Much of the excitement today centers on gene expression profiling that uses a technology called microarrays. A DNA microarray is a thin-sized chip that has been spotted at fixed locations with thousands of single-stranded DNA fragments corresponding to various genes of interest. A single microarray may contain 10,000 or more spots, each containing pieces of DNA from a different gene. Fluorescent-labeled probe DNA fragments are added to ask if there are any places on the microarray where the probe strands can match and bind. Complete patterns of gene activity can be captured with this technology.