ECE/CHE Project Assignment (Fall 2018)
Jsphill7@ncsu.edu
Wearable Sensor for Δ9-tetrahydrocannabinol Detection
Jasmine Phillips, Wilson College of Textiles, North Carolina State University, Raleigh, NC
Overview
Here, a wearable sensor for the detection of Δ9-tetrahydrocannabinol in bodily fluids will be introduced for the improvement of sample collection, accuracy, and duration of detection.
Innovation & Impact
The uses of illegal, illicit drugs has been a long-standing issue in the United States. Although there are recent debates on the legalization of marijuana, containing THC (tetrahydrocannabinol), many states are still against the use of this drug which in turn causes for the need for testing which can be useful for law enforcement as well as employers. Based on the context of the ADME cycle of drugs (absorption/distribution/metabolism/excretion), it is believed that a small but sufficient percent of the drug in question is excreted in sweat and can be tested. This makes sweat a suitable biological matrix for the monitoring of recent drug use. Currently, only two approaches are used to test for drugs in sweat. The first is for the most recent detection (less than 24 hours), which involves only the collection of sweat at one point in time. Here, an immunochromatographic test of the sample gives a qualitative result5 or drugs in sweat are collected on a cotton wipe and then extracted for confirmatory analysis6.This approach is however only useful to identify persons currently/most recently under the influence of a substance. The second approach is based on patch technology which monitors the use of a substance for a duration of time longer than what can be provided by the testing of urine. However, these patches can only be worn for the duration of one week where drugs accumulate in the collection device and degradation is limited. This method has been used extensively for those in recovery to prove the absence of drug use. Both methods have been utilized extensively due to the techniques being minimally invasive and also there being less ethical issues than those present during blood or urine testing. However, drug testing by sweat has ultimately been difficult due to issues with sample recovery and the limited sensitivities of analytical methods used previously. Here, we hope to accomplish the improvement of such methods of sample collection, accuracy, and duration by proposing a wearable sensor to detect THC in sweat. The major enabling technologies for detection via wearable systems is the sensing and data collection hardware to collect physiological data, communication hardware, and software to transport data to a specific center, followed by the data analysis techniques to extract information from the physiological data4.The anticipated outputs of a successful effort is a more reliable and sensitive wearable sensor for drug detection.
Proposed Work
Here, we propose a novel, effective, and sensitive electrochemical sensor for rapid determination of THC (see Figure 1) in sweat via gold nanoparticles. We hope to electrodeposit gold nanoparticles on a multi-walled carbon nanotube modified carbon-paste electrode. Following a method previously used to detect methadone (6-dimethylamino-4,4-diphenyl-3-heptanone), we will detect the active agent THC in biological fluids1. The voltammetry behavior of THC at this modified electrode is to be studied by way of cyclic and square wave voltammetry techniques obtaining results to compare with those gathered at the multiwalled carbon nanotube modified carbon paste electrode (MWCPE). The oxidation of THC will then be observed as well as the adsorption and diffusion process at the GNPs/MWPCE. We plan to explore several experimental parameters such as pH, scan rate, accumulation potential, as well as the duration of this method using the voltammetry response of THC. Using optimum conditions, the concentration of THC will be determined using square wave voltammetry (SWV) determining linear range, correlation coefficient, and detection limits at the MWCPE. This proposed electrode will enable the determination of THC in a pharmaceutical dosage in sweat samples. The effects of interferences will be reported as well as the analytical performance for the determination of THC at a significantly low detection limit, high sensitivity, and reproducibility in turn making the method reliable. A sweat based wearable sensor will be developed with pH as a parameter while also detecting biomarkers while maintaining full performance. However, flexibility and lifetime will be a factor needing to be explored so that the device can be used on human skin without negatively impacting the performance of the sensor. The sweat is to be detected in under 10 seconds and once the THC in sweat is detected by the system, the results will be transmitted wirelessly. A LED will then be designed to report the presence of THC in the sweat samples. As discovered recently, the sensor will be based on affinity immunoassay principles where detection can be achieved through a chemiresistive sensing mechanism. Here, an AC voltage can be applied across the electrodes and the impedance across the sensor electrodes can be measured and calibrated for a significant dosage of THC in human sweat samples7. This detection of THC will be detected over flexible and rigid substrates where detection sensitivity with gold electrodes will be observed7.
The placement of wearable sensors has a direct effect on the measurement of bodily motions, therefore the ideal placement of wearable sensors for this specific application is not yet determined and will be a challenge. However, the waist area placement of a wearable sensor will better accumulate more sweat, while still having minimal motion in this center portion of the body2, which will minimize motion artifacts on the electron-skin surface.
References
1.) Afkhami, F. Soltani-Felehgari and T. Madrakian, "A sensitive electrochemical sensor for rapid determination of methadone in biological fluids using carbon paste electrode modified with gold nanofilm," Talanta, vol. 128, pp. 203-210, 2014.
2.) F. Attal et al, "Physical Human Activity Recognition Using Wearable Sensors," Sensors (Basel, Switzerland), vol. 15, (12), pp. 31314-31338, 2015.
3.) M. A. Huestis et al, "Excretion of Δ9-tetrahydrocannabinol in sweat," Forensic Science International, vol. 174, (2), pp. 173-177, 2007;2008;.
4.) S. Patel et al, "A review of wearable sensors and systems with application in rehabilitation," Journal of Neuroengineering and Rehabilitation, vol. 9, (1), pp. 21-21, 2012.
5.) S. Pichini et al, "Usefulness of sweat testing for the detection of MDMA after a single-dose administration," Journal of Analytical Toxicology, vol. 27, (5), pp. 294, 2003
6.) N. Samyn, G. De Boeck and A. Verstraete, "The Use of Oral Fluid and Sweat Wipes for the Detection of Drugs of Abuse in Drivers," Journal of Forensic Sciences, vol. 47, (6), pp. 1380-1387, 2002.
7.) P. Selvam et al, "A wearable biochemical sensor for monitoring alcohol consumption lifestyle through Ethyl glucuronide (EtG) detection in human sweat," Scientific Reports, vol. 6, (1), pp. 23111, 2016.