Measurement of dye diffusion in agar gel by use of low-coher ence interferometry

Abstract

We demonstrate low-coherence interferometry for diffusion measurements. We have measured the diffusion coefficient of a phthalocyanine dye in 1.5% agar gel with a two-wavelength interferometer; one wavelength was matched to the absorption peak of the dye at 675 nm, while the other, 805 nm, was not affected by the dye. The diffusion coefficient of the dye was found by fitting a mathematical model for the interferometer signal to the measured low-coherence interferometry amplitude. A 95% confidence interval for the diffusion coefficient was found to be D = (2.5 +/- 0.2) x 10(-10) m2/s. The influence of speckle averaging and experiment time on the determination of the diffusion coefficient has been studied. The presented technique allows in situ characterization of diffusion in semitransparent media.

Polymeric lithography editor: Editing lithographic errors with nanoporous polymeric probes

“…With the diffusion coefficient ( D ) of ~2.5 ± 2 × 10 −10 m 2 s −1 for a small molecule in the agarose gel ( 38 ), the estimated distance ( d ) travelled by the “picked-up” ink molecules from the tip of the PLE eraser into the matrix in τ = 10 s was ~70 μm ($\mathrm{italicd}\approx \sqrt{2\mathrm{italicD}\mathrm{normal\tau }}$). That is, the absorbed molecules will travel a distance of ~70 μm from the tip into the matrix between consecutive erasing cycles (τ ~10 s).…”

Functional imaging of dye concentration in tissue phantoms by spectroscopic optical coherence tomography

“…9,[17][18][19] This requires knowledge of the difference in absorption of the sample at the probing wavelengths. An application of concentration imaging could be monitoring the diffusion of a topically applied sensitizer prior to light exposure in photodynamic therapy 20 …”

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“…NIR dyes with characteristic absorption spectra can be useful in conjunction with a spectroscopic OCT technique [123]. Another way of using dyes is the pump-probe technique, which provides contrast based on the variation in absorption when the dye molecules are excited by a pump light source [124].…”

“…Among these are microbubbles [125], engineered microspheres [126], and different types of plasmon-resonant gold nanoparticles [127,128]. Exogenous contrast agents may be used to increase the contrast between blood vessel and the surrounding tissue [125], some have an inherent selectivity to accumulate in certain types of tissue, and many offer the possibility to be targeted to specific markers [123], e. g. receptors that are expressed on diseased or cancerous cells [129]. Therefore, exogenous contrast can eventually become a valuable additional tool for OCT in medical diagnostics or biologic research.…”