Polarization effect in tip-enhanced infrared nanospectroscopy studies of the selective Y5 receptor antagonist Lu AA33810

Abstract

A novel approach of combining conventional infrared spectroscopy (IR) and atomic force microscopy (AFM) is presented to better understand the behavior of a drug adsorbed on a metal substrate at the nanoscale level. Tip-enhanced infrared nanospectroscopy (TEIRA) was used for the first time to investigate Lu AA33810, a selective brain-penetrating Y5 receptor antagonist, after immobilization on gold nanoparticles (GNPs). Here, a gold coated AFM tip and gold substrate were used to obtain the near-field electromagnetic field trapping effect. Because of the huge signal enhancement, it was possible to obtain the spectral information regarding the self-assembled monolayer of the investigated molecule. The effect of two orthogonal polarizations (p-and s-polarization modulations) of the excitation laser beam on the spectral patterns is also discussed. The results show that there is a strong relationship between the state of polarization of the incident radiation and the relative infrared band intensities. Another factor affecting the observed spectral differences is the topology of the metal substrate, which may result in the induction of a cross-polarization effect. The performed analysis indicates that the C-C bond from the cyclohexyl group is oriented almost parallel to the metal surface. Conversely, the p-and s-polarized spectral variations suggest that the O=S=O angle is high enough to enable the simultaneous interaction of both oxygen atoms with the GNPs.

Probing amyloid fibril secondary structures by infrared nanospectroscopy: experimental and theoretical considerations

“…For the first time, a complete study of three different amyloid fibrils (Aβ, α-syn and PrP) was performed using polarized resolved AFM-IR in different illumination configurations and using two types of AFM probes. Several other polarizedresolved AFM-IR studies, 41,[47][48][49][50][51][52][53][54][55] were performed using either the bottom-up or top-down illumination configuration, but none of them has discussed in detail the effect of these different illumination and tip's gold-coating.…”

Comparison between high definition FT‐IR, Raman and AFM‐IR for subcellular chemical imaging of cholesteryl esters in prostate cancer cells

“…The enhancement of CEs bands may be a consequence of a polarization effect observed previously in some anisotropic materials . In general, AFM‐IR spectra of anisotropic samples recorded using p‐ and s‐polarization can differ significantly in band intensities . Moreover, anisotropy effects observed in AFM‐IR spectra of thin samples are not limited to molecule orientation.…”

Nanoscale image of the drug/metal mono-layer interaction: Tapping AFM-IR investigations

“…AFM-IR is widely used for various applications, i.e., cancer cell [27,28] and bacteria [29,30] investigations, characterization of lipid distribution in human skin [31], protein secondary structure in cataractous human lenses [32], and polymers [33] and cultural heritage analysis [34]. Additionally, the development of the tapping AFM-IR mode has opened new possibilities in the analysis of soft and loosely bound samples such as drug-loaded polymeric nanoparticles [35], drugs partitioned within lipid-polymer hybrid films [36] and drugs adsorbed on aggregated metal nanoparticles [37,38].…”