Biomedical Engineering Reference
In-Depth Information
Fig. 8.11
Water proton NMR signal measured with the palm system (From Ref. [
3
])
of the NMR signal due to their occurrence at different time instances. Note the
difference between the values measured using the 1-chip and palm systems. While
T
2
D
722 ms obtained with the 1-chip system well approximates the true value,
T
2
D
100 ms obtained with the palm system is a substantial underestimation of
the true value, which is due to the pronounced static magnetic field inhomogeneity
of the ping-pong-ball-sized magnet used in the palm system [
6
]. Nonetheless, this
is not a fundamental problem, as repetition of the CPMG pulses at a faster rate,
which the current implementation has no provision for but is easy to incorporate,
can readily yield the correct value [
6
]. Moreover, in our T
2
-based biomolecular
sensing experiments that will be presented shortly, we focus on the relative measure
of values.
Figure
8.12
b shows a measured, down-converted NMR signal obtained in another
water proton NMR experiment using the 1-chip system, this time, after 0.05 mM
magnetic nanoparticles [Fe] (30 nm) are added in the water sample. The measured
T
2
is decreased to 93 ms. This reduction of the T
2
value in the presence of
magnetic nanoparticles, which perturb the NMR behavior, is expected from the
NMR theory [
8
].
8.4.2
NMR-Based Biomolecular Sensing
Figure
8.13
shows the detection of avidin protein using the palm system. Magnetic
particles (38 nm) coated with biotins are put into a 2
L water inside the solenoidal
