When Size Matters—Near Infrared Reflection Spectroscopy of Nanostructured Materials

Abstract

This article evaluates the applicability of near infrared (NIR) reflection spectroscopy for the physico-chemical and morphological characterisation of matter on a scale smaller than 1 micrometre (normally between 1 and 100 nanometres). The investigated materials comprise porous and non-porous silica particles, carbon based materials such as C₆₀ fullerenes, nano-crystalline diamond (NCD) and dendrimers, all of them having diameters and/or pore sizes in the nanometre range, respectively. In case of the silica packings and differently derivatised C₆₀ fullerenes, absorbance signals could be clearly assigned to corresponding surface modifications. Identification or classification of the material can be achieved successfully by principal component analysis. Nano crystalline diamond surfaces, whether H- or O-terminated, could be differentiated by a computed partial least squares (PLS) regression model with around 80% precision. Generations 0–7 of poly(amidoamine) (PAMAM) dendrimers with functionalised surface amine groups are characterised in respect of particle diameter and molecular weight. The established PLS models showed a standard error of prediction of only 0.43 nm and 12.30 kDa, respectively. NIR spectroscopy has developed as a flexible analytical method that can be utilized for fast, reliable and highly reproducible screening of matter even in the nanometer range.