Nanosensors - Nanotechnologies for Water Environment Applications - page 434

coated with capture probes can selectively enrich the analyte/target species and separate
them using a magnetic field (Olsvik et al., 1994). A number of companies like
Dynabeads from Invitrogen ( www.invitrogen.com), Avibeads from Aviva Biosciences
( www.avivabio.com), and ClinProt from Bruker Daltonics (www.bdal.com) now
produce such magnetic beads for the enrichment of DNA, RNA, and proteins.
Recovery of small amounts of DNA from matrices containing PCR inhibitors is
also becoming possible, but it is not yet ready for integration into micro- and nano-
sensors. An example is the recently reported technique named SCODA (short for
synchronous coefficient of drag alteration ) which uses nonlinear electrophoresis
principle to selectively enrich nucleic acids from a variety of complex samples (Marziali
and Thompson, 2005). This modified electrophoresis applies alternating current field
across four electrodes surrounding the electrophoresis gel, which forces the DNA to
move and concentrate at the center of the gel (Figure 13.9). By this technique, as low as
10 molecules of PhiX174 phage DNA in 5 ml could be recovered on gels within minutes
to hours without concentrating the inhibitors.
(a) (b)
Figure 13.9 (a) Nonlinear particle motion by the application of uniform rotating electric
field; numerical simulation of nonlinear electrophoresis principle (b) movement of DNA
spots (white color) under synchronous coefficient of drag alteration effect towards the
center of ultraviolet illuminated gel. Copyright Wiley-VCH Verlag GmbH & Co. KGaA
2005. Reproduced with permission.
13.11 Market Trends
Applications of micro- and nano-sensors for biological molecules are numerous
including biodefense, food industry, clinical diagnostics, and detection of pathogenic