| The ability to actively manipulate cells and microparticles on-chip is critical for numerous biological studies and applications such as flow cytometry, cell sorting, microarrays, tissue engineering, and regenerative medicine. Researchers have developed a variety of patterning techniques such as microcontact printing, optical tweezers, optoelectronic tweezers, magnetic tweezers, electro-/dielectro-phoresis, evanescent waves/plasmonics, hydrodynamic flows, and bulk acoustic wave-based acoustophoresis. However, none of these techniques simultaneously meet specifications for miniaturization, versatility, throughput, speed, and power consumption. This thesis presents an active manipulating technique named "acoustic tweezers" that utilizes standing surface acoustic wave (SSAW) to build an acoustophoresis platform which can (1) three-dimensionally focus or even line-up micro/nanoparticles in a microchannel to facilitate the flow cytometry/cell sorting; (2) pattern virtually all kinds of cells and microparticles in both one-dimensional and two dimensional manners regardless of their shape, size, charge or polarizability; (3) continuously separate particles with different sizes, densities or compressibility through a continuous flow in a microchannel. Its power intensity, approximately 500,000 times lower than that of optical tweezers, compares favorably with those of other active particle-manipulation methods. Its speed is among the highest reported in literature, and flow cytometry studies have revealed it to be non-invasive. The aforementioned advantages, along with this technique's simple design and ability to be miniaturized, render the "acoustic tweezers" technique a promising tool for various applications in biology, chemistry, engineering, and materials science.;Furthermore, the "acoustic tweezers" technique was also verified to be effective in active tuning of surface plasmons---electron density waves that can potentially merge the photonics and electronics at nanoscale. Significant advances have been made in the development of sources, filters and waveguides, so called passive plasmonics devices though, for plasmonics to reach its potential, devices such as switches and modulators - so called active devices must be perfected. This thesis discusses two "acoustic tweezers"-induced active plasmonic devices that utilize SSAW to tune the localized surface plasmon resonance (LSPR) of gold nanodisk arrays (1) through realigning the LC molecules surrounding them; and (2) through the SAW-induced charging/discharging on a piezoelectric substrate without any liquid medium. The acoustic-induced active plasmonics features low power, easy fabrication and assembly and high efficiency.;In the the appendix, there are two relative topics are included. Appendix A discusses a technique using phononic crystal composites to manipulate ultrasounds, which can be used in acoustic tweezers to confine the acoustic energy, improving its performance. Appendix B discusses nanoparticle manipulation through surface plasmon polaritrons, which is actually an alternative technology to overcome the difficulties that acoustic tweezers endure in nanoparticles (less than 500 nm) manipulation. |
