Implementation of a microfluidic conductivity sensor — A potential sweat electrolyte sensing system for dehydration detection

Abstract

As dehydration continues to plague performance athletes and soldiers, the need for improved dehydration detection is clear. We propose the use of a conductometric sensor as the foundation of a sweat-sensing patch to address this need. The conductometric sensor evaluates the conductivity of solutions with varying sodium concentrations. A lithographic process was used to fabricate a Polydimethylsiloxane (PDMS) microfluidic channel through which solution was flowed. The ionization of the solution that occurs when a voltage is applied results in an effective resistance across the channel. The measured resistance therefore, reflects the ionization of the solution and the corresponding sodium concentration. The potential application of the conductometric sensor in a sweat-sensing patch requires compatibility with a microcontroller and Bluetooth module. Thus, a circuit interface was created. A voltage divider was utilized to convert the output resistance of the sensor to a voltage that could be input into a microcontroller. An AC voltage signal with a frequency of 10 kHz was used as the source voltage of the voltage divider to minimize the faradaic impedance and the double layer effect of the ionized solution. Tests have revealed that the conductometric is capable of precisely measuring the conductivity of a sodium solution. The conductometric sensor will be applied to a sweat sensing patch through future work involving studying the link between sodium concentration in sweat and an individual's dehydration level, developing a sweat-collection method, and developing a method of consideration for the other ions contained in sweat.

Electrochemical multi-analyte point-of-care perspiration sensors using on-chip three-dimensional graphene electrodes

“…5). Ion concentrations in sweat range from lower millimolar concentrations up to peak values over 0.5 mol L −1 which is well within the reliable detection range of this sensor [5,12].…”

“…Potassium ions in general are required for correct nerve transmission and an oversupply as well as a lack thereof can cause several effects up to an abnormal heart rhythm and finally death [11]. An increased electrolyte content in sweat during workout is a direct indication for dehydration [12]. Lactate is an important biomarker for providing information on the oxygen supply in tissue and the entire anaerobic metabolism in muscles.…”

Wearable Health Devices—Vital Sign Monitoring, Systems and Technologies

“…A different technology is also under development—a technology based on microfluidic sweat analysis. Liu et al [ 56 ] uses this technology, with a microcontroller and a Bluetooth module, to continuous monitor skin perspiration. Very recently, Koh et al [ 57 ] have developed a epidermal sweat patch with microfluidic channels able to monitor sweat rate and uses biomarkers to monitor lactate, chloride, pH and glucose levels.…”

Direct Laser Writing of the Porous Graphene Foam for Multiplexed Electrochemical Sweat Sensors

“…As the enzyme-based wearable sweat sensors are often expensive with sensitivity susceptible to temperature and pH, − enzyme-free sweat sensors relying on diverse sensing materials (e.g., graphene, − laser-induced graphene (LIG), , and PEDOT/PSS hydrogel) have been developed with excellent stability in harsh environment. − Compared with graphene prepared by the complicated fabrication process, , the 3D porous graphene comes from the low-cost, rapid, and scalable direct laser writing, which also exhibits fast electron mobility, high current density, and ultra-large surface area. ,, Benefiting from large surface areas and rich surface defects induced during the laser scribing process, pristine LIG-based devices have been widely explored for the detection of small molecules. ,− However, the resulting electrochemical sensors based on the porous graphene still show limited peak response and are greatly affected by background current. Besides the biomarkers, the electrolytes in sweat can inform the body’s hydration state to alert dehydration (for avoiding impaired endurance and increased carbohydrate reliance in athletes) or hyponatremia (or low plasma sodium from overconsumption of water or sports drinks). The sweat electrolyte sensors often involve the use of the ion-selective electrode, which is expensive and not scalable. , The analysis of sweat biomarkers and electrolytes mostly relies on the electrochemical sensor array for multiplexing, which is expensive and challenging for a high-density array.…”