Fig. 2: Sensing of single biomolecules and atomic ions.
From: Single-atomic-ion detection with plasmon-enhanced whispering-gallery-mode microlasers
a, Detection of 50-nM GABA in water. The signal shows both permanent binding events—evident as step-like shifts—and transient interactions, which appear as sharp spike events. Step-like sensing events are highlighted with red circles. b, Transient spike signals corresponding to Zn2+-ion detection. c, Transient spike signals corresponding to Cd2+-ion detection. Dual lasing modes were used to monitor ion–NR interactions. d,e, Zoomed-in views of the sensing traces shown in b (d) and c (e), revealing individual spike events with higher temporal resolution. f, Simplified schematic illustrating how one gold NR contributes to a distinct sensing signal. In this specific example, the interaction of an analyte with this NR leads to a downshift on beatnote 1 and upshift on beatnote 2, similar to what is demonstrated in e.
