Rapid Pathogen Purge by Photosensitive Arginine–Riboflavin Carbon Dots without Toxicity

Materials · 4 authors, 3 centres

AI SUMMARY

FIDELITY 100%

POPULATIONL929 fibroblast cells and common pathogens (Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Bacillus subtilis, Candida albicans)

INTERVENTIONArginine-riboflavin carbon dots (Arg-RBF CDs) with UV-A light exposure

COMPARISONUnmodified Arg CDs, Arg-FSS CDs, and dark conditions

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AGENT 01 · STRUCTURED SUMMARY

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TL;DR

This study developed photosensitive carbon dots (Arg-RBF CDs) by conjugating riboflavin to arginine-based carbon dots, which achieved total eradication of Bacillus subtilis within 30 minutes of UV-A exposure. The modified carbon dots showed high biocompatibility with 91.2% fibroblast cell viability and hemolysis below 5% at 1000 μg/mL. These findings suggest Arg-RBF CDs are promising for safe, rapid photodynamic antimicrobial therapy.

Full summary

3,181 CHARS

**Background:** Photodynamic therapy using photosensitive materials offers a promising approach for rapid microbial eradication by generating reactive oxygen species (ROS) upon light activation. Carbon dots (CDs) are biocompatible, inexpensive nanomaterials with antimicrobial potential. This study aimed to enhance the photodynamic antimicrobial activity of nitrogen-doped arginine carbon dots (Arg CDs) by conjugating them with fluorescein sodium salt (FSS) or riboflavin (RBF), both of which are non-toxic and used in clinical ophthalmic applications. The goal was to achieve rapid pathogen killing without toxicity, addressing limitations of previous modifications that caused toxic effects.

**Methods:** Arg CDs were synthesized via microwave-assisted carbonization of citric acid and arginine (3:1 weight ratio) at 1000 W for 3 minutes. The CDs were then conjugated with FSS or RBF using N,N'-carbonyldiimidazole (CDI) as a coupling agent. Characterization included HR-TEM, DLS, zeta potential, FT-IR, UV-Vis, and fluorescence spectroscopy. Cytotoxicity was assessed using L929 fibroblast cells with MTT assay at concentrations 50–1000 μg/mL. Hemocompatibility was evaluated via hemolysis and blood clotting assays at 1000 μg/mL. Antimicrobial activity was tested against Gram-negative (E. coli, K. pneumoniae), Gram-positive (S. aureus, B. subtilis), and fungal (C. albicans) pathogens using microtiter dilution to determine MIC. Photodynamic activity against B. subtilis was tested under UV-A light (315–400 nm, 300 W) for 5, 15, and 30 minutes, compared to dark conditions.

**Key Results:** Arg CDs were spherical, 0.5–5 nm in size, with a graphitic lattice spacing of 0.28 nm. Zeta potentials were −5.4 ± 4.8 mV (Arg), −15.8 ± 5.2 mV (Arg-FSS), and −24.5 ± 10.2 mV (Arg-RBF). Quantum yields at 345 nm excitation were 12.5 ± 0.2% (Arg), 11.9 ± 2.7% (Arg-FSS), and 8.1 ± 0.9% (Arg-RBF); at 520 nm excitation, Arg-FSS and Arg-RBF had QY of 9.1 ± 2.0% and 23.2 ± 5.6%, respectively. Cytotoxicity: at 1000 μg/mL, cell viability was 63.0 ± 6.5% (Arg), 77.8 ± 2.2% (Arg-FSS), and 91.2 ± 0.7% (Arg-RBF). Hemolysis ratios were 3.2 ± 0.6%, 2.9 ± 0.4%, and 3.3 ± 0.8% for Arg, Arg-FSS, and Arg-RBF, respectively (all <5%). Blood clotting indices were 85.9 ± 2.5, 84.6 ± 5.0, and 87.5 ± 6.5. MIC values (mg/mL) for Arg CDs: E. coli 3.12, K. pneumoniae 6.25, S. aureus 3.12, B. subtilis 1.50, C. albicans 6.25. Modified CDs showed approximately two-fold higher MIC values. Photodynamic testing: after 30 min UV-A exposure, Arg-RBF CDs reduced B. subtilis viability to 12 ± 6%, while Arg and Arg-FSS CDs showed ~50% viability. Under dark conditions, no significant inhibition was observed. UV-A alone resulted in 93 ± 3.8% bacterial viability.

**Clinical Implications:** Arg-RBF CDs demonstrate rapid, broad-spectrum antimicrobial activity upon UV-A activation with excellent biocompatibility, making them promising for photodynamic therapy applications such as treating corneal ulcers or other localized infections. The non-toxic nature at high concentrations (up to 1000 μg/mL) supports potential intravenous use. Further in vivo studies are needed to confirm safety and efficacy.

PICO

PPOPULATION

L929 fibroblast cells and common pathogens (Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Bacillus subtilis, Candida albicans)

IINTERVENTION

Arginine-riboflavin carbon dots (Arg-RBF CDs) with UV-A light exposure

OOUTCOME

Minimum inhibitory concentration (MIC), bacterial viability after UV exposure, cell viability, hemolysis ratio, blood clotting index

STUDY TYPE

other

SPECIALTY

ophthalmology

SUMMARISED BY

AI pipeline

FIDELITY CHECK

100% · A

ORIGINAL PAPER

PMC10573186

Rapid Pathogen Purge by Photosensitive Arginine–Riboflavin Carbon Dots without Toxicity

Materials

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ABSTRACT

Photo-activatable antipathogenic carbon dots (CDs) were prepared by carbonization of citric acid and arginine (Arg) via 3 min microwave treatment for use in the eradication of common microorganisms. Nitrogen-doped Arg CDs were spherical in shape with a size range of 0.5 to 5 nm. The Arg CDs were modified with fluorescent dyes, such as fluorescein sodium salt (FSS, as Arg-FSS) and riboflavin (RBF, as Arg-RBF), to improve antimicrobial potency by enhancing their application in photodynamic therapy. The modified Arg CDs afforded fluorescence emission properties at 520 nm in the green region in addition to excellent blue fluorescence intensity at 420 nm under 345 nm excitation upon their FSS and RBF conjugation, respectively. Although the cytotoxicity of Arg CDs was decreased for Arg-RBF CDs to 91.2 ± 0.7% cell viability for fibroblasts, the Arg-based CDs could be safely used for intravenous applications at 1000 μg/mL concentration. The Arg CDs showed broad-spectrum antimicrobial activity against common pathogens and the minimum inhibitory concentration of Arg CDs was almost two-fold decreased for the modified forms without UV light. However, faster and more effective antibacterial activity was determined for photosensitive Arg-RBF CDs, with total bacterial eradication upon UV-A light exposure for 30 min.

CITATION EXPORT

Selin S. Suner, Venkat R. Bhethanabotla, Ramesh S. Ayyala et al.. Rapid Pathogen Purge by Photosensitive Arginine–Riboflavin Carbon Dots without Toxicity. Materials. (2023). https://doi.org/10.3390/ma16196512

AUTHORS

4 · 3 CENTRES

Selin S. Suner, Venkat R. Bhethanabotla, Ramesh S. Ayyala, Nurettin Sahiner

1Department of Chemistry, Faculty of Sciences & Arts, and Nanoscience and Technology Research and Application Center (NANORAC), Canakkale Onsekiz Mart University Terzioglu Campus, Canakkale 17100, Turkey; [email protected]
2Department of Chemical, Biological, and Materials Engineering, Materials Science and Engineering Program, University of South Florida, Tampa, FL 33620, USA; [email protected]
3Department of Ophthalmology, Morsani College of Medicine, University of South Florida Eye Institute,12901 Bruce B Down Blvd, MDC 21, Tampa, FL 33612, USA; [email protected]

EDITOR / REVIEWER

Junkai Ren