Benefits of Using Low-E probes:

1. Order of magnitude reduction in RF-induced heating of biological solids.

Fig. 1. Comparison of sample heating in low-E probe and in conventional single-solenoid probe of at different spectrometer frequencies, using same preparation of M2-TMD in lipid bilayers. Vertical axis shows average temperature rise in the M2-TMD sample after a single 50 kHz, 10 ms long ¹H decoupling pulse. Large rectangular sample coils were utilized (7.5x5.5x11 mm clearance).

2. ¹H tuning and RF strength are less sensitive to sample hydration, salinity.
3. Larger sample volumes can be utilized at higher fields.

Fig. 2. Effect of lossy protein sample on the strength of ¹H decoupling field — in conventional single-solenoid probe and in low-E probe. Each graph shows ¹H power input required to produce 100 kHz of decoupling field in lossy M2-TMD preparation and in non-lossy crystal, at different spectrometer frequencies. Large rectangular sample coils were utilized (7.5x5.5x11 mm clearance). Pink area is the amount of power heating the sample. Note that for such large coil volumes, conventional probes with solenoid require amount of ¹H power exceeding limits of typical 1 kW proton amplifier.

4. Excellent homogeneity of ¹H B₁ field.

Fig. 3. Comparison of RF homogeneity in low-E probe and in single solenoid probe of similar dimensions, as a ratio of amplitudes between 810 and 90 degree pulses. Note large improvement in ¹H field homogeneity. Low-frequency ¹⁵N homogeneity stays same as in solenoid due to similar aspect ratio of observe coil.

5. Simpler RF circuit.
6. No lossy ¹H traps.
7. Low-frequency sensitivity of a solenoid.

Fig. 4. RF circuit in a typical ¹⁵N—¹H PISEMA probe found in our lab.