Improving sensitivity biosensors by using micro/nano magnetic particles

Abstract

Currently micro/nanoparticles such as magnetic beads are not only used as labels to acquire signals from biosensors but they are also used to enhance the signals obtained from various biosensors. Magnetic beads or target are linked to other molecular labels such as fluorescence and chemiluminescence labels by biomolecules such as antibody to reach higher sensitivity and provide signal amplification for the measurement. This dependency on biomolecular binding has several disadvantages such as molecular binding is sensitive to environmental conditions such as pH and temperature, labels are costly and molecular binding may require extra time. In this thesis a time and cost efficient signal amplification method that does not need any biomolecular coating but based on magnetic interaction of magnetic micro/nanoparticles is developed. Magnetic particles subjected to external magnetic field are magnetized and form a local field around them, attract each other and accumulate along the magnetic field lines. These controlled accumulations can be used to amplify the pixel area or the contrast of magnetic particles. Accumulation dynamics of magnetic particles under magnetic field are studied and the application of this method to the Escherichia coli 0157:H7 sample is demonstrated. Lastly the integration of this signal amplification method to a flow chamber and a complete biosensing procedure is pursued. Magnetic micro/ nano particles that are immobilized on gold-coated surface under external magnetic field inside a flow chamber attract the iron nanoparticles in a running fluid to form chains of accumulations around them. The accumulations formed under magnetic field are used to improve the Contrast to Noise Ratio (CNR) of the images thus the sensitivity.