Nanomechanical Detection of Transition Onset.

Transitions often begin through weak precursor dynamics that reorganize a system before the dominant transformation becomes apparent, yet these early signatures can remain distributed and hidden within a single observable. Here, hollow microfluidic cantilevers resolve such onset behavior by tracking the resonance trajectory of picoliter-confined samples during controlled slow heating. Using DNA premelting as a model system, we identify a lower-temperature spectral departure that persists across three duplex sequence backgrounds before the main melting response. Projection of the same spectra into buffer-referenced response coordinates enhances the contrast of this onset-associated change without replacing the primary spectral evidence. The resulting operational marker identifies when weak local fluctuations first become mechanically consequential in the confined fluid system. More broadly, the approach detects the transition onset as a persistent reorganization of a measured trajectory rather than a large scalar signal.