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Promoting DNA Adsorption by Acids and Polyvalent Cations: Beyond Charge Screening.

Adsorbing DNA oligonucleotides onto nanoparticles is the first step for developing DNA-based biosensors, drug delivery systems, and smart materials. Since DNA is a polyanion, it is repelled by negatively charged nanoparticles, which constitute majority of commonly used nanomaterials. Adding salt such as NaCl to screen charge repulsion is a standard method to promote DNA adsorption. However, Na+ does not supply additional attractive forces. In addition, adding a high concentration of NaCl can cause aggregation of nanomaterials. In this Feature Article, we mainly summarize the methods developed in our lab to promote DNA adsorption by lowering pH and by adding polyvalent metal ions, especially transition metal ions. Various materials including noble metals (gold, silver and platinum), 2D materials (graphene oxide, MoS2, WS2 and MXene), polydopamine, and several metal oxides are discussed. In general, low pH can protonate DNA bases and nanoparticle surfaces, reducing charge repulsion and even leading to attraction, although folding of DNA at low pH can sometimes be detrimental for adsorption. Polyvalent metal ions can bridge additional interactions to achieve otherwise impossible adsorption. Based on the current understanding, a few future research directions are proposed to further improve DNA adsorption.