title: Using 2D Correlation Analysis to Enhance Spectral Information Available from Highly Spatially Resolved AFM-IR Spectra.
abstract: The recent combination of atomic force microscopy and infrared spectroscopy (AFM-IR) has led to the ability to obtain IR spectra with nanoscale spatial resolution, nearly two orders-of-magnitude better than conventional Fourier transform infrared (FT-IR) microspectroscopy. This advanced methodology can lead to significantly sharper spectral features than are typically seen in conventional IR spectra of inhomogeneous materials, where a wider range of molecular environments are coaveraged by the larger sample cross section being probed. In this work, two-dimensional (2D) correlation analysis is used to examine position sensitive spectral variations in datasets of closely spaced AFM-IR spectra. This analysis can reveal new key insights, providing a better understanding of the new spectral information that was previously hidden under broader overlapped spectral features. Two examples of the utility of this new approach are presented. Two-dimensional correlation analysis of a set of AFM-IR spectra were collected at 200-nm increments along a line through a nucleation site generated by remelting a small spot on a thin film of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). There are two different crystalline carbonyl band components near 1720 cm-1that sequentially disappear before a band at 1740 cm-1due to more disordered material appears. In the second example, 2D correlation analysis of a series of AFM-IR spectra spaced every 1 micrometer of a thin cross section of a bone sample measured outward from an osteon center of bone growth. There are many changes in the amide I and phosphate band contours, suggesting changes in the bone structure are occurring as the bone matures.
authors.affiliation: Light Light Solutions, LLC, Athens, GA 30608 USA ; Department of Materials Science and Engineering, University of Delaware, Newark, DE 19716 USA.
authors.forename: Curtis
authors.initials: C
authors.lastname: Marcott
authors.affiliation: Anasys Instruments, Santa Barbara, CA 93101 USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Lo
authors.affiliation: Anasys Instruments, Santa Barbara, CA 93101 USA.
authors.forename: Qichi
authors.initials: Q
authors.lastname: Hu
authors.affiliation: Anasys Instruments, Santa Barbara, CA 93101 USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: Kjoller
authors.affiliation: Hospital for Special Surgery and Weill Medical College and Graduate School of Medical Sciences of Cornell University, New York, NY 10021, USA.
authors.forename: Adele
authors.initials: A
authors.lastname: Boskey
authors.affiliation: Department of Materials Science and Engineering, University of Delaware, Newark, DE 19716 USA.
authors.forename: Isao
authors.initials: I
authors.lastname: Noda
keywords: atomic force microscopy; bone nanostructure; infrared spectroscopy; osteonal bone; poly(hydroxyalkanoate); two-dimensional correlation analysis