The invention relates to methods for preparing and performing quantitative PCR analyses, a new sealing device and a new use. According to the invention, a sample vessel containing the samples to be analyzed is sealed by placing a planar sealing device on the vessel to cover the samples and applying pressure on the sealing device in order to deform the sealing device so as to form a light-refracting geometry individually for the samples to be analyzed. The invention offers a convenient way of sealing the vessel and forming analysis-improving optical lenses over the samples simultaneously.
