Nanoplasmonic biosensor with integrated electrical detection

Abstract

The demand for efficient and cheap point-of-care diagnostic devices and the increasing opportunities stemming from the recent advances in nanofabrication trigger the interest in the development of a new generation of biosensors. In this thesis, a novel nanoplasmonic biosensor with integrated readout is presented. The key factor for using nanoplasmonics for biosensing is the high sensitivity of the plasmonic resonance to variations in the refractive index at the interface between the structure and the surrounding medium. This enables label-free detection of biomolecular binding events in real-time, which have recently been utilized in several biosensor applications. In contrast to conventional surface plasmon resonance sensors based on flat metal films, nanoplasmonic sensors can be used in transmission mode and do not require prism coupling. Although this is one of the main advantages of nanoplasmonics compared with conventional plasmonics, the technique still requires external detectors. This increases the complexity and the costs of the device, confining its diffusion to a narrow range of users. In this thesis, nanoplasmon-active structures have been fabricated on a light sensitive p/n junction. The photovoltaic current induced in such diodes is directly proportional to the absorbed light intensity which, at a specific wavelength, depends upon the resonance position of the nanoplasmonic structure. Hence, changes in the plasmonic resonance, as induced by biomolecular binding events, can be directly transformed into shifts in the photovoltaic current; thus allowing for a fast, reliable and easily accessible measurement technique. The results on biosensing using this concept will be presented and discussed regarding the applicability of the sensor for rapid, simple and cost-effective medical diagnostics. The challenges and the optimization of the fabrication process will be discussed.