Dielectrophoresis is a widely used technique for on-chip manipulation of polarizable objects like cells, viruses and microparticles. Recently the use of nanotechnology enabled scaling down the...Show moreDielectrophoresis is a widely used technique for on-chip manipulation of polarizable objects like cells, viruses and microparticles. Recently the use of nanotechnology enabled scaling down the dielectrophoretic trapping to the level of nanoparticles and even single molecules. We aim to develop a dielectrophoresis-based tool to trap and actuate single biomolecules in order to study them. In this thesis we have designed and simulated a nanoscale dielectrophoretic trap as well as explored the possibilities of actuating trapped nanoparticles between the two hotspots of the trap. The simulation framework developed in this thesis based on COMSOL Multiphysics and python simulations paves the way to smart engineering of single-molecule dielectrophoretic traps, which can reduce the cost and time for production and development.Show less
Single-molecule (SM) fluorescence enhancement by gold nanorods (AuNRs) has been studied in the past years using one-photon excitation, showing the possibility of 1000-fold enhancement \cite{1000...Show moreSingle-molecule (SM) fluorescence enhancement by gold nanorods (AuNRs) has been studied in the past years using one-photon excitation, showing the possibility of 1000-fold enhancement \cite{1000-fold}. Here the aim is to study SM fluorescence enhancement using two-photon excitation. This different scheme should lead to a higher excitation enhancement factor ($\sim 10^5$ times) due to the quadratic dependence of the fluorescence intensity on the excitation intensity. In this thesis the first study of two-photon-excited fluorescence enhancement of a squaraine dye using AuNRs is carried out. As a first step a study of the reshaping of the gold nanorods under pulsed illumination, needed for the two-photon experiments, is performed. It is found that a maximum power of approximately 5 $\mu$W can be used during an illumination time of 10 s without reshaping the AuNRs, even when the NRs are in resonance with the laser. After the determination of the maximum power that can be used without reshaping, SM enhancement experiments were performed (at a lower intensity) and an enhancement factor of 700 was found, which is more compatible with one-photon excitation. Independent measurements of the power dependence of the dye show a linear response, probably due to the saturation of an intermediate state in the two-photon absorption process. Thus, it is concluded that only one transition in the two-photon absorption process is enhanced, explaining the observed weak enhancement factor.Show less
