The development of drug delivery systems (DDSs) using near infrared (NIR) light and upconversion nanoparticles (UCNPs) has generated intensive interest over the past five years. These NIR‐initiated DDSs not only offer a high degree of spatial and temporal determination of therapeutic release but also provide precise control over the released dosage. Furthermore, these nanoplatforms confer several advantages over conventional light‐based DDSs—NIR offers better tissue penetration depth and a reduced risk of cellular photo‐damage caused by exposure to light at high‐energy wavelengths (e.g., ultraviolet light, <400 nm). The development of DDSs that can be activated by low intensity NIR illumination is highly desirable to avoid exposing living tissues to excessive heat that can limit the in vivo application of these DDSs. This encompasses research in three directions: (i) enhancing the quantum yield of the UCNPs; (ii) incorporation of photo‐responsive materials with red‐shifted absorptions into the UCNPs; and (iii) tuning the UCNPs excitation wavelength. This review focuses on recent advances in the development of NIR‐initiated DDS, with emphasis on the use of photo‐responsive compounds and polymeric materials conjugated onto UCNPs. The challenges that limit UCNPs clinical applications, alongside with the aforementioned techniques that have emerged to overcome these limitations, are highlighted.

P(DEGMA-co-OEGMA-b-[TMSPMA-co-VBA])@silica@magnetite polymer–nanoparticle composites have been developed as a platform for controllable drug release. The nanocomposite facilitates controllable release of therapeutic molecules through breakage of pH and heat labile Schiff base bonds that bind the molecules to the polymer. This enables dual-stimuli responsive drug release in response to the acidic microenvironment of cancerous cells and heat generated by the magnetite nanoparticles when subjected to an alternating magnetic field, thereby permitting spatial and temporal control over ‘burst’ release of the drugs. The nanocomposite has also been shown to be effective at improving magnetic resonance imaging contrast through enhancement of spin–spin relaxivity.

The preparation of a perfluorodecalin (PFD) encapsulated silica nanocapsules via a one-pot synthesis method using Pluronic F68 (PF68) stabilised PFD in water nanoemulsion as a template is demonstrated herein. The method described here simplifies previous multi-step procedures that required pre-fabrication of silica hollow spheres and post-loading of the perfluorocarbon. The size of the PFD nanoemulsion template can be varied easily by changing the concentration of PF68. Successful incorporation of PFD (78% wt) into the silica nanocapsule core and the mechanical stability of the structure were evident from ¹⁹F nuclear magnetic resonance analysis; these properties were conferred by the silica-PF68 surface structure. This significant improvement in PFD encapsulation results in higher oxygen carrying capacity compared to encapsulation without PFD as observed from oxygen solubility measurements. The nanocapsules did not show cytotoxicity against HepG2 and 3T3 cells after 24 h exposure at a concentration below 0.8 g L⁻¹ and 0.08 g L⁻¹, respectively. Ultrasound imaging of silica nanocapsules in agarose gel showed a greater than two-fold increment in echogenicity as compared to the PFD nanoemulsion at a similar concentration.

This study provides a thorough investigation on the effects of the commonly-employed microbial growth medium, namely the peptide-containing luria-bertani broth, tryptic soy broth, the glucose-containing M9 Minimal Salts Media as well as phosphate-buffered saline solution on the dissolution and microstructural transformation of zinc oxide thin film. Morphology and chemical composition of the ZnO film after incubation in the media was thoroughly characterised. In addition, the amount and rate of soluble zinc released by the ZnO thin films was quantified. Exposure of ZnO thin film in the different growth media saw formation of new zinc compounds, resulting from various chemical reactions of zinc with the medium components. Deposition of the new zinc compounds on top of the thin film caused morphological transformation of the film. Zinc leaching was observed in all of the tested media, with significantly higher extent of dissolution observed in peptide-containing organic media, such as luria bertani and tryptic soy broth. Complex organic components, such as amino acids and peptides form complexes with zinc oxide coatings, resulting in complexation-mediated leaching of zinc. Soluble zinc re-precipitates with components in the media, and therefore substantially reduced the amount of dissolved zinc. The results suggest strong influence of solution chemistry on ZnO speciation in a test medium, which have important implications for the mechanistic interpretation of ZnO toxicity.