We report on a probe modification of a quartz crystal microbalance (QCM) DNA-biosensor that permits to reversibly change the DNA sequence detected. A QCM DNA-biosensor was designed by immobilization of a 20-base DNA-disulfide probe on the gold-covered quartz surface of a 27 MHz microbalance (9 MHz, third overtone). After immobilization on the gold covered quartz surface, this probe was modified by hybridization with a 45-base DNA that includes the complementary 20-base sequence, a 5-base spacer and a non-complementary 20-base sequence. The non-complementary sequence constitutes a new probe, different from the DNA-disulfide probe, that permits the detection of a new DNA target. As this 45 bases DNA is changeable by dehybridization, successive different DNA targets can be detected. Kinetics and thermodynamic studies of the DNA-disulfide and modified biosensors indicate that the modified biosensor is as sensitive, selective, fast, renewable and reproducible as the DNA-disulfide biosensor, but with a higher hybridization ratio. This modification method offers wider investigation field and practical and economic advantages to DNA-biosensors based on irreversible immobilization of DNA probes on solid substrate. (c) 2006 Elsevier B.V. All rights reserved.