Method and a device for monitoring nucleic acid amplification reactions

A device for quantitatively measuring nucleic acid amplification reactions, comprising

• a laser capable of generating a laser beam of sufficient power to two-photon excite and two-dimensionally optically trap a fluorescent label attached to a nucleic acid sequence bound to a microparticle in a reaction volume;
• an optical system for focusing said laser beam through an objective lens to a focal volume within said reaction volume, said objective lens having a numerical aperture optimized for two-dimensionally optically trapping an individual microparticle, said system being capable of scanning said focal volume at a predetermined speed within said reaction volume;
• a detector capable of detecting fluorescence emitted from said focal volume;
• and
• a control system for momentarily interrupting or reducing said predetermined scanning speed to a second, slower scanning speed when a microparticle is present in said focal volume, thereby allowing said microparticle to be optically trapped for a period of fluorescence detection by said laser beam during said period of fluorescence detection.