Fig. 3. Frozen solution EPR on an 85-nl-volume sample at X-band.

Three EPR experiments performed with a 0.4 mm inner diameter self-resonant microhelix. Shown are the (A) continuous-wave (CW), (B) real (Re.) and imaginary (Im.) nonadiabatic rapid scan (NARS), and (C) field-swept two-pulse ESE EPR experiments of the tyrosine D radical (${\mathrm{Y}}_D^{•}$) in photosystem II with 85 nl of frozen solution sample at a temperature of 80 K. Calculated MDIFF pseudo-modulation of 0.5 mT is shown for the NARS and field-swept ESE experiments to directly compare to the continuous-wave EPR experiment. The total time for the experiments was 49, 55, and 45 min, respectively. The signal-to-noise ratio is calculated and tabulated in Table 2.