CAREER: Digital plasmonics-based nano-tweezing and nano-imaging for nano-particles

Bethel University, Saint Paul MN

Investigators

Abstract

Light is an extremely powerful tool to probe, image, and even manipulate small objects. Unfortunately, since light is a wave it is limited by diffraction, or the tendency of all waves to spread out. As a result very small nano-sized objects like the basic components of cells, single molecules, viruses, and nano-devices are too small to beindividually probed, manipulated, and imaged directly with light. However, the field of 'plasmonics' allows manipulating light with sub-wavelength precision at the surface of metallic nano-structures. Plasmons can squeeze their optical energy into ~10 nanometer spaces, an ideal size for directly interacting with nano-sized objects that are on or near these metallic surfaces. Precise manipulation of plasmons requires careful illumination with light, and extremely sensitive optical recording equipment. PI has the capability of digital and computational techniques to both: (1) excite plasmons to directly manipulate nano-objects under computer control; and (2) carefully record the behavior of plasmons to directly image the shape, size, and thickness of nano-objects. These digital techniques will open up new opportunities for scientists under precise computer control to directly study, probe, image, manipulate, and interact with nano-sized objects such as DNA, protein molecules, quantum dots, viruses, or nanoparticles. Furthermore, since this research is being performed exclusively with undergraduate students, it promises to inspire, motivate, and train many new young scientists and engineers. The emergence of digital techniques that explicitly model the propagation of light has revolutionized optical imaging and optical tweezing through 'digital holographic microscopy' and 'computer generated holography'. These techniques offer many advantages over conventional optics such as: (1) imaging or generating the full complex wave; (2) fast beam scanning with no moving parts; (3) dynamic manipulation of trapped objects; (4) eliminating aberrations and imaging through scattering media; and (5) freedom to choose any imaging modality, e.g. phase vs. amplitude contrast. Unfortunately, these powerful digital techniques have not yet been fully realized in near-field optics, and in particular, with plasmons. Indeed, plasmonic nano-imaging and nano-tweezing have recently generated immense interest to trap, probe, manipulate, and image nano-sized objects such as viruses, nanoparticles, and individual molecules. Therefore, introducing powerful digital optical techniques into the near-field promises to have a large impact. Specifically, a spatial light modulator will be used to generate computer-controlled, tightly focused plasmons for nano-tweezing and high-spatial frequency plasmonic fields for super-resolution imaging. The phase of the plasmon waves will also be imaged by designing interferometers directly into the nano-metallic substrates or by recording a digital hologram of the reflected or transmitted light. These two techniques will enable significant new capabilities such as: (1) super-resolution, high-speed plasmonic phase-contrast imaging to image the thickness of biological structures; (2) trapping and real-time manipulation of nano-metric objects for nanofabrication or sorting; and (3) optical probing of trapped nano-objects for spectroscopic characterization of single molecules.