Integration of microfluidic sample handlingwith ultra-sensitive magnetic bioassay usinghigh-Tc Superconducting Quantum InterferenceDevice readout

Abstract: Immunoassays are a very sensitive molecular diagnostics technique that uses biochemical reactions to measure concentration of biomolecules in a solution. ELISA is one of the most commonly used type, based on fluorescence, in routine medicaldiagnostics. It is time consuming and requires relatively large sample volumes. Immunoassays based on magnetic detection are being developed. They are faster, able to be made into point of care devices with biological samples often lacking magnetic background. This project focuses on developing an magnetic bioassay based on a high-Tc SQUID with magnetic nanoparticles as tags. The expected performance maybe two orders of magnitude better than ELISA techniques, while not requiring several washing steps and being able to perform in real time. Method of detection is based on utilizing a padlock DNA probe-based recognition mechanism to enhance the size ofviral flu RNA, binding the nanoparticles to the padlocks and measuring the change in amplitude of the Brownian relaxation peak of the unbound nanoparticles. This thesis has been focused on developing a microfluidic sample holder. Mircofluidics offer an advanced way to handle liquid samples, with preparation, dilution, mixing and incubation on the same chip, so called lab on a chip. During this thesis, microfluidic channels made of PDMS were created. PDMS is a suitable material because it is relatively cheap, easy to manufacture and particles or padlocks do not bind to it. Measurements of the real and imaginary parts of the AC susceptibility as a function of concentration of both non functionalized and functionalized magnetic nanoparticles were performed in the microchannel with a volume of about 3 micro liter. Extrapolating the results showed an equivalent iron content sensitivity of 2'10^5 particles at 10 Hz. This result is about one order of magnitude better than obtained in bulk samples of larger volume.