Metal-coated magnetic nanoparticles for surface enhanced Raman scattering studies

We report the optimization and usage of surfactantless, water dispersible Ag and Au-coated γ–Fe2O3 nanoparticles for applications in Surface-enhanced Raman Scattering (SERS). These nanoparticles, with plasmonic as well as super paramagnetic properties exhibit Raman enhancement factors of the order of 106 (105) for Ag (Au) coating, which are on par with the conventional Ag and Au nanoparticles. Raman markers like 2-naphthalenethiol, rhodamine-B and rhodamine-6G have been adsorbed to these nanoparticles and tested for nonresonant SERS at low concentrations. Further, to confirm the robustness of Ag-coated nanoparticles, we have performed temperature-dependent SERS in the temperature range of 77–473 K. The adsorbed molecules exhibit stable SERS spectra except at temperatures >323 K, where the thermal desorption of test molecule (naphthalenethiol) were evident. The magnetic properties of these nanoparticles combined with SERS provide a wide range of applications

Unravelling pH/pKa influence on pH-responsive drug carriers:Insights from ibuprofen-silica interactions and comparative analysis with carbon nanotubes, sulfasalazine, and alendronate

This study employs density functional theory to explore the interaction between ibuprofen (IBU) and silica, emphasizing the influence of the trimethylsilyl (TMS) functional group for designing pH-responsive drug carriers. The surface (S) and drug (D) molecules' neutral (0) or deprotonated (-1) states were taken into consideration during the investigation. The likelihood of these states was determined based on the pKa values and the desired pH conditions. To calculate the pH-dependent interaction energy (EintpH), four different situations have been identified: S0D0, S0D-1, S-1D0, and S-1D-1.The electrostatic component of interaction energy aligns favorably with its theoretical value in both the Debye-Hückel and Grahame models. The investigation has gathered first-hand experimental data on the drug loading and release of pH-responsive mesoporous silica nanoparticles. Effective drug loading was observed in the acidic environment of the stomach (pH 2-5), followed by a release in the slightly basic to neutral pH of the small intestine (pH 7.4), These findings align with existing literature. The results revealed horizontal drug adherence on silica surfaces, improving binding capabilities. Comparisons were made with combinations involving carboxylated carbon nanotubes and ibuprofen, silica, and sulfasalazine, and silica and alendronate, exploring drug loading/release dynamics associated with positive/negative interaction energies. The investigation, supported by experimental data, contributes valuable insights into pH-responsive mesoporous silica nanoparticles, offering new design possibilities for drug carriers.</p

Novel p<i>K</i>_a/DFT-Based Theoretical Model for Predicting the Drug Loading and Release of a pH-Responsive Drug Delivery System

Herein, we present a theoretical model that combines classical p<i>K</i>_a theory with quantum mechanical calculations to predict the extent of interaction between acid-/base-dependent species over a full range of pH conditions. To demonstrate the theoretical model, we have predicted the drug loading and release of a pH-responsive drug delivery system consisting of sulfasalazine, an anionic anti-inflammatory drug molecule, loaded onto the positively charged trimethylammonium (TA)-functionalized mesoporous silica nanoparticle surface. The model relies on the possible combinations of pH-dependent states of the surface (S) and drug (D) molecules as neutral (0) and deprotonated (−1) states, whose relative probabilities depend on their p<i>K</i>_a value and the desired pH. The four possible combinations were identified as S⁰D⁰, S⁰D^–1, S^–1D⁰, and S^–1D^–1, and periodic density functional theory calculations were performed for systems comprising drug fragments adsorbed onto a model TA-functionalized quartz surface to calculate the pH-dependent interaction energy (<i>E</i>_int^pH). The <i>E</i>_int^pH value was attractive at the acidic environment of stomach (pH 2–5), where a drug is loaded and repulsive at neutral or slightly basic pH in the small intestine where it is released; the behavior is in accordance with the experimentally reported data. We also validated the experimental necessity of surface functionalization