The need for fluorescently tracking RNA rose as its roles in complex cellular functions has grown to not only include mRNA, rRNA, and tRNA, but also RNAi, siRNA, snoRNA, and lncRNA, among others. Spinach is a synthetically derived RNA aptamer born out of the need for a way of studying the role of RNAs at the cellular level. This aptamer was created using Systematic Evolution for Ligands by EXponential enrichment, or SELEX, which is also known as in vitro evolution.