Rise of the 3rd dimension in nanotemperature mapping
The last decades witnessed a quest for devices responding to temperature at a distance with unprecedented space resolution, approaching the nanoscale. Such devices are valuable in both fundamental and applied science, from overheat in micromachines to hyperthermia applied to cells. Despite great advances, the response is still collected in 2D. In real systems, heat flows in 3 dimensions such that 2D nanothermometers give just a plane view of a 3D reality. The restriction to 2D emerges because space resolution is bound to time and temperature resolutions, leading to a trilemma: scanning into the 3rd dimension is time consuming and cannot be achieve without losing temperature and time resolutions. While incremental improvements have been achieved in recent years, adding the 3rd dimension to nanothermometry is crucial for further impact and requires an innovative approach. Herein, I propose the development of nano local probes with tailored magnetic properties recording critical information about local temperature in 3D. These thermometric local probes avoid the resolution trilemma by recording the most relevant temperature information instead of reading the present temperature value. In many applications, including cellular hyperthermia, most part of the current temperature reading is of minor relevance and can be dropped. The key temperature information includes the maximum temperature achieved, the surpass of a given temperature threshold, and the time elapsed after this surpass. Once recorded, this key information can be read in 3D by standard devices (such as confocal microscopes and magnetic resonance imaging scanners) without time constrains and thus keeping a high space and temperature resolution. Moreover, the reading step can be performed in-situ and/or ex-situ, decoupling probes and reading devices if needed. This widens the range of applications of nanothermometers, allowing detection in confined environments and in non-transparent media.