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    A Comparative Study of Nitrogen Doped Carbon Dots Prepared from Linear Polyethyleneimine (L-PEI) and Branched Polyethyleneimine (B-PEI): Thermal, Optical, Biocompatibility, Sensor, Antibacterial, and Light-Induced Antibacterial Activity
    (Springer/Plenum Publishers, 2025) Demirci, Sahin; Suner, Selin S.; Sahiner, Mehtap; Akcali, Alper; Guven, Olgun; Sahiner, Nurettin
    The N-doped carbon dots (CDs) prepared in the presence of citric acid (CA) as carbon source, using linear poly(ethylene imine) (L-PEI) and branched poly(ethylene imine) (B-PEI) as nitrogen doping agents were prepared via hydrothermal/solvothermal technique at 250 degrees C in a Teflon-lined autoclave. The zeta potentials of L-PEI CDs and B-PEI CDs were determined as + 9.8 +/- 4 and 0.1 +/- 0.5 mV with 47 +/- 3 and 54 +/- 5 nm sizes, respectively. Bandgap values for L-PEI CDs and B-PEI CDs were estimated as 3.06 and 3.37 eV, respectively. The fluorescence intensities of L-PEI CDs and B-PEI CDs were measured as 59,310(a.u.), and 46,370(a.u.) at 474 and 442 nm, respectively, under 400 and 320 nm excitation wavelengths and 700 V PMT voltage. A higher quantum yield% value was observed for L-PEI CDs with 37 +/- 2.9%. Both L-PEI CDs and B-PEI CDs were found biocompatible up to 1000 mu g/mL concentration with > 80% L929 fibroblast cell viability. The limit of detection (LOD) values for Fe3+ by L-PEI CDs and B-PEI CDs were determined as 0.58 and 2.14 mg/mL, respectively. Both L-PEI CDs and B-PEI CDs at 10 mg/mL concentration resulted in 50% bacterial killing for gram-negative E. coli, gram-positive B. subtilis, and yeast C. albicans microorganisms. Also, the light activation of L-PEI CDs and B-PEI CDs induces almost 70 and 40% bacterial killing for gram-positive B. subtilis in 30 min. Moreover, they have a limit of detection (LOD) value of 0.58 mg/mL for Fe3+ ions, in addition to exhibiting biocompatibility and antibacterial properties.
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    Gd(III) and Fe(III) ion crosslinked hyaluronic acid microgels composites embedding hetero atom doped carbon quantum dots render photodynamic therapy with improved bioimaging capability
    (Elsevier Science Sa, 2026) Suner, Selin Sagbas; Sahiner, Mehtap; Umut, Evrim; Sahiner, Nurettin
    In this study, we report the development of multifunctional CQ-dot@HA-Gd/Fe(III) microgels that can be readily simultaneously used in fluorescence/MR dual-mode imaging and photodynamic therapy as theragnostic agents. Nitrogen (N-) and sulfur (S-) heteroatom-doped carbon quantum dots (CQ-dot) were prepared in one step microwave treatment within 3 min as a fluorescence and photoinduced antipathogenic nanomaterial. The N/Sdoped CQ-dots were spherical shaped and < 50 nm via TEM images and showed high fluorescence intensity with 420 nm emission wavelength at maximum lambda(ex):350 nm. The N/S-doped CQ-dots were embedded into ionically crosslinked hyaluronic acid (HA) microgels, employing trivalent metal ions Gd(III) or Fe(III) ions. The prepared CQ-dot@HA-Gd/Fe(III) microgels <5 mm size range are injectable for possible intravenous administration and possess high fluorescent properties. The isoelectric point (IEP) of CQ-dot@HA-Gd and CQ-dot@HA-Fe (III) microgels was determined as pH 1.45. The CQ-dot@HA-Gd/Fe(III) microgels exhibit excellent hemocompatibility without causing noticeable hemolysis and blood clotting at concentrations up to 500 mg/mL. Furthermore, the toxicity of CQ-dot@HA-Gd/Fe(III) microgels on L929 fibroblast cells was found as 100 mg/mL concentration and provide brilliant cell imaging under DAPI filter without any fluorescence dye. Also, the CQdot@HA-Gd/Fe(III) microgel suspension afforded great MRI contrast enhancement ability. Photoinduced anticancer activity was observed for CQ-dot@HA-Gd/Fe(III) microgels even at 50 mg/mL against SK-MEL 30 melanoma cells under UV-A light treatment for 30 min. In addition, high reactive oxygen species (ROS) generation was obtained for the pathogenic bacteria cells by light-sensitive CQ-dot@HA-Gd/Fe(III) microgels upon 30 min UV-A light treatment that triggered the destruction of the Staphylococcus aureus (ATCC 6538).
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    Polyethyleneimine-Modified Piezoelectric Barium Titanate of Various Sizes Reveals Improved Antibacterial Properties
    (Wiley, 2026) Sahiner, Nurettin; Demirci, Sahin; Lako, Alba; Torres, Jorge H.; Suner, Selin S.; Sahiner, Mehtap
    The piezoelectric materials, barium titanates (BaTiO3) in various sizes 50, 200, and 500 nm, were modified with polyethyleneimine (PEI) as PEI@BaTiO3 to improve antibacterial activities. The realization of PEI modification was confirmed with the peaks appeared on the Fourier transform infrared (FTIR) spectrum of BaTiO3 nanoparticles similar to 1650 cm-1, which are assigned to N-H stretching vibrations. The isoelectric points of BaTiO3 nanoparticles increased to about pH 10 after PEI modification, which were pH 3-4 range for pristine BaTiO3 nanoparticles. BaTiO3 nanoparticles below 200 nm showed antibacterial activity against gram-negative bacteria with 25 mg/mL minimum inhibition concentration (MIC) value but determined not effectively against gram-positive pathogens. However, positively charged PEI@BaTiO3 particles render high antibacterial potency on wide range of bacteria with almost four-fold lower MIC values than pristine BaTiO3 nanoparticles. Safe concentration of BaTiO3 nanoparticles on L929 fibroblast cells was found at 100 mu g/mL with more than 90% cell viability. Cytotoxicity was slightly decreased for PEI@BaTiO3 particles, and 50 mu g/mL concentration of PEI@BaTiO3 particles could be used in vivo applications without any significant toxicity. The piezoelectric effect of pristine BaTiO3 generated a higher voltage for 50 nm particles compared to the larger particles. Also, PEI@BaTiO3 generated voltages, somewhat attenuated and rapidly decayed in time, showed high consistency.
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    Single, Double, and Multiple-Heteroatoms Doped Carbon Quantum Dots as Effective Light-Induced Antimicrobial Materials
    (Springer/Plenum Publishers, 2025) Suner, Selin Sagbas; Sahiner, Mehtap; Demirci, Sahin; Sahiner, Nurettin
    Single-, dual-, and multi-heteroatoms such as N, S, and B-doped carbon quantum dots (CQ-dots) were prepared to determine their dopant effects on anti-pathogenic activities. The CQ-dots were prepared using maleic acid (MA), poly(vinyl amine) (PVAm), cysteine (Cys), and boric acid (BA) as carbon, nitrogen, sulfur, and boron sources, respectively. In 345-415 nm emission wavelength range, 45.9 +/- 2.4% quantum yield for dual heteroatom-doped (N/B-doped) CQ-dots were attained. Antimicrobial studies revealed that N-doped CQ-dots have significant antimicrobial susceptibility to both bacteria and fungi. The zeta potential value of N-doped CQDs had -4.9 mV was changed to -9.2 and -11.5 mV upon N/S- and N/B-doping, respectively. N/B-doped CQ-dots afforded the highest antibacterial activity providing a 1.56 mg/mL minimum inhibitory concentration (MIC) value against Escherichia coli, whereas N/S-doped CQ-dots had the highest antimicrobial activity against Staphylococcus aureus and Candida albicans yeast, 0.37 mg/mL MIC values. The photodynamic antimicrobial studies of N-, N/S-, N/B-, and N/S/B-doped CQ-dots significantly eradicated the bacteria and fungus colony upon UV-A light exposure for 30 min, with > 50% microbial colonial inhibitions. Both N and N/S-doped CQ-dots exhibit higher biofilm eradication/inhibition efficacy on Candida albicans biofilm, and all CQ-dots are biocompatible according to blood compatibility and cytotoxicity analysis at 1000 mu g/mL.
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    Transformation of Cytotoxic Linear Polyethyleneimine (L-PEI) Into Biocompatible and Hemacompatible Crosslinked Particles With Antimicrobial Properties
    (Wiley, 2025) Demirci, Sahin; Suner, Selin S.; Sahiner, Mehtap; Guven, Olgun; Sahiner, Nurettin
    Linear polyethyleneimine (L-PEI) microgel/particles were prepared using glycerol diglycidyl ether (GDE) as crosslinker at various mole ratios, 10%, 25%, and 50% of L-PEI repeating unit, and designated as L-PEI-1, L-PEI-2, and L-PEI-3, respectively. All microgels were found blood compatible with < 2% hemolysis and > 80% blood clotting indexes at 1000 mu g/mL concentrations, whereas L-PEI is hemolytic (> 80% hemolysis). Similarly, L-PEI showed cytotoxicity on L929 fibroblasts even at 50 mu g/mL, while > 80% cell viability was observed for L-PEI-based particles even at 1000 mu g/mL. Although it is regarded as less cytotoxic than branched PEI, the cross-linked L-PEI particles effectively circumvent cytotoxicity as the most important limitation of L-PEI in biological applications. Additionally, the higher antimicrobial activity against Escherichia coli, gram-negative bacteria, Bacillus subtilis, gram-positive bacteria strains, and Candida albicans, yeast strains was observed for L-PEI-1 and protonated L-PEI-1 particles. Moreover, the antibacterial activity of L-PEI-1 particles was further improved after the inclusion of Ag(I) and Cu(II) ions within L-PEI particles as Ag@L-PEI-1 and Cu@L-PEI-1 composites, respectively. The lower MIC and MBC values were determined for Ag@L-PEI-1 particles against Escherichia coli and Bacillus subtilis as 0.079 and 0.312 mg/mL, respectively, and an MFC value for Candida albicans was 0.156 mg/mL for Ag@L-PEI-1 particles.