Conference Proceedings


Dermot Diamond
Shirley Coyle
Larisa Florea
Jennifer Deignan



biosensors sweat analysis sensitivity analysis chemical detectors chemistry real time microfluidics contactless conductivity detection

Wearable chemical sensing – optimizing platforms and sensitivity for real-time sweat analysis (2014)

Abstract Wearable sensors have applications in multiple aspects of health monitoring. In particular, real-time physiological and on-body measurements have benefits in many scenarios including monitoring chronic disease conditions, long-term rehabilitation programs, athletic training regimens, and tracking the wellbeing of first responders in highly dangerous environments. Sweat sensing is of particular interest due to the non-invasive nature of sampling. Comfortable wearable devices increase the likelihood of continuous use and therefore its tendency for adoption by users. However, the inherent complexity of chemical sensors has made them difficult to implement in reliable wearable systems. This is mainly due to the need for a representative sample to be in continuous contact with the sensor [1]. While this is a relatively simple task in the laboratory, environmental factors such as movement, temperature and signal interference affect real-time performance. This work presents the optimization of electrical parameters and sampling platforms to maximize the sensitivity of conductivity measurements for applications in wearable sweat sensing. A TraceDec capacitively coupled contactless conductivity detection (C4D) system was used to determine the conductivity of a range of NaCl solutions using a commercially available thin-film interdigitated microarray electrode (Micrux, Figure 1). Both Au and Pt electrodes were tested using the arrangement shown in Figures 2 and 3. Voltage, frequency and gain were adjusted over the ranges 2.5-80Vpp, 75-300kHz, and 50-150%, respectively. During optimization, human safety was taken into account with the intention of using the parameters to create a wearable device. In this context, the minimum voltage required to achieve acceptable sensitivity was selected. In addition, a range of PDMS microchips with different microchannel configurations were tested to find the maximum sensitivity over 10mM-130mM NaCl. The concentration range was chosen to encompass the average sweat conductivities in healthy ([NaCl] < 60 mM) and cystic fibrosis positive ([NaCl] ≥ 60 mM) adults before and during exercise. Multiple channels were created to optimize the design with respect to direction of flow and surface area achieved. The electrodes displayed high sensitivity, repeatability and stability over time. A linear relationship was found between concentration and voltage at high concentrations and low concentrations as shown in Figure 4. Measurements also showed high repeatability over the calibration range (relative standard deviation between 0.0087%-0.0726% for n=3) and high stability over 5 minute measurements (relative standard deviation between 0.0017%-0.0860% for n=5940) as shown in Figure 5. Good performance characteristics like these obtained in laboratory experiments are a necessary prerequisite for achieving reliable real-time on-body measurements. The results of this work will be implemented in a real-time, wearable device for monitoring the sweat conductivity. As sweat conductivity is dominated by NaCl concentration, conductivity can be used as an indicator for cystic fibrosis or to monitor the effectiveness of treatments, although it is not formally accepted as a diagnostic tool [2]. In addition, the device could aid in monitoring hydration levels of athletes in real-time. Most importantly, the optimization of a real-time sweat sampling platform could allow replacement or integration of other detection methods for sodium, or other physiological features.
Collections Ireland -> Dublin City University -> Publication Type = Conference or Workshop Item
Ireland -> Dublin City University -> Subject = Physical Sciences: Chemistry
Ireland -> Dublin City University -> Status = Published
Ireland -> Dublin City University -> Subject = Biological Sciences: Microfluidics
Ireland -> Dublin City University -> DCU Faculties and Centres = DCU Faculties and Schools: Faculty of Science and Health: School of Chemical Sciences
Ireland -> Dublin City University -> DCU Faculties and Centres = Research Initiatives and Centres: National Centre for Sensor Research (NCSR)
Ireland -> Dublin City University -> Subject = Physical Sciences: Chemical detectors
Ireland -> Dublin City University -> DCU Faculties and Centres = Research Initiatives and Centres: INSIGHT Centre for Data Analytics
Ireland -> Dublin City University -> Subject = Biological Sciences: Biosensors

Full list of authors on original publication

Dermot Diamond, Shirley Coyle, Larisa Florea, Jennifer Deignan

Experts in our system

Dermot Diamond
Dublin City University
Total Publications: 607
Shirley Coyle
Dublin City University
Total Publications: 86
Larisa Florea
Dublin City University
Total Publications: 163
Jennifer Deignan
Dublin City University
Total Publications: 12