No sweat, no gain: Flexible biofuel cells functionalized with lactate oxidase (LOx) and platinum as anode and cathode materials harvested biochemical energy from human perspiration (see picture). Substantial power was generated from human sweat in real‐life scenarios.
Here we present two types of all-printable, highly stretchable, and inexpensive devices based on platinum (Pt)-decorated graphite for glucose determination in physiological fluids. Said devices are: a non-enzymatic sensor and an enzymatic biosensor, the latter showing promising results. Glucose has been quantified by measuring hydrogen peroxide (H2O2) reduction by chronoamperometry at −0.35V (vs pseudo-Ag/AgCl) using glucose oxidase immobilized on Pt-decorated graphite. The sensor performs well for the quantification of glucose in phosphate buffer solution (0.25M PBS, pH 7.0), with a linear range between 0 mM and 0.9mM, high sensitivity and selectivity, and a low limit of detection (LOD). Thus, it provides an alternative non-invasive and on-body quantification of glucose levels in human perspiration. This biosensor has been successfully applied on real human perspiration samples and results also show a significant correlation between glucose concentration in perspiration and glucose concentration in blood measured by a commercial glucose meter. •Stretchable electrochemical biosensors for glucose determination in perspiration.•The obtained working range and sensitivity are 33μM–0.9mM and 105μAcm−2mM−1, respectively.•An alternative for the non-invasive quantification of glucose in human perspiration.•Real human perspiration were used to evaluate the inter-sensor reproducibility and trueness.
: In this paper the relationship between blood glucose concentration and palm perspiration rate is studied as a non‐invasive method. A glucose concentration range from 83 mg/dl to 116.5 mg/dl is examined. An artificial neural network (ANN) trained by the Levenberg–Marquardt algorithm is developed to detect the performance indices based on the one‐ and two‐input variables. A data set for 72 volunteers is used for this study. Data of 36 volunteers are used for training the ANN and data of 36 volunteers were reserved for testing. Results of the study are acceptable with an error of 8.38% for the Elman neural network and 8.77% for the multilayer neural network. Therefore, the palm perspiration rate may be used as a good indicator for detecting glucose concentration in blood. This non‐invasive method has advantages such as time saving, cost etc. over other methods and it is painless. The results of clinical experiments, follow‐up methods and other applications are presented.
Novel instrumentation for the estimation of ethanol concentration in sweat is proposed. It is composed of a sampling probe attached directly to the skin surface, a sweat rate meter for measuring the total amount of sweat secreted, a cold trap and a capillary gas chromatograph. The variation of ethanol concentration in sweat after ingestion has been measured precisely at intervals of 5–20 min. At the same time the ethanol concentration in blood was also determined by using a clinically authorized method. Ethanol concentrations both in sweat and blood are well related. To our knowledge, this is the first time that a clear relationship has been demonstrated during the whole elapsed period after ethanol ingestion. As the proposed method uses non-invasive sampling it may be applicable to testing for ethanol instead of the normal method using blood.
Highlights • Major advances in the development of wearable electrochemical sensors and biosensors. • Non-invasive monitoring of chemical constituents in sweat, tears, or saliva. • Monitoring of wearer's health or fitness.
Background Some methodologies used for evaluating sweat production and antiperspirants are of a stationary aspect, that is, most often performed under warm (38°C) but resting conditions in a rather short period of time. The aim is to develop an electronic sensor apt at continuously recording sweat excretion, in vivo, during physical exercises, exposure to differently heated environments, or any other stimuli that may provoke sweat excretion. Material and Methods A sensor (20 cm2) is wrapped under a double‐layered textile pad. Fixed onto the armpits, these two arrays of electrodes are connected to electronic system through an analog multiplexer. A microcontroller is used to permanently record changes in the conductance between two electrodes during exposure of subjects to different sweat‐inducing conditions or to assess the efficacy of applied aluminum hydrochloride (ACH)‐based roll‐ons at two concentrations (5% and 15%). Results In vitro calibration, using a NaCl 0.5% solution, allows changes in mV to be related with progressively increased volumes. In vivo, results show that casual physical exercise leads to sweat excretions much higher than in warm environment (37 or 45°C). Only, an exposure to a 50°C environment induced comparable sweat excretion. In this condition, sweat excretions were found similar in both armpits and both genders. Decreased sweat excretions were recorded following applications of ACH, with a dose effect. Conclusion Developing phases of this new approach indicate that usual method or guidelines used to determine sweat excretions in vivo do not reflect true energy expenditure processes. As a consequence, they probably over‐estimate the efficacy of antiperspirant agents or formulae.
Successful commercialization of wearable diagnostic sensors necessitates stability in detection of analytes over prolonged and continuous exposure to sweat. Challenges are primarily in ensuring target disease specific small analytes (i.e. metabolites, proteins, etc.) stability in complex sweat buffer with varying pH levels and composition over time. We present a facile approach to address these challenges using RTILs with antibody functionalized sensors on nanoporous, flexible polymer membranes. Temporal studies were performed using both infrared spectroscopic, dynamic light scattering, and impedimetric spectroscopy to demonstrate stability in detection of analytes, Interleukin-6 (IL-6) and Cortisol, from human sweat in RTILs. Temporal stability in sensor performance was performed as follows: (a) detection of target analytes after 0, 24, 48, 96, and 168 hours post-antibody sensor functionalization; and (b) continuous detection of target analytes post-antibody sensor functionalization. Limit of detection of IL-6 in human sweat was 0.2 pg/mL for 0-24 hours and 2 pg/mL for 24-48 hours post-antibody sensor functionalization. Continuous detection of IL-6 over 0.2-200 pg/mL in human sweat was demonstrated for a period of 10 hours post-antibody sensor functionalization. Furthermore, combinatorial detection of IL-6 and Cortisol in human sweat was established with minimal cross-talk for 0-48 hours post-antibody sensor functionalization.
•New electrochemical biosensing device for determining the blood's ethanol content (BAC).•Prototype based on bienzyme amperometric composite biosensors.•Determination of BAC by amperometric monitoring of ethanol in sweat.•BAC determination in single measurement or in continuous modes.•Successful validation with 40 volunteers. A non-invasive, passive and simple to use skin surface based sensing device for determining the blood's ethanol content (BAC) by monitoring transdermal alcohol concentration (TAC) is designed and developed. The proposed prototype is based on bienzyme amperometric composite biosensors that are sensitive to the variation of ethanol concentration. The prototype correlates, through previous calibration set-up, the amperometric signal generated from ethanol in sweat with its content in blood in a short period of time. The characteristics of this sensor device permit determination of the ethanol concentration in isolated and in continuous form, giving information of the BAC of a subject either in a given moment or its evolution during long periods of time (8h). Moreover, as the measurements are performed in a biological fluid, the evaluated individual is not able to alter the result of the analysis. The maximum limit of ethanol in blood allowed by legislation is included within the linear range of the device (0.0005–0.6gL−1). Moreover, the device shows higher sensitivity than the breathalyzers marketed at the moment, allowing the monitoring of the ethanol content in blood to be obtained just 5min after ingestion of the alcoholic drink. The comparison of the obtained results using the proposed device in the analysis of 40 volunteers with those provided by the gas chromatographic reference method for determination of BAC pointed out that there were no significant differences between both methods.
Wearable devices have emerged as powerful tools for personalized healthcare in spite of some challenges that limit their widespread applicability as continuous monitors of physiological information. Here, a materials‐based strategy to add utility to traditional dielectric sensors by developing a conformal radiofrequency (RF) construct composed of an active layer encapsulated between two reverse‐facing split ring resonators is applied. These small (down to 2 mm × 2 mm) passive dielectric sensors possess enhanced sensitivity and can be further augmented by functionalization of this interlayer material. Demonstrator devices are shown where the interlayer is: (i) a porous silk film, and (ii) a modified PNIPAM hydrogel that swells with pH or temperature. In vivo use is demonstrated by adhesion of the device on tooth enamel to detect foods during human ingestion. Such sensors can be easily multiplexed and yield data‐rich temporal information during the diffusion of analytes within the trilayer structure. This format could be extended to a suite of interlayer materials for sensing devices of added use and specificity. A small‐form‐factor, biopolymer‐based layered radiofrequency sensor is developed for sensing various solutes, pH, and temperature. An interchangeable sensitive layer determines the response to either analyte‐induced dielectric change, or pH‐ and temperature‐induced mechanical change. On‐tooth sensing is demonstrated for tracking of food intake.
Lactate concentration is studied as an indicator of physical performance in sports activities, and is also analyzed in health care applications, as well as in the food and cosmetic industries. This organic acid is routinely determined in different concentration ranges, depending on the type of samples for analysis. This paper describes the development of a screen-printed lactate oxidase (LOx) based biosensor to determine lactate in broad concentration range. The Cu-MOF (copper metallic framework) crosslinking of 0.25U LOx in a chitosan layer, allows to determine the enzymatic product generated on a platinum modified working electrode, at 0.15 V (vs SPE Ag/AgCl). The biosensor responds linearly in two different concentration ranges: a first catalysis range of 14.65 µA mM−1, from 0.75 µM to 1 mM, followed by a saturation zone from 1 to 4 mM, after which a substrate enzymatic inhibition of 0.207 µA mM−1, is observed up to 50 mM. These two ranges of analysis would allow the biosensor to be used for the determination of lactate in different types of samples, with low and high content of lactate. The method reproducibility was kept below 7% and a limit of detection of 0.75 µM was obtained. The device was successfully used in the determination of lactate in sweat and saliva, as a low cost noninvasive analysis, and also in wine samples. [Display omitted] •New dual range amperometric LOx biosensor to determine lactate in several matrices.•Lactate determination through enzymatic catalysis and inhibition.•Biosensor works with a very low number of enzymatic units.•Pt, CS and Cu-MOF, reveal a synergetic effect in the biosensor sensitivity.