Figure 4.

Microsensor characterization: (a) White-light transmission micrograph (40×, 0.85 NA) showing eight microsensors randomly distributed over a background of flat gold. The background is dark, showing the enormous level of microsensor light emission compared to the light transmission through the flat gold. (Insert) Microsensor detail: the grey line shows the trajectory of the profile in Figure 4(b). The flat gold film on the glass substrate has a spectral transmission of less than 10⁻⁴. (b) Intensity profile scan across a microsensor (convoluted by the seeing function of the optical apparatus). We aligned the microsensor so the highest intensity point of the microsensor’s emission lay at the origin of the focal axes, moved the nanostage laterally by 4 μm, keeping the focal position fixed, then scanned back along the line indicated in the insert in (a). (c) Spectra of the light emitted by a microsensor (a ∅780 polystyrene nanosphere covered with a ≈250 nm gold layer) used in Figure 5(d), in air (dot-dash line) and in PBS (solid line), and the spectrum of the light transmitted through the background flat gold film in air, ≈20 μm away from a microsensor (dash line). In all cases, we excited the microsensor using white light from the microscope illuminator (0.3 NA).