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Figure 1. Schematic principle of the giant magnetoresistive sensor. (A) Capture Abs (blue) immobilized on the sensor surface are used to capture the target antigens (yellow; [B] ); after washing away free unbound species (C) , biotinylated probe Abs are added into the system, where only the Abs specific for the target antigens will bind and any unbound free Abs are washed away. (D) Streptavidin-modified magnetic particles are bound to the sandwiches via streptavidin-biotin interactions. (E) As the magnetic tags diffuse to the GMR sensor surface and bind the detection Ab, the magnetic fields from the magnetic particles are detected by the underlying GMR sensor in real time in the presence of a small external modulation magnetic field. Ab: Antibody; GMR: Giant magnetoresistive; SN: South/North. Reproduced with permission from [15].
(Figure omitted. See article PDF.)
Figure 2. Detection of small molecules using magnetic particle-aptamer and glucose meter. (A) First, DNA invertases are immobilized on the magnetic particle-aptamer conjugate surface through hybridization. (B) Then target molecules are captured by the magnetic partricle surface aptamers, releasing invertases from the magnetic particle. (C) After magnetic separation, sucrose is added to initiate the invertase-catalyzed glucose production. Target quantitation is realized by measuring the glucose concentration using a glucose meter. Reproduced with permission from [31].
(Figure omitted. See article PDF.)
Currently, the assay used most often in clinical disease diagnosis is ELISA, an antibody (Ab)-based technique using a surface immobilized Ab1 and an enzyme-linked Ab2 to sandwich the target, converting each target into an Ab1/target/Ab2 sandwich for sensitive enzymatic detection. Although widely used, its sensitivity is often limited by factors such as low activity of surface-bound Abs, inefficient target capture and slow binding kinetics [1]. As a result, ELISA often cannot provide the speed and particularly the sensitivity required for early diagnosis, owing to the extremely low level of biomarkers. Therefore there is great clinical need for the development of faster, more sensitive assays for early diagnosis. In this regard, magnetic particles (MPs) have recently received significant research interests owing to their unique magnetic properties and low toxicity [2]. They can be easily functionalized with stable, nontoxic protective coatings for bioconjugation [3-5]. Their tiny particle size combined with strong superparamagnetic properties allow for the formation of stable dispersion in...