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
To sense the movement or piling up of single charges, a system interacting strongly with these charges is required. An available system, having these properties, is a single electron transistor ...Show moreTo sense the movement or piling up of single charges, a system interacting strongly with these charges is required. An available system, having these properties, is a single electron transistor (SET). The electric fi eld caused by the charge, strongly changes the resistance of the SET. Yet experiments opt for a less invasive charge sensor. Such a proposed charge sensor is a single fluorescent dye molecule. The distinguishable zero phonon lines (ZPL's) of the fluorescence of the molecules shifts strongly by the Stark e ffect. The lineshift of each molecule can be tracked with an excitation laser, allowing to observe the change in charging. Tracking the ZPL's of multiple molecules allows the observation of slow charge movement. The optical charge sensing method needs to be tested on devices fabricated on a glass substrate. In particular devices, which exhibit single electron charging. These devices have been constructed with electron beam lithography (EBL). Nanoparticles, representing an island to hold the charge, have been trapped between nano-electrodes using dielectrophoresis. The nanogaps have been created by electromigration or by EBL. Eventually, nano-electrodes were also fabricated on glass by coating the glass with a 1,5 nm Cr layer. This coating was removed afterwards with plasma etching. The project focused on the fabrication of the devices. The deposition of fluorescent dye molecules and tracking the lineshifts was left for subsequent experiments. A fluorescence microscope, also necessary for the lineshift measurements, was used to observe quantum dots. Proposed experiments with quantum dots are the tracking of the movement of quantum dots in a strong alternating electric fi eld or the eff ect of a high electric field on the fluorescence of a quantum dot in a nano-electrode junction.Show less
