Nanofluidics as a tool for parallelized single nanoparticle characterization: Fluorescence single nanoparticle catalysis and size determination through 1D Brownian motion

Abstract: Nanoparticles exist widely in nature and are objects of study in many scientific disciplines due to their high performance in a wide range of applications. With modern techniques that facilitate creating and shaping of nanoparticles into ever more complex shapes and compositions, characterization of particle properties is essential. Nanoparticles are typically heterogeneous and techniques with single particle resolution are necessary to avoid the ensemble averaging that is otherwise prevalent. Plenty of methods have been developed to characterize single particle properties, but they all have their own restrictions and limitations, and additional methods are still needed to complement existing methods. This thesis is based on two novel methods for single nanoparticle characterization. The first method, parallelized nanofluidic fluorescence microscopy, evaluates the fluorescence downstream of single Au nanoparticles, each one in its own nanochannel, to measure the turnover frequency during catalytic reduction at the particle surfaces. It facilitates measurements of catalytic turnover frequency from single Au nanoparticles of different sizes and shapes measured in a parallelized fashion to ensure identical reaction conditions and synchronous measurement. The second method, Nano-SMF, monitors the Brownian motion of fluorescent particles flowing through an array of nanochannels and determines the particle sizes based on the particle movement. It provides characterization of size and multiple fluorescence intensities for thousands of individual fluorescent particles with high throughput and for complex size distributions, which are prevalent in biological systems. Both methods utilize nanofluidic flow systems to keep the readout signal in focus of the microscope and separate the nanoparticles and the signals emanated by them within parallel nanochannels. Together they showcase how nanofluidics provides a practical and versatile platform for single nanoparticle characterization.