An engineered nanocavity that can hold a stable state can also hold a single molecule still long enough to watch it. The storage and sensing work share a substrate, a fabrication route and most of a geometry problem — they differ mainly in what the cavity is asked to contain.
A nanocavity for sensing is defined by its narrowest point. Tighten the waist and the optical field concentrates, which raises signal; open it and molecules can actually get in and out, which is what makes the instrument usable on a real sample. The two pull in opposite directions and there is no setting that wins both.
Forty nanometres is the canonical floor — the tightest geometry the design treats as buildable. An eighty-nanometre augmented waist is under evaluation as an alternative, and it is a real trade rather than a free improvement: signal drops to about half of what the 40 nm floor delivers, in exchange for access that suits a molecular-regime branch of the work.
Both figures are simulation candidates. No cavity has been fabricated, and no molecule has been observed in one.
Conventional single-molecule work usually fights diffusion: the molecule you want to watch wanders out of the observation volume. CRUCIBLE approaches that by making the volume small enough — below an attolitre — that a single molecule inside represents a substantial concentration, and gating it with a nanopore so entry and exit become events you control rather than accidents you tolerate.
The attraction is that it turns an observation problem into a fabrication problem. If the cavity and the gate can be made repeatably, the sensing follows. That is a good trade for a laboratory whose strength is materials and process chemistry, and it is the same imprint-cure-fire-seal route the storage work uses — which means one fabrication result would advance both.