A process for concentrating nucleic acid molecules (5a, 5b), on a surface of a sensor field of a biochip, the process comprising the following steps: (a) providing magnetic beads, with transfer molecules (3a, 3b, 3c) immobilized thereon, which are capable of hybridizing to a portion of the nucleic acid molecules (5a, 5b), thereby forming complexes which comprise said magnetic beads, said transfer molecules (3a, 3b, 3c) and said nucleic acid molecules; providing a surface of a sensor field (103a, 103b, 103c), which forms a part of a surface of a biochip, wherein capture molecules are immobilized on said surface, wherein said capture molecules specifically hybridize to a portion of the nucleic acid molecules (5a, 5b) wherein the nucleic acid sequences of the capture molecules and transfer molecules (3a, 3b, 3c), are chosen in such a way that the melting temperature of the hybrid between a nucleic acid molecule (5a, 5b) and a transfer molecule (3a, 3b, 3c) is lower than the melting temperature of the hybrid between a nucleic acid molecule (5a, 5b) and a capture molecule; and providing a magnetic field generator; (b) incubating the magnetic beads with the nucleic acid molecules (5a, 5b), at a temperature T1 which is below the melting temperature of the hybrids between the nucleic acid molecules (5a, 5b) and the transfer molecules (3a, 3b), thereby allowing the nucleic acid molecules (5a, 5b) to hybridize to the transfer molecules (3a, 3b); (c) applying a magnetic field through the magnetic field generator, thereby moving the nucleic acid molecules (5a, 5b) bound to the magnetic beads through the magnetic field to the surface of the biochip, thereby bringing in contact the nucleic acid molecules (5a, 5b) bound to the magnetic beads with a surface of the sensor field (103a, 103b); (d) increasing the temperature from a temperature T1 to a temperature T2, which is above the melting temperature of the hybrids of the nucleic acid molecules (5a, 5b) and the transfer molecules (3a, 3b) and which is below the melting temperature of the hybrids of the nucleic acid molecules (5a, 5b) and the capture molecules, thereby dissolving the nucleic acid molecules from the magnetic beads and allowing binding of at least one portion of the nucleic acid molecule (5a, 5b) to the capture molecule; (e) moving the magnetic beads away from the surface of the biochip by switching off the magnetic field; (f) repeating the steps (b) to (e). (a) providing magnetic beads, with transfer molecules (3a, 3b, 3c) immobilized thereon, which are capable of hybridizing to a portion of the nucleic acid molecules (5a, 5b), thereby forming complexes which comprise said magnetic beads, said transfer molecules (3a, 3b, 3c) and said nucleic acid molecules; providing a surface of a sensor field (103a, 103b, 103c), which forms a part of a surface of a biochip, wherein capture molecules are immobilized on said surface, wherein said capture molecules specifically hybridize to a portion of the nucleic acid molecules (5a, 5b) wherein the nucleic acid sequences of the capture molecules and transfer molecules (3a, 3b, 3c), are chosen in such a way that the melting temperature of the hybrid between a nucleic acid molecule (5a, 5b) and a transfer molecule (3a, 3b, 3c) is lower than the melting temperature of the hybrid between a nucleic acid molecule (5a, 5b) and a capture molecule; and providing a magnetic field generator; (b) incubating the magnetic beads with the nucleic acid molecules (5a, 5b), at a temperature T1 which is below the melting temperature of the hybrids between the nucleic acid molecules (5a, 5b) and the transfer molecules (3a, 3b), thereby allowing the nucleic acid molecules (5a, 5b) to hybridize to the transfer molecules (3a, 3b); (c) applying a magnetic field through the magnetic field generator, thereby moving the nucleic acid molecules (5a, 5b) bound to the magnetic beads through the magnetic field to the surface of the biochip, thereby bringing in contact the nucleic acid molecules (5a, 5b) bound to the magnetic beads with a surface of the sensor field (103a, 103b); (d) increasing the temperature from a temperature T1 to a temperature T2, which is above the melting temperature of the hybrids of the nucleic acid molecules (5a, 5b) and the transfer molecules (3a, 3b) and which is below the melting temperature of the hybrids of the nucleic acid molecules (5a, 5b) and the capture molecules, thereby dissolving the nucleic acid molecules from the magnetic beads and allowing binding of at least one portion of the nucleic acid molecule (5a, 5b) to the capture molecule; (e) moving the magnetic beads away from the surface of the biochip by switching off the magnetic field; (f) repeating the steps (b) to (e).