Disclosed are compositions and methods for quantitation and calibration of images in fluorescence microscopy. Also provided are tissue phantoms that contain known amount(s) of fluorophore standard(s), as well as components and diagnostic kits containing the same for use in various histological analyses. In certain embodiments, three distinct nucleic-acid based assays provide improvements over conventional TUNEL methods to facilitate precise quantitation of a variety of nucleic acids obtained from a biological sample.