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 μT Hz^(-1/2). In cell-culture medium, a 10.7-μM proton-equivalent dose shortens T₁ from 23.4 ± 2.3 to 9.0 ± 1.2 μs, yielding concentration and pH sensitivities of 6.46 μM 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.