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The cell membrane is a biological membrane that separates the interior of all cells from the outside environment. The main challenge in studying its structure and interactions with pharmaceuticals is the ability to understand the nanoscale chemical changes in the different structural molecules.
The limitations in understanding the nanoscale properties and interactions of various functional materials, such as fuel cells, solar cells, batteries, monolayers (MLs) of biological compounds (e.g., phospholipid 1,2-distearoyl-sn-glycero-phosphatidylcholine) and catalysts, created the need for IR nanospectroscopy. IR nanospectroscopy enables the extraction of detailed chemical information at the nanoscale and the identification of properties that influence the overall performance of functional materials.
IR nanospectroscopy adopts various aspects to complete a complex study. For example, to identify nanoscale properties and their influence on the functionality of halide-perovskite solar cells and catalytic nanoparticles, IR nanospectroscopy techniques utilize photo thermal-induced resonance (PTIR) and scattering scanning near-field optical microscopy (s-SNOM).
By employing nano-infrared microscopy and spectroscopy in combination with atomic force microscopy, it is possible to identify and chemically detect domain formation of two constituents, as well as obtain the IR spectra of these species with a spatial resolution on the nanoscale. Atomic force microscopy-based infrared spectroscopy (AFM-IR) enables chemical analysis and compositional mapping with a spatial resolution that is significantly below standard optical diffraction limits. The technique causes an AFM probe tip to locally detect thermal expansion in a sample produced by absorption of infrared radiation.
The technological progress in this field of IR nanospectroscopy has been advanced by the development of narrowband lasers, which have broad wavelength tunability, and the availability of other broadband sources such as synchrotrons, with high brightness.
Applications of IR Nanospectroscopy
Studying the chemical nature of the pit membranes of xylem cells
In angiosperms, the nano-sized pores present in pit membranes enable the passage of water under negative pressure, due to the obstruction by gas bubbles under normal conditions.
Characterization of the chemical composition of cell wall structures by synchrotron infrared nanospectroscopy and atomic force microscopy-infrared nanospectroscopy (with high spatial resolution) reveals the presence of significant peaks of cellulose, phenolic compounds, and proteins in the pit membranes.
The analysis of the complex chemical composition of inter-vessel pit membranes explains the mechanism of the flow of water and presence of bubbles between adjacent xylem cells.
Structural mapping and analysis of protein complexes
Nano Fourier Transform Infrared Nanospectroscopy (nano-FTIR) is capable of mapping protein structure with 30 nm lateral resolution. It can also analyze the sensitivity of individual protein complexes.
IR nanospectroscopy with high-resolution atomic force microscopy helps to analyze protein model systems (such as insulin fibril) and visualizes the process of protein self-assembly into oligomeric aggregates and amyloid fibrils. These studies are directly associated with the onset and development of a wide range of human neurodegenerative diseases.
Mapping a single metaphase chromosome
Infrared nanospectroscopy (AFM-IR) is used to study euchromatin and heterochromatin of single human metaphase chromosomes in 10 nm chemical spatial resolution.
This demonstrates how infrared nanospectroscopy enables the chemical characterization of minimal amounts of sample.
The chemical fingerprint of hair melanosomes
The in-situ characterization of chemical and structural properties of sheep hair, with a spatial resolution of 25 nm using infrared nanospectroscopy, reveals the presence of keratin intermediate filaments (IFs) in anisotropic molecular ordering.
White-haired sheep lack melanosomes. However, in black sheep hair, spatially resolved single melanosomes of the vibrational modes of pheomelanin and eumelanin were found.
Thus, IR nanospectroscopy not only allowed a better understanding of the keratin chemical and its structural packing in different hair phenotypes but also avoided harsh chemical extractive methods used in previous studies.