Abstract
The application of metal nanoparticles as an efficient drug delivery system is one of the directions of cancer therapy development. However, this strategy requires precise information about how the drug interacts with the applied nanocarrier. In this study, atomic force microscopy combined with infrared spectroscopy (AFM-IR) was used for the first time to investigate the erlotinib adsorption structure on two different types of 15 nm metal nanoparticle mono-layers, namely, silver nanoparticle (AgNP) and gold nanoparticle (AuNP) mono-layers. Because the metal nanoparticles are loosely bound samples, only the tapping AFM-IR mode is suitable for the collection of IR maps and spectra for such a system. The obtained results indicated the relevance of the AFM-IR technique for characterizing drug interactions with a metal mono-layer surface. The investigated drug interacts with the AgNPs mainly through phenyl rings and methoxy moieties, while quinazoline, amino, and ethoxy moieties appear to be farther from the surface. For the AuNPs, the interaction occurs through both the phenyl ring and the quinazoline moiety. Additionally, the aliphatic groups of erlotinib directly participate in this interaction. The novelty of the present work is also related to the use of the tapping AFM-IR mode to study metal NP mono-layers with a drug adsorbed on them. The collected IR maps for the most enhanced erlotinib bands show specific areas with very high signal intensity. The connection between these areas and the “hot spots” typical for the surface plasmon resonance phenomenon of metals is considered.
Highlights
The development of target-cell-specific delivery as a new approach to increase the cytotoxic effects of drugs inside cancer cells is highly desirable [1]
Such phenomena prove that this nanospectroscopy technique in connection with techniques such as SERS can be successfully applied for in-depth molecular adsorption characterization
This fact is important because the metal surface selection rules used for adsorption geometry interpretation of typical surface-enhanced infrared absorption (SEIRA) spectra, which are commonly known and well characterized [8, 9], provided reliable conclusions for the atomic force microscopy combined with infrared spectroscopy (AFM-infrared spectroscopy (IR)) technique
Summary
The development of target-cell-specific delivery as a new approach to increase the cytotoxic effects of drugs inside cancer cells is highly desirable [1]. AFM-IR combines the nanometre resolution of atomic force microscopy with the ability to perform chemical analysis owing to the acquisition of local infrared spectra [22,23,24,25] In this approach, the local absorption is ruled by the photothermal effect. Those SERS data do not answer the question of how the drugs interact locally with the applied metal nanoparticles It is still an open question of whether the surface selection rules commonly known for the conventional SEIRA technique could be applied to interpret the AFM-IR results of molecules immobilized on a metal surface. To the best of the authors’ knowledge, these are the first investigations using the tapping AFM-IR mode to study drug adsorption on metal nanoparticle mono-layers
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