Figure 4.

Summary of particle detection data. (a) A wide range of particle sizes with radii from 2 to 100 nm were detected. For human interleukin-2 and mouse IgG, an effective particle radius was calculated based on spheres having the same molecular weights as the individual molecules. The solid lines are theoretical predictions based on the reactive sensing principle. Errors bars represent the known polydispersity of our samples. (b) The resonance wavelength shift (blue trace) over time of the microtoroid as polystyrene latex nanoparticles 10 nm radius bind to the microtoroid’s surface. As a nanoparticle binds, the resonance frequency of the toroid changes. This change appears as a ‘step’ in the plot of resonance frequency shift over time. The step-fit is shown as a red dashed line (inset). Zoom-out of the toroid response over the full recording range of 10 s. Remaining data sets are shown in Supplementary Figs. S3 and S4.