Tracking Molecular Signatures at ppb Sensitivity Using Fluctuational Kinetics in Metal–Organic Frameworks

Biological systems achieve parts-per-billion (ppb) sensitivity in gas detection by tracking molecular fluctuations over time─a level of precision that remains difficult to replicate in engineered sensors. Conventional sensing relies on adsorption processes that require activation energies (<i>E</i>_<i>a</i>) ∼10 <i>k</i>_B<i>T</i>, resulting in exponentially long equilibration times and limited selectivity due to small differences in <i>E</i>_<i>a</i> among analytes. Here, we show that volatile organics interacting with a ∼200 nm-thick nanoporous metal-organic framework (MOF), when subjected to shear-induced strain via a quartz crystal microbalance (QCM), exhibit a secondary fluctuational adsorption time scale distinct from the steady-state response. This emergent kinetic signature allows for reliable molecular discrimination at sensitivities down to ∼100 ppb. Our approach introduces a new selectivity metric based on dynamic adsorption kinetics, opening avenues for real-time molecular identification in environmental monitoring, portable diagnostics, and selective detection in chemically complex settings.