Extended Data Fig. 1: Comparison of different sensing platforms.

The x-axis indicates the distance between the qubit and the target molecule, and the y-axis indicates the sensor sensitivity. Circles (and star) indicate systems that have been delivered into cells. Open boxes denote systems that have not been delivered into cells. Typical state-of-the-art sensitivities for vapor cells (green)^74,75,76, SQUIDs (brown)^77,78,79,80, Nitrogen-vacancy centres in bulk diamond (blue boxes)^{49,81,82,83,84}, Nitrogen-vacancy centres in nanodiamonds (blue circle)^13,85,86,87, and molecular qubits in a non-aqueous host (red boxes)^33,35 are indicated. An ensemble of \(773\times {10}^{6}\) EYFP molecules in aqueous solution (i.e., this work) is indicated by a star. The red circle indicates the projected sensitivity of a single EYFP protein. We note that in a fusion protein the relevant length scale determining the sensitivity is the separation of the EYFP protein to the target protein (i.e., the size of the EYFP protein) and not the diffraction-limited excitation volume.