Optically addressable and programmable spins in DNA
Optically addressable spins, traditionally studied in semiconductors and, more recently, in (bio)chemical systems, are central to quantum technologies, yet existing platforms lack scalable and accessible site-specific programmability. Here, we show that DNA can serve as a functional nanoscale scaffold for optically addressable spin systems. By incorporating flavin chromophores into synthetic oligonucleotides, we generate spin-correlated radical pairs (SCRPs) that can be manipulated by radiofrequency (RF) fields and read out using optically detected magnetic resonance (ODMR). Pulsed ODMR resolves spin dynamics on sub-microsecond timescales under ambient conditions, while DNA sequence design enables atomically precise tuning of both the ODMR response and the associated spin chemistry with single-base resolution. DNA secondary structure provides an additional layer of functionality: duplex formation inverts the pulsed ODMR contrast, indicating a switch in the spin multiplicity of the SCRP precursor. The synthetic accessibility and chemical programmability of oligo-nucleotides as hosts for optically addressable spins are demonstrated through a series of proof-of-concept applications, including sensing, programmable SCRP positioning, and spin-enhanced molecular beacons. Our results establish DNA as a versatile scaffold for engineered spin systems, providing a platform for future applications ranging from quantum sensing and programmable spin arrays to bioimaging and RF-controlled molecular switches for gene regulation.