Photothermal AFM-IR spectroscopy and imaging: Status, challenges, and trends

Abstract

This article focuses on the atomic force microscopy-infrared (AFM-IR) technique and its recent technological developments. Based on the detection of the photothermal sample expansion signal, AFM-IR combines the high spatial resolution of atomic force microscopy with the chemical identification capability of infrared spectroscopy to achieve submicrometric physico-chemical analyses. Since the first publication in 2005, technological improvements have dramatically advanced the capabilities of AFM-IR in terms of spatial and spectral resolution, sensitivity, and fields of applications. The goal of this paper is to provide an overview of these developments and ongoing limitations. We summarize recent progress in AFM-IR implementations based on the major AFM contact, tapping, and peak force tapping modes. Additionally, three new trends are presented, namely, AFM-IR applied to mineral samples, in fluid and a novel, purely surface sensitive AFM-IR configuration, to probe top layers. These trends demonstrate the immense potential of the technique and offer a good insight into the scope of AFM-IR.

Using mid infrared to perform investigations beyond the diffraction limits of microcristalline pathologies: advantages and limitation of Optical PhotoThermal IR spectroscopy

“…Moreover, a chemical analysis based on IR lasers at the nanometer scale still constitutes a challenge. For example, Mathurin et al [97] shows experimental data which reveal significant differences in the agreement between AFM-IR and conventional FTIR data, depending on the studied mineral. More precisely, the spectra recorded in AFM-IR and FTIR microscopy are very similar in the case of the smectite (Figure 6a).…”

Profile of an “at cutting edge” pathology laboratory for pathological human deposits: from nanometer to in vivo scale analysis on large scale facilities

“…Imaging of the topology of biopsies, deposited on low-e microscope slides and based on SEM observations and chemical characterization with µRaman and/or µFTIR spectroscopies, can be complemented by NanoIR [112][113][114][115][116][117][118][119][120][121][122]. NanoIR, for which two experimental configurations are possible, presents novel opportunities.…”

“…The first configuration is associated with 500 nm spatial resolution and is based on a pump-probe architecture using two laser sources, one for mid-infrared excitation (the pump) and the other one for measuring the photothermal effect (the probe) [112]. The second configuration combines an atomic force microscope (AFM) and IR lasers [115,116] and produces a spatial resolution of 10 nm [122].…”

“…Finally, we must underline that polarization of the lasers used in NanoIR spectroscopy, either in the visible or the IR range, means that the intensity, and position of IR bands may vary, in the latter case by up to a few cm −1 . This can impose limitations on the precision of any description of abnormal biopsy deposit chemistry [122].…”

Compressed AFM-IR hyperspectral nanoimaging of single Leishmania parasites

“…The spectral measurements of Leishmania brasiliensis promastigotes were carried out with a nanoIR2-s (Bruker (former Anasys), USA) photothermal expansion-based microscope combining atomic force microscopy with a local thermal expansion effect 28,29 . A schematic The projection shown in Fig.…”