AFM–SEIRA nanospectroscopy imaging of the drug adsorption on the PtNP monolayers

In this study, for the first time, 20–nm and 55–nm sized platinum nanoparticle (PtNPs–20 and PtNPs–55, accordingly) monolayers were employed as surface–active substrates for atomic force microscopy in combination with surface–enhanced infrared spectroscopy (AFM–SEIRA) measurements. The spectroscopic considerations have been enriched by the precise physicochemical characterization of PtNPs. The obtained data show that the applied monolayers ensure sufficient AFM–SEIRA signal enhancement, therefore allowing to perform a detailed description of erlotinib (a drug approved in non–small cell lung cancer therapy) adsorption on these surfaces with ultra–high spatial resolution. The main finding of AFM-SEIRA investigations revealed similar adsorption geometry of erlotinib on both 20-nm and 55-nm PtNP monolayers via the quinazoline and –CH2 moieties. Moreover, the application of PtNPs monolayers with different nanoparticle sizes allowed to visualize two mechanisms of plasmon coupling effect − either between neighbouring NPs or between NPs and AFM tip, as can be seen on AFM-SEIRA intensity maps.