AFM-IR, or atomic force microscope infrared-spectroscopy, is an analytical technique used to characterize unknown substances on a nanoscale level by combining atomic force microscopy and infrared spectroscopy.
What is atomic force microscopy?
This is a type of scanning probe microscopy used to image the surface of a substance, but at an atomic level. It can map the surface structure of different substances to understand how different structures interact with each other. This is done using a cantilever, which is similar to a vinyl record needle.
However, rather than converting the surface of the record into sound, it converts the atomic forces of a surface into readable data. The interaction between the cantilever tip and the sample changes the height of the cantilever. These changes in height are used to map the surface at a nanometre precision.
This technique uses the distinctive vibrational energy of specific functional groups and atoms to work out which chemical groups are present in a sample. An unknown substance is exposed to infrared radiation, which excites certain chemical groups.
Different chemical bonds within the substance produce energy of varying wavelengths, and this information can be used to deduce the chemical structure. Infrared spectroscopy has also been developed into infrared microscopy, where the absorption of infrared radiation allows chemical analysis with spatial resolution, which can be used to provide images based on the contrast in chemical structure within a sample.
Bringing the two methodologies together
Both of these techniques are very powerful and thus combining these two technologies together into AFM-IR offers great potential. Using these two techniques together, unknown substances can be precisely mapped with accuracy at the atomic scale.
A source of infrared radiation is focused onto a location on the sample underneath the tip of the AFM cantilever. The absorption of infrared radiation by the sample causes thermal expansion, which is detected by the cantilever. This allows both the compositional mapping of the sample and the identification of the different molecules involved.
What are the advantages of AFM-IR?
Both infrared spectroscopy and infrared microscopy have a limited spatial resolution which limits the extent to which they can form a clear image. Atomic force microscopy, on the other hand, has a nanoscale spatial resolution, rather than the microscale level set in infrared analysis. Therefore, AFM-IR allows the infrared analysis to a much smaller scale and with much higher accuracy.
Atomic force microscopy has to rely on properties it can measure, such as friction, elasticity and magnetism. The introduction of infrared analysis allows for much higher quality chemical analysis.
Applications of AFM-IR in polymer research
AFM-IR is widely used for polymer development, protein research, microbiology, and many other potential areas of research. New polymers are being constantly developed for use in industries, such as medicine, food, and other technologies, and AFM-IR can be very useful to study these materials and their structure.
Applications of AFM-IR in life science
Infrared spectroscopy can be used to identify biological molecules, and AFM-IR can provide an improved and accurate method to study samples. AFM-IR is already being used for sub-cellular imaging, the study of cellular interactions, and measuring both bacterial and animal cells. This technique is also being used to study the structure of proteins, and how misfolding of these proteins can lead to the development of diseases, such as Alzheimer’s or Parkinson’s.