Photothermal Disintegration of 3T3 Derived Fat Droplets by Irradiated Silica Coated Upconversion Nanoparticles

Excessive accumulation of fat cells leads to obesity—a predominantly urban public health concern. Photothermal therapy (PTT) can be a novel strategy to control the fat droplets using deep penetrating infra-red light absorption in upconversion nanoparticles (UCNPs). First, silica (SiO₂) coated UCNPs embedded in commercial butter is shown to demonstrate photothermal heating (with photothermal conversion efficiency ≈60%) to gain a maximum temperature rise of ≈26 ºC (to 50 ºC) when exposed to 980 nm laser (5 min, 1 W) irradiation that melts the butter. The same UCNPs @SiO₂ are used to study the PTT effect in mouse 3T3 cell derived fat cells in vitro. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay on differentiated 3T3 cells reveals low cytotoxicity (cell viability >70%) up to 400 ppm concentration of the UCNP@SiO₂. Absorption studies on Oil Red O stained fat droplets, in 3T3 cells incubated with 50 ppm (50 μL) of UCNP@SiO₂, shows 50% (untreated control = 100%) decrease of the 510 nm band post irradiation indicating ≈50% of droplet disintegration by PTT. Time lapse videography shows severe droplet agitation resulting in cytoskeletal re-arrangement in the irradiated, as well as only resistively heated cells with the UCNPs confirming a thermal effect.