Fluorescent MoS₂ Quantum Dot–DNA Nanocomposite Hydrogels for Organic Light-Emitting Diodes

In this study, we report the synthesis of water-soluble MoS₂ quantum dots (MoS₂, QD) by a hydrothermal one-step method. These QDs were mixed in an aqueous solution of 2 kbp DNA to form fluorescent nanocomposite hydrogels at a very low concentration of the nucleic acid (1.0% (w/v), normal gelation occurs at 2% (w/v)). The melting temperature T_melt of these gels was 50 ± 2 °C while the hydrogels melt at 40 ± 2 °C, and the low-frequency storage modulus/gel strength G₀ was 40 ± 2 Pa (9 ± 2 Pa for hydrogel). This clearly implied that MoS₂ acted as a pseudo-cross-linker in the nanocomposite hydrogel formation. The remarkable synergy of interaction between DNA and QDs can be gauged from the fact that the gel strength and melting temperature increased with QD content regardless of the fact that both carried negative charge. Dynamic light scattering studies showed arrested dynamics at the onset of gelation, and the gel transition time or ergodicity breaking time τ_EB decreased with the increase in QD concentration. Small-angle X-ray scattering data captured the internal structure of these gels. Thus, we have a unique nanocomposite DNA-based hydrogel that is fluorescent, and in 2-D, this soft matter remarkably exhibits the behavior of an organic light-emitting diode (OLED), which imparts sufficient novelty to this work.