On paramagnetic beads

Fig. 12.5. Triplex affinity capture method. The triplex is formed in slightly acidic conditions (I). The complex is captured on paramagnetic beads and washed (11) and the duplex eluted with a mild alkaline buffer.

Figure 13 Schematic of the overall sandwich immunoassay based on paramagnetic beads. (From Ref. 3.)...

Fig. 53.2. DPV hybridization response of 2.5 pg mL-1 of BC-T on magnetic graphite-epoxy composite electrode. Conditions amount of paramagnetic beads, 50 pg amount of AuNPs, 9x 1012 hybridization time, 15 min hybridization temperature, 42°C oxidation potential, + 1.25 V oxidation time, 120 s DPV scan from + 1.25 V to 0 V step potential, 10 mV modulation amplitude, 50 mV scan rate, 33.5 mVs-1 non-stirred solution. With permission from Ref. [3].

A magnetic cell separator was constructed on a Si wafer to separate cells that were labeled with paramagnetic beads (FeO nanocrystals 50 nm) from unlabeled ones. The magnetic force was generated from thin magnetized wires (10 pm wide, 0.2 pm thick) formed by depositing a cobalt-chrome-tantalum alloy in pre-etched 0.2-pm-deep trenches. These wires were parallel and were oriented at 45° to the hydrodynamic flow direction of cells [278]. 

Fig. 9. Enzyme electrochemiluminescence (ECL) immunoassay protocol, (a) Trinitrotoluene (TNT) and dini-trophenyl of haptenylated dextran compete for antibody-binding sites, (b) Antibodies attached to dextran bound to streptavidin-coated paramagnetic beads, (c) ECL detection of enzyme-labelled antibodies magnetically concentrated on electrode. Reprinted from Wilson et al. [68], Copyright (2003), with permission...

Fig. 8.1. Oligo-dT beads (cellulose, paramagnetic) can be modified to obtain specific probes on these beads. Both ss (I) and ds (II) DNA can be used. In the case of ds DNA, both strands can be linked to the beads. Unless the DNA is digested with a restriction enzyme prior to hybridization, complementary strands may be coupled to the beads. Purification of one of the two poly(dA)-containing ends after restriction but before hybridization to the beads will yield strand-specific probes.

Yehle et al. (1987) immobilized avidin to carboxyl-modified paramagnetic beads and blocked the amino groups on the avidin with succinic anhydride. A biotin-labeled probe is hybridized to its target... 

RNA to be studied can be selectively purified by hybridization on solid supports or in agarose chromatography or centrifugation. Conventional solid phases have included nitrocellulose or activated cellulose and affinity columns. Recently, nylon or, particularly, paramagnetic beads have become very useful since hybridization is much faster, reaches completion rapidly, leaches less capture nucleic acid and they allow convenient washes. 

Several of the previously described methods are readily adapted for the purification of specific mRNAs. Most convenient is the system based on the use of paramagnetic beads (Table 3.16) in which the oligo(dT) should be replaced by specific oligomers. Alternatively, the (reverse) capture or sandwich assays described in Section 8.3 are well suited for hybrid selection. 

ZH Fan, S Mangru, R Granzow, P Heaney, W Ho, Q Dong, R Kumar. Dynamic DNA hybridization on a chip using paramagnetic beads. Anal Chem 71 4851 -4859, 1999. 

Fig. 3. Functionalization of monomaleimido-Nanogold 1.4nm diameter (A). Schematic representation (not in scale) of the analytical protocol (B) (I) Immobilization of the biotinylated CF-A probe onto streptavidin-coated paramagnetic beads (MB) (II) addition of the Target CF to the first hybridization event (III) addition of monomaleimido-nanogold (AuNPs) functionalized with signalling thiolated CF-B probe to the second hybridization event (IV) accumulation of final conjugate on the surface of the M-GECE and (V) magnetically trigged direct DPV electrochemical detection of AuNPs tags in the conjugate.

One application example on the microfluidic LSI platform is the extraction of nucleic acids (NA) from a small amount of cells [126, 127] for cell-based assays. For the extraction of NA from a cell suspension, the cell membrane has to be destroyed first (chemical lysis of the cell). Afterwards, the NA are specifically separated from the residual cell components using a solid phase extraction method based on an NA affinity column (paramagnetic beads). This extraction protocol is completely implemented on the microfiuidic... 

DNA probes, the first one linked with paramagnetic beads and the second one modified with Au-NPs via biotin-streptavidin affinity reactions. Zheng et al. [67] employed this detection methodology for the development of a specific electrochemical aptasensor for the detection of thrombin. The sensor was based on a sandwich format of magnetic nanoparticle/thrombin/Au-NP and signal amplification by forming network-like thiocyanuric acid/Au-NPs. A detection limit of 7.82 aM was achieved. 

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