Studying the Effect of Ionic Composition concentration and Immobilization Buffer pH on Single-Stranded DNA Adsorption onto Carbon Nanoparticles

Abstract

Carbon nanoparticles have emerged as versatile platforms in nucleic acid–based biosensing owing to their tunable surface chemistry and strong affinity toward single-stranded DNA (ssDNA). The efficiency and stability of ssDNA adsorption onto carbon nanomaterials critically determine the performance of such systems and are strongly governed by buffer conditions, particularly ionic composition, ionic strength, and pH. In this work, the effects of stabilizing buffer ionic composition and pH on ssDNA adsorption onto carbon nanoparticles were systematically investigated. Buffers containing controlled concentrations of mono- and divalent cations were examined across a defined pH range to elucidate their influence on DNA–nanoparticle interactions. The results indicate that increasing ionic strength enhances ssDNA adsorption primarily through ionic screening, leading to attenuation of electrostatic repulsion between the negatively charged DNA backbone and carbon surface. Furthermore, divalent cations induce additional enhancement via ionic bridging effects, promoting stronger and more stable adsorption. Buffer pH was found to modulate adsorption behavior by altering surface charge density and protonation states, with mildly acidic to neutral conditions favoring increased adsorption efficiency compared to alkaline environments. Notably, the simultaneous optimization of buffer pH and ionic composition produced a synergistic enhancement in adsorption kinetics, surface coverage, and hybrid stability. These findings provide mechanistic insight into the electrostatic and ionic contributions governing ssDNA adsorption and offer rational guidelines for buffer design in DNA–carbon nanoparticle interfaces for biosensing and bioanalytical applications.