Herein, we report a simple green platform based on a novel type of polymer dots (Pdots) as a sensitive and rapid “off-on” fluorescent probe for ratiometric Fe³⁺ and Cu²⁺ detection. The ratiometric probe has been designed using green-emitting PIM-1 Pdots and red-emitting PFTBT Pdots as detecting probes and internal stable standard probes, respectively. The dual-emission characteristics of PIM-1/PFTBT Pdots allowed us to apply ratiometric ion determination based on aggregation-caused quenching (ACQ) of PIM-1 Pdots at 490 nm, while the red emission intensity kept highly stable. The role of porosity and surface carboxylic groups of PIM-1 to achieve high sensitivity and selectivity using quantum-mechanical calculation and cellular imaging was successfully demonstrated so that the detection limit of 7.4 nM for Fe³⁺ and 14.8 nM for Cu²⁺ was obtained. The “on” process with excellent selectivity was realized by the introducing of glutathione (GSH) into PIM-1/PFTBT/Cu²⁺ and Cytochrome c (Cyt c) into PIM-1/PFTBT/Fe³⁺ with fluorescence recoveries of the blank sample 92 % and 91 %, respectively. The proposed strategy detects GSH and Cyt c with a good linearity ranging from 300 nM to 1800 nM and 10 nM to 120 nM by the limit of detection of 85.3 nM and 0.6 nM, respectively. This combinational off-on strategy provides a promising nanosensing platform for monitoring Fe³⁺ and Cu²⁺ in the environmental samples and introduces a sensitive probe with high biocompatibility for intracellular target imaging.