Juan Han

Date of Award

January 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

David D. Pierce

Second Advisor

Julia J. Zhao

Abstract

Metal-containing nanoparticles (MCPs) have been applied in fields ranging from environmental monitoring to biomedicine. This breadth is due to the outstanding behavior of MCPs as catalysts and imaging agents, and the ease with which nanoparticle morphology, composition, and reactivity (such as agglomeration) can be controlled. The work described in this dissertation will have two fundamentally different foci that are both essential for further development of MCPs as tools for chemical and bioanalysis. The first focus is on particle-by-particle characterization MCPs and the second focus is on creation of new composite MCPs. A total of four projects are included in this dissertation as follows.

The first project shows how to optimize a relatively new analysis method, single-particle inductively-coupled plasma mass spectrometry (spICP-MS), for the particle-by-particle characterization of MCPs. Bulk analysis methods such conventional ICP-MS produce an aggregate signal derived from many particles at once, whereas spICP-MS produces a discrete per-particle signal that is monitored over time to produce an ensemble of per-particle signals. Bulk analysis is very reliable for obtaining accurate average metal content per particle because the signal is inherently an average for many particles. However, all per-particle information is lost with bulk analysis methods. Conversely, spICP-MS provides a very rare window into the per-particle composition of MCPs; however, its method parameters such as particle concentration, ICP ionization efficiency, and dwell time must be carefully optimized for accurate per-particle analysis. This work demonstrates how to optimize spICP-MSfor large MCPs—a particularly challenging size range—by using standard samples of gold nanoparticles ranging from 30 nm to 150 nm. The second project uses properly optimized spICP-MS conditions to measure per-particle metal concentration of large-sized (> 100 nm) silica nanoparticles prepared by the water-in-oil microemulsion method and doped with tris(2,2’-bipyridyl)ruthenium(II). This is a well-studied MCP model that provides numerous avenues for bulk analysis (e.g., absorption spectrophotometry) and comparison with spICP-MS findings. Despite excellent correspondence of all methods for average Ru content over a wide range in doping levels, the per-particle doping level provided by spICP-MS does not—remarkably—adhere to a simple Gaussian-like distribution but shows a highly unusual geometric distribution. This result means, contrary to common assumption, the per-particle concentration of metal-dopant in silica nanoparticles prepared by the water-in-oil microemulsion method varies significantly per particle. These findings demonstrate that spICP-MS provides an essential per-particle window into MCP composition that is entirely missing with conventional bulk analysis methods. They also show that spICP-MS screening should become a routine characterization for new MCPs.

The third project shows how to prepare and apply a ratiometric and fluorescent MCP for the sensitive and selective in vitro imaging of copper ions (Cu2+). This MCP contains conjugated polymer dots prepared from polydioctylfluorene (PFO), doped with a silica nanoparticle (PFO@SiO2), and assembled with red emissive gold nanoclusters (AuNCs) at the PFO@SiO2 surface to form a sandwich nanostructure, PFO@SiO2@AuNCs. This nanostructure exhibits two fluorescence emission peaks associated with the PFO polymers (438 nm) and AuNCs (630 nm). When Cu2+ coordinates with carboxyl groups on the AuNCs, the AuNC emission decreases in contrast to the constant PFO emission. This behavior provides a highly sensitive and selective ratiometric signal that can be applied for in vitro imaging and determination of Cu2+ in biological samples. The fourth project develops a turn-off type fluorescence resonance energy transfer (FRET) method based on a MCP composite that is sensitive to cysteine. The composite consists of AuNCs conjugated with polyvinylcarbazole polymer nanoparticles (PVK PNs) that demonstrate a strong FRET between two distinct fluorescence emission peaks under excitation of 342 nm. The MCP composite is highly sensitive to cysteine concentration though a quenching process at 630 nm due to the decomposition of aurophilic bonds consisting of Au(I)-thiolate ligands under high pH value and the etching ability of cysteine toward gold atoms. The MCP composite shows potential for determination of other biomolecules.

Download

Share

COinS