natural convections are found to be strongest at an optimal temperature difference of ~18 °C - 23 °C across the droplet which in turn facilitate mixing and promote the specific starch-amylase enzymatic reaction. Subsequently, the large (~80%) variation in the electrical resistance across the droplet is correlated to detect the level of the α-amylase in the analyte. Importantly, the sensor can detect even in the limits of 15-110 units/liter. Further, the sensitivity of flexible sensors is ~8.6% higher than the non-flexible one. Interestingly, the sensitivity of the proposed sensor has been nearly three-times than the previously reported optical ones. The results of patch-sensor match very closely with the standard path-lab tests while detecting unknown level of amylase in serum. The prototype has shown significant potential to translate into an affordable device for the real-time detection and easy prognosis of pancreatic disorders.

This paper presents a polymer strain sensor integrated with\ud an NFC tag to detect strain semi-quantitatively. The strain\ud sensor is fabricated using flexible and transparent polymer\ud Polydimethylsiloxane (PDMS) microchannel having\ud conductive polymer poly (3,4-ethylenedioxythiophene)\ud polystyrene sulfonate (PEDOT:PSS) as an active material.\ud The sensor was tested with different bending conditions\ud and it was found that the resistance increases with higher\ud bending. A maximum of 3 order change in resistance was\ud observed for ~100 bending. The sensor was finally tested\ud using a custom-developed passive NFC tag having an LED\ud connected in series with the strain sensor and powered from\ud the reader via the NFC antenna in the tag.

This paper presents poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate polymer microchannel (diameter ≈175 µm) based stretchable strain sensor developed inside polydimethylsiloxane substrate. The microchannel diameter changes when subjected to various strains, leading to change in the resistance of strain sensor. The sensor exhibits about three order (ΔR /R 0 ≈ 1200) increase in the resistance (R ) for 10% applied strain (ΔL /L , L = length of the sensor). This leads to a gauge factor (GF Δ (ΔR /R 0)/(ΔL /L ) of ≈12 000, which is about ≈400 times higher than most of the reported polymer‐based strain sensors. The sensor is evaluated up to a maximum strain of 30%, which is the standard strain limit associated with human body parts such as fingers and wrists. The sensor exhibits a considerably good average degree of hysteresis (

In this work, a compact affordable and portable spectral imaging system is presented. The system is intended to be employed in general applications, such as material classification or determination of the concentration of chemical species together with colorimetric sensors. The imaging device is reduced to a small digital color detector with an active area of 3 × 2mm2. This device provides a quantification of the incident emission in the form of four digital words corresponding to its averaged components blue, green, red, and near infrared. In this way, the size of the image is reduced to one pixel. The wavelength selection is carried out by means of a LED array disposed surrounding the color detector. The LEDs are selected to cover the wavelength range from 360 to 890 nm. A sequential measurement protocol is followed, and the generated data is transmitted to an external portable device via a Bluetooth link where a classification protocol is implemented in a custom-developed Android™ application. The presented system has been applied in three different scenarios involving material classification, meat freshness monitoring, and chemical analysis. The analysis of the data using principal components shows that it is possible to find a set of wavelengths where the classification of the samples is optimal., This work was supported by project CTQ2016-78754-C2-1-R from the Spanish Ministry of Economy and Competitiveness.

A smartphone-based platform for the diagnosis of parasitic infections has been developed, tested and validated. The system is capable of making automatic and accurate analysis of millimetric colorimetric arrays in centrifuge collection tubes, which are well established tools used in clinical analysis. To that end, an Android-based software application has been developed, making use of the smartphone rear camera, enabling precise image processing of the colorimetric spot arrays. A low-cost plastic accessory has been developed using 3D-printing to provide controlled illumination, xed sample positioning and cell phone attachment. The platform was then tested repeatedly for its size detection, edge blurriness and colour detection capabilities. A minimum spot radius of 175 m is detectable when using the developed app, with a tolerance of 15%, corresponding to 0.25%of the area where the spot array is printed. Spot edge de nition has been studied up to 40% of blurriness, resulting in a low average percentage error of 1.24%. Colour detection follows the well-known Gamma correction function. Finally, the whole platform was tested and validated using real DNA to analyse for accurate discrimination of Trypanosomatid species, which are responsible for devastating diseases in humans and livestock. The smartphone-based platform can be further extended to other clinical analysis. Its simplicity and reliable performance mean it can be used in remote, limited-resource settings by relatively unskilled technicians/nurses, where diagnostic laboratories are sparsely distributed. The results can however be sent easily via the smartphone to medical experts as well as government health agencies., This work was supported in part by the Spanish Ministry of Economics and Competitivity under Project CTQ2016-78754-C2-1-R, in part by the European Regional Development Fund (ERDF), and in part by the DestiNA Genomica SL provided reagents, samples and Spin-Tube devices. The work of P. Escobedo was supported by the Spanish Ministry of Education, Culture and Sport (MECD), under Grant (FPU13/05032).

The development of a contactless readout system for High Frequency (HF) tags and its application to relative humidity monitoring is presented. The system consists of a Colpitts oscillator circuit whose frequency response is determined by a built-in logic counter of a microcontroller unit. The novel readout strategy is based on the frequency response change due to the inductive coupling between the coil of the Colpitts oscillator and the load impedance of a parallel LC resonator tag, as a result of the variation of the humidity sensing capacitor. The frequency is monitored with a low cost microcontroller, resulting in a simple readout circuit. This passive LC tag has been directly screen-printed on a humidity-sensitive flexible substrate. The readout circuit experimental uncertainty as frequency meter was 4 kHz in the HF band. A linear temperature drift of (-1.52 ± 0.17) kHz/⁰C was obtained, which can be used to apply thermal compensation if required. The readout system has been validated as a proof of concept for humidity measurement, obtaining a significant change of about 260 kHz in the resonance frequency of the Colpitts oscillator when relative humidity varies from 10% to 90%, with a maximum uncertainty of ±3% (±2 SD). Therefore, the proposed readout system stands as a compact, low-cost, contactless solution for chipless HF tags that avoids the use of bulky and costly equipment for the analog reading of wireless passive LC sensors., This work was supported by project CTQ2016-78754-C2-1-R from the Spanish Ministry of Economics and Competitivity. P. Escobedo wants to thank the Spanish Ministry of Education, Culture and Sport (MECD) for a pre-doctoral grant (FPU13/05032).

A portable device based on a colorimetric sensor to determine the atmospheric level of CO2 gas is presented in this work. The system is based on a low-cost, low-power System on a Chip (SoC) microcontroller with integrated Wi-Fi. A user-friendly application was developed to monitor and log the CO2 measurements when the system is connected to a Wi-Fi network. The sensing membrane is directly deposited on the surface of the colour detector, thus reducing the complexity of the system. This sensing membrane is formed by a pH indicator α-naphtholphthalein, tetramethylammonium hydroxide pentahydrate, 1-ethyl-3-methylimidazolium tetrafluoroborate, Tween 20 and hydroxypropyl methylcellulose as the hydrophilic polymer. The system has been fully characterized, obtaining response and recovery times of 1.3 and 2.5 s, respectively, a limit of detection of 51 ppm, and an average resolution of 6.3 ppm. This portable device was applied for the in-situ determination of CO2 gas in the atmosphere inside classrooms in several secondary schools. The measurements were taken during complete workdays and the results were statistically compared with the same measurements taken using a commercially available non-dispersive infra-red (NDIR) device. No significant statistical differences were found between the results obtained using both devices. A complete statistical treatment of the measurements made with the proposed portable device was carried out. The obtained results show that the concentration of CO2 gas in some schools was higher than the desired concentration, with regard to influencing the student's health, safety, productivity and comfort. This demonstrates the need to control this parameter to ensure appropriate indoor environmental quality (IEQ).

In this work we present a novel technique to estimate the resonance frequency of LC chipless tags (inductor-capacitor parallel circuit) with improved sensitivity and linearity. The developed reader measures the power consumption of a Colpitts oscillator during a frequency sweep. The readout circuit consists of a Colpitts oscillator with a coil antenna, varactor diodes to change the oscillator frequency, analog circuitry to measure the power consumption and a microcontroller to control the whole system and send the data to a PC via USB. When an LC tag is inductively coupled to the oscillator, without contact, a maximum power peak is found. As shown by an experimental calibration using an LC tag made on FR4 substrate, the frequency of this maximum is related to the resonance frequency. Both parameters, power consumption and resonance frequency, present an excellent linear dependence with a high correlation factor (R 2 = 0.995). Finally, a screen-printed LC tag has been fabricated and used as relative humidity sensor achieving a sensitivity of (−2.41 ± 0.21) kHz/% with an R 2 of 0.946.

In this work we describe a passive screen printed flexible tag for gas monitoring that can be used in sealed environments. The developed measurement system is based on chemical sensors that are sensitive to gases concentration presenting optical response, luminescent or colourimetric. The measuring electronics consist of a LED for optical excitation of the sensing membrane and a high resolution digital colour detector for the reading of the optical signal. A microcontroller receives and processes the data enabling the detection threshold for the corresponding gas. The whole system is powered by two miniaturized solar cells that provide 4 V and up to 250 μA each one. This system can run in sunlight or using a bright artificial light as the only energy source. The information of the inner environmental conditions regarding the gas concentration is transmitted to the user through a simple optical code using colour light-emitting diodes. These LEDs are activated to indicate whether the concentration of the monitored gas is within the expected limits, or not. Two prototypes based on this architecture and only changing the sensing module have been developed and applied for the determination of two common gases: oxygen and carbon dioxide. In the first case, a luminescent chemical sensor is used while in the second, the sensing membrane presents a colourimetric response. Both types of sensors can be used in this design. Resulting limits of detection are compatible with assessment of modified atmosphere packaging.

Here, we present a technique for the determination of the gaseous oxygen concentration 2 inside packed food. It is based on the use of a luminescent membrane sensitive to O2 that is optically excited and read by a smartphone. The flash of the smartphone along with an optical filter is used as the light source for the optical stimulation of the membrane. The luminescence generated, which is quenched by the surrounding gaseous oxygen, is registered by the rear camera of the same device. The response parameter is defined by combining the registered intensities at two different wavelength ranges corresponding to the emission and the absorption peaks of the sensitive membrane. Thanks to this novel response parameter, the sensitivity is increased and, more importantly, the thermal dependence of the membrane is significantly reduced. This approach allows the use of a luminescent O2-sensitive membrane for intelligent packaging with no need of any associated electronics for its excitation and reading. This means that an oxygen sensor is developed, where a luminescent compound acts as an indicator, therefore combining the advantages of both schemes, that is, the simplicity and reduced cost of indicators with the high sensitivity and accuracy of selective sensors., This work was supported by the Spanish Ministry of Economics and Competivity through the Project CTQ2016-78754-C2-1-R. The work P. Escobedo Araque was supported by the Spanish Ministry of Education, Culture and Sport under Grant FPU13/05032. The work of I. Pérez de Vargas-Sansalvador was supported in part by the European Union’s Horizon 2020 Research and Innovation Program (Multisens) under Grant 706303, in part by the Talentia Postdoc Program launched by the Andalusian Knowledge Agency, in part by the European Union’s Seventh Framework Program, in part by the Marie Skłodowska-Curie actions (COFUND) under Grant 267226, and in part by the Ministry of Economy, Innovation, Science and Employment of the Junta de Andalucía.

A versatile, compact and low-cost analytical platform has been designed, tested and validated to be used in the point-of-care settings. This passive measurement system is powered and complemented by a standard smart- phone including a programmed application for measurement configuration and data processing as well as wireless results sharing. Electrochemical and electrochemiluminescence analytical techniques can be configured and realized by this platform that employs standard screen-printed electrodes for the sample managing and off- the-shelf electronic components. The power, electrical and optical signal processing have been studied in depth. The system can harvest energy up to 22.5 mW, set up a voltage in the range of±1.15 V, and measure potentials in a range of 600 mV with an uncertainty of 1 mV, and current from 2 μA to 0.75 mA with a resolution of 1.1 μA. Moreover, standard tests have been performed to the platform consisting of amperometric, potentiometric, cyclic voltammetry and electrochemiluminescent analytical techniques, showing excellent agreement with a reference instrument. Finally, our design has also been applied to glucose, pH and H2O2 determinations, providing the full analytical parameters which are in very good agreement with the reference instrument results. Ranges (0.065–0.75 M, 0.62–100mM and 3–9 pH units for glucose, H2O2 and pH, respectively) and limits of detection (0.024 M and 0.03mM for glucose and H2O2, respectively) make this low-cost platform (< US$8) suitable for analytical applications.

In this work we present a full-passive flexible multigas sensing tag for the determination of oxygen, carbon dioxide, ammonia, and relative humidity readable by a smartphone. This tag is based on near field communication (NFC) technology for energy harvesting and data transmission to a smartphone. The gas sensors show an optic response that is read through high-resolution digital color detectors. A white LED is used as the common optical excitation source for all the sensors. Only a reduced electronics with very low power consumption is required for the reading of the optical responses and data transmission to a remote user. An application for the Android operating system has been developed for the power supplying and data reception from the tag. The responses of the sensors have been calibrated and fitted to simple functions, allowing a fast prediction of the gases concentration. Cross-sensitivity has also been evaluated, finding that in most of the cases it is negligible or easily correctable using the rest of the readings. The election of the target gases has been due to their importance in the monitoring of modified atmosphere packaging. The resolutions and limits of detection measured are suitable for such kinds of applications.

This work presents the design, fabrication, and characterization of a passive printed radiofrequency identification tag in the ultra-high-frequency band with multiple optical sensing capabilities. This tag includes five photodiodes to cover a wide spectral range from near-infrared to visible and ultraviolet spectral regions. The tag antenna and circuit connections have been screen-printed on a flexible polymeric substrate. An ultra-low-power microcontroller-based switch has been included to measure the five magnitudes issuing from the optical sensors, providing a spectral fingerprint of the incident electromagnetic radiation from ultraviolet to infrared, without requiring energy from a battery. The normalization procedure has been designed applying illuminants, and the entire system was tested by measuring cards from a colour chart and sensing fruit ripening.