Although the electronic properties of conducting films have been widely explored in optoelectronic fields, the optical absorption abilities of surface-coated films for photothermal conversion have been relatively less explored in the production of antibacterial coatings. Here, we present catechol-conjugated poly(vinylpyrrolidone) sulfobetaine (PVPS) and polyaniline (PANI) tightly linked by ionic interaction (PVPS:PANI) as a novel photothermal antibacterial agent for surface coating, which can absorb broadband near-infrared (NIR) light. Taking advantage of the NIR light absorption, this coating film can release eminent photothermal heat for the rapid killing of surface bacteria. The NIR light triggers a sharp rise in photothermal heat, providing the rapid and effective killing of 99.9% of the Gram-positive and -negative bacteria tested within 3 min of NIR light exposure when used at the concentration of 1 mg/mL. Although considerable progress has been made in the design of antibacterial coatings, the user control of NIR-irradiated rapid photothermal destruction of surface bacteria holds increasing attention beyond the traditional boundaries of typical antibacterial surfaces.

Growing microbial resistance that renders antibiotic treatment vulnerable has emerged, attracting a great deal of interest in the need to develop alternative antimicrobial treatments. To contribute to this effort, we report magnetic iron oxide (Fe3O4) nanoparticles (NPs) coated with catechol-conjugated poly(vinylpyrrolidone) sulfobetaines (C-PVPS). This negatively charged Fe3O4@C-PVPS is subsequently encapsulated by poly(3,4-ethylenedioxythiophene) (PEDOT) following a layer-by-layer (LBL) self-assembly method. The obtained Fe3O4@C-PVPS:PEDOT nanoparticles appear to be novel NIR-irradiated photothermal agents that can achieve effective bacterial killing and are reusable after isolation of the used particles using external magnetic fields. The recyclable Fe3O4@C-PVPS:PEDOT NPs exhibit a high efficiency in converting photothermal heat for rapid antibacterial effects against Staphylococcus aureus and Escherichia coli. In this study, antibacterial tests for repeated uses maintained almost 100% antibacterial efficiency during three cycles and provided rapid and effective killing of 99% Gram-positive and -negative bacteria within 5 min of near-infrared (NIR) light exposure. The core-shell nanoparticles (Fe3O4@C-PVPS:PEDOT) exhibit the required stability, and their paramagnetic nature means that they rapidly convert photothermal heat sufficient for use as NIR-irradiated antibacterial photothermal sterilizing agents.

Water soluble fluorescent carbon nanoparticles (FCP) obtained from a single natural source, mango fruit, were developed as unique materials for non-toxic bio-imaging with different colors and particle sizes. The prepared FCPs showed blue (FCP-B), green (FCP-G) and yellow (FCP-Y) fluorescence, derived by the controlled carbonization method. The FCPs demonstrated hydrodynamic diameters of 5-15 nm, holding great promise for clinical applications. The biocompatible FCPs demonstrated great potential in biological fields through the results of in vitro imaging and in vivo biodistribution. Using intravenously administered FCPs with different colored particles, we precisely defined the clearance and biodistribution, showing rapid and efficient urinary excretion for safe elimination from the body. These findings therefore suggest the promising possibility of using natural sources for producing fluorescent materials.

We report a stimuli-responsive fluorescent nanomaterial, based on graphene oxide coupled with a polymer conjugated with photochromic spiropyran (SP) dye and hydrophobic boron dipyrromethane (BODIPY) dye, for application in triggered target multicolor bioimaging. Graphene oxide (GO) was reduced by catechol-conjugated polymers under mildly alkaline conditions, which enabled to formation of functionalized multicolor graphene nanoparticles that can be induced by irradiation with UV light and by changing the pH from acidic to neutral. Investigation of these nanoparticles by using AFM, fluorescence emission, and in vitro cell and in vivo imaging revealed that they show different tunable colors in bioimaging applications and, more specifically, in cancer-cell detection. The stability, biocompatibility, and quenching efficacy of this nanocomposite open a different perspective for cell imaging in different independent colors, sequentially and simultaneously.

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