Active and Ultrasensitive Chemical and Biosensing through Optothermally Generated Microbubble

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 v works based on an optothermally generated microbubble (OGMB). OGMB is a micronsized 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. DEDICATION vi Dedicated to my mother who is my pride, inspiration, strength and my life. vii ACKNOWLEDGMENTS At the beginning, all the praise to Almighty for giving me the capability for successful completion of this work. I would like to express my sincere indebtedness to all who have given me the chance to finish this research. Without their generous sup...

Directional Control of Transient Flows Generated by Thermoplasmonic Bubble Nucleation

“…Several proof-of-principle applications based on bubble-induced flow have been demonstrated, such as increasing the detection rate of surface-based sensors , and manipulating nanostructures. , However, in most of these studies, the created bubbles were tens to hundreds of microns in size. Such large bubbles do not allow for rapid and dynamic flow control because of the diffusion limited slow expulsion of dissolved gas, accumulated in the bubble from the surrounding water, after illumination has ceased. , Though the bubble lifetime can be decreased by using degassed water, , this is not feasible in most practical applications. , As a solution to this issue, Jones et al recently demonstrated that spatially isolated gold nanoantennas are able to produce micron-sized bubbles that can be modulated at up to kHz frequencies in air-equilibrated water. , The reason for this is that it is now the spatial extension of the plasmonic antenna that determines the bubble size rather than the illuminated area, as in previous experiments with distributed plasmonic arrays. − Furthermore, it was found that a very strong transient, producing mm/s flow velocities close to the antenna, is induced as a microbubble form .…”

“…Several proof-of-principle applications based on bubbleinduced flow have been demonstrated, such as increasing the detection rate of surface-based sensors 12,13 and manipulating nanostructures. 14,15 However, in most of these studies, the created bubbles were tens to hundreds of microns in size.…”