Halloysite Nanotube/Polydopamine Nanohybrids as Clay-Based Photothermal Agents for Antibacterial Applications

Abstract

Nanoparticles with light-to-heat conversion properties play vital roles in the design of photothermal materials that can be remotely heated via light activation. Halloysite nanotubes (HNTs), versatile natural clay nanoparticles, were converted into efficient photothermal agents by functionalizing them with polydopamine, a polymer with light-to-heat conversion properties. By varying the polydopamine functionalization reaction conditions such as dopamine concentration, reaction time, and the nature of the HNTs, HNT-polydopamine (HNT-PDA) nanohybrids comprising different amounts of polydopamine were obtained. HNT-PDA nanohybrids presented significant temperature elevations when irradiated with 808 nm laser light, reaching 250 °C in 2 min, and were demonstrated to be effective photothermal agents, whose light-to-heat conversion properties and the degree of lightactivated temperature elevations can be easily tuned by controlling the polydopamine content through reaction conditions. The photothermal effect of HNT-PDA nanohybrids was demonstrated to be stable over multiple laser light-activation cycles, allowing their reusability. In addition to infrared laser light activation, HNT-PDA nanohybrids were also shown to be activated by other light sources of more practical importance such as a solar simulator, an infrared incandescent lamp, and a light-emitting diode (LED) lamp, demonstrating their versatility as photothermal agents. As one of the potential applications of HNT-PDA nanohybrids, their light-activated antibacterial activity was evaluated. The viability of Staphylococcus aureus (S. aureus) treated with HNT-PDA nanohybrids was reduced by 6.3 log when irradiated with infrared laser light for 5 min, whereas bacteria not treated with the nanohybrids stayed alive under the same irradiation conditions. Comprising natural, nontoxic, cost-effective components, HNT-PDA nanohybrids are promising nanoparticles as versatile clay-based photothermal agents that can be utilized in various photo-driven applications.

Polydopamine-Coated Halloysite Nanotubes for Sunlight-Triggered Release of Active Substances

“…Coating of HNTs with polydopamine was demonstrated to result in photothermal HNT−PDA nanoparticles presenting NIR light-activated temperature elevations before. 22 Here, HNT−PDA nanoparticles were used as nanocarriers for the loading of carvacrol as a model active substance and further functionalized with lauric acid as a heat-activatable stopper.…”

“…HNT–PDA nanocarriers were prepared by the oxidative polymerization of the dopamine monomer in the presence of HNTs, as reported earlier. , 5 g of HNTs were dispersed in 500 mL of purified water (10 mg/mL) with ultrasonication (Qsonica, Q700) for 30 min at 40% amplitude with 3 s pulse on and 2 s pulse off in an ice bath. Then, 3 g of dopamine monomer was added to the dispersion (6 mg/mL) and the pH was adjusted to 8.5 with a Tris-base powder.…”

“…In this work, an environmentally responsive controlled release system that allows the release of active substances from HNT nanocarriers to be controlled by sunlight was developed. HNTs were demonstrated to acquire a photothermal character by their functionalization with polydopamine before . Polydopamine, a mussel-inspired adhesive protein mimic that can be easily deposited on many surfaces, also attracts attention as a significant photothermal agent due to its strong NIR absorption and high light-to-heat conversion efficiency.…”

“…HNTs were demonstrated to acquire a photothermal character by their functionalization with polydopamine before. 22 Polydopamine, a mussel-inspired adhesive protein mimic that can be easily deposited on many surfaces, also attracts attention as a significant photothermal agent due to its strong NIR absorption and high light-to-heat conversion efficiency. Here, polydopamine-functionalized HNT nanohybrids (HNT−PDA) with photothermal properties were utilized as light-responsive nanocarriers for the encapsulation of carvacrol, the active component of the essential thyme oil, selected as a model volatile active substance in this study.…”

Covalent Assembly of Clickable Carbon Nanodots in Water-in-Oil Emulsion for Enhanced Antibacterial Photothermal Therapy

“…Antibacterial photothermal therapy (PTT), as a noninvasive treatment technology, utilized PTT agents (PTAs) to convert light into local heat for killing bacteria within a few minutes. − More importantly, the generated heat can permanently rupture cell membranes and irreversibly denature cellular proteins, preventing bacteria from developing new resistance by mutating drug binding sites. − Therefore, there is an urgent need to develop novel PTAs for the PTT of drug-resistant bacteria.…”