Wearable Sensor for Blood Alcohol Responds in Under 100 Seconds

Measuring blood alcohol in real time is a significant unmet need in law enforcement and healthcare, especially in emergency situations. Individual alcohol consumers may want to measure their blood alcohol (BAC) before driving or operating equipment. The coming internet of things (IoT) may require wearable sensors for a wide variety of applications. Wireless two-way communication between the sensor and the host network will provide more convenient communication than that provided by “umbilical cords.”

Current protocols for the assay of BAC involve sampling by drawing blood, an invasive process. Furthermore, people taking blood thinners such as warfarin need special care in drawing a blood sample. Breath analyzers are useful, but users must deal with interferences. Transdermal sensors have the added disadvantage of slow (0.5 to 2.0 hr) response time.

A paper by a team at the University of California at San Diego (UCSD, La Jolla) describes a new wearable tattoo-based sensor that responds quickly (<100 sec) to BAC.1 It uses flexible electronics to communicate with external Bluetooth-enabled devices, including cell phones and computers.

Compared to other transdermal devices, the device stimulates local perspiration in the sensor cell by delivering pilocarpine, a sweat-inducing drug, across the skin using constant current iontophoresis. The induced sweat carries ethanol through the skin to the sensing area, where a printed alcohol oxidase sensitive electrode and a Prussian blue counterelectrode measure the oxidation current amperometrically. Responses can be obtained in less than 100 sec after alcohol consumption.

Electrodes, including a pair of Ag/AgCl electrodes for iontophoresis, were printed on temporary transfer tattoo paper from Hemmi Papilio Supplies (Rhome, Texas). The position of the electrodes in the tattoo is a critical design feature.

Sensor performance was evaluated with a cohort of 90, first in buffer medium and then on humans, using a protocol approved by the local FDA Institutional Review Board. The assay protocol was optimized to include variability of individuals to consumption and response to ingesting alcohol (beer or wine) in two doses. Possible interferences from sweat components such as glucose, uric acid, lactate, ascorbic acid and creatine were investigated and found to be negligible.

After the sensors and protocols were optimized with benchtop instruments, they were connected to a commercial off-the-shelf (COTS) integrated, wearable printed circuit board that provided control and Bluetooth telemetry. This board has been used in other chemical sensors developed in the Joseph Wang lab at UCSD.

After in vitro performance of the sensor was demonstrated, it was ready for testing with humans. Conventional BAC measurements obtained with a breathalyzer were used for comparison. In three subjects, the correlation had an r value of 0.912. The calibration curve obtained by plotting the response current versus BAC gave a slope of 102 uA/BAC% with a correlation coefficient of r2 = 0.999 for a single individual. Responses vary, probably reflecting patient weight and hence dilution.

More work will be required to show the sensor’s utility in settings such as law enforcement and toxicology. Since most of the parts are printed on the wearable tattoo, the cost of the sensor is low. The paper did not reference the need for individual calibration or how long the device can measure BAC as the body clears the ethanol, nor did it mention the lifetime of pilocarpine or whether it can recharged.

In any case, the UCSD team successfully designed an integrated device that solves or avoids existing problems with blood alcohol assays.

Reference

  1. Kim, J.; Jeerapan, I. et al. Noninvasive alcohol monitoring using a wearable tattoo-based iontophoretic-biosensing system. ACS Sensors; pub. online 7-12-2016.

Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected].

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