Multivariate spectral analysis of pH SERS probes for improved sensing capabilities. (14th March 2016)

• Record Type: Journal Article
• Authors: Williams, Adam; Flynn, Kevin John; Xia, Zhidao; Dunstan, Peter Roger
• Is Part Of: Journal of Raman spectroscopy. Volume 47:Number 7(2016)
• Page Start: 819
• Page End: 827
• Publication Date: 2016-03-14
• Subjects: pMBA -- pH sensors -- decarboxylation -- PCA -- SERS; Raman spectroscopy -- Periodicals; 535.846
• DOI: 10.1002/jrs.4910
• Languages: English
• ISSNs: 0377-0486

Abstract

Abstract : Adsorption of functional groups to the surface of plasmonic nanoparticles provides a platform for localised optical sensing. Over the past decade, nanoscale sensors for intracellular pH measurement based on surface‐enhanced Raman spectroscopy (SERS) have been developed. However, the approaches by which pH‐SERS measurements are made and analysed can greatly impact the precision and accuracy of pH calibration. To improve pH nanosensors, the sources of experimental variation must be determined and the data must be optimally analysed. Here we report the plasmon‐induced decarboxylation of para ‐mercaptobenzoic acid (pMBA) pH reporters attached to gold nanoparticles and conclude a strong association with laser power. The detrimental decarboxylation of pMBA has profound implications on the sensitivity and reliability of the pH sensor. Decarboxylation spectral signatures map directly onto those that are typically used to record pH changes, and, hence, the greatest implication of decarboxylation of pH sensors is inaccurate or false pH reporting. Here a more robust spectral analysis for pH sensing based upon an optimal spectral region for pH calibration is presented together with a unique application of the multivariate statistical technique, principal component analysis (PCA). PCA interprets complex spectral dynamics, and by direct comparisons with the typically employed ratiometric analysis, a significant improvement in generating accurate pH sensing is demonstrated. An application of these methods in determining the pH of internalised nanosensors in macrophage cells further promotes these step changes in pH measurement methodology via the avoidance of disruptive spectral signatures that arise in real applications. Copyright © 2016 John Wiley & Sons, Ltd. Abstract : By using a surface enhanced Raman spectroscopy approach, adsorption of para ‐mercaptobenzoic acid to the surface of plasmonic nanoparticles provides a platform for localised optical sensing of pH. Here a robust spectral analysis for pH sensing is presented based upon avoidance of decarboxylation, selection of an optimal spectral region for pH calibration and combination with a unique application of principal component analysis. A demonstration of these methods in determining the pH of internalised nanosensors in macrophage cells is presented.