Hydrogel microlaser on chip for biomedical and physical applications

Abstract

Biological microlasers have positioned themselves as a potent tool for the detection and identification of biomolecules in the last decade. The key advantages of laser-based detection over fluorescence-based methods include signal amplification, tighter linewidth, and superior signal-to-noise ratio, culminating in a remarkable increase in detection sensitivity. Moreover, due to the nonlinearity of the signal at the lasing threshold, laser emission can offer improved axial spatial resolution. The vast diversity in laser parameters such as threshold, intensity, and transverse mode makes lasers suitable candidates for anti-counterfeiting techniques. Despite of recent progress in achieving lasing for molecular biosensing and anti-counterfeiting labeling, the challenges in raw material fabrication and physical property limitations often lead to micro-lasers that lack versatility and functionality in real world applications. Therefore, this dissertation explores the potential of using reconfigurable materials hydrogels to develop a platform that is versatile and well-suited for both chemical sensing and physical anticounterfeiting. For better understanding of this dissertation, we begin with a brief review with the introduction of biological lasers and characteristics of hydrogels, then we introduce the background of applications in biochemistry and security techniques (Chapter 1 and Chapter 2). In Chapter 3 and 4, we successfully developed a Whispering Gallery Mode (WGM) hydrogel biological microlaser, capable of detecting variations in molecular distances and differentiating molecular sizes based on lasing threshold. The study also demonstrates the microlaser's ability to encapsulate and analyze living organisms with superior sensitivity compared to traditional fluorescence analysis. Moving to physical applications in Chapter 5 and Chapter 6, we harnessed the inherent properties of hydrogels to create tunable microlasers for anti-counterfeiting purposes. Through enzyme-based reactions, the hydrogel's internal structure 15 and its corresponding lasing emission were manipulated, enabling a novel approach for information encoding and encryption. Furthermore, the fusion of Förster Resonance Energy Transfer (FRET) lasers and hydrogel's structural randomness yielded a high-capacity optical encoding method, adding an advanced layer of security against counterfeiting. These key findings of this research underscores the immense potential and versatility of hydrogel microlasers, bridging the fields of biophotonics and information security and opening new avenues for future applications and investigations.