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.

The ground for direct procurement is section 40, subsection 2, paragraph 2 of the Act on Public Procurement and Concession Contracts (1397/2016). According to section 40, subsection 2, paragraph 2, a contracting entity may opt for direct procurement if only a certain supplier can implement the procurement for a technical reason, or for a reason related to protecting an exclusive right, on the further condition that there are no reasonable alternatives or substitute solutions, and that the absence of competition is not due to an artificial narrowing of the terms and conditions of the procurement. The contracting entity has identified three potential suppliers of force microscopy-based imaging systems on the market. However, after discussions, demonstrations and detailed analysis conducted with suppliers, the conclusion is that Molecular Vista is the only one that can reach < 5 nm resolution with relevant biological samples, by applying the photo-induced effect in their PiFM instruments. The first measurements with VistaScope led to a coauthored publication with Molecular Vista (Kesari, K. K., O’Reilly, P., Seitsonen, J., Ruokolainen, J., & Vuorinen, T. (2021). Infrared photo-induced force microscopy unveils nanoscale features of Norway spruce fibre wall. Cellulose, 28(11), 7295-7309). In this paper it was demonstrated that the lateral resolution of the spectral imaging mode was < 5 nm. Later, the contracting entity has done similar measurements in collaboration with Molecular Vista and Montan Universität Leoben, Austria, with their Vista One instruments. In these measurements, we have repeatedly reached the < 5 nm resolution. Thus, our experience on the measurements during the past few years is that only IR PiFM can reach the required < 5 nm resolution with the samples that are of primary interest for us. Techniques based on the photothermal effect may perform well with other types of samples, but we haven’t found single evidence from literature, demonstrations and user interviews that these techniques could achieve the required lateral resolution, e.g., with ultrathin wood sections. Based on the aforesaid, only Vista One IR PiFM System of Molecular Vista fulfils the requirements set for the chemical nanoimaging system.