Dual-channel radially polarized surface plasmon microscopy for sensitive detection of fluorescent and non-fluorescent nano-objects
Date Issued
2011
Date
2011
Author(s)
Sung, Chih-Hsiang
Abstract
Due to the advantage of surface sensitivity, various SPR biosensors for scientific research fields or personal medicine markets have been reported. However, especially for SPR imaging applications, the designs are usually based on prism-coupling method and ensuing chips with array patterns. In fact, these designs entail the disadvantages of a limited spatial resolution and non uniform detection regions. Although several super-resolution microscopes have been proposed and developed, systems are usually complicated and high-costs. In this thesis, we adopt the surface plasmon resonance technique to build a brand new imaging system. Alongside fluorescence, SPR absorption can also be exploited towards better imaging and understanding of the surface properties.
Towards this aim, we demonstrate a dual-channel radially-polarized surface plasmon microscopy (SPM) system with capability down to single nanoparticle detection. For nanospheres stained with fluorescent molecules, we are able to simultaneously collect the fluorescence and elastic scattering images. These two complementary emitted signals lead to well co-localized images. The improved resolution and higher sensitivity of this system are enabled by use of a radial polarizer and a high numerical aperture objective. It provides TM-polarization status to the entire incident beam, which results in the formation of a dark circular ring in the reflected image. The fluorescence intensity is then clearly enhanced by more than 50% under radial polarization as compared to a linear one, while azimuthal polarization being fully TE is ineffective and serves as a reference.
We first applied this technique to detect a single fluorescent sphere of 20 nm in diameter, which potentially reveals unique information as compared to other measurements on bulk films. Moreover, it also provides a way to compensate for the blinking characteristic of the fluorescence, which does not affect the elastic scattering channel. We are currently extending this technique to stained biological objects such as DNA strands and cell membranes in liquid environments. This technique has been extended to study two photon fluorescence (TPF) signals from organometallic nanospheres, as well as second harmonic generation (SHG) signals from non-centrosymmetric nanocrystals via a multiphoton confocal microscope. In relation with this research, metallic ion enhanced fluorescence and quenching effects from quantum dots are fundamental topics currently under investigation.
Subjects
surface plasmon resonance
surface plasmon microscopy
radial polarization
dual-channel
nanoparticle
second-harmonic generation
two-photon fluorescence
Type
thesis
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