Monitoring cells local temperature variation using nitrogen-vacancy (NV) centers in nanodiamonds

The growing interest in understanding the complex mechanisms that regulate biological processes has prompted the study and the improvement of quantum sensors, potentially capable of detecting a wide class of physical quantities of biological interest. Among the various sensors proposed for biological applications, nitrogen-vacancy (NV) centers in artificial diamond have emerged as a truly promising solution primarily thanks to their excellent bio-compatibility. Such NV sensors can be synthesized of nanometer size. The nanodiamonds can be inserted inside cells and, if properly functionalized, they can be targeted to organelles, such as mitochondria, or ion channels. In addition to the advantages regarding their chemical and structural composition, the NV sensors have distinguished themselves thanks to their sensitivity respect different physical quantity, such as magnetic and electric fields, temperatures and pressures variations. Although the sensitivity achieved by the NV quantum sensors is not yet sufficient to detect the very weak electromagnetic fields generated by biological processes, the thermal variation generated at the cellular level seem at the moment a more attractive field of application. Temperature is an important parameter for the regulation of intracellular processes and its detection is fundamental for a more complete understanding of them. Cellular activity and metabolism can affect the local temperature in cells and pathological conditions such as cancer, Parkinson and Alzherimer's disease can alter it. In this sense, local temperature monitoring within cells is also important for clinical application. Here we will present our experimental setup dedicated to local temperature measurement in neuronal cell cultures. The measurement technique is based on optically detected magnetic resonance (ODMR) with the NV centers in the nanodiamonds, suitably engineered to be sensitive and at the same time bio-compatible. We will demonstrate a proof of principle experiment in which we measure the local temperature variation in cultured hippocampal neurons. The temperature sensitivity is 3 K/Hz ^l/2 . In addition we will show how the nanodiamonds with a size of around 200 nm are internalized by the neurons.