Polymer Length Governs DNA Adsorption Dynamics on Mineral Surfaces

DNA adsorption onto mineral surfaces plays a crucial role in controlling its biogeochemical cycling, environmental stability, and accessibility for diverse environmental DNA (eDNA) applications. While eDNA exists in a wide range of polymer lengths, a limited understanding of how DNA polymer length influences adsorption and competition on mineral surfaces hinders accurate interpretations of its mobility and persistence in natural systems. Here, we address this knowledge gap by investigating the role of DNA polymer length (99 bp to ∼20,000 bp) on interactions with selected environmentally relevant minerals, including Fe(III)-(oxyhydr)oxides (goethite, 2-line ferrihydrite), clays (kaolinite, montmorillonite) and hydroxyapatite. Controlled batch experiments at neutral pH show that adsorption from model uniform DNA solutions increases with increasing polymer length for Fe(III)-(oxyhydr)oxides and clays, with the reverse trend observed for hydroxyapatite. During competitive adsorption experiments (using 99 and 2000 bp DNA), the order of addition influenced the extent of adsorption. However, under simultaneous addition─closely reflecting natural environmental conditions, where both polymers compete for binding sites─shorter DNA polymers exhibited preferential adsorption across all minerals. We hypothesize that this preferential adsorption may contribute toward the enhanced environmental persistence of shorter DNA polymers, including the exclusive preservation of small DNA polymers (<100 bp) over long time scales. These findings underscore the critical role of polymer length in DNA adsorption and provide a basis for mechanistic insights into the factors influencing its preservation and fate in natural environments with implications for a range of DNA-based technologies.