Metal and Lanthanide Ion-Co-doped Synthetic and Salmon DNA Thin Films

Researchers have begun to use DNA molecules as an efficient template for arrangement of multiple functionalized nanomaterials for specific target applications. In this research, we demonstrated a simple process to co-dope synthetic DNA nanostructures (by a substrate-assisted growth method) and natural salmon DNA thin films (by a drop-casting method) with divalent metal ions (M²⁺, e.g., Co²⁺ and Cu²⁺) and trivalent lanthanide ions (Ln³⁺, e.g., Tb³⁺ and Eu³⁺). To identify the relationship among the DNA and dopant ions, DNA nanostructures were constructed while varying the Ln³⁺ concentration ([Ln³⁺]) at a fixed [M²⁺] with ion combinations of Co²⁺-Tb³⁺, Co²⁺-Eu³⁺, Cu²⁺-Tb³⁺, and Cu²⁺-Eu³⁺. Accordingly, we were able to estimate the critical [Ln³⁺] (named the optimum [Ln³⁺], [Ln³⁺]_O) at a given [M²⁺] in the DNA nanostructures that corresponds to the phase change of the DNA nanostructures from crystalline to amorphous. The phase of the DNA nanostructures stayed crystalline up to [Tb³⁺]_O ≡ 0.4 mM and [Eu³⁺]_O ≡ 0.4 mM for Co²⁺ ([Tb³⁺]_O ≡ 0.6 mM and [Eu³⁺]_O ≡ 0.6 mM for Cu²⁺) and then changed to amorphous above 0.4 mM (0.6 mM). Consequently, phase diagrams of the four combinations of dopant ion pairs were created by analyzing the DNA lattice phases at given [M²⁺] and [Ln³⁺]. Interestingly, we observed extrema values of the measured physical quantities of DNA thin films near [Ln³⁺]_O, where the maximum current, photoluminescence peak intensity, and minimum absorbance were obtained. M²⁺- and Ln³⁺-multidoped DNA nanostructures and DNA thin films may be utilized in the development of useful optoelectronic devices or sensors because of enhancement and contribution of multiple functionalities provided by M²⁺ and Ln³⁺.