Title

Active and Ultrasensitive Chemical and Biosensing through Optothermally Generated Microbubble.

Author

Farzia Karim

Date of Award

1-1-2020

Degree Name

Ph.D. in Electro-Optics

Department

Department of Electro-Optics

Advisor/Chair

Advisor: Chenglong Zhao

Abstract

Rapid and sensitive detection of harmful chemicals or biological samples is essential for medical study and industrial applications. For example, in the food industry, it is an urgent demand to detect hazardous chemicals or pathogens and then efficiently eliminate contaminated sources from the food production chain to protect people from toxic food-borne infection. In addition, toxic chemicals, pesticides and pathogens are also responsible for water, air and soil contamination. Therefore, rapid and sensitive detection of toxic chemicals or pathogens are very important to ensure food safety and evaluating environmental pollution. Most of the sensing systems for detecting chemical or biological samples apply a passive sensing method, in which binding of analytes to the sensor happens through free diffusion. Due to this free diffusion of analytes in a passive sensing method, diffusing process takes several hours even days, especially when the analytes are at low concentrations and therefore suffer from so called diffusion limit. A higher sensitivity can be achieved in passive sensing methods, with nanoscale sensors but at a cost of reduced speed and vice versa. Therefore, speed and sensitivity of sensing need to be traded off. Active sensing methods, in which analytes are actively concentrated towards the sensor, can be used to break the diffusion limit of sensing and significantly improve the sensitivity. In this work, an ultrasensitive and cost-effective chemical and biosensing platform has been developed under ambient condition to demonstrate active sensing of analytes. This method works based on an optothermally generated microbubble (OGMB). OGMB is a micron-sized bubble that is generated on a liquid-solid interface through laser heating. Due to the strong convective flow induced by OGMB, nanoparticles or analytes can be attracted towards the OGMB and deposited on the surface of a substrate. We have successfully fabricated nanogap-rich structures by generating an OGMB on a glass substrate. The nanoparticles in the nanogap-rich structures form many nanogaps that are ideal for surface enhance Raman scattering (SERS) due to the plasmonic resonance of nanogap-rich structures. Analytes for example any chemical or biological samples can be actively concentrated on the nanogap-rich structure for SERS detection. The OGMB-assisted active sensing method can improve the detection limit of analytes by an order of magnitude compared to that with a passive sensing and thus overcome the diffusion limit of conventional passive sensing methods. Therefore, we expect that, OGMB-assisted active sensing method will find potential applications in advanced chemical and bio-sensing.

Keywords

Optics, Electromagnetics, Electrical Engineering, Engineering, Nanoscience, Nanotechnology, Physics, Solid State Physics, optothermally generated microbubble, active and ultrasensitive chemical and biosensing

Rights Statement

Copyright 2020, author

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