Fast and sensitive detection of hemoglobin and other paramagnetic species using coupled charge and spin dynamics in strongly fluorescent nanodiamonds

TL;DR

This paper introduces a rapid, highly sensitive method using dense nanodiamond ensembles to detect paramagnetic species like hemoglobin and gadolinium with ultrashort acquisition times, advancing biosensing capabilities.

Contribution

It presents a novel approach leveraging coupled spin and charge dynamics in nanodiamonds for fast, sensitive detection of paramagnetic species, improving upon traditional NV center techniques.

Findings

Detected subnanomolar Gd spins within 10 ms

Achieved high sensitivity with dense NV ensembles in nanodiamonds

Demonstrated potential for biosensing and bioimaging applications

Abstract

Sensing of a few unpaired electron spins, such as metal ions and radicals, is a useful but difficult task in nanoscale physics, biology, and chemistry. Single nitrogen-vacancy (NV) centers in diamond offer high sensitivity and spatial resolution in the optical detection of weak magnetic fields produced by a spin bath, but often require long acquisition times, of the order of seconds. Here we use a novel approach, based on coupled spin and charge dynamics in dense NV ensembles in strongly fluorescent nanodiamonds (NDs) to sense external magnetic dipoles. We apply this approach to various paramagnetic species, including gadolinium complexes, magnetite nanoparticles and hemoglobin in whole blood. Taking advantage of the high NV density, we demonstrate detection of subnanomolar amounts of Gd spins with ultrashort acquisition time approaching 10 ms. Strong luminescence, high sensitivity and short acquisition time make dense NV- ensembles in NDs a powerful tool for biosensing and bioimaging applications.