Visualization of controlled fragrance release from cyclodextrin inclusion complexes by fluorescence imaging

Evaluation of odour release is important for the development of encapsulated fragrances. However, the use of existing instrumental analysis or gas-sensor technologies for odour-release evaluation is time- and labour-consuming. This paper introduces a fluorescence imaging system that can be used as a simple but effective tool to visualize the moisture-activated release of fragrance from cyclodextrin inclusion complexes. The visualization is based on the fluorescence changes of samples caused by the release of fragrance molecules from the cavity of cyclodextrin. Fluorescence spectroscopy investigations proved that different strategies could be used in the visualization depending on the molecular characters of the encapsulated fragrances. In the case of fragrance molecules with fluorescence (typically methyl anthranilate: MA), the change of fluorescence intensity was derived from the changed microenvironment of MA - from the encapsulated state to the released state. For the fragrance molecules without fluorescence (typically menthol), an appropriate fluorescent probe (7-amino-4-methylcoumarin: AMC) was used, and the fluorescence change was observed due to the interactions between AMC and the released menthol molecules. The real-time releases were visualized by two-dimensional/three-dimensional surface plots of the fluorescence images using image-processing software. Both the burst release occurring on the short time scale and the slow, natural release in ambient conditions can be demonstrated by the proposed visualization technique.