Research on light controlled drug delivery release systems has shown great potential in biomedical applications. However, in general the photo response of molecules is based on UV excitation. In biomedical applications longer wavelength NIR light is preferable since it shows deeper tissue penetration and is less detrimental to tissue. We report on the synthesis of LiYF₄:Tm³⁺/Yb³⁺ functionalized(UCNP) with a lipid bilayer and azobenzene. The nanoconstruct synthesised is hydrophilic shows excellent colloidal stability and biocompatibility. The nanocomposite can be used as a drug delivery system making use of NIR light excitation (980 nm) to induce the multiphoton process known as upconversion. The LiYF₄ Tm³⁺/Yb³⁺ nanoparticles emit in the UV, visible and/or near-infrared. Fluorescence energy transfer (FRET) from the upconverting nanoparticles (UV emission) to the azobenzene triggers the photoswitching of the azobenzene from the trans to the cis. The photoswitching of the azobenzene molecules disrupts conformation of the supported lipid bilayer thus releasing the drug.

Recently, photosensitive drug delivery systems, which make use of a nitrobenzyl-type ‘photocaged’ anticancer drug conjugated to another small or macromolecule. In each of these cases drug release from the conjugate was mediated by UV light. A major limitation of this approach for in vivo drug release is the low tissue penetration ability of UV light and inevitable DNA damage. A potential solution is afforded by UCNPs loaded with photocaged doxorubicin (DOX) onto the surface of the UCNPs via a photocleavable linkage.