Mueller matrix microscopy is a promising non-invasive tool for pathological diagnosis due to its sensitivity to microstructures and its non-reliance on high spatial resolution. Such technique is sensitive to anisotropy, but the majority of such information is deeply hidden within the orientation parameters such as αq, αr, αP and αD. Analysis of them is challenging because orientation parameters varies when the sample’s spatial azimuthal angle changes relative to the imaging system, and the range boundary imposed by the arctan function prevents the parameters from forming a continuous distribution. As the result, the use of orientation parameters is generally avoided during quantitative analysis, despite the rich information they encode. In an effort to resolve these challenges, we propose a novel method for analyzing orientation parameters extracted from Mueller matrix polarimetry. The angular pixel values in the parameter images are unwrapped by assuming continuity, transforming the distorted distribution into one that is statistically viable. The unwrapped orientation parameters are then used for pathological slides analysis. Frequency distribution histograms of the orientation parameters before and after unwrapping are compared, the validity of the proposed method is demonstrated.
The whispering gallery mode (WGM) biosensor is a micro-optical platform capable of sensitive label-free detection of
biological particles. Described by the reactive sensing principle (RSP), this analytic formulation quantifies the response
of the system to the adsorption of bioparticles. Guided by the RSP, the WGM biosensor enabling from detection of virus
(e.g., Human Papillomavirus, HPV) to the ultimate goal of single protein detection. The latter was derived from insights
into the RSP, which resulted in the development of a hybrid plasmonic WGM biosensor, which has recently
demonstrated detection of individual protein cancer markers. Enhancements from bound gold nanoparticles provide the
sensitivity to detect single protein molecules (66 kDa) with good signal-to-noise (S/N > 10), and project that detection of
proteins as small as 5 kDa.
The reactive sensing principle applied to hybrid plasmonic whispering gallery mode biosensor has recently demonstrated detection of individual protein cancer markers. The rough surface of a gold nanoparticle affixed to the resonator surface acts like a nanoscopic antenna, significantly boosts the local electric field within the cavity mode. Adsorption of a target protein onto this nanoscopic antenna results in an enhanced response of the resonator system to the binding event. We have demonstrated detection of individual protein molecules (66 kDa) with good signal-to-noise (S/N > 10), and project that detection of proteins as small as 5 kDa are possible.
Our hybrid plasmonic whispering gallery mode biosensor has recently demonstrated detection and characterization of the smallest known RNA virus. A gold nanoparticle affixed to the resonator surface acts like a nanoscopic antenna, enhancing locally the electric field within the cavity mode. When a target analyte binds with this nanoscopic antenna the result is an enhanced response (spectral shift) of the resonator system to the binding event. We have observed shift enhancements ~70× over the response of the bare resonator, thereby permitting the detection and characterization of all known viral particles and even some large protein molecules.
The BioPhotonics community is buzzing at the prospect that ulta-small bio-nanoparticles such as Polio virus and protein can be detected label-free in their native state and sized one at a time. As the awareness that the claim of label-free single protein sensing through the frequency shift of a bare microcavity by A.M. Armani et al in Science in 2007 fades from lack of independent experimental confirmation or a viable physical mechanism to account for the magnitude of the reported wavelength shifts, a new approach has captured the community’s interest. It is a product of a marriage between nano-optics and micro-photonics, and is poised to take label-free sensing to the limit.
We report the label-free detection and sizing of the smallest individual RNA virus, MS2 by a spherical microcavity. Mass of this virus is ~6 ag and produces a theoretical resonance shift ~0.25 fm upon adsorbing an individual virus at the
equator of the bare microcavity, which is well below the r.m.s background noise of 2 fm. However, detection was
accomplished with ease (S/N = 8, Q = 4x105) using a single dipole stimulated plasmonic-nanoshell as a microcavity wavelength shift enhancer. Analytical expressions based on the “reactive sensing principle” are developed to extract the radius of the virus from the measured signals. Estimated limit of detection for these experiments was ~0.4 ag or 240 kDa below the size of all known viruses, largest globular and elongated proteins [Phosphofructokinase (345 kDa) and Fibrinogen (390 kDa), respectively].
We describe and demonstrate a physical mechanism that substantially enhances the label-free sensitivity of a
Whispering-Gallery-Mode biosensor for the detection of individual nanoparticles in aqueous solution. It involves the
interaction of dielectric nanoparticle in an equatorial carousel orbit with a plasmonic nanoparticle bound on the orbital
path. As a 60 nm dielectric particle parks on plasmonic hot spots we observe frequency shifts that are considerably
enhanced consistent with a simple reactive model. Using the same model the label free detection of a single bovine
serum albumin (BSA) molecule is projected.
Single polystyrene nanoparticles are detected from resonance wavelength fluctuations in toroidal
and spherical microcavities. The magnitude of the wavelength-shift signal follows a reactive
mechanism with inverse dependence on mode volume. By reducing the size of a microsphere
cavity we demonstrate sensitivity to single Influenza A virions. Furthermore, we introduce a
novel mechanism for trapping and accumulation of nanoparticles at the microcavity-sensorregion
by utilizing light-force exerted in evanescent field gradients.
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