Chemical imaging of pharmaceutical materials: fabrication of micropatterned resolution targets

Resolution targets composed of thick poly(ethylene glycol) (PEG) lines on silicon substrates have been fabricated using the method of micromolding in capillaries (MiMIC). Patterns of three parallel lines with equal width and spacing have been prepared, with widths between 5 and 25 microm. Raman chemical images of the PEG-on-silicon devices as well as the metal-on-glass masks used to prepare the devices were measured. The Raman images were used to determine the impulse response of the instrument by comparing the measured images to model functions prepared by convolution of a test impulse function with the object functions of the devices. Impulse widths for PEG-on-silicon targets were approximately two times greater than impulse widths for metal-on-glass targets. The results provide a quantitative measure of the influence of light-matter interactions on the spatial resolution achievable with chemical imaging instruments. This work shows that microfluidic channels can be used to produce robust patterns of PEG on silicon, and these patterns are realistic resolution targets for spectroscopic chemical imaging of pharmaceutical materials.