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Diffusion Kinetics & Permeation Concentration of Human Stratum Corneum Characterization by Terahertz Scanning Reflectometry

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Terahertz reflectometry and spectrometry was used to investigate the permeation kinetics and concentration profile of active ingredients in to the stratum corneum. To our knowledge this is the first effort of direct, non-invasive, and real-time measurement of kinetics and concentration gradient of analytes in to stratum corneum. Moreover, this is a general method that is applicable to any substrate and analyte combinations. It was found that the analyte concentration in stratum corneum of 1% hydrocortisone solution in propylene glycol is significantly higher than 1% caffeine in deionized water. These findings are important for quantifying transdermal drug delivery formulation with these solvents and can be extended to other analytes and solvents. Terahertz spectra of untreated stratum corneum vs. those treated with 10 mM N-0915 solution were distinctively different. Additionally, the N-0915 treated specimen exhibits prominent absorption peaks in the 7.27 THz, 11.88 THz and 18.42 THz region while the spectrum of blank specimen exhibits a monotonous increase of absorbance with frequency. This indicates the importance of broadband terahertz spectroscopy of a range of 20 THz or more to be able to probe molecular events.

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Drug Delivery Technology

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