Chemiluminescent carbon nanodots for dynamic and guided antibacteria

Photodynamic therapy (PDT), which employs the reactive oxygen species (ROS) produced by the light-excited photosensitizers to achieve the diagnosis and treatment of diseases, has been emerged as a clinical strategy to cure various bacteria-related infections. Nevertheless, the requirement of external light source for the PDT has seriously limited their practical applications in the diagnosis and therapy of deep tissue lesions. Herein, the dynamic and guided antibacteria therapy with chemiluminescent carbon nanodots (CDs), reported in the journal of Light-Science & Applications, has solved this problem.

 

CL, as one kind of luminous emission triggered by chemical reaction, has evoked widespread attention as the self-illuminated light source to achieve the PDT in various inflammation-related diseases, such as arthritis, peritonitis, tumor, etc. Hence, a research team led by Prof. Chong-Xin Shan from Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, China has prepared the chemiluminescent CDs and further designed the CL-dynamic/guided antibacteria (CDGA). The self-illuminating CDGA exhibits an excellent in-vivo imaging quality in detecting wound infections and internal inflammation caused by bacteria toxin at early stage and presents the bacteriostatic rate of 96.94% ~ 99.99% towards the gram-positive/negative bacteria.

 

With the merit of long persistent afterglow and deep penetration of the near-infrared (NIR) emission, the CDGA can be employed as activatable imaging agents for in vivo CL image of inflammation-related ROS. As shown in Fig. 1a, the mixed aqueous solution of CDGA and H₂O₂ illustrates diverse CL emission intensity in a laboratory dish, enabling the CDGA to describe the distribution of H₂O₂. Whereas, with the NIR CL emission and CL plot from the CL distribution, the in vivo CL imaging can be used to investigate the ROS level and distribution in different inflammation sites. Herein, two hind of bacterial inflammation models are established with the bacterial exotoxin of Zymosan A (ZA) to induce inflammation and further generate excessive H₂O₂. As shown in Fig. 1b, the epidermal wound models are established by directly treating the mouse wound with ZA to simulate the wound bacterial infection. In the model, the skin with wound can emit more intense CL emission compared with the common skin after spraying the CDGA aqueous solution (Fig. 1c), confirming the existence of ZA-induced inflammation. Meanwhile, the CL emission distribution in the wound can present the different severity of symptoms for the possible bacterial infection. Moreover, the CDGA also exhibit excellent performance in the in vivo CL bioimaging of deep-penetrated inflammation. The inflammatory mouse models are established through intraperitoneal injection with ZA to simulate the intra-abdominal bacterial infection. After 24 hours, the deep-penetrated inflammation bioimages of mouse models are subsequently captured after the injection of the CDGA. As shown in Fig. 1d, the intra-abdominal sites of mice treated with ZA exhibit higher CL signals compared with the control group. The CL diagnostic signals of ZA-treated mice with deep abdominal tissue are almost 2.5-times higher than that for the control mice. Moreover, after the infected mice with deep abdominal tissue are remedied with an antioxidant glutathione (GSH), the CL signals of the ZA/GSH-treated mice show a 40% reduction (Fig. 1e). As an inflamed-to-normal contrast signals, the enhanced-to-reduced CL intensity can efficiently monitor the variation of bacterial infection in living animals. These investigations indicate the CDGA can be used as inflammation-responsive imaging agent in living body, which is potential for the long-term bioimaging and bacterial infection monitoring.

 

As previous report, the production of ¹O₂, •OH and •O₂- from photochemical reaction can cause effective oxidative damage on the bacterial membrane. In the sites of bacterial infection, the inflammatory microenvironment with highly expressed H2O2 can trigger the CL emission of CDGA and further achieve self-illuminated PDT, implying their potential applications as nanomedicine for the antibacterial applications. In this work, the Flat counting images of E. coli treated with the CDGA under dark condition are firstly investigated. As shown in Fig. 2a, the CDGA exhibit the bacteriostatic rate of 98.76% for the E. coli. On the condition, the antibacterial activities of the CDGA intuitively are further investigated. As shown in Fig. 2b and 2c, the viabilities and morphologies of E. coli before and after treated with CDGA are observed by the LIVE/DEAD staining and scanning electron microscope (SEM). In the confocal laser scanning microscope (CLSM) images of SYTO 9 and PI stained bacteria, the control group without CDGA treatment exhibit green fluorescence, corresponding to the normal living bacteria. However, the experimental group treated with the CDGA show bright red fluorescence, indicating the death of bacteria induced by the CDGA. Meanwhile, the SEM images exhibit obvious morphological changes. In these E. coli bacteria, the control group exhibit spherical shapes and rod-shaped, with glossy and unharmed membranes, while the bacteria incubated with CDGA display partial wrinkling and disruption of bacterial membrane. The altered membranes indicate the damages of bacterial membranes induced by the ROS-based PDT, which is consistent with the expected antibacteria mechanism of CDGA.

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