title: Transmission resonance Raman spectroscopy: experimental results versus theoretical model calculations.
abstract: A laser spectroscopic technique is described that combines transmission and resonance-enhanced Raman inelastic scattering together with low laser power (< 30 mW) and good spatial resolution (< 200 μm) as operational features. The monitoring of the transmitted inelastic scattering  provides an increased signal-to-noise ratio because the low fluorescence background and, on the other hand, the resonant character of the laser excitation, leads to enhanced analytical sensitivity. The spectroscopic technique was applied to investigate the carotenoid content (specifically  the β-carotene concentration) of distinct samples that included fruits, reaching a detection limit of the order of hundreds of picograms in solid samples, which is below the level needed for typical food control analysis. Additional features of the present development are direct  sampling, noninvasive character, and fast analysis that is not time consuming. From a theoretical point of view, a model for the Raman signal dependence on the sample thickness is also presented. Essentially, the model considers the sample to be homogeneous and describes the underlying physics  using only three parameters: the Raman cross-section, the laser-radiation attenuation cross-section, and the Raman signal attenuation cross-section. The model was applied successfully to describe the sample-size dependence of the Raman signal in both β-carotene standards and carrot roots.  The present technique could be useful for direct, fast, and nondestructive investigations in food quality control and analytical or physiological studies of animal and human tissues.
authors.affiliation: Unidad de Láseres y Haces Moleculares, Instituto Pluridisicplinar, Universidad Complutense de Madrid, Juan XXIII-1°, 28040-Madrid, Spain.
authors.forename: Alicia G
authors.initials: AG
authors.lastname: Gonzálvez
authors.forename: Ángel
authors.initials: Á
authors.lastname: González Ureña
mesh_terms: D018552:Daucus carota / Q000737:chemistry; D005504:Food Analysis / Q000379:methods; D057230:Limit of Detection; D008962:Models, Theoretical; D013059:Spectrum Analysis, Raman / Q000379:methods* / Q000592:standards; D019207:beta Carotene / Q000032:analysis / Q000737:chemistry
chemical_list: D019207:beta Carotene