Label-free detection of microRNAs (miRNAs) is crucial for early cancer diagnostics. Existing field-effect methods are limited by Debye screening. This study uses nitrogen-vacancy (NV) centers in diamond to measure magnetic noise from paramagnetic counter ions (Mn²⁺) interacting with miRNAs. Molecular dynamics simulations show that miRNA interaction with the diamond surface leads to Mn²⁺ accumulation and increased magnetic noise. Experiments confirm this, showing increased NV spin relaxation contrast, indicating higher Mn²⁺ concentration. This overcomes Debye screening limitations and opens avenues for next-generation quantum biosensors.

Justas Zalieckas, Martin M. Greve, Luca Bellucci, Giuseppe Sacco, Verner Håkonsen, Valentina Tozzini, Riccardo Nifosi