Hybrid DNA–Carbon Dot–Poly(vinylpyrrolidone) Hydrogel with Self-Healing and Shape Memory Properties for Simultaneous Trackable Drug Delivery and Visible-Light-Induced Antimicrobial Photodynamic Inactivation

Abstract

A two-step methodology for simultaneous conjugation of DNA and poly(vinylpyrrolidone) (PVP) polymer to a single carbon quantum dot (CD) is demonstrated for the first time to fabricate a pH-responsive DNA−CD−PVP hybrid hydrogel. Cross-linking in the hydrogel was achieved using CD as the common nucleus through the formation of DNA I-motif conformation at neutral to acidic pH and noncovalent interaction of PVP that infuse self-healing and shape memory properties in the hydrogel. The hydrogel is capable of loading and sustained delivery of drugs for more than 2 weeks as demonstrated using a model drug, Hemin. The quenching of fluorescence of CD by Hemin was trackable even through simple visual monitoring, which showed that Hemin can diffuse from the loaded part to the unloaded part of the hydrogel during the self-healing process. Most significantly, the chosen CD generates reactive oxygen species (ROS) upon visible light irradiation, armoring the hydrogel with worthy antimicrobial activity. Biocompatibility of the DNA−CD−PVP hydrogel was established on human fibroblast cells, indicating their potential use in biomedical area pertaining to wound healing.

Covalent Conjugation of Carbon Dots with Plasmid and DNA Condensation Thereafter: Realistic Insights into the Condensate Morphology, Energetics, and Photophysics

“…Additionally, we found reduced cell viability on irradiating the CD-pUC19 condensates up to 1 h of light exposure that confirms toxicity issues at the higher time of light exposure irrespective of the synthetic methodology (hydrothermal or thermal decomposition) (Figure S16, Supporting Information ). 21 …”

“…CDs were synthesized by the thermal decomposition method with citric acid and cysteamine as substrates in water, the latter being the source of N and S dopants. − The CD solution was purified by centrifugation to remove larger aggregates and dialysis to remove smaller undesirable fluorophores and starting materials. The CD revealed a semispherical morphology with an average diameter of ∼15 nm through atomic force microscopy (AFM) and transmission electron microscopy (TEM) analysis (Figure A,B).…”

“…Previous research has shown that many CDs are adept at ROS generation on irradiation by normal light in the visible region. − This prompted us to irradiate the CD and CD-pUC19 condensates with visible light from a tungsten source (100 W, 30 cm distance) and evaluate any possible ROS generation using nonfluorescent dihydrorhodamine 123 (DHR 123) that is converted into fluorescent rhodamine 123 on exposure to ROS (Figure ). Although the amount of ROS generated from CD present in CD-pUC19 condensates was found to be consistently lower than pristine CD, the ROS generation ability of the CD is still significantly retained so as to be visually detectable with DHR 123 (Figure S14, Supporting Information).…”

“…CDs were synthesized by the thermal decomposition method by dissolving cysteamine (8.7 mmol, 0.64 g) and citric acid (10 mmol, 2.10 g) in 10 mL of water. , The clear solution was transferred to a 50 mL beaker and heated at 200 °C on a hot plate for 2 h. The yellowish viscous solution obtained was diluted to 50 mL with water and centrifuged at 10,000 rpm to settle down the large particle and collect the supernatant. Then, the resultant solution was filtered through a 0.2 μm syringe filter to remove large aggregates.…”

“…Moreover, the pioneering work by Victor Bloomfield had reported the thermodynamics of the DNA condensation process, the understanding of which is important in the context of the co-condensation of DNA with CD, which is often ignored. ,, Additionally, to the best of our knowledge, none of the CDs involved in DNA condensation reported so far meant for gene transfection applications have been evaluated for reactive oxygen species (ROS) generation on photon excitation, including natural light. This is a highly probable photophysical aspect of the CD other than fluorescence. − The ROS generation ability of the CD essentially requires additional measures for storage and relevant toxicity evaluation to determine its suitability for in vivo applications. Unfortunately, toxicity studies done so far applicable to CD–DNA condensates only partially account for the CDs’ concentration.…”