Design of magnetically manipulable fluorescence sensors for single-molecule sensing in vivo

Single-molecule sensing has great potential in mapping the intracellular environment. By dispersing sensors throughout a cell and its periphery, the sensors can measure the spatial variation of a variable of interest. However, many sensing methods show high sensor-to-sensor variability in readouts, increasing the noise such mapping experiments. We overcome this obstacle by moving a single sensor from point to point. To accomplish this, we bind fluorescent sensors to a magnetic nanoparticle, which is then manipulated using a closed-feedback magnetic trap. By simultaneously monitoring the trap with scattering, fluorescence, and contrast imaging channels, we can obtain a comprehensive picture of the local environment and perform optical experiments in and around cells. We present two model systems for intracellular single-molecule sensing: NV centers and DNA-based molecular beacons. We successfully bind these sensors to the magnetic carrier particle and perform readout at single-molecule sensitivity. This technology has potential in mapping cellular processes using both quantum and classical single-molecule sensors.