Monitoring of Lactate in Interstitial Fluid, Saliva and Sweat by Electrochemical Biosensor: The Uncertainties of Biological Interpretation

Abstract

Lactate electrochemical biosensors were fabricated using Pediococcus sp lactate oxidase (E.C. 1.1.3.2), an external polyurethane membrane laminate diffusion barrier and an internal ionomeric polymer barrier (sulphonated polyether ether sulphone polyether sulphone, SPEES PES). In a needle embodiment, a Pt wire working electrode was retained within stainless steel tubing serving as pseudoreference. The construct gave linearity to at least 25 mM lactate with 0.17 nA/mM lactate sensitivity. A low permeability inner membrane was also unexpectedly able to increase linearity. Responses were oxygen dependent at pO2 < 70 mmHg, irrespective of the inclusion of an external diffusion barrier membrane. Subcutaneous tissue was monitored in Sprague Dawley rats, and saliva and sweat during exercise in human subjects. The tissue sensors registered no response to intravenous Na lactate, indicating a blood-tissue lactate barrier. Salivary lactate allowed tracking of blood lactate during exercise, but lactate levels were substantially lower than those in blood (0–3.5 mM vs. 1.6–12.1 mM), with variable degrees of lactate partitioning from blood, evident both between subjects and at different exercise time points. Sweat lactate during exercise measured up to 23 mM but showed highly inconsistent change as exercise progressed. We conclude that neither tissue interstitial fluid nor sweat are usable as surrogates for blood lactate, and that major reappraisal of lactate sensor use is indicated for any extravascular monitoring strategy for lactate.

Mechanistic Assessment of Metabolic Interaction between Single Oral Commensal Cells by Scanning Electrochemical Microscopy

“…This concentration, notably, is similar to the lactate concentration of saliva in healthy humans with a range within 3.5 mM. 34 Another theoretical curve over C. matruchotii is simulated, where lactate diffusing from adjacent S. mitis permeates the C. matruchotii BM, and is readily oxidized by C. matruchotii. In this case, the rapid consumption of lactate appreciably decreases the lactate concentration near C. matruchotii, thus resulting in much smaller tip currents than currents only governed by BM permeability without lactate consumption (Figure 4C, red closed circles and blue open circles, respectively).…”

Opportunities and challenges in the diagnostic utility of dermal interstitial fluid

“…However, the correlation is not strong for all small molecules. For example, for lactate, which was believed to be a strong contender for ISF detection, concentrations in blood and ISF do not correlate well 91 . Still, the rapid equilibration of many small hydrophilic molecules suggests that most would be strong candidates for continuous monitoring in dermal ISF.…”

Wearable Electrodes for Lactate: Applications in Enzyme‐Based Sensors and Energy Biodevices

“…One study successfully sets an example of immobilizing LOx on platinum electrode using glutaraldehyde as a crosslinker in a dip-coating technique. [100] With the use of crosslinkers covalently interlinking enzymes and electrodes, this cross linking provides much greater durability and stability than van der Waals or hydrophobic interactions and can prevent enzymes from leaching out. Cross linking is simple and inexpensive in general, hence the reason why it is widely used in industrial applications.…”