Beer-Lambert's law, A = [sigma]cl, relates spectral absorbance, A, to AuNP concentration, c, and optical pathlength
, I, using a material- and wavelength-specific absorbance coefficient, [sigma] [17, 36].
Wyatt, "Estimation of optical pathlength through tissue from direct time of flight measurement," Physics in Medicine and Biology, vol.
Zaccanti, "Variability of human brain and muscle optical pathlength in different experimental conditions," in Photon Migration and Imaging in Random Media and Tissues, vol.
Textured surfaces are known to scatter the light passing through thin-film solar cells, thereby increasing the optical pathlength in the cells and hence the overall absorptance.
Since the absorption difference of planar and AIT glass without any film is quite small ([2.1.sub.%abs]), the gain in the optical absorptance is mainly due to the increased optical pathlength in the silicon film.
Essenpreis, "A monte carlo investigation of optical pathlength
in inhomogeneous tissue and its application to near-infrared spectroscopy," Phys.
Explicitly, photometric absorbance measurements from the vascular portions of the image are coupled with an estimation of the optical pathlength using the imaged vascular diameter (and assuming circular vessel cross sections).
Challenges of measuring total Hgb concentration, compared to relative measurements such as Sp[O.sub.2], lie in the contributions of other skin chromophores, variations in blood vessel location and density, variation in spectral signatures of oxy- and deoxyhemoglobin in the NIR regime, and changes in vessel diameter and subsequent optical pathlength during pulsation.
The optical pathlength
(1 mm) was set by stainless steel spacers between the sapphire windows of the optical cell.
The Beer-Lambert law of absorption spectroscopy indicates that glucose absorbance values depend on the absorptivity, concentration, and optical pathlength
. Molar absorptivity is fixed at each wavelength by the vibrational absorption properties of glucose.
Water or other aqueous reagent is dispensed from the pipettor into microplate wells, and the optical pathlength
in each well is determined in a microplate spectrophotometer.
Intelligent use of two optical pathlengths
within one gas cell gives the system wide dynamic range.