Publication InformationLi, B.; Calvet, A.; Casamayou-Boucau, Y.; Morris, C.; Ryder, A.G. (2015) 'Low-content quantification in powders using Raman spectroscopy: a facile chemometric approach to sub 0.1% limits of detection'. Analytical Chemistry, 87 (6):3419-3428. PublisherAmerican Chemical Society Low-content quantification in powders using Raman spectroscopy: a facile chemometric approach to sub 0.1% limits of detection.Boyan Li, Amandine Calvet, Yannick Casamayou-Boucau, Cheryl Morris, and Alan G. Ryder* Nanoscale Biophotonics Laboratory, School of Chemistry, National University of Ireland, Galway, Galway, Ireland.* To whom correspondence should be addressed.Tel: +3539149 2943 Email: alan.ryder@nuigalway.ie ABSTRACT A robust and accurate analytical methodology for low-content (<0.1%) quantification in the solid-state using Raman spectroscopy, sub-sampling, and chemometrics was demonstrated using a piracetam-proline model. The method involved a 5-step process: collection of relatively large number of spectra (8410) from each sample by Raman mapping, meticulous data pretreatment to remove spectral artefacts, use of a 0-100% concentration range partial least squares (PLS) regression model to estimate concentration at each pixel, use of a more-accurate, reduced concentration range PLS model to accurately calculate analyte concentration at each pixel, and finally statistical analysis of all 8000+ concentration predictions to produce an accurate overall sample concentration. The relative prediction accuracy was ~2.4% for a 0.05~1.0% concentration range and the limit of detection was comparable to high performance liquid chromatography (0.03% versus 0.041%). For data pretreatment, we developed a unique cosmic ray removal method and used an automated baseline correction method, neither of which required subjective user intervention and thus were fully automatable. The method is applicable to systems, which cannot be easily analyzed chromatographically such as hydrate, polymorph, or solvate contamination.

. (2010) 'Study of water adsorption in PolyN-isopropylacrylamide) thin films using fluorescence emission of 3-hydroxyflavone probes'. Macromolecules, 43 (22):9488-9494. Publisher ACS PublicationsLink to publisher ' Abstract:The non-contact, measurement of water uptake in micro-scale (1-100 µm), thermoresponsive Poly(N-isopropylacrylamide) thin films is challenging. We assessed the efficacy of three different 3-Hydroxyflavone (3-HF) based fluorophores; to monitor water uptake in pNIPAM thin films close to the Lower Critical Solution Temperature (LCST) at 25 and 37 ºC. These 3-HF fluorophores undergo excited state intramolecular proton transfer, yielding emission from normal (N*) and tautomeric (T*) excited-state forms. The emission intensity ratio, log(I N* /I T* ) and N* band position are environmentally sensitive. Water adsorption in pNIPAM thin films follows a non-linear, two phase process: at low relative humidity, the adsorbed water disrupts polymerfluorophore hydrogen bonding, yielding small changes in log(I N* /I T* ) ratios, and overall intensity, at higher relative humidity, these intensity parameters (but not fluorescence lifetime) change dramatically, indicating a larger change in local polarity. These probes are thus sensitive indicators of water uptake in pNIPAM.

The use of microscale thin polymer films is widespread in biomedical science and engineering, with applications in areas such as tissue engineering, drug delivery, microfluidic devices, bio-adhesion mediators, and bio-actuators. Much attention is devoted to the use of functional polymers that display stimuliresponsive behavior with the intention of providing "smart" coatings. One potential example is the use of thin thermoresponsive polymer films as drug eluting coatings on medical devices, where not only does the polymer function as a drug reservoir but it also acts as a biocompatibility modulator to improve device performance.Often these thin polymer coatings have to be applied to complex geometries, which can cause problems for in-situ analysis. Another important consideration is the fact that these films have large surface area to mass ratios and thus water uptake can be significant. This is serious because coating stability, device efficacy, and long-term storage are influenced by the physiochemical properties of the polymer which are modulated by water content. Thus, there is a need for a rapid, non-contact, non-destructive, analytical method capable of analyzing thermoresponsive polymers in solution, and in-situ of the solid-state on medical devices. Fluorescence spectroscopy based methods can deal with both sample types and provide additional benefits in terms of high sensitivity and low probe concentrations, which provide for minimal sample disruption. This article gives a brief overview of the application of various fluorescence methods for the physicochemical characterization of thermoresponsive polymers such as poly (N-isopropylacrylamide), PNIPAm.

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