Ultrasensitive detection of bioanalytes based on signal amplification of coil-integrated giant magnetoimpedance biosystems

- GMI-based biosystem was fabricated employing standard microfabrication technique, and a micro-solenoid coil was integrated with the sensing elements for signal amplification strategy of signal tags.
- Streptavidin-coupled Dynabeads and a-fetoprotein (AFP) bioconjugates were used as model analytes to verify this signal amplification strategy based on this biosystem.
- A markedly improved sensitivity compared to previous similar immunosensors was achieved. A minimum detectable limit of 3 ng/ml (30 particles) for streptavidin-coupled Dynabeads and 0.2 ng/ml for AFP were achieved, respectively.
- Blood samples detection of AFP was carried out on this biosystem, and 1 ng/ml AFP could be detected.
- A new detection method with the separation of the sample and the detector was proposed, which protects the biosensor from being contaminated and damaged during sample preparation and addition. The new detection method also enables the biosensor to be quickly reused without washing and with a convenient sample change.

This article reports a novel separable bioanalyte detection system that combines magnetic nanoparticle labels with giant magnetoimpedance (GMI). The GMI sensor was fabricated via standard microfabrication techniques, and a micro-solenoid coil was integrated with the sensing elements to amplify the signal tags. To verify the feasibility of this strategy, streptavidin-coupled Dynabeads and a-fetoprotein (AFP) bioconjugates were utilized as model analytes, while double antibody sandwich immunoassays and streptavidin-biotin binding assays were employed to immobilize and label AFP on an Au-film coated wafer. The resulting biosystem exhibited markedly improved sensitivity compared to other similar biosensors: A minimum detectable limit of 3 ng/ml for streptavidin-coupled Dynabeads and 0.2 ng/ml for AFP were achieved, respectively. In addition to its very high detection sensitivity, the proposed biosystem can be conveniently manipulated, is not contaminated or damaged by chemical solutions, and is reusable without cleaning. The results presented here may considerably enhance the practical applications of GMI sensors in bio-magnetic-field sensing.