Microscopic examination of unstained cell and tissue specimens often suffers from a lack of contrast between individual cells and the background matrix or between individual parts of cells. In order to alleviate this difficulty, stains that are taken up differentially by cells or parts of cells have been used for over a century.
Because of the manner in which microscope slides with tissue samples are prepared (see Elias, J., "Immunohistopathology: A practical Approach to Diagnosis" ASCO Press, 1990, pp. 3-4, for examples of such preparation), the size and/or location of a tissue sample on a microscope slide can vary considerably within a relatively large area of the slide. In order to apply a stain to the correct location on a slide and to provide rinsing and other manipulation steps at appropriate times and in proper amounts, until recently all such staining operations were carried out by hand. However, modern laboratories that examine large numbers of tissue specimens find it desirable to automate the staining process. Accordingly, a number of manufacturers have developed equipment for automated staining of tissue samples on slides.
For example, U.S. Pat. No. 4,985,206 describes an apparatus and process for automating the application of staining reagents to a thin tissue section mounted on a microscope slide. The apparatus and method use a channel-defining element that is assembled with the microscope slide to provide an enclosure of capillary dimensions into which liquids can be injected. Liquids are added sequentially to the capillary space, where the addition of a new liquid forces out the previous liquid. A plurality of these assemblies of microscope slides and specialized covers can be placed in a rack on an apparatus for automated addition of liquids.
A further automated immunostaining apparatus, known as the Ventana 320.TM. is produced by Ventana Medical Systems, Inc. This apparatus applies a liquid known as Liquid Coverslip.TM. to each slide prior to reagent addition. Liquid Coverslip.TM. is a non-aqueous material having a density less than that of water. When a reagent dissolved in water is added to a microscope slide, the reagent sinks to the bottom of the Liquid Coverslip.TM. layer, spreading across the surface of the slide. Slides are organized on a carousel which rotates beneath a dispensing head of the apparatus for application of reagents or wash fluids.
Yet another apparatus, known as the Jung Histostainer Ig.TM. Automated Immunostainer, is produced by Leica Instrument GmbH. This is also a carousel-type device, but reagents are applied by a spraying operation rather than by dropping liquid onto an organic film. The apparatus contains a permanent reagent spraying head that can be moved along a single axis to provide spray coverage over a microscope slide located on the rotating tray when the slide is rotated into position underneath the head. Excess reagent is removed by a permanent clearing nozzle which blows air in a pressure front across the slide, forcing excess liquid off at the completion of the reagent incubation step.
A further apparatus is the subject of U.S. Pat. No. 5,439,649. This device includes an arm moveable in three dimensions attached to a framework. A hollow tip head is carried on the arm, and includes a wash/blow head for dispensing reagents and clearing the slides. The reagent application tip can be attached to the hollow tip head or removed by a pre-selected movement of the arm.
All of these devices attempt to solve certain conflicting goals in automated apparatuses of this type. For example, it is desirable to minimize the use of expensive or toxic reagents, particularly reagents used in immunostaining (e.g. antibodies and other reagents of biological origin), while insuring complete coverage of the microscope slide by the reagent. However, the penultimate-referenced spraying operation above uses an excess of reagent, which must then be removed in order to obtain satisfactory coverage. Other techniques require additional manipulative steps, such as the use of a hand-assembled cover or an additional liquid reagent to provide for proper spreading of the reagent. It is considered desirable to have an automated apparatus that can use regular microscope slides without additional manipulation and that does not require the use of either excess reagent or the use of an organic liquid with additional manipulation and disposal steps.
In addition, current automated equipment used in the staining of cells and tissues on microscope slides are limited in the functions they can perform, such as removing the wax or embedding medium surrounding the tissue specimen, and by concerns with cross-contamination between slides or between reagents.
Accordingly, further developments that allow individual slides to be treated differently in a single batch operation and that provide an automated procedure which uses reagents efficiently remain desirable.
Furthermore, it is also considered desirable to provide the capability of performing additional functions associated with tissue staining procedures in an automated device, without substantial risk of cross-contamination.
It is therefore an object of the invention to provide an automated staining apparatus that is readily programmable to allow automated staining of individual microscope slides with different techniques in a single operation without user intervention.
It is a further object of this invention to provide an automated staining apparatus that uses staining reagents efficiently with a minimum of waste and without extraneous steps.
It is a still further object of this invention to provide an automated staining apparatus that can perform additional preparation steps as part of a completely automated staining protocol.
It is also an object of this invention to provide an automated staining apparatus that minimizes the risk of cross-contamination between slides, reagents and solutions.