Biomedical Engineering Reference
In-Depth Information
Figure 2.8
Scheme of the bio-barcode assay. Stage I: Analyte
molecules are sandwiched between magnetic microspheres
and bio-barcodes (gold nanoparticles conjugated to
antibodies and DNA barcodes); Stage II: the microspheres are
magnetically precipitated; Stage III: the DNA barcodes
precipitated in Stage II are released and detected by
hybridization to a 2 - D array.
the inverse cube of the distance between the particles and the sensing resistor.
Thus, sensitivity to labels located on the far side of the plastic backing support of
a lateral fl ow device would be low. In order to overcome this problem, Tondra has
suggested that sensing elements could be fabricated directly onto the backing
material, thereby placing them in closer proximity to magnetic labels in the porous
membrane [38] .
2.6
Bio-Barcode Assays Based on Magnetic Microspheres
In its most common embodiment, the bio-barcode approach uses magnetic sepa-
ration to carry out multiplexed nucleic acid assays and immunoassays [39, 40].
Bio-barcodes are gold nanoparticles conjugated to recognition molecules and DNA
barcodes. In multiplexed assays, target molecules are sandwiched between capture
probe molecules conjugated to magnetic microspheres and bio-barcodes, as shown
in Figure 2.8. The magnetic microspheres, and the bio-barcodes bound to them,
are magnetically separated and washed, after which the barcodes are released and
detected by hybridization to a 2-D array. Multiplexed assays for both antigenic and
nucleic acid target molecules have been reported in which released barcodes are
detected by sandwiching them between arrays of capture probes and reporter
probes. In most cases, the reporter probes are labeled with gold nanoparticles that
are detected after silver enhancement.
2.7
Spectrally Encoded Suspension Arrays of Magnetic Microspheres
The fi rst suspension arrays to be introduced were based on nonmagnetic micro-
spheres encoded with fl uorescent dyes [6, 41]. For this method of encoding, the
