Irene Andreu

Grafting density is the key parameter governing colloidal stability and structure for polymer-grafted nanoparticles (PGNPs). Existing methods to quantify grafting density either destroy the sample, require prior knowledge of polymer molecular weight Mn, or rely on complex instrumentation. Here, we present a nondestructive optical approach that determines grafting density directly from shifts in the localized surface plasmon resonance peak caused by the grafted polymer changing the local effective refractive index. To interpret this shift, the grafted polymer chains are approximated as cylindrical segments passing through differential spherical shells to obtain radial profiles for the polymer volume fraction and refractive index across the polymer corona. The local refractive-index profile is weighted by the plasmonic near-field decay to calculate the effective refractive index sensed by the nanoparticle. The grafting density is finally determined by iteratively adjusting the effective refractive index until the calculated refractive-index sensitivity of the polymer-grafted nanoparticle matches that of the gold core. The grafting densities obtained from this optical method quantitatively agree with established experimental benchmarks across different polymer Mn, grafting densities, nanoparticle sizes, and solvents. Our approach uses common laboratory equipment, eliminates the need for prior knowledge of polymer Mn, and preserves the sample for further experiments, bypassing challenges provided by existing characterization approaches. Together, these advantages provide a framework for predicting and understanding the physical and chemical properties of PGNPs for specific applications.

Polymer-grafted nanoparticles (PGNPs) are a class of hybrid materials with properties intermediate between those of polymer and colloidal systems. Here, we assess how polymer conformation and solvent interactions govern structural stability, phase transitions, and aggregation kinetics in suspensions of gold nanoparticles (AuNPs) grafted with polystyrene of varying molecular weights. When suspended in cyclohexane, the PGNPs exhibit a two-step transition as a function of temperature in which the polymer corona contraction precedes aggregation below the upper critical solution temperature. Time-dependent dynamic light scattering measurements reveal that this aggregation follows a diffusion-limited aggregation process in which the hydrodynamic size increases with time according to a power law with an exponent α ≈ 1/3. This exponent is significantly lower than that observed for colloidal systems. We attribute this discrepancy to a combination of long-range interactions and the viscoelasticity of the grafted layer facilitating rearrangements within the aggregate. Our findings provide quantitative measurements of PGNP phase behavior by quantifying the rate of aggregation, combining polymer thermodynamics and colloidal physics.

Micro and nanoplastics pose a growing environmental threat with complex implications for human health.

Significant amounts of aerosolized Cr–Fe–Ni nanoparticles were detected in wild Dittrichia viscosa grown near steel manufacturing activities. Most of these nanoparticles were found on the plant shoots likely internalized via a foliar uptake process.

Inelastic scattering from molecules because of vibrational modes produces unique Raman shifts, allowing these analytes to be detected with high specificity. Because Raman scattering is weak, surface-enhanced Raman scattering (SERS) has been used as a label-free technique for the detection of a variety of analytes at low concentrations. Using simple solution-based colloidal processing techniques, we have fabricated gold-coated carbon-black nanoparticles that show enhanced Raman activity. By varying the fabrication conditions, we create particles of different surface morphologies, allowing control over the peak wavelength for localized surface plasmon resonance (LSPR). By matching the LSPR wavelength to the incident laser wavelength, we get the highest signal from two model analytes, 4-nitrobenzenethiol (4-NBT) and Congo Red (CR). Our straightforward room-temperature -solution-based approach for making tunable SERS-active particles expands the range of incident radiation wavelengths that can be used for the detection of analytes using Raman scattering.

This study investigates the potential spread of cadmium selenide quantum dots in laboratory environments through contact of gloves with simulated dry spills on laboratory countertops. Secondary transfer of quantum dots from the contaminated gloves to other substrates was initiated by contact of the gloves with different materials found in the laboratory. Transfer of quantum dots to these substrates was qualitatively evaluated by inspection under ultraviolet illumination. This secondary contact resulted in the delivery of quantum dots to all the evaluated substrates. The amount of quantum dots transferred was quantified by elemental analysis. The residue containing quantum dots picked up by the glove was transferred to at least seven additional sections of the pristine substrate through a series of sequential contacts. These results demonstrate the potential for contact transfer as a pathway for spreading nanomaterials throughout the workplace, and that 7-day-old dried spills are susceptible to the propagation of nanomaterials by contact transfer. As research and commercialization of engineered nanomaterials increase worldwide, it is necessary to establish safe practices to protect workers from the potential for chronic exposure to potentially hazardous materials. Similar experimental procedures to those described herein can be adopted by industries or regulatory agencies to guide the development of their nanomaterial safety programmes.

We report a size fractionation of titania (TiO₂) nanoparticles absorbed from the environment and found within wild Dittrichia viscosa plants. The nanoparticles were isolated by extraction and isolation from distinct plant organs, as well as from the corresponding rhizosphere of wild, adult plants. The collected nanoparticles were characterized by scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDS). More than 1200 TiO₂ nanoparticles were analyzed by these techniques. The results indicated the presence of TiO₂ nanoparticles with a wide range of sizes within the inspected plant organs and rhizospheres. Interestingly, a size selective process occurs during the internalization and translocation of these nanoparticles (e.g., foliar and root uptake), which favors the accumulation of mainly TiO₂ nanoparticles with diameters 2 nanoparticles analyzed, the fraction of the particles with dimensions 2 nanoparticles among the rhizosphere and the plant organs could have impacts on the food chain and further biologicals effects that are dependent on the size of the TiO₂.