Optics: measuring and testing – By shade or color – With color transmitting filter
Patent
1992-06-18
1995-06-27
Evans, F. L.
Optics: measuring and testing
By shade or color
With color transmitting filter
2504581, 377 10, G01N 1514, G01N 2164
Patent
active
054284511
DESCRIPTION:
BRIEF SUMMARY
This invention concerns a method and apparatus for counting particles.
Existing particle counters, for example, for counting microbial cells, are cumbersome and expensive devices commonly employing a significant power source either to maintain a high voltage field, as in the Coulter system, or laser illumination as in the conventional flow cytometer. It would be convenient in many cases count particles accurately in the field using a system readily capable of transportation and using a portable power source, e.g., batteries.
U.S. Pat. No. 4,075,462 describes a particle analyser system in which images of particles are focused onto an array of light sensitive electronic elements. Only photodiodes are specifically described. The particles pass through a light path directly from a light source to the light sensitive array, thus providing a shadow image of the particles, while bubbles, which should not be counted, show up as having an apparent central aperture. Such a system is less well adapted to counting cells, which are normally relatively transparent, than more solid particles and does not lend itself to counting differentially stained particles.
Patent Abstracts of Japan, Vol 10, No. 212 (P-480) (2268), Jul. 24, 1986 and JP-A-6151569 describe a cell identifying device in which cells pass through a rectangular light beam and the intensity of forward and backward scattered light is measured as well as the spectral distribution of fluorescence. The scattered light is passed to a one-dimensional array of photosensors and is repeatedly scanned, the information being processed by a computer to enable the required cell identification to be effected. Forward and backward scatter of incident light can only give information on the granularity or surface structure of the cells while the fluorescence spectrum also gives information concerning the natural fluorescent chromophores on the cell surface. There is no suggestion that images of the cells are produced. The light scattered from the cells is not focused or collimated and the photosensor array is only one-dimensional, which does not lend itself to cell counting, where it is necessary to distinguish clearly the boundaries between the individual cells. Further, there is no attempt to prevent the scattered incident light from reaching the photosensors, for example by interpolation of a transmittance filter and, indeed, measurement of the scattered incident light is an essential part of the system.
BRIEF DESCRIPTION OF THE FIGURE
The Figure is an exploded perspective view of the components constituting the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The present invention is based in part on the concept of using an array of charge coupled devices (CCDs) as the counting device to count fluorescent particles. It is proposed, to project an image of the fluorescent particles onto the CCD array such that the area of the image of an individual particle is approximately the same as the area of at least one CCD. The particles are irradiated from the side and the incident irradiation is filtered out from the light falling on the CCD array, using one or more transmittance filters. However, in conventional, commercially available CCD arrays (chips) the area of each CCD, although very small, is larger than that of a typical microbial or other cell or cell nucleus or of many other particles, such as dust particles, which it may be require to count. Thus a preferred form the invention includes projecting a magnified image of the particle. This avoids the problem that a single CCD will provide a signal deriving from several particles simultaneously, thus preventing the possibility of counting individual particles.
The term CCD array as used herein refers to an array of photosensitive CCDs which may for example, be of the frame-field or interline transfer type and may produce the required signals by current or voltage sensing. Such arrays are normally provided as integral CCD chips for use, for example, in solid state cameras and one comm
REFERENCES:
patent: 4075462 (1978-02-01), Rowe
patent: 4295199 (1981-10-01), Curry et al.
patent: 4550417 (1985-10-01), Nunogaki et al.
patent: 4576477 (1986-03-01), Corbet et al.
patent: 5147806 (1992-09-01), Kamin et al.
Patent Abstracts of Japan, vol. 10, No. 212, Jul. 24, 1986, JP 61-51569.
Lea Tor E.
Naess Harald K.
Pedersen Bjorn K.
Diatec Instruments A/S
Evans F. L.
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