Quantitative measurement of the resolution and sensitivity of confocal microscopes using line-scanning fluorescence correlation spectroscopy

Spatial resolution and the sensitivity to detect a fluorophore are the two most important optical parameters that characterize a confocal microscope. However, these are rather difficult to estimate quantitatively. We show that fluorescence correlation spectroscopy (FCS) provides an easy and reliable measure of these quantities. We modify existing schemes for performing FCS on a commercial confocal microscope to carry out these measurements, and provide an analysis routine that can yield the relevant quantities. Our method does not require any modification of the confocal microscope, yet it yields a robust measure of the resolution and sensitivity of the instrument.