Self-Assembly of Nanoporous Silica Particles for Tagging and Sensing Applications
Meso(nano)porous silica particles are of broad interest for many photonic applications,
filtration, drug delivery, catalysis. Through a self-assembly process, one can achieve
silica particles spanning in size from microns to tens of nanometer. In the early stage
of self-assembly it is observed that 20-50 nm seed particles are formed with hexagonally
packed open cylindrical nanochannels. ... read moreHowever, what is unknown is how these seed-like
particles aggregate and self-align their pores to form final multi-micron particles with
self-sealed channels extended over the entire particle.. In the course of this research,
we examined the assembly mechanism of mesoporous multi-micron size silica particles with
long cylindrical pores of 4-5 nm in diameter.We further showed that the observed
alignment of channels was thermodynamically favored by a decrease in the Gibbs free
energy of the particles. Besides a fundamental understanding of the mechanism of
morphogenesis and pore formation, we demonstrated that the results of this finding could
be further extended to make multi-hierarchical, sponge-like structured particles. Such
particles can be used for controlledrelease of various substances from semi-sealed
cylindrical pores of the particles. Next, we focused on fluorescent silica particles
formed by loading fluorescent dye inside the sealed nanochannels. Such photonic
materials find applications in tagging/labeling of biological cells and as tracers.
Previous works have shown that physical encapsulation of dye leads to ultrabright
properties. However, the nature of ultrabrightness was unclear. Here we investigated the
ultrabrightness phenomenon observed for dye hosting nanoparticles and micron size
discoid-shaped particles. This investigation revealed that the ultrabrightness was
caused by a specific hydrophobic nanoscale environment around the encapsulated dye
molecules offered by surfactant molecules inside the nanochannels. This environment
allows dye molecules to be packed in concentrations which are not attainable for free
dye without quenching of fluorescent properties. The close proximity of the encapsulated
dye molecules to each other allows them to utilize the quantum energy transfer between
dyes with complementary emission and absorbance (donor-acceptor pairs), which is called
Forster resonance energy transfer (FRET). Using FRET, we demonstrated ultrabright
temperature nanosensor (nanothermometers). Nanothermometers were assembled by
encapsulating two different dyes, in which one of them was temperature-sensitive while
the other acted as reference. The FRET based sensor comes with an advantage where a
single excitation source can be used to excite the particle fluorescence. To demonstrate
the working principle of nanothermometers, a 3D temperature distribution around a hot
wire immersed in hydrogel-particles system was measured. The observed experimental
results were validated by computation.
Thesis (Ph.D.)--Tufts University, 2017.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Igor Sokolov.
Committee: Jeffrey Guasto, Marc Hodes, Fiorenzo Omenetto, and Mingdi Yan.
Keyword: Mechanical engineering.read less