Thermal-AFM under aqueous environment

Tofani, Franesca (2020) Thermal-AFM under aqueous environment. PhD thesis, University of Glasgow.

Abstract

The aim of this thesis is to describe the work developing and demonstrating the use of Scanning Thermal Microscopy (SThM) in an aqueous electrically conductive environment for the first time. This has been achieved by using new instrumentation to allow conventional SThM probes to measure and manipulate the temperature of non-biological and biological samples. For the latter, the aqueous environment is crucial to allow in-vitro experimentation, which is important for the future use of SThM in the life sciences. SThM is known to be a
powerful technique able to acquire simultaneous topographic and thermal images of samples. It is able to measure the microscopic thermal properties of a surface with nanoscale spatial resolution. However, SThM has traditionally been limited to use in vacuum, air and electrically inert liquids. The aqueous Scanning Thermal Microscopy (a-SThM) described in this thesis is an entirely novel technique that opens up a new field for thermal-AFM.
The first challenge addressed in this work was the adaptation of a commercial Multimode Nanoscope IIIa AFM to permit electrical access to a SThM probe completely immersed in aqueous solutions. By employing a newly designed probe holder and electronic instrumentation, the probe could then be electrically biased without inducing electrochemical reactions. This approach permitted conventional microfabricated thermal probes to be operated whilst fully immersed in water.
This innovation allowed SThM measurements under deionized (DI) water to be performed on a simple solid sample (Pt on Si3N4) and the results compared with in-air scans and accurate 3D Finite Element (FE) simulations. Once the validity of the technique was proven, its performance was investigated, including crucially the limit of its thermal-spatial resolution; this was investigated using nanofabricated solid samples (Au on Si3N4) with well-defined features. These results were compared to the FE model, allowing an understanding of the
mechanisms limiting resolution to be developed. In order to demonstrate the advantages granted by the water’s superior thermal conductivity compared to air or other liquids, non-contact thermal images were also acquired using the same samples.
The final part of this thesis was focused on extending SThM into the biological area; a completely new field for this technique. New results are presented for soft 4 samples: I-collagen gel and collagen fibrils, which were thermally manipulated using a self-heated SThM probe. This successfully demonstrated the possibility of using heat to alter a biological sample within a very well localised area while being operated for long time in an aqueous environment. The difference in force response originated from the AFM scans with different levels of self-heating further proved the robustness of the technique. Finally, the technique was employed to study MG-63 living cells: The SThM probe was left in contact with each cell for a pre-determined period of time, with and without self heating. The results demonstrated that only the heated cells, directly beneath the probe tip died, tallying with the highly localised temperature gradient predicted by FE analysis.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Scanning thermal microscopy, liquid environment, aqueous- SThM.
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
• Supervisor's Name: Dobson, Dr. Phil and Weaver, Professor Jonathan
• Date of Award: 2020
• Depositing User: Ms Francesca Tofani
• Unique ID: glathesis:2020-81653
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 15 Sep 2020 14:31
• Last Modified: 15 Sep 2020 14:31
• URI: https://theses.gla.ac.uk/id/eprint/81653