Microgravimetric DNA sensor based on quartz crystal microbalance: comparison of oligonucleotide immobilization methods and the application in geneticdiagnosis

We report on the study of immobilization DNA probes onto quartz crystal osc illators by self-assembly technique to form variety types of mono- and mult i-layered sensing films towards the realization of DNA diagnostic devices. A 18-mer DNA probe complementary to the site of genetic beta -thalassaemia mutations was immobilized on the electrodes of QCM by covalent bonding or e lectrostatic adsorption on polyelectrolyte films to form mono- or multi-lay ered sensing films by self-assembled process. Hybridization was induced by exposure of the QCMs immobilized with DNA probe to a test solution containi ng the target nucleic acid sequences. The kinetics of DNA probe immobilizat ion and hybridization with the fabricated DNA sensors were studied via in-s itu frequency changes. The characteristics of QCM sensors containing mono- or multi-layered DNA probe constructed by direct chemical bonding, avidin-b iotin interaction or electrostatic adsorption on polyelectrolyte films were compared. Results indicated that the DNA sensing films fabricated by immob ilization of biotinylated DNA probe to avidin provide fast sensor response and high hybridization efficiencies. The effects of ionic strength of the b uffer solution and the concentration of target nucleic acid used in hybridi zation were also studied. The fabricated DNA biosensor was used to detect a set of real samples. We conclude that the microgravimetric DNA sensor with its direct detection of amplified products provide a rapid, low cost and c onvenient diagnostic method for genetic disease. (C) 2001 Elsevier Science B.V. All rights reserved.