Spin manipulated nanoscopy with nitrogen vacancy centres in nanodiamonds
Creators: name: Barbiero, Martina
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400909
subject: Photonic and electro-optical devices, sensors and systems (excl. communications)
classificationCode: 510204
subject: Photonics, optoelectronics and optical communications
classificationCode: 510804
subject: Quantum optics and quantum optomechanics

description: Nowadays, fluorescence microscopy has become the imaging technique mainly employed for medical and biological applications in vitro and in vivo. A light beam is absorbed by an organic or inorganic specimen and subsequently re-radiated. This physical phenomenon is called fluorescence of phosphorescence. It is possible to reconstruct morphological and structural images of biological samples by staining them with fluorescent dyes. The increasing application of fluorescence microscopy has led to the development of super-resolution techniques, able to visualise fine details of biological structures, beyond the diffraction limit. The far-field super-resolution techniques mainly used are stimulated emission depletion (STED), ground state depletion (GSD) and single molecules localisation techniques such as stochastic optical reconstruction microscopy (STORM) and photoactivated localisation microscopy (PALM). These techniques have all achieved lateral (x-y) resolution down to tens of nanometers, allowing single molecule super-resolution imaging.<br><br>Fluorescent nanoparticles are indispensable candidates for optical imaging. Negatively charged nitrogen vacancy (NV- ) centres in nanodiamonds (NDs) have attracted significant interest due to their outstanding optical and magnetic properties. In the recent years super-resolution fluorescence imaging with NDs has substantially improved our ability to comprehend subcellular processes. In particular, optically detected magnetic resonance (ODMR) of the single electron spin of NV- centres at room temperature has enabled a new all-optical imaging approach to measure magnetic fields of complex biological systems. Therefore, the ability to readout the magnetic sensitive NV- electron spin at the nanoscale is of paramount importance for super-resolution optical magnetic imaging.<br><br>STED microscopy has provided nanoscale resolution combined with spin readout of individual NV- centres in NDs. However, this super-resolution method based on scanning mechanism is not suitable for magnetic imaging of dynamical processes of living cells such as neuronal firing. On the other hand, the wide-field view of the STORM-spin methods allows for parallel acquisition and imaging of cellular dynamics from multiple NV- centres.<br><br>The aim of this thesis is to demonstrate a novel super-resolution technique called spin manipulated nanoscopy that enables imaging and spin readout of single NV- centres in blinking NDs. The method is applied for super-resolution optical imaging of magnetic fields generated from biological cells.<br><br>Fluorescence intermittency or blinking is observed after reducing the size of NDs with an oxidation process at 450°C for 2 h and 30 min at 600°C or at 600°C for 2h. With the effect of oxidation not widely investigated, we study the opto-magnetic properties of NV- centres in blinking NDs. We demonstrate first evidence of the ODMR spectrum in blinking NDs. We find that at the ODMR frequency the fluorescence of NV- centres exhibits intermittence that confirms the blinking phenomenon. Further, with an oxidation at 600°C for 2 h we observe a reduction of the ODMR linewidth which improves the magnetic sensitivity of NDs to small magnetic fields.<br><br>Super-resolution imaging based on blinking localisation in conjunction with ODMR has not been researched in NV- centres in nanoparticle form. A super-resolution method, called spin manipulated nanoscopy, is developed to image single NV- centres in blinking NDs. The method combines wide-field localisation with nanoscale spin manipulation at the ODMR frequency. For the first time the NV- magnetic sensitive spin in blinking NDs is imaged based on spin manipulated microscopy. The maximum transverse resolution of 34 nm is achieved. Further, two collectively blinking NV- centres are resolved based on spin manipulated microscopy. Two adjacent fluorescent features are imaged at 23 nm distance, peak to peak.<br><br>Finally, we investigate the magnetic capabilities of NDs by measuring local magnetic fields from iron oxide magnetic nanoparticles (MNPs). MNPs are then implemented to label the membrane of biological cells. We apply spin manipulated nanoscopy with blinking NDs for nanoscale reconstruction of magnetic fields generated from magnetically labelled biological cells. The maximum transverse resolution of 25 nm is achieved. The magnetic sensitivity achieved is 16 μT√Hz . The presented method adds a greater value for the application of NDs as biomarkers for superresolved magnetic imaging in life science