Built-in electric field-boosted attomolar Pb²⁺ sensing on carboxylated black phosphorene

Lead ion (Pb²⁺) contamination poses a severe and persistent threat to environmental safety and human health, demanding ultrasensitive and selective detection strategies. Herein, we fabricate a carboxyl-functionalized black phosphorene-modified surface plasmon resonance sensor (Au+BP-COOH) with built-in electric field enhancement for attomolar-level and highly selective Pb²⁺ detection. The Au/BP-COOH junction generates a strong interfacial built-in electric field, which strengthens near-field electromagnetic coupling and amplifies the SPR optical response, thereby boosting the detection sensitivity. Meanwhile, abundant oxygen-containing sites on BP-COOH enable efficient and preferential interaction with Pb²⁺. Our sensor achieves a detection limit of 10⁻¹⁹ M, 14 orders of magnitude lower than that of bare Au, and exhibits remarkable selectivity against Cd²⁺, Cu²⁺, Zn²⁺, Ni²⁺, Ca²⁺, and Mg²⁺. This label-free and straightforward platform provides a reliable route for ultratrace heavy-metal monitoring in environmental and food-safety applications.