Abstract
Scanning probe microscopies and spectroscopies, especially AFM and Confocal Raman microscopy are powerful tools to characterize biological materials. They are both non‐destructive methods and reveal mechanical and chemical properties on the micro and nano‐scale. In the last years the interest for increasing the lateral resolution of optical and spectral images has driven the development of new technologies that overcome the diffraction limit of light. The combination of AFM and Raman reaches resolutions of about 50–150 nm in near‐field Raman and 1.7–50 nm in tip enhanced Raman spectroscopy (TERS) and both give a molecular information of the sample and the topography of the scanned surface. In this review, the mentioned approaches are introduced, the main advantages and problems for application on biological samples discussed and some examples for successful experiments given. Finally the potential of colocated AFM and Raman measurements is shown on a case study of cellulose‐lignin films: the topography structures revealed by AFM can be related to a certain chemistry by the colocated Raman scan and additionally the mechanical properties be revealed by using the digital pulsed force mode. Microsc. Res. Tech. 80:30–40, 2017. © 2016 Wiley Periodicals, Inc.
Highlights
Complexity and hierarchy are the surnames of almost all biological materials
The fact that biological materials can be very sensitive to the surrounding conditions special measurement accessories might be needed to observe their native state
While the atomic force microscopy (AFM) scans the top, the Raman scattering is acquired from the bottom part of the sample with a high NA objective, which limits the measurement to transparent samples only
Summary
Complexity and hierarchy are the surnames of almost all biological materials. The specific arrangement of a few elements (mainly C, H, O, and N, sometimes combined with Ca, P, S, or Si) gives rise to numerous structures with high entanglement and specific functionalities. While the AFM scans the top, the Raman scattering is acquired from the bottom part of the sample (bottom illumination) with a high NA objective, which limits the measurement to transparent samples only In top illumination, another not so optimal version of the combined set up is to use special shaped tips for the AFM which enable the laser light to excite the sample from the top at the free-tip area. Top and side illumination arrangements allow only relatively low magnification (203 or 503) objectives with high working distance (with normally NA not higher than 0.5) (Berweger and Raschke, 2010) since AFM holder and cantilever need a certain space to operate This reduces dramatically the spatial resolution of the Raman image. 1–100 nm –Flatness –Depending on the set up: transparent samples –Chemistry with high lateral resolution
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
