The invention relates to methods for depositing samples having the features of the preamble of claim 1, in particular to methods for forming sample arrays in compartments of reaction substrates or reaction plates, such as microtitre plates for example, and to devices for implementing such methods.
It is generally known in biochemistry and genetic engineering to carry out chemical reactions with very small sample volumes using an array technique, in which the reactants are deposited as sample arrangements (arrays) on substrates, brought to reaction and observed. The substrates used are typically glass surfaces onto which very small amounts of sample (e.g. pl volumes) are applied for example by means of so-called picking-spotting tools. Picking-spotting tools have the advantage that the samples can be positioned with high accuracy. However, it is disadvantageous that operation thereof is time-intensive and places particular requirements on the substrate and its physical accessibility. As an alternative, the samples can be applied to the substrate in a contactless manner by means of piezoelectric dispensers, and these have advantages in terms of the speed and the ability to be used in the case of different forms of substrate.
However, contactless deposition of samples, in which no contact takes place between the sample dispenser and the substrate surface, may give rise to reduced accuracy in terms of sample positioning. The droplets or particles of sample move along a trajectory from the sample dispenser to the substrate, wherein the course of the trajectory is known only if the dispenser has been carefully calibrated and can easily be disrupted by external influences. This poses a problem in particular when producing arrays with high sample densities.
Particular problems may arise during the contactless positioning of samples onto substrates which are made at least partially of plastics materials. Experience has shown in practice that it has to date not been possible to use piezoelectric dispensers to produce dense arrays on plastic substrates with high accuracy and reproducibility.
There is particular interest in forming arrays on the bottoms of the compartments of reaction plates, such as microtitre plates or nanotitre plates for example. These reaction plates usually comprise wells made of plastic. When samples are deposited into the wells by means of piezoelectric dispensers, the samples often do not land at the intended positions on the bottom of the well but rather on the walls of the well for example.