Towards density-optimal DNA storage with practical bijective coding

DNA storage is a promising solution to data explosion due to its high density and longevity. However, existing coding methods struggle to efficiently avoid error-prone sequences while retaining usable ones, leading to low density and high copy numbers. Here we show Siyuan Code, a DNA storage codec that achieves theoretically optimal density. Our method maps binary data to nearly all suitable low-error sequences in a one-to-one manner, using our data structure to catalog and avoid error-prone patterns. This allows operation under very strict biochemical constraints with minimal redundancy. Experiments demonstrate a storage density of 1.66 bits per nucleotide and a capacity of 41 exabytes per gram of DNA, with perfect data retrieval using only six copies per strand. Encoding and decoding speeds reach approximately 1 megabyte per second on commodity hardware, comparable to early USB flash drives. These results bring DNA storage closer to practical deployment.