RESUMEN
We compare measurements of the Brownian relaxation response of magnetic nanobeads in suspension using planar Hall effect sensors of cross geometry and a newly proposed bridge geometry. We find that the bridge sensor yields six times as large signals as the cross sensor, which results in a more accurate determination of the hydrodynamic size of the magnetic nanobeads. Finally, the bridge sensor has successfully been used to measure the change in dynamic magnetic response when rolling circle amplified DNA molecules are bound to the magnetic nanobeads. The change is validated by measurements performed in a commercial AC susceptometer. The presented bridge sensor is, thus, a promising component in future lab-on-a-chip biosensors for detection of clinically relevant analytes, including bacterial genomic DNA and proteins.
Asunto(s)
Biopolímeros/análisis , Técnicas Biosensibles/instrumentación , Conductometría/instrumentación , Separación Inmunomagnética/instrumentación , Magnetismo/instrumentación , Difusión , Diseño de Equipo , Análisis de Falla de Equipo , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
The volume amplified magnetic nanobead detection assay [Strömberg, M., Göransson, J., Gunnarsson, K., Nilsson, M., Svedlindh, P., Strømme, M., 2008. Nano Letters 8, 816-821] was investigated with respect to bead size, bead surface coverage of probe oligonucleotides, bead concentration and rolling circle amplification (RCA) time, with the objective to improve the understanding of the microscopic mechanisms influencing the assay. The most important findings for future biosensor development were the following: (i) small beads exhibit a much reduced tendency to cross-link several RCA products, thus enabling use of both complex magnetisation turn-on and turn-off detection strategies, whereas larger beads only allow for turn-off detection; (ii) small beads exhibit faster immobilisation kinetics, thus reducing the time for diagnostic test completion, and also immobilise in larger numbers than larger beads. Finally, (iii) by demonstrating qualitative dual-target detection of bacterial DNA sequences using 130 and 250nm beads, the bioassay was shown to allow for multiplexed detection.