Fig. 1. Principle of PNMs and their coupling-tailored sensing capabilities.

(A) Schematic illustration of a PNM unit cell consisting of standing polymer triangles covered in an optically dense layer of gold on a SiO₂ substrate. (B) A symmetric, standing dipolar rod featuring a dipole moment p₁ normal to the incoming electric field E; thus, no coupling is possible. Transforming the rod into a triangle allows coupling of its dipole moment p₂ to E, controlled by the asymmetry parameter α. (C) Tuning α allows for precise control over the radiative loss of the PNMs, capable of tailoring the absorbance from zero to unity. The UC, CC, and OC regimes are marked with different colors. (D) Schematic illustration of a coupling-tailored PNM array for molecular sensing, which consists of size-scaled PNM units in different coupling conditions. (E) Absorbance-modulated sensing based on the coupling-tailored PNM array, in which the analyte’s signal appears as envelope of the scaled PNM resonances. The sensitivity strongly depends on the coupling regime, with the lowest sensitivity around the CC condition and the highest in the UC and OC regime with negative and positive modulations, respectively.