Functional magnetic beads

S. Centi, S. Laschi, M. Franek, and M. Mascini, A disposable immunomagnetic electrochemical sensor based on functionalized magnetic beads and carbon-based screen-printed electrodes (SPCEs) for the detection of polychlorinated biphenyls (PCBs). Anal. Chim. Acta 538, 205—212 (2005). 

Stop the reaction by desalting the reaction mixture by SPE onto RP-cartridges, by RP-HPLC or SEC, or by functionalized magnetic beads (see Note 12). 

An aptamer-based sandwich assay with electrochemical detection for thrombin analysis in complex matrixes using a target-capturing step by aptamer-functionalized magnetic beads was recently reported (Centi et al., 2007). The aptamer-sensing layers were fabricated on a surface of screen-printed electrodes. The high sensitivity of this sensor was demonstrated in the analysis of thrombin in buffer, spiked serum, and plasma. The concentrations detected by the electrochemical assay were in agreement with simulation software that mimics the kinetics of thrombin formation. 

A different approach based on the use of an enzyme as a traditional amplifying label and aptamer-functionalized magnetic beads has been developed and applied to the detection of thrombin directly into human plasma (Centi et al., 2007b). The assay is based on electrochemical transduction coupled to magnetic particles,... 

Another example of electrochemical aptasensor based on Au-NPs as labels for the detection of thrombin is reported by Zheng et al. [28]. The assay was based on a sandwich format, in which the aptamerl (15-mer DNA aptamer with an amino group at its 5 end) was immobilized onto carboxyl functionalized magnetic beads. Such aptamer-coated magnetic beads were used for capturing and separation. Thrombin and Au-NP-labeled aptamerll were then added to... 

Staphylococcal enterotoxin B (SEB) is a potent bacterial protein toxin responsible for food poisoning, as well as a potential biological warfare agent. An afBnity probe has been prepared by inunobilizing anti-SEB antibody on the surface of paratol-uene-sulfonyl-functionalized magnetic beads. Immobilization and affinity capture procedures were optimized to maximize the density of anti-SEB IgG on the surface of magnetic beads and the amount of captured SEB. MALDI-MS detection of the emiched SEB from different matrices, such as cultivation media of S. aureus strains and raw milk samples (Schlosser et al. 2007). 

Zhang, B., Tang, D., Liu, B., Cui, Y., Chen, H., Chen, G., 2012. Nanogold-functionalized magnetic beads with redox activity for sensitive electrochemical immunoassay of thyroid-stimulating hormone. Anal. Chim. Acta 711, 17—23. 

Fig. 7. (a) Example chromatin assembly curve recorded at 1.3 pN force applied to the magnetic bead. A magnification of the squared portion of the curve is also presented, (b) Assembly curve of the same DNA molecule, subjected to difference forces in the course of a single assembly round (forces were adjusted by adjusting the distances between the cuvette and the external magnet as indicated). The lines drawn indicate that the assembly rate changes as a function of force. Note the immediate response of the assembly reaction to the changing force. 

Pflueger, E., Mueller, E. A, and Anderer, F. A. (1990) Preservation of cytotoxic function during multicycle immunomagnetic cell separations of human NK cells using a new type of magnetic bead J Immunol Methods 129, 165—173... 

Selection is based upon the functional properties of the evolved protein (phenotype). Binding to antigen immobilized in the wells of a microtiter plate or on the surfaces of magnetic beads are frequently used approaches. Flow cytometry sorting systems, some of which can sort up to 108 cells/h, represent a promising new class of selection technique. 

Another possibility is to take advantage of functionalised moving beads, which are inherent to the bead injection system (see 2.4.1). The analyte interacts with a specific reagent on the bead surface, thus forming a detectable species on the solid phase. Alternatively, an auxiliary reagent can be introduced into the system to perform this function [240]. By stopping the beads at the detector, the chemical species formed can be directly detected. The use of magnetic beads to achieve this has been comprehensively reviewed [201]. 

---