Eu-MOF@Ce-MOF heterostructure and molecularly imprinted polymer composite system for SARS-CoV-2 point-of-care detection.

Metal-organic frameworks (MOFs) have attracted growing interest as advanced sensing materials due to their structural tunability and functional versatility. The responsiveness of MOF-based sensors is typically governed by changes in either the metal centers or organic linkers, making it essential to engineer novel architectures that enhance sensing performance. In this work, we present a MOF-on-MOF heterostructure (Eu-MOF@Ce-MOF), composed of a europium-based framework (Eu-MOF) and a cerium-based counterpart (Ce-MOF), synthesized via a two-step hydrothermal strategy. The Eu-MOF was first prepared using 3,5-dicarboxybenzeneboronic acid (BBDC) as the linker with Eu (III) as the metal node, while Ce-MOF was synthesized using similar synthetic conditions with Ce (III). Subsequently, Ce-MOF was anchored onto the surface of Eu-MOF to form a dual-emission MOF-on-MOF heterostructure. To further expand the applicability of this hybrid material, we integrated it with molecularly imprinted polymers (MIPs) to construct the Eu-MOF@Ce-MOF@MIP composite, which serves as both a carrier matrix and an active sensing platform. This system enabled highly selective and sensitive detection of the SARS-CoV-2 spike protein (SP) via fluorescence quenching, achieving a low detection limit (LOD) of 0.012 μM. A smartphone-integrated sensing platform was developed to facilitate on-site detection of SP in complex real samples. The results demonstrated high selectivity, reproducibility, and long-term stability, with additional validation using simulated biological matrices (serum and urine) confirming the robustness of the method. This study establishes a versatile and portable sensing strategy for SARS-CoV-2 detection, with broad implications for point-of-care detection and biosensing applications.