In collaboration with Anasys Instruments and the Getty Conservation Institute, we have developed a sub-micron analytical technique; heated tip AFM desorption coupled with several analytical techniques, designed with the goal of unambiguously identifying organic components in cultural heritage objects. This new approach uses an atomic force microscope (AFM) to image, sample, and collect material by proximal probe thermal desorption at submicron resolution, well below the optical diffraction limit. The sampled material is transferred to a specialized substrate and then analyzed in a separate step by a combination of high resolution laser spectroscopy and mass spectrometry (LMS). This powerful combination provides detailed information in three dimensions: spatial mapping, high resolution spectroscopy and mass spectrometry.
This method is applicable to the cross section samples typically used in conservation science research, with the spatial resolution necessary to isolate small quantities of organic material in discrete layers of a cross section, and the sensitivity to provide molecularly specific identification of materials present in very low concentrations.
This method retains the bulk of the sample, which may be retained and/or used for analysis by other complementary techniques. By separating the microscopy and the chemical analysis steps it becomes possible to apply other analytical techniques at the submicron scale. We employ LMS as the second step, which combines multiphoton ionization and double resonance spectroscopy with mass spectrometry. This approach collects simultaneously both vibronically resolved optical spectra and fragment-free mass spectra for molecules of interest. The high resolution wavelength selectivity in our ionization step (a) allows for detection of a specific analyte in a mixture, eliminating the need for sample preparation, (b) provides the necessary high sensitivity, and (c) provides unique selectivity in the identification of the compound.
The data from the AFM-LMS system will enable identification of specific organic red colorants (the first set of target molecules under study) used in works of cultural heritage significance without the need for complex extraction from the matrices in which the colorants are found. In addition, this technique will provide the ability to study the fundamental spectroscopy of these materials with unprecedented spatial and spectral resolution.