A molecular device for the simultaneous magnetic-induced heating and temperature measurement. Mapping temperature distribution inside a cell

Abstract

As nanotechnology progresses, new demands and new challenges arise. lndeed, the increased interest on hyperthermia therapies in nanomedicine has opened the need for an accurate control of heat transfer and heat release by a precise monitoring of the temperature. A straightforward solution to this demand would be the development of efficient and sensitive nanoparticles embedding both heaters and thermometers, something that despite intense activity in the recent years had resisted scientific efforts. Here we report the development of such device: a nanoplatforrn consisting in a magnetic nanoparticle incorporating a molecular thermometer just on the surface of the heater, thus having an unprecedented thermal contact and a quasi-instantaneous onset of temperature gradient from the heater to the medium. The heater/thermometer nanoplatform was prepared from iron oxide cores functionalized with Eu3+ and Tb3+ complexes, coated with a P4VP-b-P(PMEGAco-PEGA) copolymer and dispersed in water to obtain an aqueous ferrofluid suspension. The thermometric response results from thermally activated energy transfer between Eu3+- and Tb3+-emitting levels and triplet energy states of the ligands and of the host matrix. The beads thermometric performance is evaluated using the relative sensitivity Sr= (::/T)/:: which ranges from 0.5 to 5.8%/K, 295-315 K (maximum sensitivity of 5.8%/K at 296 K). Upon 10 consecutive temperature cycles between 297 and 310 K, the therrnometer reproducibility is 99.5%,. The time fluctuations of the therrnometric parameter :: are always below O. 7%. The uncertainty of the temperature measurement is 0.5 K. The heater/thermometer nanoplatforrn is applied to monitor local temperature changes under ac magnetic fields. A semiconductor thermometer immersed in the ferrofluid and an infrared camera focused on the container wall were used for comparative purposes. A multiple-pulse protocol is illustrated in the Figure showing differences between the fast and direct temperature reading of the molecular thermometer and those from the (indirect) semiconductor and IR ones. Such differences are related to heat flow at the nanoscale and could not be observed before using more conventional systems. In addition, we show here the temperature mapping near the nucleus of Opossum kidney cells incubated with the nanoparticles.