Optical analysis

Details Optical analysis Optical analysis

1988-07-05

1990-05-22

Scott, Jr., Leon

Optics: measuring and testing

For size of particles

By particle light scattering

356338, 350 9618, G01N 1502

Patent

active

049272683

DESCRIPTION:

BRIEF SUMMARY
This invention relates to optical analysis and in the most important example to the analysis using optical techniques of biological material such as protein or other macromolecules, cells, viruses, tissue fragments and the like.
Over a wide range of particle size--extending from perhaps below a nanometer to around a millimeter--optical methods are favoured for determination of parameters such as particle size, concentration, velocity and shape. The methods that can be used are varied and include scattering, thermal lensing, fluorescence and photophoresis. Known scattering techniques can conveniently be classified as those which utilise:
(i) the diffraction pattern of a population of light scattering particles in the spatial (Fraunhofer) or temporal (photon correlation) mode, or
(ii) the intensity of light scattered by an individual particle as it passes through an illuminated scattering volume. optics and computer processing but have proved to be useful with small particles which are all of the same size. Extending the technique to cope with two or more different particle species involves a significant increase in processing capability. The technique is not regarded as practical for use with particle populations which have a large number of different species, such as those occuring in biological systems. It is further the case that Fraunhofer and photon correlation techniques are unsuited for use with larger particles.
The analysis of light scattered by a single particle is inherently more informative as well as being less expensive computationally. The mechanisms by which particles are addressed by the interrogating optical beam can be regarded as falling into two main areas.
In the first technique the fluid sample containing particles of interest is manipulated to form a narrow stream sufficiently small to present only one particle at a time to the scattering volume. It is a disadvantage of this technique that the hydrodynamic sheath required to carry the stream of particles past the measuring zone requires sophisticated fluid handling and the fine orifice from which the particle-containing sample is introduced into the hydrodynamic sheath is notoriously prone to blocking. The equipment is often bulky and requires samples to be separately analysed off-line.
In a second approach, the optical measuring volume is configured to be sufficiently small to address only one particle at a time within a suitably dilute particulate suspension. By using finely focused laser beams, high intensities of light can be concentrated into measuring volumes of less than about 10-3 microliters.
The analysis of light scattered by a particle passing through a laser beam has the merit of simplicity but the technique suffers from a major draw-back. The light scattered from a relatively large particle which merely "clips" the edge of the beam may be similar to that from a smaller particle passing through the centre of the beam. If these events are not distinguished, the scattering analysis may be ambiguous.
This problem has been overcome in one known arrangement (see for example APPLIED OPTICS Vol. 25 No. 5 pp 653-657) by using two laser beams of different wavelengths which are configured to be concentrically aligned, one beam being smaller in diameter than the other. The internal beam is disposed centrally of the outer beam. A particle passing through the internal narrow beam is thus known to be, at that instant, central to the outer beam and the resultant scattered light signal from the inner beam is used to trigger or gate the collection of scattered light from the outer beam. In the absence of detected light from the inner beam (this absence being indicative of an off-centre particle) scattered light from the outer beam is ignored. The two signals are differentiated by using two detectors filtered to respond only to one wavelength or the other.
The known system comprises two lasers producing beams which are focused to the required concentric configuration by a combination of lenses, mirrors, beam-splitters and prisms. Each of t

REFERENCES:
patent: 4387993 (1983-06-01), Adrian
patent: 4564598 (1986-01-01), Briggs
patent: 4678326 (1987-07-01), Harjunman
patent: 4752131 (1988-06-01), Eisenlauer et al.
patent: 4801205 (1989-01-01), Tatsuno
patent: 4834497 (1989-03-01), Angel
Applied Optics, vol. 25, No. 5, 1 Mar. 1986 (US), J. C. F. Wang et al.: "In Situ Particle Size Measurements Using A Two-Color Laser Scattering Technique", pp. 653-657, See Paragraph II, . . .
Analytical Chemistry, vol. 58, No. 8, Jul. 1986 (Columbus, Ohio, US).

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