Single platform spin-spin nuclear relaxation time (1H NMR) based technique for assessing dissolution and agglomeration of CuO nanoparticles

This study proposes a single platform tool to capture aggregation and dissolution behaviour of copper oxide nanoparticles in acellular conditions using spin-spin nuclear relaxation time data. The spin-spin nuclear relaxation time gathered from pulsed ¹H Nuclear magnetic resonance (NMR) spectroscopy can be mathematically translated to the wetted surface area of nanoparticles. The effect of suspension media (artificial lung fluid, algal growth media, and 1 mM NaNO<inf>3</inf>) and CuO nanoparticle concentrations (500 mg/L, 250 mg/L, and 100 mg/L) on dissolution, hydrodynamic size, and wetted surface area were determined for seven days. The data obtained through ¹H NMR spectroscopy was compared with conventional techniques used for measuring dissolution (atomic absorption spectroscopy) and agglomeration (Centrifugal particle sedimentation, Dynamic light scattering). Dissolution experiments showed CuO nanoparticles to have a range of dissolution from 6% to 90%, based on the nature of media. Hydrodynamic size measurements captured the increment in the size of nanoparticles (73% increase) due to aggregation, and reduction in the size of the nanoparticles (88% decline) due to dissolution. Similarly, the temporal variation in the spin-spin nuclear relaxation time of the nanoparticles ranging from 0.25% to 72% detected dissolution and agglomeration of nanoparticles in three different media conditions. The temporal variation in the wetted surface area with respect to concentration and suspension media ranged from 2 m²/g to 380 m²/g. We have determined experimentally the complex interplay between size reduction-wetted surface area-dissolution of nanoparticles and how it evolves over 7 days period for CuO nanoparticles.