Biosensing Using Long-Range Surface Plasmon-Polariton Waveguides

Abstract

Specific detection of biological matter is one of the key elements in a wide range of modern fields such as food industry, medicine, environmental and pharmaceutical industries. Generally, current common methods of detection (e.g. ELISA) involve molecular labelling, requirements for well-trained personnel and lengthy experimental procedures such as bacteria culture. All of the above issues result in high costs for biological analysis, and consequently, high costs for medical service, therapeutic drugs and various food products. Biosensors, on the other hand, can provide quick and cheap solutions to these problems. The field of optical biosensors is dominated by the method of surface plasmon resonance, which so far has attracted a lot of attention in the pharmaceutical industry. Investigation of long-range surface plasmon-polariton waveguides as an application for biosensing is still very novel, and most of it exists in the venue of theoretical discussions and modelling. The objective of this thesis is to demonstrate the capability of the novel optical biosensor based on plasmonic waveguides to selectively detect various biological entities in solutions. The experiments were conducted on photolithographically fabricated sensors consisting of straight gold waveguides embedded in low-refractive index fluoropolymer CYTOP and a microfluidic channel. As a proof-of-concept, a demonstration of basic sensing experiments such as detection of change in refractive index of bulk solution and non-specific adsorption of bovine serum albumin is provided. Further investigation of the sensor capabilities involved specific detection of human red blood cells and leukemia markers. Red blood cell detection was based on ABO blood grouping and included the estimation of limit of detection and signal-to-noise ratio for single cell detection. Finally, a clinically relevant problem of B-cell leukemia marker detection was targeted. The sensor demonstrated the ability to detect the relative abundance of similar proteins (immunoglobulin kappa and lambda) in a complex fluid (human serum). In addition, an experimental study on the optimization of the sensor for sensitivity was conducted.