Abstract
The transdermal extraction of interstitial fluid using low frequency ultrasound offers a potential minimally invasive method of obtaining a fluid sample for home blood glucose monitoring. Here, the application of low frequency ultrasound (20 kHz) is shown to enhance the transdermal transport of interstitial fluid across hairless rat skin. Using ³H₂O as a tracer injected intravenously, a measurable amount of water (> 1 []L) was extracted. Piezoelectric transducers were imbedded in the extraction chamber and used to correlate ultrasound spectral properties to the amount of fluid extracted. Results indicate that the highest amount of water extracted occurs when the acoustic coupling media on the surface of the skin is cavitating, resulting in mild ablation of the stratum corneum and a reduction in its resistance to water mass transfer. The ability to detect very low glucose concentrations (<< 2 mM), which is necessary for the analysis of the extracted interstitial fluid, has been demonstrated with two different types of techniques: (1) a glucose responsive electrode fabricated by immobilizing glucose oxidase (GOX) within redox polymer hydrogels composed of poly(ethylene glycol) tetra acrylate (PEG-TA) and poly[vinyl Os(bis-bipyridine)₂Cl]-co-allylamine (Os-PVP-AA), an electron donor/acceptor that allows the transfer of electrons from the enzymatic oxidation/reduction reaction to the electrode surface, and (2) a fluorescent assay, which quantifies the presence of glucose via the production of hydrogen peroxide catalyzed by GOX and horseradish peroxidase (HRP). In order to assess the safety of low frequency sonophoresis, sections of ultrasound treated hairless rat skin were submitted for histologic analysis. Neither short, nor long-term damage to the dermis was present after exposure to the described ultrasound conditions. Skin samples were also examined using a scanning electron microscope (SEM) to aid in the development of a hypothesis for a possible mechanism for fluid transport.
Cantrell, Jeffrey Travis (2000). The determination of glucose in sonophoretically extracted interstitial fluid and the characterization of ultrasound parameters. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2000 -THESIS -C3662.