Nonmagnetic Biomarker Detection by Nanocatalytic-Amplified Quantum Spin Relaxometry

Nitrogen-vacancy (NV) centers in diamond demonstrate advantages in biosensing due to their exceptional photostability and long spin coherence time. However, clinical applications of NV centers are significantly limited because their spin states lack responsiveness to nonmagnetic biomolecules. This work presents a nanocatalytic-amplified quantum sensing platform targeting tyrosinase (TYR), a key biomarker for melanoma. The platform achieves ultrasensitive detection of nonmagnetic biomarkers through nanocatalytic signal transduction. Specifically, we develop plasmonic nanodiamond (FND@Au-Ag) functionalized hydrogel microneedles. The captured TYR triggers a cascade reaction that induces the nanocatalytic generation of hydroxyl radicals (•OH), thereby establishing an AND logic gate based on the dynamic response mechanism of spin relaxation time (T₁). By integrating three-modal signals (fluorescence, colorimetry, and T₁), the platform achieves a wide dynamic detection range of 0.01-200 U/mL and an ultralow detection limit (0.003 U/mL) for TYR. Ultimately, a genetic algorithm-optimized backpropagation neural network is developed to enhance the reliability of concentration prediction in complex biological matrices. This work proposes an approach to minimally invasive melanoma screening, overcoming the inherent limitations of traditional quantum sensing systems in detecting nonmagnetic biomarkers.