Technische Universität Wien
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AFM-based nanoscale spectroscopy

We use photothermal expansion based infrared (PTIR or AFM-IR) spectroscopy for nanoscale chemical characterization. This technique achieves 20 nm spatial resolution optical spectroscopy by combining an infrared laser with an atomic force microscope (AFM). AFM-IR is broadly applicable to

  1. organic samples

    1. polymer films
    2. organic fibers
    3. monolayers

  2. biological samples

    1. microorganisms
    2. biofilms
    3. biopolymers
    4. amyloid fibrils

  3. inorganic samples

    1. dielectrics
    2. semiconductors
    3. 2D materials

A AFM-IR measurement provides an AFM topography image, as well as local infrared spectra and infrared absorption images.

Contact us, to find out if AFM-IR can give vital insights into your nanoscale sample.

 

Theory of photohermal expansion nanoscale spectroscopy

An AFM-IR setup consists of two parts, a pulsed tunable laser (such as the mid-IR EC-QCL lasers used in the Lendl group) and a conventional AFM. To perform an AFM-IR measurement, the sample is placed in the AFM and the laser is focused on the tip of the AFM cantilever. Each laser pulse leads to a local thermal expansion of the sample when it is absorbed. This expansion is sensitively detected by the AFM cantilever. Due to this nearfield detection scheme, the diffraction limit does not apply and spatial resolution of 20 nm or better can be demonstrated.

AFM-IR spectra have been demonstrated to be directly comparable to far-field FTIR spectra.

Key publications

Analysis of individual nanoscale drug carriers

Liposomes are used to encapsulate chemotherapeutics for targeted release therapy. However, quantitation of encapsulated chemicals remains a challenge. While bulk methods exist that can determine an average encapsulation efficiency, information on a single liposome basis is inaccessible. In a collaboration between TU Wien (Lendl group, Weiss group) and the National Institute for Standards and Technology we tackled this problem using AFM-IR.

Karin Wieland was able to demonstrate zeptomole sensitivity and chemical specificity by takin tapping mode AFM-IR images and spectra of individual liposomes. The work was published in Nano Research

The image below shows a topography image of a liposome (a) as well as two AFM-IR absorption images for a lipid (b) and chemotherapeutic (c). The overlay of these images reveals the location of the chemotherapeutic within the liposomes (d). AFM-IR spectra (e) allows selection of imaged bands and comparison with reference spectra. All scale bars are 100 nm. (Image reproduced with permission from Karin Wieland's doctoral thesis.)