Lenz Lenses in a Cryoprobe: Boosting NMR Sensitivity Toward Environmental Monitoring of Mass-Limited Samples

Nuclear magnetic resonance (NMR) spectroscopy is commonlyemployedin a wide range of metabolomic research. Unfortunately, due to itsrelatively low sensitivity, smaller samples become challenging tostudy by NMR. Cryoprobes can be used to increase sensitivity by coolingthe coil and preamplifier, offering sensitivity improvements of & SIM;3to 4x. Alternatively, microcoils can be used to increasemass sensitivity by improving sample filling and proximity, alongwith decreased electrical resistance. Unfortunately, combining thetwo approaches is not just technically challenging, but as the coildecreases, so does its thermal fingerprint, reducing the advantageof cryogenic cooling. Here, an alternative solution is proposed inthe form of a Lenz lens inside a cryoprobe. Rather than replacingthe detection coil, Lenz lenses allow the B-1 field froma larger coil to be refocused onto a much smaller sample area. Inturn, the stronger B-1 field at the sample provides strongcoupling to the cryocoil, improving the signal. By combining a 530I.D. Lenz lens with a cryoprobe, sensitivity was further improvedby 2.8x and 3.5x for H-1 and C-13, respectively, over the cryoprobe alone forsmall samples. Additionally, the broadband nature of the Lenz lensesallowed multiple nuclei to be studied and heteronuclear two-dimensional(2D) NMR approaches to be employed. The sensitivity improvements and2D capabilities are demonstrated on 430 nL of hemolymph and eighteggs (& SIM;350 & mu;m O.D.) from the model organismDaphnia magna. In summary, combining Lenz lenseswith cryoprobes offers a relatively simple approach to boost sensitivityfor tiny samples while retaining cryoprobe advantages.

Automated summary

Nuclear magnetic resonance (NMR) spectroscopy is widely used in metabolomic research but has low sensitivity for small samples. This study proposes using Lenz lenses inside a cryoprobe to focus a larger coil's magnetic field onto a smaller sample area, improving signal strength and sensitivity. By combining a Lenz lens with a cryoprobe, sensitivity was further improved by 2.8x and 3.5x for H-1 and C-13, respectively, for small samples.