Ratiometric Detection of DNA and Protein in Serum by a Universal Tripyridinyl RuII Complex–Encapsulated SiO2@Polydopamine Fluorescence Nanoplatform

Fluorescence ratiometric biosensors are valuable tools for the accurate and sensitive prediction and diagnosis of diseases. However, seldom have fluorescence ratiometric biosensors for protein and DNA been reported because of the shortage of suitable nanoscale scaffolds. Herein, a tripyridinyl RuII complex–encapsulated SiO2@polydopamine (Ru–SiO2@PDA) nanocomposite was designed as a universal platform for fluorescence ratiometric detection of DNA and protein in serum samples. The Ru–SiO2@PDA nanocomposites have a narrow size distribution, exhibit good biosafety, and are convenient for the postmodification of biorecognition elements. Under irradiation, they can emit a stable and strong luminescence at 650 nm and simultaneously quench the fluorescence emitted from the fluorophores getting close to them. Once the capture probes such as single-stranded DNA and aptamer are assembled, the fluorophores labeled on them are then brought close to their PDA shell and quenched. However, the biorecognition behaviors change the probe's configuration and take the fluorophore far away from the PDA shell. Correspondingly, the fluorescence recovers and its ratio to the constant fluorescence reference is linear to the targets' concentration. Using a D-catalyst and thrombin as model analytes, the Ru–SiO2@PDA-based nanoplatform shows high sensitivity and good accuracy in the serum sample analysis. Regarding these attractive properties, the Ru–SiO2@PDA nanoplatform provides a new avenue for the accurate and sensitive fluorescence assay of a wide range of targets in complex systems.