BioSolids CryoProbe

Increasing Sensitivity Without Sample Modification

While being extremely versatile, NMR has the inherent challenge of being insensitive. One strategy to improve the sensitivity which does not require sample modification is cryogenically cooling the RF coil and preamplifier electronics. The reduced level of thermal noise generated by the RF coil, network, and preamplifier lead to a boost in signal-to-noise on the order of 3 while keeping the sample in its original composition and with its natural line width. This progress report shows results obtained with our first 600 MHz 3.2 mm HCN triple resonance CPMAS CryoProbe prototype.  

The probe is designed for standard bore magnets and compatible with the well proven CryoPlatform. Cryogenic cooling of the RF coil and preamplifier electronics yields a sensitivity gain of more than 3 compared to conventional probes. This gain is achieved with the sample staying at room temperature.

The probe reaches MAS rates of 20 kHz with 3.2 mm rotors and the MAS3 unit. The CPMAS CryoProbe can be lowered while in the cold state with a new probe lift allowing for easy and safe rotor exchange. Automatic tuning and matching adds to the probe’s comfortable and safe operation.

Advanced Characterization of API

Thanks to the superior sensitivity of the probe, advanced characterization of an API can be performed without resorting to isotopic labeling. This is illustrated with a CC double quantum correlation on vitamin B12 at natural abundance. The refocused INADEQUATE has notoriously low sensitivity, and it would have taken more than one month acquisition time on a RT probe.

biosolids CryoProbe
A) Vitamin B12 B) 2D 13C-13C INADEQUATE on natural abundance Vitamin B12. 80 increments of 1024 scans each, acquired within a total experimental time of 3 days and 9 hours. The spectrum was processed using covariance.

CP and Double-CP based Experiments

The CPMAS CryoProbe is developed for standard and advanced CP-based experiments in structural biology.

BioSolids CryoProbe
Standard signal-to-noise comparison for 13C with glycine, illustrating the more than 3-fold enhancement factor compared to a traditional room temperature probe with the same amount of sample material. The spectrum shows that the magic angle is well set and that 1H high power decoupling is stable.

Combining High Sensitivity with NUS

The high sensitivity of the new probe in combination with Non-Uniform Sampling techniques enables a dramatic reduction of experiment times. The CPMAS CryoProbe allows up to 10 times faster data acquisition for sensitivity limited samples.

biosolids CryoProbe
Combining the high sensitivity with NUS can be used to significantly improve the spectral resolution or reduce the experimental time. A) shows a CC correlation on uniformly labeled fMLF using traditional sampling (~4 h), B) shows the same experiment using 25% NUS sampling (~1 h).