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

Abstract

Adsorbing DNA oligonucleotides onto nanoparticles is the first step in developing DNA-based biosensors, drug delivery systems, and smart materials. Since DNA is a polyanion, it is repelled by negatively charged nanoparticles, which constitute the majority of commonly used nanomaterials. Adding salt such as NaCl to screen charge repulsion is a standard method of promoting DNA adsorption. However, Na + does not supply additional attractive forces. In addition, adding a high concentration of NaCl can cause the aggregation of nanomaterials. In this feature article, we mainly summarize the methods developed in our laboratory to promote DNA adsorption by lowering the pH and by adding polyvalent metal ions, especially transition-metal ions. Various materials including noble metals (gold, silver, and platinum), 2D materials (graphene oxide, MoS 2 , WS 2 , 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 DNA folding at low pH can sometimes be detrimental to adsorption. Polyvalent metal ions can bridge additional interactions to achieve otherwise impossible adsorption. On the basis of the current understanding, a few future research directions are proposed to further improve DNA adsorption.

Metal-Doped Polydopamine Nanoparticles for Highly Robust and Efficient DNA Adsorption and Sensing

“…In addition, no direct correlation was observed between the surface charge and the DNA adsorption efficiency (compare parts B and C of Figure 1), highlighting that the role of the metal ions for DNA adsorption was beyond charge screening. 24 Furthermore, we noticed that the DNA adsorption efficiency was dependent on the duration of PDA synthesis. As shown in Figure 1D, for all of the metal ions, after 2 h of polymerization, the DNA adsorption efficiency drastically decreased.…”

“…Therefore, although a fraction of the doped metal ions were likely present on the surface, they were not enough to reverse or even neutralize the surface charge. In addition, no direct correlation was observed between the surface charge and the DNA adsorption efficiency (compare parts B and C of Figure ), highlighting that the role of the metal ions for DNA adsorption was beyond charge screening …”

“…To promote DNA adsorption on such nanomaterials, adding salt (e.g., NaCl) for charge screening , or lowering pH − are the commonly used methods. Recently, polyvalent metal ions also have been used to bridge DNA adsorption. − …”

Ion Beam Nanopatterning of Biomaterial Surfaces

“…While less relevant in the context of medical implants, DNA adsorption at various technologically relevant surfaces is an important issue in bioanalysis and biosensing [110][111][112]. The adsorption of plasmid DNA at ion beam-nanopatterned TiO 2 surfaces was investigated by Majumder et al [113].…”

Effective Repulsion Between Oppositely Charged Particles in Symmetrical Multivalent Salt Solutions: Effect of Salt Valence

“…Salt ions can regulate the effective interactions among polyelectrolytes such as colloids [1][2][3][4][5][6][7], nucleic acids [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], and proteins [23][24][25][26][27][28][29], and consequently impact diverse physical phenomena including the structural assembly of polyelectrolytes [30], the stability of colloids [31,32], and the collapse of nucleic acids [33][34][35]. Generally, a polyelectrolyte solution is often modeled through the Poisson-Boltzmann (PB) equation since the equation has a simple form and is rather successful in predicting the properties of polyelectrolytes in aqueous and monovalent salt solutions [36,37].…”