Upconverting/magnetic Janus-like nanoparticles integrated into spiropyran micelle-like nanocarriers for NIR light- and pH- responsive drug delivery, photothermal therapy and biomedical imaging

The integration of multiple functionalities into single theranostic platforms offers new opportunities for personalized and minimally invasive clinical interventions, positioning these materials as highly promising tools in modern medicine. Thereby, magneto-luminescent Janus-like nanoparticles (JNPs) were developed herein, and encapsulated into near-infrared (NIR) light- and pH- responsive micelle-like aggregates (Mic) for simultaneous magnetic targeting, biomedical imaging, photothermal therapy, and pH- NIR-light activated drug delivery. The JNPs consisted of NaYF₄:Yb,Tm upconverting nanoparticles (UCNPs) on which a well-differentiated magnetite structure (MNPs) grew epitaxially. JNPs were encapsulated together with doxorubicin (Dox) into micelle-like aggregates formed with the stimuli-responsive Poly(NIPAM-co-Spiropyran) copolymer, which responds to UV light, temperature changes, and pH variations, so as to form the JNP-Dox@Mic nanocarrier. Based on physicochemical characterizations, the mechanism for the NIR-activated release of Dox from the JNP-Dox@Mic aggregates is suggested: i) activation of the upconverting emissions with 975 nm light, ii) energy transfer to the material's lattice via nonradiative relaxation, inducing a local temperature increase, iii) resonance energy transfer (RET) from the UV-emission bands to the micelle-like aggregates, and iv) reversible isomerization of the hydrophobic Spiropyran (SP) moiety to a hydrophilic zwitterionic merocyanine (MC) form, leading to Dox delivery. Furthermore, the strong light-to-heat conversion ability of the JNPs was demonstrated through thermal imaging analysis, reaching temperatures up to 108 °C upon irradiation for 60 seconds. The efficacy of these nanocomposites for pH- and NIR-light-induced controlled release was demonstrated using electrophoretic separations and tested against MCF-7 breast cancer cells. While non-irradiated samples of JNP-Dox@Mic were innocuous up to 200 μg.mL⁻¹, irradiation with 975 nm light for 5 minutes reduced cell viability to 26 %. These findings highlight the effective synergy between JNPs and micelle-like aggregates, resulting in versatile heterostructures that could be evaluated for multimodal therapy and imaging strategies.