Fig. 1.

Picoliter NMR. a Overview of ambient-temperature NMR techniques for small volumes. Points represent experimental values for minimum-detectable nuclear spin concentration in 1 s with SNR = 3 for different techniques: microslot⁷, microcoil⁸, cryogenic probes²², atomic vapor magnetometers²⁵, giant magnetoresistance (GMR) sensors²³, anistropic magnetoresistance (AMR) sensors²⁴, single NV centers¹⁴, and NV-doped nanogratings (this work). The solid red line is the projected sensitivity for diamond nanogratings (Eq. (1)), exhibiting volume^−1/2 scaling (see Supplementary Note 1). Solid blue lines indicate constant numbers of spins. b Epifluorescence diamond NMR set-up. c The sensor region consists of dense, high aspect-ratio diamond nanogratings fabricated via interferometric lithography and doped with NV centers. d Experimental geometry. The analyte’s precessing nuclear statistical polarization produces an oscillating magnetic field, which is sensed by adjacent near-surface NV centers