Femtomolar limit of detection with a magnetoresistive biochip

• Published in: Biosensors & bioelectronics 2009-04, Vol.24 (8), p.2690-2695
• Main Authors: Martins, V.C., Cardoso, F.A., Germano, J., Cardoso, S., Sousa, L., Piedade, M., Freitas, P.P., Fonseca, L.P.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biosensing Techniques - instrumentation; Biotechnology; DNA - analysis; DNA - chemistry; DNA - genetics; DNA hybridization; Electric Impedance; Electrochemistry - instrumentation; Equipment Design; Equipment Failure Analysis; Fundamental and applied biological sciences. Psychology; In Situ Hybridization - instrumentation; Limit of detection; Magnetic focusing; Magnetic labels; Magnetics - instrumentation; Magnetoresistive biochip; Nanotechnology - instrumentation; Oligonucleotide Array Sequence Analysis - instrumentation; Reproducibility of Results; Sensitivity and Specificity; Spin-valve
• ISSN: 0956-5663; 1873-4235
• DOI: 10.1016/j.bios.2009.01.040

In this paper the biological limit of detection of a spin-valve-based magnetoresistive biochip applied to the detection of 20mer ssDNA hybridization events is presented. Two reactional variables and their impact on the biomolecular recognition efficiency are discussed. Both the influence of a 250nm diameter magnetic particle attached to the target molecule during the hybridization event and the effect of a magnetic focusing system in the hybridization of pre-labeled target DNA (assisted hybridization) are addressed. The particles carrying the target molecules are attracted to the probe active sensor sites by applying a 40mA DC current on U-shaped aluminium current lines. Experiments comparing pre-hybridization versus post-hybridization magnetic labeling and passive versus magnetically assisted hybridization were conducted. The efficiency of a passive hybridization is reduced by about 50% when constrained to the operational conditions (sample volume, reaction time, temperature and magnetic label) of an on-chip real-time hybridization assay. This reduction has shown to be constant and independent from the initial target concentration. Conversely, the presence of the magnetic label improved the limit of detection when a magnetically assisted hybridization was performed. The use of a labeled target focusing system has permitted a gain of three orders of magnitude (from 1pM down to 1fM) in the sensitivity of the device, as compared with passive, diffusion-controlled hybridization.