Fast quantitative fluorescence authentication of milk powder and vanillin by a line-scan hyperspectral system.

We present a fast hyperspectral line-scan fluorescence imaging system to verify the feasibility of quantitative fluorescence authentication of powders. Vanillin, which is restricted for use in milk powder, especially in milk powder for infants, is mixed with milk powder in different mass concentrations (5%, 10%, 30%, 50%, 70%, and 90%). Mixed powders are located on a motorized linear stage. A 405 nm line laser is utilized to excite the fluorescence of the sample. Based on galvo scanning, we can generate a laser line with high spatial resolution and high-intensity density on the samples. An imaging spectrometer with a complementary metal-oxide semiconductor (CMOS) camera as detector is built. The spectral range of the spectrometer is 365-810 nm, with about 1 nm spectral resolution. One snapshot of the CMOS can acquire the fluorescent spatial and spectral information of a line region in 100 ms. By scanning the motorized linear stage, we obtain the fluorescence hypercube of the sample. A 100×1926×1216 hypercube, which covers an area of 15  mm×5  mm, is obtained in 50 s. The imaging speed can be enhanced further by increasing the intensity of the excitation laser and the sensitivity of the area camera. Fully constrained least squares, a linear spectral mixture analysis, is utilized to analyze the hypercube obtained by our homemade imaging spectrometer, thus obtaining the pixel concentration of vanillin in each mixed powder. Linear regression analysis is used for the pixel concentration and mass concentration of vanillin. A linear relationship with coefficient of determination R2 equal to one is observed, which demonstrates the capability of fluorescence hyperspectral quantitative analysis in powders.