Raman on a disc: high-quality Raman spectroscopy in an open channel on a centrifugal microfluidic disc.

The implausible combination of centrifugal disc microfluidics and un-covered channels provides a simple way in which Raman spectroscopy can be implemented in industrially-relevant lab-on-a disc technology. Here we demonstrate these advantages by detecting very low concentrations of melamine in liquid milk, without pre-processing, without surface enhancement of the Raman signal and with no evidence of spectral contamination from the polymeric chip itself. A limit of detection (LOD) of 203 ppm for melamine in milk was achieved from Raman spectra of milk after drying. The centrifugal disc rotation and microchannel geometry results in rapid and reliable filling of the channels and in meniscus shape control, enabling reproducible Raman detection with quantitative precision.

Refractive index gratings in electro-optic polymer thin films.

Refractive index gratings have been inscribed in polymer thin films by permanently photobleaching the organic chromophore PYR-3 dopant. The grating inscription process was investigated in detail for the purpose of improving the diffraction efficiency (η) of the PYR-3 doped polymer gratings. Three processes were identified that contributed to the η of the first diffracted order: a periodic change in the refractive index due to photobleaching of the PYR-3, formation of the surface relief grating as a consequence of free volume change during bleaching, and the introduction of periodic, strain-induced changes in the refractive index.