Magnetoresistive sensors for measurements of DNA hybridization kinetics - effect of TINA modifications

We present the use of magnetoresistive sensors integrated in a microfluidic system for real-time studies of the hybridization kinetics of DNA labeled with magnetic nanoparticles to an array of surface-tethered probes. The nanoparticles were magnetized by the magnetic field from the sensor current. A local negative reference ensured that only the specific binding signal was measured. Analysis of the real-time hybridization using a two-compartment model yielded both the association and dissociation constants k(on), and k(off). The effect of probe modifications with ortho-Twisted Intercalating Nucleic Acid (TINA) was studied. Such modifications have been demonstrated to increase the melting temperature of DNA hybrids in solution and are also relevant for surface-based DNA sensing. Kinetic data for DNA probes with no TINA modification or with TINA modifications at the 5′ end (1 × TINA) or at both the 5′ and 3′ ends (2 × TINA) were compared. TINA modifications were found to provide a relative decrease of k(off) by a factor of 6-20 at temperatures from 57.5 °C to 60 °C. The values of k(on) were generally in the range between 0.5-2 × 10(5) M(−1)s(−1) and showed lower values for the unmodified probe than for the TINA modified probes. The observations correlated well with measured melting temperatures of the DNA hybrids

Characterization of fine particles using optomagnetic measurements

Measurements of optical transmission in an oscillating magnetic field are used to determine the magnetic moment and hydrodynamic size of magnetic nanoparticles.</p