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AFM-IR technology

The nanoIR combines atomic force microscopy (AFM) with the precise chemical identification of infrared spectroscopy. With this pioneering technology, the nanoIR system is a robust, proven platform which leverages the advantages of both these techniques, delivering the unprecendented ability to chemically identify sample components at the sub 100 nm lateral resolution.

Conventional IR Microspectroscopy

Power of IR microspectroscopy

Spatial resolution limits of IR microspectroscopy

nanoIR – Infrared Nanospectroscopy

Overcoming resolution limits of infrared spectroscopy

The Science Behind the Solution

Power & limits of AFM

Bringing chemical characterization to AFM

Power of IR microspectroscopy
IR microspectroscopy has already demonstrated itself as a powerful tool for spatial mapping chemical content in a wide variety of applications[1-3], leading to over 15,000 publications in 2009. It has been used to characterize numerous materials critical in industry[4], especially polymeric materials [5-11] . Exciting applications have also been demonstrated in biology,[12] including analysis of plant materials,[13-15], bone[16-21], single cells[22], and strain identification in yeasts[23] and bacteria[24], for example. There have also been many biomedical applications, including applications in pharmaceuticals,[25-27] and medical diagnosis,[28-32]

Spatial resolution limits of IR microspectroscopy

Despite its widespread applications, infrared microspectroscopy has fundamental spatial resolution limits set by both the laws of optics and practical design constraints. Fourier Transform IR spectroscopy is generally limited to a spatial resolution of three times the wavelength of the IR radiation. With Attenuated Total Reflection (ATR) may achieve resolution approaching the wavelength. The table below shows practical resolution limits faced by conventional IR spectroscopy.

IR Spectroscopy Method Practical resolution
Limit
Transmission FTIR ~10-30 μm
ATR ~3-10 μm

With nanoIR, you can overcome these diffraction limits.

Overcoming resolution limits of infrared spectroscopy

The nanoIR system breaks through resolution limits in conventional IR spectroscopy by using the tip of an atomic force microscope probe to measure infrared absorption. The sample is illuminated by a tunable IR source. When IR radiation is absorbed by a region of the sample, the region heats up. The heat generates a rapid thermal expansion pulse that can be detected by the AFM cantilever tip. This technique beats the “far field” optical diffraction limit because the absorbed radiation is measured by the tip in the extreme near field.

With the nanoIR system, the tip of an AFM is used to measure local thermal expansion resulting from absorption of IR light. Even though the focused spot of IR radiation is on the scale of many microns, the thermal expansion can be spatially resolved with the AFM tip on scales well below the optical diffraction limit.

The Science Behind The Solution
The nanoIR system uses a pulsed, tunable IR source to excite molecular absorption in a sample that has been mounted on a ZnSe prism. The IR beam illuminates the sample by total internal reflection similar to conventional ATR spectroscopy. As the sample absorbs radiation, it heats up, leading to rapid thermal expansion that excites resonant oscillations of the cantilever. The induced oscillations decay in a characteristic ringdown.

The ringdown can be analyzed via Fourier techniques to extract the amplitudes and frequencies of the oscillations. Measuring the amplitudes of the cantilever oscillation as a function of the source wavelength creates local absorption spectra; the oscillation frequencies of the ringdown are related to the mechanical stiffness of the sample. The IR source can also be tuned to a single wavelength to simultaneously map surface topography, mechanical properties, and IR absorption in selected absorption bands.

Power & limits of AFM

Atomic force microscopy (AFM) has been enormously successful addressing problems in basic nanoscale research as well as applied problems in materials science and engineering. The AFM has also been widely credited with enabling the multi-billion dollar research investments in nanoscience and nanotechnology. A clear gap in AFM capabilities, however, is the ability to chemically characterize regions of the sample. In fact, the ability to identify material under the tip of an AFM has been identified as one of the “Holy Grails” of probe microscopy. While AFM can measure mechanical, electrical, magnetic and thermal properties of materials, it has lacked the robust ability to chemically characterize unknown materials.

Bringing chemical characterization to AFM

The ability to identify material under the tip of an AFM has been identified as one of the “Holy Grails” of probe microscopy. With the nanoIR instrument, Anasys Instruments brings robust chemical characterization to the AFM. The nanoIR uses infrared spectroscopy to provide chemical analysis of samples on the sub-micron length scale. Infrared spectroscopy measures the wavelength dependent absorption of radiation that results from excitations of specific molecular vibrations. The resulting absorption spectra provide rich information about the chemical content of material under the AFM tip.

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19. Paschalis, E.P., et al., FTIR Microspectroscopic Analysis of Normal Human Cortical and Trabecular Bone. Calcified Tissue International 61(6): 480-486, 1997.

20. Paschalis, E.P., et al., FTIR Microspectroscopic Analysis of Human Iliac Crest Biopsies from Untreated Osteoporotic Bone. Calcified Tissue International 61(6): 487-492, 1997.

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22. Lasch, P., et al., FT-IR spectroscopic investigations of single cells on the subcellular level. Vibrational Spectroscopy 28(1): 147-157, 2002.

23. Wenning, M., et al., Fourier-Transform Infrared Microspectroscopy, a Novel and Rapid Tool for Identification of Yeasts. Appl. Environ. Microbiol. 68(10): 4717-4721, 2002.

24. Kansiz, M., et al., Fourier Transform Infrared microspectroscopy and chemometrics as a tool for the discrimination of cyanobacterial strains. Phytochemistry 52(3): 407-417, 1999.

25. Reich, G., Near-infrared spectroscopy and imaging: Basic principles and pharmaceutical applications. Advanced Drug Delivery Reviews 57(8): 1109-1143, 2005.

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30. Lasch, P., et al., Imaging of colorectal adenocarcinoma using FT-IR microspectroscopy and cluster analysis. Biochimica et Biophysica Acta (BBA) – Molecular Basis of Disease 1688(2): 176-186, 2004.

31. MORDECHAI, S., et al., Possible common biomarkers from FTIR microspectroscopy of cervical cancer and melanoma. Journal of Microscopy 215(1): 86-91, 2004.

32. Fernandez, D.C., et al., Infrared spectroscopic imaging for histopathologic recognition. . Nat Biotechnol. 23: 469-474, 2005.