Visible Light-Activated Carbon Dots for Inhibiting Biofilm Formation and Inactivating Biofilm-Associated Bacterial Cells

Biofilm Inhibition on Medical Devices and Implants Using Carbon Dots: An Updated Review

Biofilms are an intricate community of microbes that colonize solid surfaces, communicating via a quorum-sensing mechanism. These microbial aggregates secrete exopolysaccharides facilitating adhesion and conferring resistance to drugs and antimicrobial agents. The escalating global concern over biofilm-related infections on medical devices underscores the severe threat to human health. Carbon dots (CDs) have emerged as a promising substrate to combat microbes and disrupt biofilm matrices. Their numerous advantages such as facile surface functionalization and specific antimicrobial properties, position them as innovative anti-biofilm agents. Due to their minuscule size, CDs can penetrate microbial cells, inhibiting growth via cytoplasmic leakage, reactive oxygen species (ROS) generation, and genetic material fragmentation. Research has demonstrated the efficacy of CDs in inhibiting biofilms formed by key pathogenic bacteria such as Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Consequently, the development of CD-based coatings and hydrogels holds promise for eradicating biofilm formation, thereby enhancing treatment efficacy, reducing clinical expenses, and minimizing the need for implant revision surgeries. This review provides insights into the mechanisms of biofilm formation on implants, surveys major biofilm-forming pathogens and associated infections, and specifically highlights the anti-biofilm properties of CDs emphasizing their potential as coatings on medical implants.

Quantum dots: a next generation approach for pathogenic microbial biofilm inhibition; mechanistic insights, existing challenges, and future potential

Quantum Dots (QDs) have emerged as versatile nanomaterials with origins spanning organic, inorganic, and natural sources, revolutionizing various biomedical applications, particularly in combating pathogenic biofilm formation. Biofilms, complex structures formed by microbial communities enveloped in exopolysaccharide matrices, pose formidable challenges to traditional antibiotics due to their high tolerance and resistance, exacerbating inefficacy issues in antibiotic treatments. QDs offer a promising solution, employing physical mechanisms like photothermal or photodynamic therapy to disrupt biofilms. Their efficacy is noteworthy, with lower susceptibility to resistance development and broad-spectrum action as compared to conventional antibiotic methods. The stability and durability of QDs ensure sustained biofilm activity, even in challenging environmental conditions. This comprehensive review delves into the synthesis, properties, and applications of Carbon Quantum Dots (CQDs), most widely used QDs, showcasing groundbreaking developments that position these nanomaterials at the forefront of cutting-edge research and innovation. These nanomaterials exhibit multifaceted mechanisms, disrupting cell walls and membranes, generating reactive oxygen species (ROS), and binding to nucleic materials, effectively inhibiting microbial proliferation. This opens transformative possibilities for healthcare interventions by providing insights into biofilm dynamics. However, challenges in size control necessitate ongoing research to refine fabrication techniques, ensure defect-free surfaces, and optimize biological activity. QDs emerge as microscopic yet potent tools, promising to contribute to a brighter future where quantum wonders shape innovative solutions to persistently challenging issues posed by pathogenic biofilms. Henceforth, this review aims to explore QDs as potential agents for inhibiting pathogenic microbial biofilms, elucidating the underlying mechanisms, addressing the current challenges, and highlighting their promising future potential.

Evaluation of combined carbon dots and ciprofloxacin on the expression level of pslA, pelA, and ppyR genes and biofilm production in ciprofloxacin-resistant Pseudomonas aeruginosa isolates from burn wound infection in Iran

OBJECTIVES

Antimicrobial resistance and biofilm formation are increasingly significant public health concerns. This study aimed to examine the antibacterial and antibiofilm properties of carbon dots (C-dots) alone and in combination with antibiotics against biofilm-forming isolates of Pseudomonas aeruginosa.

METHODS

The antibacterial property of C-dots was investigated by broth microdilution method against ATCC PAO1 and P. aeruginosa clinical isolates. The antibacterial effect of the C-dots and ciprofloxacin combination was investigated using the checkerboard method. The antibiofilm effect of the C-dots alone and its combination with ciprofloxacin was evaluated using the microtiter plate method. Subsequently, the toxicity of each agent was tested on L929 fibroblast cells. In the end, the effects of C-dots on the expression levels of pslA, pelA, and ppyR genes were determined using real-time quantitative PCR.

RESULTS

The combination of C-dots and ciprofloxacin exhibited a synergistic effect. Additionally, this compound substantially decreased bacterial growth (P < 0.0001) and inhibited biofilm formation at MIC (96 µg/mL) and sub-MIC (48 µg/mL) concentrations (P < 0.0053, P < 0.01). After being exposed to C-dots at a concentration of 1mg/mL for 24 hours, the survival rate of L929 cells was 87.3%. The expression of genes pslA, pelA, and ppyR, associated with biofilm formation in P. aeruginosa, was significantly reduced upon exposure to C-dots (P < 0.0023).

CONCLUSIONS

The findings demonstrate a promising new treatment method for infections. Furthermore, reducing the dosage of antibiotics can lead to an improvement in the toxic effects caused by dose-dependent antibiotics and antimicrobial activity.

Light-Based Anti-Biofilm and Antibacterial Strategies

Biofilm formation and antimicrobial resistance pose significant challenges not only in clinical settings (i.e., implant-associated infections, endocarditis, and urinary tract infections) but also in industrial settings and in the environment, where the spreading of antibiotic-resistant bacteria is on the rise. Indeed, developing effective strategies to prevent biofilm formation and treat infections will be one of the major global challenges in the next few years. As traditional pharmacological treatments are becoming inadequate to curb this problem, a constant commitment to the exploration of novel therapeutic strategies is necessary. Light-triggered therapies have emerged as promising alternatives to traditional approaches due to their non-invasive nature, precise spatial and temporal control, and potential multifunctional properties. Here, we provide a comprehensive overview of the different biofilm formation stages and the molecular mechanism of biofilm disruption, with a major focus on the quorum sensing machinery. Moreover, we highlight the principal guidelines for the development of light-responsive materials and photosensitive compounds. The synergistic effects of combining light-triggered therapies with conventional treatments are also discussed. Through elegant molecular and material design solutions, remarkable results have been achieved in the fight against biofilm formation and antibacterial resistance. However, further research and development in this field are essential to optimize therapeutic strategies and translate them into clinical and industrial applications, ultimately addressing the global challenges posed by biofilm and antimicrobial resistance.

Nanocellulose-Based Passivated-Carbon Quantum Dots (P-CQDs) for Antimicrobial Applications: A Practical Review

Passivated-carbon quantum dots (P-CQDs) have been attracting great interest as an antimicrobial therapy tool due to their bright fluorescence, lack of toxicity, eco-friendly nature, simple synthetic schemes, and possession of photocatalytic functions comparable to those present in traditional nanometric semiconductors. Besides synthetic precursors, CQDs can be synthesized from a plethora of natural resources including microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC). Converting MCC into NCC is performed chemically via the top-down route, while synthesizing CODs from NCC can be performed via the bottom-up route. Due to the good surface charge status with the NCC precursor, we focused in this review on synthesizing CQDs from nanocelluloses (MCC and NCC) since they could become a potential source for fabricating carbon quantum dots that are affected by pyrolysis temperature. There are several P-CQDs synthesized with a wide spectrum of featured properties, namely functionalized carbon quantum dots (F-CQDs) and passivated carbon quantum dots (P-CQDs). There are two different important P-CQDs, namely 2,2'-ethylenedioxy-bis-ethylamine (EDA-CQDs) and 3-ethoxypropylamine (EPA-CQDs), that have achieved desirable results in the antiviral therapy field. Since NoV is the most common dangerous cause of nonbacterial, acute gastroenteritis outbreaks worldwide, this review deals with NoV in detail. The surficial charge status (SCS) of the P-CQDs plays an important role in their interactions with NoVs. The EDA-CQDs were found to be more effective than EPA-CQDs in inhibiting the NoV binding. This difference may be attributed to their SCS as well as the virus surface. EDA-CQDs with surficial terminal amino (-NH₂) groups are positively charged at physiological pH (-NH³⁺), whereas EPA-CQDs with surficial terminal methyl groups (-CH₃) are not charged. Since the NoV particles are negatively charged, they are attracted to the positively charged EDA-CQDs, resulting in enhancing the P-CQDs concentration around the virus particles. The carbon nanotubes (CNTs) were found to be comparable to the P-CQDs in the non-specific binding with NoV capsid proteins, through complementary charges, π-π stacking, and/or hydrophobic interactions.