Handheld NMR Systems and Their Applications for Biomolecular Sensing - Point-of-Care Diagnostics on a Chip - page 172

Fig. 8.1 2-kg portable NMR system (From Ref. [ 2 ])

cost. Nonetheless, NMR systems remain bulky, heavy, and expensive, with their
use limited in hospitals, testing facilities, and laboratories. A case in point is
the state-of-the-art commercial benchtop NMR system of [ 1 ], which weighs
approximately 120 kg.
The large size is due to the following reason. An NMR system consists of a
magnet to produce a static magnetic field, a sample coil, and an RF transceiver to
generate an RF magnetic field and to monitor the resonance. Since a larger-sized
magnet tends to yield a stronger NMR signal even for the same static magnetic field
strength and hence relaxes the sensitivity requirement on the transceiver design,
large magnets are used, leading to the bulky size, where the magnet is by far the
largest component.
To miniaturize an NMR system, we took an approach opposite to the convention:
we chose to use small magnets, and to detect the NMR signal substantially weak-
ened by the small magnets, we developed highly sensitive RF transceivers. Further-
more, we integrated the RF transceiver onto silicon integrated circuit (IC) chips. As
small magnets are used, the transceiver integration makes sense: in a conventional
system where a large and expensive magnet dominates the system size and cost, inte-
gration of the RF transceiver would hardly reduce either the system size or the cost.
Our efforts first led to the construction of a portable NMR system shown in
Fig. 8.1 [ 2 ]. Occupying only 2.5 L and weighing only 2 kg, this system is 60 times
lighter, 40 times smaller, yet 60 times more spin-mass sensitive than the state-of-the-
art benchtop NMR system of [ 1 ]. It uses a small magnet, the size of a hamburger