Development of acoustofluidic scanning nanoscope
The largest obstacle in nanoscale microscopy is the diffraction limit. Although several means of achieving sub-diffraction resolution exist, they all have shortcomings such as cost, complexity, and processing time, which make them impractical for widespread use. Additionally, these technologies struggle to find a balance between a high resolution and a large field of view. In this introduction of dissertation, we provide an overview of various microsphere based super resolution techniques that address the shortcomings of existing platforms and consistently achieve sub-diffraction resolutions. Initially, the theoretical basis of photonic nanojets, which make microsphere based super resolution imaging possible, are discussed. In the following sections, different type of acoustofluidic scanning techniques and intelligent nanoscope are explored. The introduction concludes with an emphasis on the limitless potential of this technology, and the wide range of possible biomedical applications.First, we have documented the development of an acoutofluidic scanning nanoscope that can achieve both high resolution and large field of view at the same time, which alleviates a long-existing shortcoming of conventional microscopes. The acoutofluidic scanning nanoscope developed here can serve as either an add-on component to expand the capability of a conventional microscope, or could be paired with low-cost imaging platforms to develop a stand-alone microscope for portable imaging. The acoutofluidic scanning nanoscope achieves high-resolution imaging without the need for conventional high-cost and bulky objectives with high numerical apertures. The field of view of the acoutofluidic scanning nanoscope is much larger than that from a conventional high numerical aperture objective lens, and it is able to achieve the same resolving power. The acoutofluidic scanning nanoscope automatically focuses and maintains a constant working distance during the scanning process thanks to the interaction of the microparticles with the liquid domain. The resolving power of the acoutofluidic scanning nanoscope can easily be adjusted by using microparticles of different sizes and refractive indices. Additionally, it may be possible to further improve the performance of this platform by exploring additional microparticle sizes and materials, in combination with various objectives. Altogether, we believe this acoutofluidic scanning nanoscope has potential to be integrated into a wide range of applications from portable nano-detection to biomedicine and microfluidics. Next, we developed a dual-camera acoustofluidic nanoscope with a seamless image merging algorithm (alpha blending process). This design allows us to precisely image both the sample and the microspheres simultaneously and accurately track the particle path and location. Therefore, the number of images required to capture the entire field of view (200 × 200 μm) by using our acoustofluidic scanning nanoscope is reduced by 55-fold compared with previous designs. Moreover, the image quality is also greatly improved by applying an alpha blending imaging technique, which is critical for accurately depicting and identifying nanoscale objects or processes. This dual-camera acoustofluidic nanoscope paves the way for enhanced nanoimaging with high resolution and a large field of view. Next, we developed an acoustofluidic scanning nanoscope via fluorescence amplification technique. Nanoscale fluorescence signal amplification is a significant feature for many biomedical and cell biology research area. Different types of fluorescence amplification techniques were studied; however, those technologies still need a complex process and rely on an elaborate optical system. To conquer these limitations, we developed an acoustofluidic scanning nanoscope via fluorescence amplification with hard PDMS membrane technique. The microsphere magnification by photonic nanojets effect with the hard PDMS could deliver certain focal distance to maximize the amplification. Moreover, a bidirectional acoustofluidic scanning device with an image processing also developed to perform 2D scanning of large field of view area. In the image processing procedure, we applied a correction of lens distortion to provide a restored distortion image. This fluorescence amplification via acoustofluidic nanoscope allow us to afford a nanoscale fluorescence imaging. Next, we developed an intelligent nanoscope that combines machine learning and microsphere array-based imaging to: (1) surpass the diffraction limit of the microscope objective with microsphere imaging to provide high-resolution images; (2) provide large field-of-view imaging without the sacrifice of resolution by utilizing a microsphere array; and (3) rapidly classify nanomaterials using a deep convolution neural network. The intelligent nanoscope delivers more than 46 magnified images from a single image frame so that we collected more than 1,000 images within 2 seconds. Moreover, the intelligent nanoscope achieves a 95% nanomaterial classification accuracy using 1,000 images of training sets, which is 45% more accurate than without the microsphere array. The intelligent nanoscope also achieves a 92% bacteria classification accuracy using 50,000 images of training sets, which is 35% more accurate than without the microsphere array. This platform accomplished rapid, accurate detection and classification of nanomaterials with miniscule size differences. The capabilities of this device wield the potential to further detect and classify smaller biological nanomaterial, such as viruses or extracellular vesicles. Lastly, this chapter serves a conclusion. Here, I discuss current issues regarding the acoustofluidic scanning nanoscope across review the current limitations of the technology and give suggestions for different direction of microsphere imaging. Moreover, I provide my perspective on the future development of acoustofluidic scanning nanoscope and potential new applications. I discuss how the technologies developed in this dissertation can be improved and applied to new applications in nanoimaging.
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