Patent GB-1380756-A (GB)
Title: Multisensor particle sorter
IPC: G01N15/12
Filed: 1972-12-04
Abstract: 1380756 Particle analysis UNITED STATES ATOMIC ENERGY COMMISSION 4 Dec 1972 [23 Dec 1971] 55921/72 Headings G1A and G1N Minute particles in suspension in a fluid are analyzed and sorted by passing the fluid through a flow chamber illuminated by a high intensity light source, determining a plurality of physical and chemical parameters of the particles, at least one parameter being determined photo-electrically, to produce analogue electrical signals which are compared with standard values to produce a sorting signal, jetting the fluid from the flow chamber, periodically disturbing the jet to produce droplets such that each particle is isolated in a single droplet, electrically charging droplets containing particles producing the sorting signal and electrically deflecting the charged drops to separate them from the uncharged drops. As shown, Fig. 2, a sample comprising biological cells suspended in a fluid is passed through a tube 1 into a flow chamber 3 where it is illuminated by a laser beam 4. Fluorescence radiation 9 emitted at right angles to the source beam and small-angle forward-scattered radiation 11 are measured photo-electrically and together with a signal representing cell volume are processed to determine the characteristics of each cell. The fluid jets from the flow chamber which is vibrated by means of an ultrasonic Piezo-electric transducer 31 to break the jet into droplets 13. Droplets containing cells whose characteristics fall onside specified standards are electrically charged by plates 5 and then deflected by a static electric field between plates 8 into a container 7. The flow chamber comprises an inner conductive tube (1) through which the sample fluid is passed, surrounded by a tube (19) of insulating material through which cell-free fluid is passed. The ends of the tubes narrow to form jets so that the cells emerge singly and are surrounded by a co-axial sheath of fluid. The jet emerges within a cuvette (23) also containing fluid and enclosed in a conductive housing (24) forming an electrical screen which is provided with three ports (35, 36) for the radiation beams. A conductive tube (54) supplies fluid to the cuvette. This tube and the conductive sample tube (1) form the electrodes of a Coulter counter in which the passage of a cell through the jet orifice changes the electrical impedance between the electrodes in accordance with the volume of the cell. The sample jet surrounded by the sheath of fluid together with further fluid from the cuvette to maintain the pressure passes out through an aligned aperture in the flow chamber in the form of a jet which is broken into droplets by vibrations applied to the chamber. The photo-metric system comprises an argonion laser the beam of which is shaped to an elliptical cross-section by cylindrical lenses. The sample cells are stained with a fluorescent dye which is bound for example to the DNA or RNA in the cell. When excited by the laser beam the dye fluoresces and the radiation emitted in a direction perpendicular to the incident radiation is focused on to a pinhole by a pair of lenses between which is arranged a filter. A photo-multiplier positioned behind the pinhole detects the fluoresence radiation to produce a signal indicating the amount of the chemical to which the dye is bound contained in the cell. The radiation scattered in the forward direction at small angles, i.e. between 0.5 and 2 degrees, is detected by means of a lens and a photo-diode, an angled reflector being arranged in the centre of the beam path to eliminate the direct beam and radiation scattered less than 0.5 degree which would otherwise overwhelm the detector. The electrical signal produced indicates the size and shape of the cell. It is mentioned that a second fluorescence measurement at a different wavelength or a light absorption measurement may be made. The cell volume signal together with the fluorescence and scattered radiation signals are processed to identify abnormal cells and to provide information in the form of a print-out or histogram and signals may also be displayed on an oscilloscope. Block diagrams of the processing arrangement are given which indicate possible combinations of the input signals to form differences and ratios for application to a dual parameter analyzer utilizing a two-dimensional pulse-height discriminator. The signals or combinations thereof are also selected for application to a single dimensional pulse-height discriminator for controlling the sorting mechanism via a suitable delay. A delay is also included in the signal path from the volume measuring transducer since this signal is generated before the cell enters the radiation path.