Tesis doctorales: TESEO

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Ministerio de Educación, Cultura y Deporte - Gobierno de España

Título: ADVANCED FORCE SPECTROSCOPY APPLICATIONS: THREE-DIMENSIONAL AFM AND SINGLE-MOLECULE FORCE SPECTROSCOPY
Autor: Uhlig, Manuel Ralph
Universidad: Universidad Autónoma de Madrid
Departamento: Física teórica de la materia condensada
Fecha de Lectura: 04/03/2020
Programa de doctorado: Programa de Doctorado en Física de la Materia Condensada, Nanociencia y Biofísica por la Universidad Autónoma de Madrid; la Universidad de Murcia y la Universidad de Oviedo
Dirección:
- GARCÍA GARCÍA, RICARDO (Director)
Tribunal:
- PÉREZ PÉREZ, RUBÉN (presidente)
- POLOP JORDA, CELIA (secretario)
- Dong, Mingdong (vocal)
- MARTÍN JIMÉNEZ, DANIEL (vocal)
- Stellacci, Francesco (vocal)
Descriptores:
- FISICA
- FISICA TEORICA
Marcador: https://www.educacion.gob.es/teseo/mostrarRef.do?ref=1863999Añadir a favoritos.
Resumen:
When it comes to the nanoscale, the Atomic Force Microscope (AFM) is one of the most widely used tools in science and technology. Its success is based on its atomic-scale resolution and force sensitivity down to the level of individual bonds. Arguably, the AFM's most particular advantage is its outstanding versatility. It can be applied to virtually any sample, from single molecules at low temperatures in ultra-high vacuum, over polymers in ambient conditions to living cells in their liquid growth medium. The reason for such a universality lies in the AFM's unique working principle based on the sensing of forces. Most intuitively, forces arise primarily from mechanical interactions, which is why the AFM emerged as the reference tool to quantify local mechanical properties at the nanoscale. However, forces are actually footprints of a plethora of physical quantities such as viscosity, charge, surface potential or magnetization. Knowing these quantities opens up many avenues to study complex physical, biological and chemical processes. There is a large number of AFM modes aiming to quantify forces. Some of the most successful ones fall into the category of AFM Force Spectroscopy. Before the invention of the AFM, the field of force spectroscopy was pioneered by the surface force apparatus. This instrument paved the way for the understanding of forces between two objects separated by nanoscale distances. Based on that, AFM force spectroscopy advances further by providing a locally confined probe, thereby achieving up to atomic-scale spatial resolution in all three dimensions. Some of the most important current activities and frontiers of the field are related to the speed and sensitivity limits of established force spectroscopy tools. More sophisticated techniques such as high-speed AFM force spectroscopy or 3D-AFM have emerged recently to eventually overcome current limitations. High-Speed force spectroscopy has bridged the temporal gap between unbinding experiments and molecular dynamics simulations. 3D-AFM has been developed as a versatile tool to study solid-liquid interfaces with atomic-scale resolution. This thesis is dedicated to address different aspects of these techniques in order to improve the instrument's performance and to gain further insight into complex samples. It is divided into six chapters which are briefly outlined in the following. Chapter 1 introduces the AFM in general, places it in the historical context and summarizes its main functionalities and components. A special focus lies on reviewing AFM approaches to study solid-liquid interfaces, in particular the three-dimensional AFM (3D-AFM). Chapter 2 is dedicated to the development of a software suite for a 3D-AFM operated in amplitude modulation. The goal of this chapter is twofold: First, to have a tool at hand for analyzing the data presented throughout this thesis. Second, to provide a foundation for establishing 3D-AFM as a technique to study solid-liquid interfaces easily accessible for other scientists. Chapter 3 presents an application of 3D-AFM to a class of materials that has attracted immense interest over the last decade: 2D materials. The solid-liquid interface of a variety of layered materials immersed in ultrapure water is studied, including mono-, few-, and multilayer sheets of graphene and transition metal dichalcogenides. The images reveal a universally occurring structuring of the liquid in the vicinity of the surfaces. It is shown that the observations are related to the hydrophobicity of these surfaces and their interaction with airborne adsorbates. Chapter 4 follows up on the findings of Chapter 3. 3D-AFM is used to study the solid-liquid interface of pentacene thin-films in electrolyte solution. The obtained results are not only of potentially high relevance for technological applications of this class of materials, but also represent an important step forward in the capabilities of 3D-AFM applied on topographically complex surfaces. Chapter 5 is devoted to a 3D-AFM study of the muscovite mica-electrolyte interface. By increasing the sensitivity of the 3D-AFM, K+ ions adsorbed to the mica surface are visualized and features of individual ions and their hydration structure are identified. A comparison with reported X-ray reflectivity data verifies the results. The findings strengthen 3D-AFM as a unique tool for studying solid-liquid interfaces with very high out-of-plane and unrivaled in-plane resolution. Chapter 6 addresses three different aspects of force spectroscopy at the single-biomolecule level: The first section investigates up to which limit the use of Hooke's law is justified in fast single-molecule force spectroscopy (SMFS). Experiments are performed on the biotin-avidin system that demonstrate deviations from the standard description of forced unbinding. By developing an analytical equation of motion for SMFS, the observations are explained in terms of cantilever dynamics occurring at high velocities. With the help of simulations, a general criterion is found for the range of accuracy of Hooke's law. A correction factor is provided and applied on the experimental data to recover the intrinsic unbinding forces at any speed. The second section is devoted to biorecognition, i.e., SMFS employed to localize and identify species at the nanoscale. The technique is used to verify a functionalization protocol which promotes locally restricted adsorption of avidin onto the active element of a biosensor. The third section aims to determine the mechanical response of a single antibody by using AFM indentation. A stiffness value for the elastic response of an IgG antibody is obtained and compared to MD simulations performed on the same protein.

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