Survey of Information Encoding Techniques for DNA

The yearly global production of data is growing exponentially, outpacing the capacity of existing storage media, such as tape and disk, and surpassing our ability to store it. DNA storage - the representation of arbitrary information as sequences of nucleotides - offers a promising storage medium. DNA is nature's information storage molecule of choice and has a number of key properties: it is extremely dense, offering the theoretical possibility of storing 455 EB/g, it is durable with a half-life of approximately 520 years which can be increased to thousands of years when chilled and stored dry, and is amenable to automated synthesis and sequencing. Furthermore, the potential exists for using biochemical processes that act on DNA for performing highly parallel computations. Whilst biological information is encoded in DNA as triplet sequences of nucleotides (also referred to as bases or base pairs) (A,T,G, or C), i.e., base 4 - known as codons - there are many possible encoding schemes that can map data to chemical sequences of nucleotides for synthesis, storage, retrieval and computation. However, there are several biological constraints, error-correcting factors and information retrieval considerations that encoding schemes need to address for DNA storage to be viable. This comprehensive review focuses on comparing existing work done in encoding arbitrary data within DNA, particularly the encoding schemes used, methods employed to address biological constraints, and measures to provide error-correction. Furthermore, we compare encoding approaches on the overall information density they achieve, as well as the data retrieval method they use, i.e., sequential or random access. We will also discuss the background and evolution of the encoding schemes.