As opposed to traditional photoluminescence and ultra-violet based optical sensing, we present here a sensing system based on resolved optically active polarization with promising applications. It is based on the ultrathin CdSe nanoplatelets (NPLs) when modified with either L or D-cysteine molecules (L/D-cys) as bio-to-nano ligands. The chiral ligand transfers its chiroptical activity to the achiral nanoplatelets with an anisotropy factor of ∼10⁻⁴, which unlocks the chiral excitonic transitions and allows lead ion detection with a limit of detection (LOD) as low as 4.9 nM. Simulations and modelling based on time-dependent density functional theory (TD-DFT) reveal the chiral mechanism of L/D-cys capped CdSe NPLs. The presented CD-based sensing system illustrates an alternative possibility of using chiral CdSe NPLs as competitive chiral sensors for heavy metal ion detection.