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Magnetic bead-based biosensors are becoming a hot spot in biomedical fields. A Dynabeads-labeled immunoassay has been developed using a micro fluxgate biosensor for the detection of alpha fetoprotein (AFP) and carcinoembryonic antigen (CEA). The micro fluxgate sensors with a rectangular permalloy core with sides of equal width and three-dimensional solenoid coils are fabricated by micro-electro-mechanical-system (MEMS) technology, including thick photoresist lithography and electroplating. The immune reaction of biomarkers is accomplished on a separated Au film substrate surface with a self-assembled layer. Sandwich immunoassay is used to specifically capture and label the biomarker. Dynabeads are conjugated into the biomarker by a streptavidin–biotin system. The micro fluxgate-based sensing system was characterized firstly in different concentrations of Dynabeads. It is found that a concentration as low as 0.1 μg ml−1 (90 Dynabeads) can be detected by this sensing system with an external magnetic field in the range of 643 μT to 1180 μT. The AFP and CEA with different concentrations were detected by the sensing system. The results reveal that a minimum detectable concentration of 1 pg ml−1 was achieved in the measuring ranges of 724 μT to 1150 μT for AFP, and 670 μT to 1110 μT for CEA. Compared with a micro fluxgate sensor with a ribbon core for the detection of biomarkers, the micro fluxgate sensor with an electroplated permalloy core possesses a wider linear measuring range, and could make it possible to integrate a micro fluxgate-based biosensing system produced on a large scale, with an expanded application field and reduced costs.

We describe a giant magnetoimpedance (GMI) biochip platform for the detection of streptavidin-coupled magnetic Dynabeads of different sizes. The GMI sensor based on micro-patterned Co-based amorphous ribbons (Metglas® 2714A) with a meander structure was fabricated by micro-electro-mechanical-systems (MEMS) technology. A gold film was then deposited on the GMI element to act as a support platform for immobilizing various concentrations of magnetic Dynabeads (1 μm and 2.8 μm). The results indicate that Dynabeads of 1 μm in diameter with a concentration as low as 5 μg mL−1 can be detected by using the ribbon-based GMI sensor, and that the detection limit for Dynabeads of 2.8 μm diameter was 1 μg mL−1. Besides, using the same number of magnetic Dynabeads with different sizes, the GMI responses were significantly enhanced after coating the 2.8 μm Dynabeads. The ribbon-based micro-integrated GMI biosensor is easy to fabricate and is expected to be used for the detection of very low concentrations of Dynabead-labeled biomarkers.