Continuous real-time monitoring of critical bioprocesses has intuitive appeal as an improvement over discrete sampling. I was impressed with a paper reporting the development of a tattoo electrochemical sensor for measuring lactate in sweat.1 This noninvasive sensor is applied directly to the skin.
Carbon nano fibers provide the conduction between the electrodes and connection pads. Lactate oxidase is the active enzyme in the working electrode. The lactate is oxidized to pyruvate with the release of two electrons. Tetrathiafulvalene (TTF) is added to reduce the oxidation potential. The tattoo of the counter, reference, and working electrode is created by screen-printing.
The product was applied to the skin. After lengthy in vitro evaluation for mechanical and electrical properties, utility of the tattoo was confirmed during a strenuous cycling workout involving 10 humans. The lactate centration of human sweat varied up to 25 mM. The sensor confirmed the expected profile from the exercise protocol. Plus, two patients were given inactive (lactate oxidase deficient) sensors. These showed no signal.
Many of us will recall pictures of athletes “hitting the wall” from lactate toxicity due to extreme exertion in endurance events such as a marathon. While this sensor was only connected umbilically to a stationary recording device, one can easily envision a readout attached to the wrist, etc.
The authors deserve credit for designing a practical epidermal electrochemical biosensor for real-time monitoring of sweat lactate. The fact that the design is durable yet temporary is an added benefit. Plus it appears to use well-established and low-cost fabrication technology.
- Jia, W.; Bandodkar, A.J. et al. Electrochemical tattoo biosenors for real-time noninvasive lactate monitoring in human perspiration. Anal. Chem. 2013, 85(14), 6553–60.
Robert L. Stevenson, Ph.D., is a Consultant and Editor of Separation Science for American Laboratory/Labcompare; e-mail: email@example.com.