Basic principles for external spins sensitive and nanoscale Quantum Sensing.a/4H-SiC-YIG sensor for ODPELDOR with a single V2 spin probe (red dot) and a plane of external target spins, like spins labels (arrows); on the left of dashed-dot line, a 2D spin labeled lipid membrane 5 nm thick, on the right, the model in green. Boz and B1y: external static and microwave magnetic fields. Bdip,z (x) is the spatially dependent dipolar magnetic field produced by the YIG ferromagnetic nanostripe located on the opposite 4H SiC surface. b/OD-PELDOR pulse sequence for quantum sensing including synchronized optical and microwave pulses. c/Simplified scheme showing a top view of the SiC-YIG quantum sensor: SiC is in gray,the red dot is the V2 single color center, the dashed red rectangle is the YIG nanostripe present on the opposite surface of the SiC membrane, through which a 1D nanophotonic waveguide has been designed in a 2D photonic cristal made of air holes in SiC. The 1D optical waveguide is coupled to the optical fiber by an appropriate coupler. Ky,ex, Ky,det : excitation and PL light wavevectors.