Infrared Photo-induced Force Microscopy (IR PiFM) System

Infrared Photo-induced Force Microscopy (IR PiFM) is a unique analytical technique that allows spectral imaging of materials with a high lateral resolution of < 5 nm. The material sample is radiated with a tunable IR laser, and the photo-induced force between the sample and a metal coated cantilever tip is recorded. The magnitude of the short-range force depends on two factors: (i) the non-contact distance between the sample surface and the tip, and (ii) the content of the functional groups that absorb the IR radiation at a specific wavenumber. The instrument will be part of the Bioeconomy Infrastructure at Aalto University, where atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been used for imaging the physical structure of materials at < 5 nm resolution. Biological materials typically have features in this scale, such as cellulose elementary fibrils (width ca. 3-4 nm) and cell membranes (thickness ca. 3-10 nm). AFM, SEM and TEM do not reveal the chemical identity of the structures. Thus, PiFM will complement these methods with its ability to provide detailed chemical information at < 5 nm scale in plant cell walls and other highly organized materials. The most essential requirement of the spectral nanoimaging system is < 5 nm lateral resolution with biological specimen, such as ultramicrotome sections (thickness ca. 200-500 nm) of plants. Without this specification it is impossible to identify the smallest substructures, for example, in plant cell walls. The instrument should be able to cover the middle infrared region (ca. 800-4000 cm-1) that is typically reached with a combination of tunable OPO and QCL lasers. The substances of interest include, e.g., polysaccharides, polyphenols, proteins and lipids, which have characteristic absorption bands spread in the whole MIR region. Without the OPO laser, the essential O-H and C-H stretching vibrations cannot be covered. A closed sample chamber is required to study the biological samples alternatively in dry or humid air or nitrogen atmosphere. By purging the chamber with gas flow, it becomes possible to study, for example, the interaction of water with specific layers of cell walls.