Light scattering by microscopic spheres behind a glass–air interface

Jory, M. J.; Perkins, Elaine A.; Sambles, J. R.

doi:10.1364/josaa.20.001589

Cited by 8 publications

(17 citation statements)

References 37 publications

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“…Many biosensors technologies involve the detection of particles adsorbed on a surface. These methods, including examples such as evanescent light scattering and surface plasmon resonance [1], [2], require that the particle to be detected be captured onto the surface of the sensor for detection. However, the effectiveness of such detection methods can be limited when used to detect colloidal bioparticles, since low particle concentrations and dominance of effects such as buoyancy or Brownian motion can limit the contact between sensor surface and particle.…”

mentioning

confidence: 99%

Optimizing particle collection for enhanced surface-based biosensors

Hoettges

Hughes

Cotton

et al. 2003

IEEE Eng. Med. Biol. Mag.

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T here exists a number of applications where a method of rapid detection of particlulate biomatter on the micron-and submicron scale, such as cells, bacteria, proteins, and viruses, is of great importance. Such applications include the development of point-of-care diagnostic devices for the detection of rare cells, the testing of water quality for the detection of microorganisms , and the monitoring of the environment for the detection of bioweapons such as anthrax. In order to detect such particles, a highly sensitive biosensor must be employed. Many biosensors technologies involve the detection of particles adsorbed on a surface. These methods, including examples such as evanescent light scattering and surface plasmon resonance [1], [2], require that the particle to be detected be captured onto the surface of the sensor for detection. However, the effectiveness of such detection methods can be limited when used to detect colloidal bioparticles, since low particle concentrations and dominance of effects such as buoyancy or Brownian motion can limit the contact between sensor surface and particle. Dielectrophoresis is the motion of particles caused by induced polarization effects in inhomogeneous electric fields [3]-[5]. Depending on the electrical properties of the medium and the particle, it can be attractive or repulsive, which we term positive and negative dielectrophoresis respectively. In the case of positive dielectrophoresis, the particle moves toward the greater field inhomogeneity, and in negative dielec-trophoresis it moves away from the field inhomogeneity. Since electrodes induce the electric field, the field inhomo-geneity is greatest at the edges of the electrodes; therefore, the particles move either toward or away from the electrodes. Used for a range of biomedical settings including the manipulation of bacteria (e.g., [6]-[8]), viruses (e.g., [9]-[11]), and cells such as cancers and algae (e.g., [12]-[15]), the technique has been used in conjunction with methods such as bulk light scattering [16] and evanescent light scattering [17] to detect the motion of particles. However, conventional dielec-trophoretic methods also present limitations. Where the particles are attracted to the surface on which microelectrodes have been patterned, the collection generally occurs along the edge of the electrodes; many sensing devices require collection to take place primarily on top of the electrode (metal) surface (e.g., [1]). Secondly, since field inhomogeneity reduces rapidly with distance from the electrode edge, the trapping of small particles (e.g., bacteria and viruses) has in the past only taken place using electrodes with very fine structures (sometimes of the order of a few µm) and very constrained volumes in which the particles can be detected (of the order of a few nanoliters). In addition to dielectrophoretic forces, another form of behavior is observed in particle solutions when exposed to lower-frequency nonuniform fields. This phenomenon occurs due to a combination of dielectrophoresis and ac-...

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confidence: 99%

Optimizing particle collection for enhanced surface-based biosensors

Hoettges

Hughes

Cotton

et al. 2003

IEEE Eng. Med. Biol. Mag.

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“…By using the method described in Ref. 41, a single microscopic sphere is placed on the surface of a fusion-drawn glass slide 42 [fusion-drawn glass is chosen as it has low surface roughness (ϳ13 nm)]. The reverse surface of the slide is then refractive-index matched to a modified prism assembly.…”

Section: Methodsmentioning

confidence: 99%

Light emission from whispering-gallery modes in microscopic spheres

2003

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The emission of light from whispering-gallery modes excited in microscopic spheres is examined. An evanescent wave is produced by total internal reflection of an optical beam at a planar glass-air interface. This evanescent wave is used to excite whispering-gallery modes in single microscopic spheres placed behind the glass-air interface. The intensity of light emitted into the air half-space from such spheres is measured as a function of scattering angle for both p- and s-polarized input beams. These data are compared with a simple theory for the emission from a point source above a planar glass substrate.

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“…In this case, extended Mie theory was shown to provide general solution in the form of angle-dependent Mueller matrix [8]. The theory was experimentally tested measuring light scattered by glass microspheres at the air-glass interface below the critical angle [9] and the scattering was then enhanced by introducing a thin gold film on top of the glass and achieving surface plasmon resonance [10]. In the case of surface-enhanced Raman scattering (SERS), the excited surface plasmons are localized and, while the electromagnetic contribution to enhancement is well understood [11][12][13], including the influence of hot spots [14,15], the theory was not extended until now to quantify the evanescent wave excitation by SERS.…”

Section: Introductionmentioning

confidence: 99%

“…This can be attributed to the fact that the hot spot axes are not, in reality, randomly oriented, as we assumed when deriving Eqs. (7)(8)(9). One can see on SEM micrographs that silver clusters had a predominantly flat arrangement.…”

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confidence: 97%

Surface-enhanced Raman scattering at a planar dielectric interface beyond critical angle

Pristinski¹,

Ru²,

Tan³

et al. 2008

Opt. Express

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Light refraction at the planar boundary of dielectric media prevents light propagation in the higher refractive index medium at angles beyond the critical value. This limitation is lifted when the evanescent wave is excited at the lower refractive index side of the interface. In this work we quantify polarization and angle dependence of surface-enhanced Raman scattering (SERS) intensity beyond the critical angle. Specifically, Raman spectra of thiocyanate molecules adsorbed on clustered silver nanoparticles at the water-glass interface were acquired using evanescent excitation and detection. Detected SERS signal polarization and scattering angle dependence are shown to be in agreement with a simple model based on excitation and radiation of a classical dipole near a lossless interface.

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Light scattering by microscopic spheres behind a glass–air interface

Cited by 8 publications

References 37 publications

Optimizing particle collection for enhanced surface-based biosensors

Optimizing particle collection for enhanced surface-based biosensors

Light emission from whispering-gallery modes in microscopic spheres

Surface-enhanced Raman scattering at a planar dielectric interface beyond critical angle

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