Biomedical Engineering Reference
In-Depth Information
subsequent introduction of free D-Phe led to displacement of the antibody-
nanoparticle complex and a dispersion of the clustered nanoparticles. For the
conditions sampled, the T
2
changed by more than 100 ms for 500
μ
M
D - Phe and
by about 10 ms for 5
μ
M
D-Phe. The group reported a limit of detection of 0.1
μ
M
and a coeffi cient of variation (CV) of
5% [63]. The kinetics of this sensor was rela-
tively rapid (Figure 1.10), which was in general agreement with kinetic theory for
dispersive assays [59]. Figure 1.10 also shows that almost two orders of magnitude
in dynamic range were achieved for this MRSw. Additionally, interference studies
showed that the cross-reactivity to L-Phe was 0.075% [63]. As with all MRSw bion-
sensors, the selectivity of the MRSw was determined by the selectivity of the
binding agent, which was anti- D - AA antibody in this case.
The competitive-dispersive format was used for three other small-molecule
MRSws used to measure glucose, the hemagglutinin (HA) peptide, and folic acid
[65]. For glucose, the nanoparticles were decorated with two glucosamine hydro-
chlorides and pre-complexed with the glucose-binding protein, concanavalin A.
The addition of glucose led to a quantitative change in T
2
of over 40 ms within
50 min, using a kinetic reading, and a limit of detection of
<
50 mg dl
- 1
for glucose.
For the detection of the infl uenza HA peptide, the nanoparticles were functional-
ized with HA peptide and pre-clustered with anti-HA antibody. This sensor had a
T
2
change of
<
50 n
M
HA. The folic acid biosensor consisted of nanoparticles decorated with folic acid,
and an anti-folic acid antibody that pre-clustered the nanoparticles. The addition
of folic acid led to T
2
changes over 120 ms with reaction completion times of almost
20 min and a limit of detection of
>
150 ms over a time of 100 min, and a limit of detection of
<
<
3 n
M
[65] .
Figure 1.10
A stereoselective, small - molecule,
dispersive magnetic relaxation switch
biosensor. The addition of D-Phe to a solution
of D - Phe - functionalized CLIO nanoparticles
and antibody that binds
D
amino acids
(anti-D-AA) led to a dispersion of the
antibody-nanoparticle complex as a function
of time. The rate and magnitude of the
change in T
2
increased with increasing
amounts of D - Phe [63] . Original fi gure
provided by Dr Lee Josephson, Center for
Molecule Imaging Research, Massachusetts
General Hospital, Boston, MA. Reproduced
with permission from Ref. [63]; 2004,
© Wiley-VCH Verlag GmbH & Co. KGaA.
