Structural, optical, and bioimaging characterization of carbon quantum dots solvothermally synthesized from o-phenylenediamine.

Carbon quantum dots as a novel type of carbon nanomaterials have attracted the attention of many researchers because of their unique optical, antibacterial, and anticancer properties as well as their biocompatibility. In this study, for the first time, carbon quantum dots were prepared from o-phenylenediamine dissolved in toluene by a solvothermal route. Subsequently, the prepared carbon quantum dots were encapsulated into polyurethane films by a swelling-encapsulation-shrink method. Analyses of the results obtained by different characterization methods (AFM, TEM, EDS, FTIR, photoluminescence, and EPR) indicate the significant influence of the precursor on structural, chemical, and optical properties. Antibacterial and cytotoxicity tests showed that these dots did not have any antibacterial potential, because of the low extent of reactive oxygen species production, and showed low dark cytotoxicity. By investigating the cellular uptake, it was established that these dots penetrated the HeLa cells and could be used as probes for bioimaging.

Highly Efficient Antibacterial Polymer Composites Based on Hydrophobic Riboflavin Carbon Polymerized Dots.

Development of new types of antimicrobial coatings is of utmost importance due to increasing problems with pathogen transmission from various infectious surfaces to human beings. In this study, new types of highly potent antimicrobial polyurethane composite films encapsulated by hydrophobic riboflavin-based carbon polymer dots are presented. Detailed structural, optical, antimicrobial, and cytotoxic investigations of these composites were conducted. Low-power blue light triggered the composites to eradicate Escherichia coli in 30 min, whereas the same effect toward Staphylococcus aureus was reached after 60 min. These composites also show low toxicity against MRC-5 cells. In this way, RF-CPD composites can be used for sterilization of highly touched objects in the healthcare industry.

Chronic wound dressings - Pathogenic bacteria anti-biofilm treatment with bacterial cellulose-chitosan polymer or bacterial cellulose-chitosan dots composite hydrogels.

Since the pathogenic bacteria biofilms are involved in 70% of chronic infections and their resistance to antibiotics is increased, the research in this field requires new healing agents. New composite hydrogels were designed as potential chronic wound dressings composed of bacterial cellulose (BC) with chitosan polymer (Chi) - BC-Chi and chitosan nanoparticles (nChiD) - BC-nChiD. nChiD were obtained by gamma irradiation at doses: 20, 40 and 60 kGy. Physical and chemical analyses showed incorporation of Chi and encapsulation of nChiD into BC. The BC-Chi has the highest average surface roughness. BC-nChiD hydrogels show an irradiated dose-dependent increase of average surface roughness. New composite hydrogels are biocompatible with excellent anti-biofilm potential with up to 90% reduction of viable biofilm and up to 65% reduction of biofilm height. The BC-nChiD showed better dressing characteristics: higher porosity, higher wound fluid absorption and faster migration of cells (in vitro healing). All obtained results confirmed both composite hydrogels as promising chronic wound healing agents.

Photoactive and antioxidant nanochitosan dots/biocellulose hydrogels for wound healing treatment.

Bacterial infection and their resistance to known antibiotics delays wound healing. In this study, nanochitosan dots (nChiD) produced by gamma irradiation have been encapsulated in bacterial cellulose (BC) polymer matrix to study the antibacterial potentials of these nanocomposites and their possible usage in wound healing treatment (scratch assay). Detailed analyses show that nChiDs have disc-like shape and average diameter in the range of 40 to 60 nm depending of the applied dose. All nChiDs as well as BC-nChiD nanocomposites emit green photoluminescence independently on the excitation wavelengths. The new designed nanocomposites do not have a cytotoxic effect; antioxidant analysis shows their moderate radical scavenging activity whereas antibacterial properties show significant growth inhibition of strains mostly found in difficult-to-heal wounds. The obtained results confirm that new designed BC-nChiD nanocomposites might be potential agent in wound healing treatment.

Bactericidal and antioxidant bacterial cellulose hydrogels doped with chitosan as potential urinary tract infection biomedical agent.

Therapy of bacterial urinary tract infections (UTIs) and catheter associated urinary tract infections (CAUTIs) is still a great challenge because of the resistance of bacteria to nowadays used antibiotics and encrustation of catheters. Bacterial cellulose (BC) as a biocompatible material with a high porosity allows incorporation of different materials in its three dimensional network structure. In this work a low molecular weight chitosan (Chi) polymer is incorporated in BC with different concentrations. Different characterization techniques are used to investigate structural and optical properties of these composites. Radical scavenging activity test shows moderate antioxidant activity of these biocompatible composites whereas in vitro release test shows that 13.3% of chitosan is released after 72 h. Antibacterial testing of BC-Chi composites conducted on Gram-positive and Gram-negative bacteria causing UTIs and CAUTIs (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) and encrustation (Proteus mirabilis) show bactericidal effect. The morphology analysis of bacteria after the application of BC-Chi shows that they are flattened with a rough surface, with a tendency to agglomerate and with decreased length and width. All obtained results show that BC-Chi composites might be considered as potential biomedical agents in treatment of UTIs and CAUTIs and as a urinary catheter coating in encrustation prevention.

Graphene quantum dots as singlet oxygen producer or radical quencher - The matter of functionalization with urea/thiourea.

Due to their low cost and possible green synthesis, high stability and resistance to photobleaching, graphene quantum dots (GQDs) can be considered as one of the class of carbon nanomaterials which may have great potential as an agent for photosensitized oxygen activation. In such a way, GQDs can be used as a theranostic agent in photodynamic therapy. In this work pristine GQDs, GQDs irradiated with gamma rays and GQDs doped with N and N, S atoms are produced using a simple, green approach. By using different techniques (AFM, HR-TEM, SEM-EDS, FTIR, XRD, PL and UV-Vis) we investigated structural and optical properties of the new types of GQDs. We showed that GQDs functionalized with thiourea (GQDs-TU) completely lost the ability to produce singlet oxygen (1O2) upon photoexcitation while functionalization with urea (GQDs-U) improves the capability of GQDs to produce 1O2 upon the same conditions. Thus, presented GQDs modification with urea seems like a promising approach for the production of the efficient photosensitizer. On the opposite, GQDs-TU are efficient OH quencher. Due to high singlet oxygen production and low cytotoxicity below 100 µg/mL against HeLa cells, GQDs-U is a good candidate as an agent in photodynamic therapy at this concentration.

Antibacterial photodynamic activity of carbon quantum dots/polydimethylsiloxane nanocomposites against Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae.

Despite great efforts, the design of antibacterial surfaces is still a challenge. In this work, results of structural, mechanical, cytotoxic and antibacterial activities of hydrophobic carbon quantum dots/polydimethylsiloxane surfaces are presented. Antibacterial action of this surface is based on the generation of reactive oxygen species which cause bacteria damage by oxidative stress. At the same time, this surface was not cytotoxic towards the NIH/3T3 cells. Swelling-encapsulation-shrink method is applied for encapsulation of hydrophobic carbon quantum dots in medical grade silicone-polydimethylsiloxane. XPS and photoluminescence spectroscopy analyses confirm that hydrophobic carbon quantum dots have been encapsulated successfully into polydimethylsiloxane polymer matrix. Based on stress-strain test the improvement of mechanical properties of these nanocomposites is established. It is shown by electron paramagnetic resonance spectroscopy and luminescence method that nanocomposite generates singlet oxygen initiated by 470 nm blue light irradiation. Antibacterial testing shows the nanocomposite in the form of foil kills Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae and is very effective after only a 15 min irradiation.

Modification of Structural and Luminescence Properties of Graphene Quantum Dots by Gamma Irradiation and Their Application in a Photodynamic Therapy.

Herein, the ability of gamma irradiation to enhance the photoluminescence properties of graphene quantum dots (GQDs) was investigated. Different doses of γ-irradiation were used on GQDs to examine the way in which their structure and optical properties can be affected. The photoluminescence quantum yield was increased six times for the GQDs irradiated with high doses compared to the nonirradiated material. Both photoluminescence lifetime and values of optical band gap were increased with the dose of applied gamma irradiation. In addition, the exploitation of the gamma-irradiated GQDs as photosensitizers was examined by monitoring the production of singlet oxygen under UV illumination. The main outcome was that the GQDs irradiated at lower doses act as better photoproducers than the ones irradiated at higher doses. These results corroborate that the structural changes caused by gamma irradiation have a direct impact on GQD ability to produce singlet oxygen and their photostability under prolonged UV illumination. This makes low-dose irradiated GQDs promising candidates for photodynamic therapy.

Photodynamic antibacterial effect of graphene quantum dots.

Synthesis of new antibacterial agents is becoming increasingly important in light of the emerging antibiotic resistance. In the present study we report that electrochemically produced graphene quantum dots (GQD), a new class of carbon nanoparticles, generate reactive oxygen species when photoexcited (470 nm, 1 W), and kill two strains of pathogenic bacteria, methicillin-resistant Staphylococcus aureus and Escherichia coli. Bacterial killing was demonstrated by the reduction in number of bacterial colonies in a standard plate count method, the increase in propidium iodide uptake confirming the cell membrane damage, as well as by morphological defects visualized by atomic force microscopy. The induction of oxidative stress in bacteria exposed to photoexcited GQD was confirmed by staining with a redox-sensitive fluorochrome dihydrorhodamine 123. Neither GQD nor light exposure alone were able to cause oxidative stress and reduce the viability of bacteria. Importantly, mouse spleen cells were markedly less sensitive in the same experimental conditions, thus indicating a fairly selective antibacterial photodynamic action of GQD.