Fig. 4.

(A) The burst counts of fluorescent polystyrene beads (10⁶ particles/mL, 100 nm in diameter) with different confocal region sizes (n = 3). The confocal regions were formed by a combination of the pinhole size (diameter) and the objective lens magnification, indicated beneath each bar. (B) Estimation of the signal-to-noise ratio with different confocal region sizes. A solution containing fluorescent polystyrene beads (10⁶ particles/mL) and fluorescein (10 nM) was assayed. Ratios of the photon burst intensity to the noise level were obtained.