Chemistry: analytical and immunological testing – Including sample preparation – Volumetric liquid transfer
Reexamination Certificate
1999-09-30
2001-10-16
Noland, Thomas P. (Department: 2856)
Chemistry: analytical and immunological testing
Including sample preparation
Volumetric liquid transfer
C073S863310
Reexamination Certificate
active
06303387
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for the transfer and dispensing small volumes of liquid, especially appropriate in the contexts of biological or chemical analyses and to a method for making the apparatus.
BACKGROUND OF THE INVENTION
During the execution of tests or cultures on biological molecules or cell cultures, plates formed from molded thermoplastic material, e.g. polycarbonate or polystyrene, are usually used today. Usually, the multi-well plate which is used has dimensions of about 80×125 mm, and the wells have a diameter of about 8 mm. These dimensions are normalized in industry due to the large variety of apparatuses, which have been developed for automatic analyses. The wells of these plates are often filled with a collection of pipettes, which are displaced manually or by robotized device. The samples of the products formed in the wells are collected for example with the aid of a collection of needles, of stainless steel or the tips of plastic material, which are immersed in the wells.
Given that it is desirable to carry out a large number of analyses on a single plate, the use of plates having an increasingly large number of wells per plate is growing. An increasingly large number of wells on the same standardized plate gives wells of very small volume, thereby it is then necessary to have tools at one's disposal which enable dispensing small volumes of liquid. Many devices exist for dispensing liquids in small doses ranging from volumes of one milliliter to fractions of a milliliter. Current developments bearing on multi-well plates include progress relating to micro-well and micro-plate technology, it being possible for example to have up to 10,000 wells per square centimeter (see especially U.S. Ser. No. 08/747,425). These wells are separated by a distance of about 100 &mgr;m, each well having a depth of 15 to 30 &mgr;m and a diameter of 20 to 50 &mgr;m. In order to perform tests with the aid of these micro-plates, it is necessary to be able to carry out accurate transfers of liquid volumes ranging from a thousandth to a millionth of a cubic millimeter; transfers to and from such micro-wells. Classical micro-syringes are unable to manipulate such small volumes; thereby it is necessary to make liquid handling apparatuses, which are conceived in a radically novel manner.
A tool is currently on sale, which comprises a matrix of stainless steel pins arranged so that each pin is aligned on a well from a 96-well plate. A drop attaches to an individual pin under the action of the forces of surface tension and can then be transferred. The tool has 30 precision grooves cut into the pins, near to their tip, for determining the volume dispensed. These pins are advertised as capable of dispensing volumes of 1 mm
3
and larger to wells or membrane surfaces.
Micro-syringes use a liquid reservoir comprising a capillary tube (or liquid chamber) and a piston for dispensing the liquid by pushing it out through a needle. Such a system is not suited to the delivery of liquid volumes in the order of a thousandth to a millionth of a cubic millimeter.
It would be desirable to have a method at one's disposal for transferring and dispensing volumes in the order of a thousandth to a millionth of a cubic millimeter into micro-wells of a micro-plate with a good reproducibility. (It is recalled here, in order to facilitate reading the present text, that 1 mm
3
=1 &mgr;l=10
−6
1). The invention relates to such a method of transferring and depositing a drop, notably of biological material or of a reagent, onto a surface or into a well or a depression as well as the tool associated with said method.
It would also be desirable to have a method for making a tool for transferring and dispensing volumes in the order of a thousandth to a millionth of a cubic millimeter into micro-wells of a micro-plate. The invention relates to such a method of making a tool for transferring and depositing a drop, notably of biological material or of a reagent, onto a surface or into a well or a depression as well as the tool resulting from the method.
SUMMARY OF THE INVENTION
The present invention uses the tip of a solid fiber or rod, for depositing microscopic drops having volumes between a thousandth and a millionth of a cubic millimeter. The use of a rod or fiber having controlled wetting and non-wetting properties allows a simple delivery of precisely controlled liquid volumes from a few cubic millimeters to a millionth of a cubic millimeter and less. The Applicant has found that, in the case of a non-wettable rod, which has a wettable tip, the volume of a liquid drop formed by dipping the rod into a liquid reservoir is constant and reproducible. The volume of the drop can be controlled by the size of the cross section of the lower surface of the rod. The larger this size, the larger the volume of the drop that can be suspended from the tip is. A small supplementary control of the volume of liquid deposited on the pin can be obtained by varying the depth; the speed of immersion and/or removal of said pin. The diameter of the cross section of the lower surface of the rod (diameter of the rod, in the hypothesis of a cylindrical rod) is preferably less than the capillary length of the liquid or in the order of this length. Drops smaller than a cubic millimeter, made with a cross sectional diameter of the lower surface of the rod much smaller than the capillary length of the liquid do not experience significant influences due to gravity.
The object therefore of the present invention is a liquid transfer tool which enables delivering a liquid volume of a few cubic millimeters to less than a cubic millimeter into a well or onto a substrate surface (to said transfer is therefore generally associated the distribution of the liquid, but this association is not however inescapable. The drop taken can be dried on the tip of the rod for analysis ends: see later); said transfer tool characteristically comprises:
at least one rod having a wettable tip of pre-determined cross section and at least one non-wettable side; and
a support structure for said rod.
Said rod advantageously has its wettable extremity or tip and its non-wettable side(s). Advantageously, this is a rod of constant cross section, notably a rod in the form of a cylinder; the radius of its circular cross section generally being between 2 nmm and 1 &mgr;M with the result that the diameter of said circular cross section is less than or equal to the capillary length of the liquid.
According to preferred embodiments:
said tool of the present invention has several rods whose arrangement and separation are such that they are aligned on the wells distributed on a plate of several wells;
its rod(s) is(are) in metal, ceramic, glass, polymer or in a composite material;
the tip of its rod(s) is hydrophilic and the side surface of said rod(s) is hydrophobic or the tip of its rod(s) is oleophilic and the side surface of said rod(s) is oleophobic;
the tip of its rod(s) is coated with a material, which does not adhere biological materials.
Another object of the present invention is the use of said transfer tool, namely methods of transfer and distribution of small liquid volumes (of a few cubic millimeters to less than a cubic millimeter) according to which:
a transfer tool is at one's disposal which has at least one rod whose lower surface of predetermined cross section is wettable and of which at least one side surface is non-wettable;
said rod is immersed into a liquid-containing reservoir for a pre-determined period of time and at a pre-determined depth;
said rod is removed from said reservoir so that a drop of liquid is retained on the lower surface of said rod;
said rod is positioned above a receptor medium; and
the drop is placed in contact sNith the surface of said receptor medium; (context of the deposit of the liquid in a receptor medium; or
a transfer tool is at one's disposal which has at least one rod whose lower surface of pre-determined cross section is wettable and
Birch William
Carre Alain
Francois Eric
Beall Thomas R.
Corning Incorporated
Noland Thomas P.
LandOfFree
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