Fluorescence microscopy of inkjet prints

Abstract

Inkjet printing technology has been developing rapidly during recent years, pressing the ink and paper manufacturers to develop a better understanding of the mechanism of fixation of inkjet dye into the substrate. The aim of the work described in this thesis was to investigate the three-dimensional distribution of inkjet dye in paper and the interaction between dye and paper using advanced fluorescence microscopy techniques, Confocal Laser Scanning Microscopy (CLSM), and Two-photon Fluorescence Lifetime Imaging Microscopy (2P-FLIM). It has been shown that CLSM is a valuable, non-destructive, rapid technique for threedimensional imaging of printed samples and evaluation of print quality. The intrinsic fluorescence of both the inkjet dye and the paper substrate can be used to determine the spread and penetration of ink droplets in different inkjet papers. The optical sectioning capability of CLSM enables the position of the ink layer relative to the paper surface and the penetration depth of the ink to be quantified. It was observed that while in the microporous type of inkjet paper the penetration depends on the quantity of ink in the printed sample, in the swellable type of inkjet paper the penetration is almost the same for different amounts of ink. 2P-FLIM has been employed to spatially map, in three-dimensions, fluorescence lifetimes by measuring the lifetime at each pixel in the image. Fluorescent molecules in both the ink and paper were analysed. Because the fluorescence lifetime is affected by the local molecular environment, the fluorescence lifetime maps provide information on the interaction between inkjet dye and paper. Analysis of fluorescence lifetime maps reveals the interaction between dye molecules and silica or alumina particles in the paper, variations of the molecular environment within a single ink dot and that interaction between dye and paper is affected by pH.