'Hi-Fi Nanoscience'

: Exploring the nanoscale with optical pickup units

Abstract

In this work, an optical pickup (OPU) (Model: HD85/650, Sanyo, Japan) is adapted for several developments in surface microscopy techniques. A principle investigation studies the application of OPUs into high-speed atomic force microscopy (HS-AFM), a technique for measuring 3D topographical maps on the nanoscale. OPUs contain a high-fidelity linear displacement detection system of ~6 µm range, a narrow laser spot size (~1 µm) and a high measurement bandwidth of (~45 MSs⁻¹), making the device well suited to nanoscale displacement sensing at high-speeds. An OPU-based HS-AFM is developed in this work that can image large areas (millimetres) at high rates of 2 megapixels/s, high tip velocity (10 mms⁻¹) with area imaging rate of 25 µm²s⁻¹. It is compared against an existing commercial instrument to show sub-nanometre displacement sensitivity via the detection of the primary and secondary modes of a free (MSNL) HS-AFM cantilever in air with amplitudes equal to 0.838 ± 0.24 nm and 0.125 ± 0.04 nm, respectively. 
The OPU HS-AFM developed in this work was applied in a study, which imaged CRISPR-Cas9 molecules, used as a programmable nanoparticle for DNA mapping. It was shown that the OPU HS-AFM could be applied in a genomics application by identifying the spacing of the CRISPR-Cas9 molecule on a TERT gene (expected: 46.9 nm; measured: 47.7 ± 8.1 nm) and HER2 gene (expected: 114.1 nm; measured: 108.2 ± 17.1 nm) within the measurement uncertainty. The abundancy of these genes can be used for clinical purposes as the over expression of the HER2 gene can be an indication of breast cancer. A pair of OPUs were later incorporated into an HS-AFM to monitor and assist in developing a high-speed sample scanner, which was manufactured via stereography 3D-printing. Whilst the dual axis parallel flexure scanner had typically been operated in 'open-loop' mode while conducting HS-AFM, the monitoring of the true motion of the scanner in real-time with the OPUs was shown to reduce the lateral imaging error by up to a mean of 19 nm per pixel (i.e. 40 % reduction in lateral error). 
Subsequently, the OPU was adapted for high-speed optical profilometry (HS-OP) as a non-contact technique to help 'bridge the gap' between the HS-AFM lateral imaging scale (~10⁻⁹ m) and other optical lateral imaging scales (>10⁻⁶ m) under ambient conditions. It is shown that the HS-OP is capable of imaging an area of 100x that of the HS-AFM in the same time. Presented applications of this instrument include topography mapping of a UO2 thin film, real-time capture of the evaporation of a saline solution microdroplet on a metal surface and imaging of the surface features of a Tilia Cordata leaf. Throughout the development and research in this thesis, several image processing techniques were implemented to enable successful study and scalability of the captured surface microscopy images. Principally, a method is presented for automatic feature correlation and stitching of composite surface microscopy images to help link the techniques developed here to large length scales. In each instance, the algorithm used is presented and a case study undertaken to evaluate their significance.

Date of Award	23 Jun 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Oliver D Payton (Supervisor) & John C C Day (Supervisor)