Plasmonic-Enhanced Dual-Channel Nanodiamonds Fluorescence Emission Coupled with Quantum Sensing for Simultaneous Quantification of Multiple Biomarkers

Accurate identification of multiple biomarkers in a single test is essential for early cancer diagnosis yet remains difficult with conventional wavelength- or potential-resolved methods due to signal crosstalk and background interference. To address this, we develop a novel multiplexed biosensing strategy that uses dual-mode modulation of quantum-charge-state-dependent fluorescence and spin-dependent optically detected magnetic resonance (ODMR) in nitrogen-vacancy (NV) centers within nanodiamonds. Specifically, in a sandwich bioassay on a silver nanoisland array, probes made from fluorescent nanodiamonds (FNDs) and their plasmonic counterparts (PFNDs) are distinctly modulated: silver nanoislands enhance neutral NV centers (NV⁰) emission from FNDs, while gold nanoparticles in PFNDs suppress NV⁰ and boost negative NV centers (NV^-) signals. Moreover, gold nanoparticles diversify the ODMR frequencies under near-infrared excitation via photothermal effects. By leveraging these independent quantum sensing mechanisms, we simultaneously quantified three microRNAs (miRNA-155, miRNA-96, and miRNA-21) with detection limits of 1.09, 1.49, and 1.40 fM, respectively. This work advances NV center-based multiplexed biosensing and offers a highly sensitive, reproducible platform with clinical potential in early cancer diagnosis.