Mobile nanodiamond quantum sensors in liquids are affected by Brownian rotation, variable photon collection, and perturbations from optical trapping. Here we assemble 40-nm nitrogen-vacancy nanodiamonds on porous, birefringent vaterite microspherulites, creating mobile sensors with a polarization-addressable body frame and a chemically active carbonate interface. Under 976-nm trapping, the sensors retain spin resonance and longitudinal relaxation, with less than 7% variation in contrast and an approximately 1-MHz resonance shift at 0.8 W. Zeeman-split resonances resolve magnetic fields from 0 to 0.8 mT, with a response metric of 78--144 $μ$ T Hz $^{-1/2}$ . In cell-culture medium, a 10.7- $μ$ M proton-equivalent dose shortens $T_1$ from $23.4 \pm 2.3$ to $9.0 \pm 1.2$ $μ$ s, yielding concentration and pH sensitivities of $6.46$ $μ$ M Hz $^{-1/2}$ and $6.54$ mpH Hz $^{-1/2}$ , respectively. A 500-fold larger proton dose in ethanol produces a weaker response. A grand-canonical charge-regulation model links proton chemical potential to interfacial switching, establishing a route to multimodal quantum sensing in complex liquids.Mobile nanodiamond quantum sensors in liquids are affected by Brownian rotation, variable photon collection, and perturbations from optical trapping. Here we assemble 40-nm nitrogen-vacancy nanodiamonds on porous, birefringent vaterite microspherulites, creating mobile sensors with a polarization-addressable body frame and a chemically active carbonate interface. Under 976-nm trapping, the sensors retain spin resonance and longitudinal relaxation, with less than 7% variation in contrast and an approximately 1-MHz resonance shift at 0.8 W. Zeeman-split resonances resolve magnetic fields from 0 to 0.8 mT, with a response metric of 78--144 $μ$T Hz$^{-1/2}$. In cell-culture medium, a 10.7-$μ$M proton-equivalent dose shortens $T_1$ from $23.4 \pm 2.3$ to $9.0 \pm 1.2$ $μ$s, yielding concentration and pH sensitivities of $6.46$ $μ$M Hz$^{-1/2}$ and $6.54$ mpH Hz$^{-1/2}$, respectively. A 500-fold larger proton dose in ethanol produces a weaker response. A grand-canonical charge-regulation model links proton chemical potential to interfacial switching, establishing a route to multimodal quantum sensing in complex liquids.

quant-pharXiv:2608.09434Aug 11, 2026

Quantum Sensing using Nitrogen Vacancy (NV) Centers in Nanodiamonds under Extreme Conditions

Kin On Ho, King Yau Yip, King Yiu Yu +5 more

Bulletin of the American Physical SocietyMar 15, 20210 citations

Engineering Nanodiamonds for Quantum Sensing: Material Constraints at the Nanoscale

Ashutosh Rathi, Keisuke Oshimi, Kento Sasaki +6 more

Optically addressable solid-state spin defects have emerged as powerful multimodal quantum sensors, with nitrogen-vacancy (NV) centers in bulk diamond providing benchmark quantum control and sensitivity under ambient conditions. Embedding such defects in nanodiamonds (NDs) extends these capabilities to mobile probes capable of accessing complex biological and nanoscale environments. Reduced dimensions, however, introduce constraints beyond volumetric spin impurities, notably enhanced lattice strain and surface-induced noise sources, which shorten NV spin relaxation times (T1 and T2) and destabilize the NV charge state, as well as resulting in pronounced particle-to-particle variability in NDs typically produced by top-down approaches. These effects complicate both sensing performance and the quantitative interpretation of multimodal signals in realistic environments. This article provides a structured perspective on the physical mechanisms by which material properties constrain NV behavior in NDs, together with mitigation strategies that shape the robust use of these mobile quantum sensors for biosensing and nanoscale science.Optically addressable solid-state spin defects have emerged as powerful multimodal quantum sensors, with nitrogen-vacancy (NV) centers in bulk diamond providing benchmark quantum control and sensitivity under ambient conditions. Embedding such defects in nanodiamonds (NDs) extends these capabilities to mobile probes capable of accessing complex biological and nanoscale environments. Reduced dimensions, however, introduce constraints beyond volumetric spin impurities, notably enhanced lattice strain and surface-induced noise sources, which shorten NV spin relaxation times (T1 and T2) and destabilize the NV charge state, as well as resulting in pronounced particle-to-particle variability in NDs typically produced by top-down approaches. These effects complicate both sensing performance and the quantitative interpretation of multimodal signals in realistic environments. This article provides a structured perspective on the physical mechanisms by which material properties constrain NV behavior in NDs, together with mitigation strategies that shape the robust use of these mobile quantum sensors for biosensing and nanoscale science.

quant-pharXiv:2608.04489Aug 6, 2026

μ

T Hz

^{-1/2}

. In cell-culture medium, a 10.7-

μ

M proton-equivalent dose shortens

T_1

from

23.4 \pm 2.3

9.0 \pm 1.2

μ

s, yielding concentration and pH sensitivities of

6.46

μ

M Hz

^{-1/2}

and

6.54

mpH Hz

^{-1/2}

, respectively. A 500-fold larger proton dose in ethanol produces a weaker response. A grand-canonical charge-regulation model links proton chemical potential to interfacial switching, establishing a route to multimodal quantum sensing in complex liquids.