Poly acrylic acid solution

For the synthesis of the γ-Fe₂O₃/SiO₂/RhB NPs, reagent grade chemicals were used as received from the manufacturers. Iron (III) sulfate hydrate, iron (II) sulfate heptahydrate (ACS, 99%), citric acid (CA, 99%), tetraethoxysilane (TEOS, 99.9%) and NH₄OH (28–30%) were supplied by Alfa Aesar (Lancashire, UK). Acetone (AppliChem GmbH) and absolute ethanol (Carlo Erba, reagent - USP) were used as received. (3-Aminopropyl)triethoxysilane (APS; silane-NH₂, 99%), tetraethoxysilane (TEOS; 98%), ethyl acetate (EA), dichloromethane (DCM), dimethylformamide (DMF), Rhodamine B isothiocyanate (RhB), poly(acrylic acid) solution (25 wt. % in water) and polyvinyl pyrrolidone (PVP, 40 kDa) were obtained from Sigma-Aldrich (St. Louis, MO, USA).
Cellulose acetate (CA, Mn = 30000 g/mol) was obtained from Sigma-Aldrich and used without further purification. Acetone (Technical Grade 99.5% - Panaska Trading CO) was the solvent used in the preparation of CA polymer solutions that were further electrospun.

To prepare a 200 ml batch of PAA:nanoalum, 10.8 g of 50% w/v 2000 Da poly(acrylic acid) solution (Sigma-Aldrich) was added to 180 ml of 10 mg Al/ml Alhydrogel® “85” (Sergeant Adjuvants) gel and mixed in a 500 ml sterile PETG bottle (Nalgene). The mixture was adjusted to pH 7 with 1–10 M NaOH solution and then QS to 200 ml with DI water. A silverson high shear mixer was used to homogenize the mixture at 5000–10,000 rpm for 5–10 min to break up large AlO(OH) aggregates. To further reduce particle size down to the nanometer scale, the Alhydrogel-PAA mixture was microfluidized in the M110P microfluidizer (Microfluidics, Inc.) at 30,000 psi for ten passes. The re-circulating water bath, used to control the M110P’s cooling coil temperature, was set to 4 °C. The target particle size of the microfluidized sample (60–80 nm) was confirmed with dynamic light scattering (DLS; Zetasizer ZS, Malvern Instruments) before sterile filtering with 0.2 µm PES membrane. Particle size, zeta potential and pH of the filtered PAA:nanoalum material were recorded at the date of manufacture. Unless otherwise specified, all studies were performed with a PAA:nanoalum preparation containing 27 mg/ml 2 kDa PAA and 9 mg/ml elemental aluminum.