Gold nanorods (GNRs) are plasmonic nanoparticles of which the plasmon resonance wavelength is influenced by the near-field surroundings. Even binding of single proteins with GNRs can cause a shift...Show moreGold nanorods (GNRs) are plasmonic nanoparticles of which the plasmon resonance wavelength is influenced by the near-field surroundings. Even binding of single proteins with GNRs can cause a shift in their resonance wavelength. Previous studies have used this resonance shift to detect single binding events of proteins with GNRs. However, those results are limited in their throughput and sensitivity. Here we use a multifocal two-photon microscopy technique to measure hundreds of single GNRs simultaneously with high spectral sensitivity and signal-to-noise ratio. Using numerical simulations we determined how we can optimise the homogeneity of the illumination pattern over an area of 200 × 200 µm2 and minimise the melting of GNRs during measurements. Finally, we measured GNRs in various concentrations of fibronectin proteins and found an increase in power spectral density of the two-photon luminescence signal for fibronectin concentrations of 1.25 µg/mL to 2.5 µg/mL. Through a better understanding of the setup, we can now perform reliable spectral measurements of hundreds of individual GNRs. This should make two-photon microscopy techniques more competitive with bio-sensing experiments based on scattering of GNRs.Show less
A common problem in Magnetic Resonance Force Microscopy (MRFM) is the spin-induced damping of the cantilever, which drastically limits the sensitivity to spin signals. In order to solve this...Show moreA common problem in Magnetic Resonance Force Microscopy (MRFM) is the spin-induced damping of the cantilever, which drastically limits the sensitivity to spin signals. In order to solve this problem, we have developed improvements to a Persistent Current Switch (PCS) that make it less dissipative and capable of creating a stronger magnetic field at the sample. On top of this, the low noise level that our detection setup requires is conserved. The improvements are based on the use of a low-temperature magnetic core material called MetGlas [1]. We have measured the full B-H curve of the MetGlas and verified that it decreases the current required to switch a Niobium wire to the resistive state by a factor of 30. Furthermore, we have used this data to calculate the performance of a transformer made using this material, and we have calculated the expected extremely low noise level that this circuit will cause in our SQUID.Show less
In this thesis we investigate conductivity changes due to magnetite in agarose gels mimicking grey brain matter. We use conventional MRI sequences to acquire B + 1 phase maps. Using the homogeneous...Show moreIn this thesis we investigate conductivity changes due to magnetite in agarose gels mimicking grey brain matter. We use conventional MRI sequences to acquire B + 1 phase maps. Using the homogeneous Helmholtz equation and the B + 1 phase-only approximation, we reconstruct conductivity maps. The current sensitivity of the reconstructions is too low to detect conductivity changes due to magnetite nanoparticles in the concentration found in the brain of Alzheimer’s disease patients. Nevertheless, we have promising indications that we have been able to observe a change in the standard deviation of the conductivity due to the presence of magnetite.Show less
Gold nanorods are used in various sensing applications. Through observation of their Surface Plasmon Resonance (SPR) at optical wavelengths, they offer a bridge to length scales below the...Show moreGold nanorods are used in various sensing applications. Through observation of their Surface Plasmon Resonance (SPR) at optical wavelengths, they offer a bridge to length scales below the diffraction limit. In a confocal Interference Scattering Microscopy (iSCAT) setup fluctuations of the SPR may be detected fast enough to draw conclusions about diffusion in the vicinity of the nanorod. We characterize such a setup and find its optimal working point.Show less
