Quantum Sensing of Lanthandie Binding Tags with Relaxometer of NV Center in Diamond

Lanthanide binding tags (LBTs) stand out as a prominent group of fluorescent probes that are extensively utilized in biological detection. However, research on LBTs has predominantly emphasized their fluorescence properties, which frequently compromised by background fluorescence noise. Investigating magnetic properties could optimize detection methodologies that offer enhanced sensitivity and specificity. This study measures the response of a relaxometer based on ensemble nitrogen-vacancy (NV) centers in diamond to various amounts of LBTs with gadolinium ions, determining the detection limit of LBTs to be 25 fmol. A detection scheme employing the NV relaxometer to detect specific binding between LBTs and target is then proposed and demonstrated. Specifically, the study assesses the relaxometer's response to various concentrations of the interaction between the modified LBTs and Receptor-Binding Domain (RBD) of SARS-COVID-2 spike protein, with the detection threshold reaching ≈2 pmol. The research provides a potential application platform for biomarker detection under picomole concentration by using NV centers to detect the magnetism of LBTs.