Screen printed electrochemical sensors for real-time sodium monitoring in sweat

We report on the preparation of disposable potentiometric sensor strips for monitoring sodium in sweat. We also present their integration in a microfluidic chip used to harvest sweat in-situ during exercise. The sensor-chip is integrated with a miniaturized electronic platform able to transmit data wirelessly in real time during a stationary cycling session in a controlled environment

Non invasive detection of biological fluids: a new perspective in monitoring pH in saliva and sodium in sweat

The chemical composition of body fluids contains crucial information about the state of health of an individual. While many efforts have been already directed toward real time analysis of blood and urine, there is still a pressing need for new solutions to non-invasively monitor other fluids like saliva and sweat1. Towards this aim, the main technological challenge is the development of devices that are at the same time low-cost, minimally invasive and wearable, so that they could be used for in situ and real-time monitoring of physiological conditions2. For example, continuous recording of sodium levels in sweat could be an informative tool to assist clinicians in prescribing a more personalised treatment of diseases such as Cystic Fibrosis3 and in assessing athletes’ performances4. Similarly, the monitoring of pH levels in saliva provides valuable information for the treatment of pathologies where physiological mouth conditions are compromised, like in Gastroesophageal Reflux Disease (GERD)5. Ion Selective Electrodes (ISEs) are potentiometric sensors designed to detect specific ions in blood and saliva. Using dual-screen printed electrodes as substrates, we were able to reduce their production cost, improve reproducibility, and combine pH5 and sodium ISEs with solid contact reference electrodes. In our design, the sensors will be interfaced to two miniaturized potentiometric platforms (WIXEL for pH and Tyndall Mote for sodium detection) that were wirelessly connected to a base station. For pH measurements, the device will be accommodated into a gum shield. For sodium detection instead, we will use a microfluidic channel to convey sweat to the electrodes. The mote communication platform was adapted so that it could be worn on the upper shoulder through a fiber strip

Wearable chemical sensing – sensor design and sampling techniques for real-time sweat analysis

Wearable chemical sensors have the potential to provide new methods of non-invasive physiological measurement. The nature of chemical sensors involves an active surface where a chemical reaction must occur to elicit a response. This adds complexity to a wearable system which creates challenges in the design of a reliable long-term working system. This work presents the design of a real-time sweat sensing platform to analyse sweat loss and composition. Sampling methods have an impact on composition therefore skin encapsulation needs to be avoided so as not to disrupt normal sweating patterns. Sensors ideally need to be placed close to the sampling site which may be subject to motion artefacts [1]. The design of this device takes into account sample collection and delivery, sensor placement and associated electronics. The overall design is ergonomic to interface with the contours of the body. Results of lab-based simulations and real-time exercise trials are presented. This device can offer valuable information regarding hydration status and electrolyte balance which may be especially important for optimised rehydration during or after sports activities. [1] Curto, V. F. S. Coyle, R. Byrne, N. Angelov, D. Diamond, F. Benito-Lopez., Sens. Actuators, B, 2012, 175, 263-270

Personal sensing wear: the role of textile sensors

Wearable sensors for fitness tracking are becoming increasingly popular and are set to increase as smartwatches begin to dominate the wearable technology market. Wearable technology provides the capacity to track long-term trends in the wearer’s health. In order for this to be adopted the technology must be easy to use and comfortable to wear. Textile based sensors are ideal as they conform to the body and can be integrated into the wearer’s everyday wardrobe. This work discusses fabric stretch sensors that can measure body movements. An application using a sensor glove for home assessment of Rheumatoid Arthritis is presented. This work is the result of a multidisciplinary effort, involving expertise in material science and functional design, computer science, human health and performance and influenced by the end user needs

Wearable fluidics – the key to bringing chemistry and biology into on-body measurements

Despite the wide range of applications and tremendous potential of implantable sensors targeting chemo/bio-markers, bringing actual practical devices fully to market continues to be inhibited by significant technological barriers associated with long-term reliability, which is a key requirement for implants. This is so, even with devices that appear to be well engineered, focused on apparently fairly solid markets, and based on well-established sensing principles. Wearable chem/bio-sensors offer an interesting approach, intermediate between the long-term vision of implantable devices, and the single use-disposable devices that are the current dominant use model. For example, wearable patch-type devices employing minimally invasive sampling of interstitial fluid for continuous glucose monitoring target a use period of about one week. However, despite this apparently rather modest target, large scale adoption is still frustratingly elusive, and products are being withdrawn from the markets [ ]. Moves by Google into the biosensing space are an interesting development, with the focus again being on how to gain access to sample fluids through which key biomarkers like glucose can be tracked in a non-invasive manner via a limited duration use model. Google are focusing on glucose monitoring through a contact lens that can be powered inductively (no batteries), can communicate wirelessly, function for 24 hours (lenses are changed daily), has an integrated electrochemical sensor, and is in contact with a sample fluid (aqueous humour) with glucose composition related (somewhat fuzzily) to that of blood [ ]. Similarly, the period up to the launch of the Apple iWatch witnessed a frenzy of speculation about whether it would have an integrated glucose monitoring capability [ ]. In the end, the iWatch was launched, with no mention of any integrated chem/bio-sensing capability. However, once these initial applications are delivered, and the wearable platforms more clearly resolved, the drive for more value will place the spotlight on other sensing technologies that can implemented on-body to provide new types of information. In this respect, chemical sensors and biosensors are obvious candidates for integration. Clearly, however, these devices are inherently more complex and less dependable than the well-established physical sensors, as reflected in the difficulties in bringing these sensors to market [ ]. In this paper, I will examine the issues that currently limit the applicability of chemo/bio-sensors in wearable scenarios, and present ways through which these more complex sensors can be successfully integrated as part of a wearable sensing platform

Development of a sensitive, low-cost and user-friendly centrifugal microfluidic cartridge for multi-analyte environmental monitoring

This paper describes the development of a simple centrifugal cartridge for the analysis of nitrite, ammonia and phosphate from a water sample. The cartridge is operated in combination with the Centrifugal Microfluidic Analysis System (CMAS)[1] which incorporates rotational control with optical and communication components for portable analysis of environmental and biomedical samples[1,2]. An LED and a photodiode allow colorimetric determination of specific analytes depending on which reagent-based analytical method is employed. Bluetooth wireless communications provides automatic uploading of analytical data to cloud-based information systems. Microfluidic discs consisting of three PMMA (Poly(methyl methacrylate)) layers bonded together by two PSA (Pressure Sensitive Adhesive) layers were prepared. The sample was transported from a single chamber to three aliquoting chambers at a low rotational frequency prior to the actuation of dissolvable film valves[3] at an increased rotational frequency to facilitate sample transport to reaction/detection chambers. Ammonia standards were analysed using a modified Berthelot method, the stannous chloride method was used to detect orthophosphate levels while a diazotization method was employed to determine nitrite concentration. Photodiode analysis on the CMAS platform obtained LOD’s of 0.233 ppm for ammonia and 0.189 ppm for orthophosphate and 50 ppb for nitrite

‘SWEATCH’ – A platform for real-time monitoring of sweat electrolyte composition

Since the initial breakthroughs in the 1960’s and 70’s that led to the development of the glucose biosensor, the oxygen electrode, ion-selective electrodes, and electrochemical/optochemical diagnostic devices, the vision of very reliable, affordable chemical sensors and bio-sensors capable of functioning autonomously for long periods of time (years), and providing access to continuous streams of real-time data remains unrealized. This is despite massive investment in research and the publication of many thousands of papers in the literature. It is over 40 years since the first papers proposing the concept of the artificial pancreas, by combining the glucose electrode with an insulin pump. Yet even now, there is no chemical sensor/biosensor that can function reliably inside the body for more than a few days, and such is the gap in what can be delivered (days), and what is required (minimum 10 years) for implantable devices, it is not surprising that in health diagnostics, the overwhelmingly dominant paradigm for reliable measurements is single use disposable sensors. Realising disruptive improvements in chem/bio-sensing platforms capable of long-term (months, years) independent operation requires a step-back and rethinking of strategies, and considering solutions suggested by nature, rather than incremental improvements in available technologies