Researchers at the University of Glasgow are part of an international team that has used light to read the magnetic spin of electrons inside a metal-organic framework for the first time. The university says the result is a step towards using these porous crystalline materials to detect chemicals with very high sensitivity.
Metal-organic frameworks, or MOFs, have been seen as promising for quantum sensing, but optical detection of spins inside them had not been shown before. The team built on optically detected magnetic resonance (ODMR), a technique that uses light to read spin qubits in quantum sensors. Glasgow’s contribution was led by Dr Sam Bayliss and Dr Alistair Inglis of the James Watt School of Engineering, whose group read the spins in a framework synthesised at the University of Tokyo. Bayliss described MOFs as “essentially molecular scaffolds”.
The collaboration also involved the University of Sheffield, Saitama University, JEOL Ltd., the Institute for Molecular Science and Kobe University. Optically detected spins offer higher sensitivity and finer spatial resolution than electron spin resonance, which relies on microwave detection. Diamond nitrogen-vacancy centres are a well-studied alternative, but their spins sit in crystal defects, which limits how far they can be controlled and how they interact with outside substances.
Spins that come from molecules can be designed chemically, so their structure and spin properties can be tuned. MOFs also fix the position and orientation of the electron spins, and target chemicals can be taken up into their pores and detected through close-range interactions with the spins. Inglis said the spin resonance reveals information about the surrounding environment as well as the molecules, so the materials could act as sensors, and that loading target molecules into the pores could allow sensing at the molecular scale. He said the next steps are making the method work at more practical temperatures and tuning the chemistry to strengthen the signal.
Because MOFs can be built in many different ways by changing their ligands and crystal structures, the team believes the approach could be extended to a wide range of related materials. A library of frameworks, each responding differently to particular chemicals, could work as a “quantum nose” that identifies substances from their response patterns. The findings are published in the Journal of the American Chemical Society in a paper titled Optically Addressable Spins in a Metal-Organic Framework.
