In DNA data storage, the massive sequence complexity creates challenges in repeatable and efficient information readout. Here, our study clearly demonstrated that PCR created significant DNA amplification biases due to its inherent mechanism of inefficient priming, product-as-template, and error-spreading prone, which greatly hinder subsequent applications such as data retrieval in DNA-based storage. To mitigate the amplification bias, we recruited an isothermal DNA amplification by combining strand displacement amplification (SDA) with magnetic beads (MB) DNA immobilization for robust, repeated, and low-bias amplification of DNA oligo pool, comprising over 100 thousand oligos, in a primer-free and low-error-spreading fashion. Furthermore, we introduced oligo pool normalization (OPN), a cost-effective and scalable method for normalizing an oligo pool, by which oligo pools comprising from 256 to 1024 distinct oligos were simply modified with improved Gini-index. Therefore, we believe that the combination of SDA and OPN can provide an ideal amplification mechanism for a low-bias copy of a large oligo pool, which is of vital importance for successful data retrieval in DNA information storage.
Keywords: DNA; DNA data storage; isothermal amplification; low-bias amplification; polymerase chain reaction (PCR); strand displacement amplification.