Infrared scanning near‐field optical microscopy investigates order and clusters in model membranes

Abstract

SummaryDue to its surface sensitivity and high spatial resolution, scanning near-field optical microscopy (SNOM) has a significant potential to study the lateral organization of membrane domains and clusters. Compared to other techniques, infrared near-field microscopy in the spectroscopic mode has the advantage to be sensitive to specific chemical bonds. In fact, spectroscopic SNOM in the infrared spectral range (IR-SNOM) reveals the chemical content of the sample with a lateral resolution around 100 nm (Cricenti et al., 1998a(Cricenti et al., , 1998b(Cricenti et al., , 2003.Model lipid membranes were studied by IR-SNOM at several wavelengths. Topographical micrographs reveal the presence of islands at the surface and the optical images indicate the formation of locally ordered multiple bilayers -both critically important features for biotechnology and medical applications.

High-sensitivity infrared vibrational nanospectroscopy in water

“…The diffraction limit restricts the spatial resolution of far-field mid-infrared (λ≈3–15 μm) microscopy to the micrometer scale. To perform mid-infrared spectroscopy at the nanoscale, three major techniques have been developed: near-field scanning optical microscopy (NSOM 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 21 ), infrared photoexpansion nanospectroscopy (AFM-IR 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 22 ) and photoinduced force microscopy (PiFM) 19 , 20 . For operation in air, all these techniques have demonstrated a sensitivity of or close to a molecular monolayer and a spatial resolution of 10–30 nm, which is principally limited by the apex radius of the atomic force microscope (AFM) tip.…”

“…Mid-infrared vibrational spectroscopy is a universal label-free tool for identifying molecular compounds in chemical and biological samples on the basis of their ‘fingerprint’ vibrational absorption lines. Vibrational spectroscopy with nanometer spatial resolution can reveal the chemical composition of samples at the nanoscale, and several scanning-probe techniques have been developed to address this need 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 . It is also highly desirable to study biological and chemical samples in their native aqueous environments rather than in air.…”

Instruments in Biotechnology and Medicine

“…Combinations with atomic force microscopy, laser tweezers, and immunolabeling, among others, extend the opportunities for application in life sciences from single fluorescently labeled molecules such as DNA or proteins up to whole cells and chromosomes (for examples, see [317][318][319][320][321][322]). SNOM is particularly suited to labeling cell surface membrane proteins, since the illumination depth is limited to tens of nanometers.…”

Visualization and measurement of the local absorption coefficients of single bilayer phospholipid membranes using scanning near-field optical microscopy

“…Although most of the applications of aperture SNOM are in the visible wavelength range however it can be also used in the other spectral region by using probes with different operating wavelengths. For instance, infrared range aperture SNOM (IR-SNOM) is previously being used to study the formation of locally ordered multiple bilayers lipid membranes [33]. Though there are some applications of SNOM to study the molecular organization of homogeneous lipid membranes however the ability of SNOM to perform local absorption imaging of lipid membranes is yet to be explored.…”