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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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    BPEI-Based N-Doped Carbon Dots with Sensitive and Selective Cu2+ Ion-Sensing Ability
    (Mdpi, 2025) Demirci, Sahin; Torres, Jorge H.; Sahiner, Nurettin
    In this research, we examined the potential sensor characteristics of branched polyethyleneimine (BPEI)-derived carbon dots (CDs) synthesized using BPEI as a nitrogen source and citric acid (CA) as a carbon source, specifically for the recognition of various metal ions. Among the BPEI CDs produced with different amounts of BPEI to CA BPEI:CA ratios of 0.5:1, 1:1, and 2:1 w/w, named as BPEI0.5 CD, BPEI1 CD, and BPEI2 CD, respectively. The BPEI0.5 CD, which contains the least BPEI, exhibited the highest fluorescence intensity: 50,300 a.u. in a 0.6 mg/mL solution were recorded as lambda(em): 420 nm at lambda(ex): 360 nm and 600 V PMT voltage with 5 nm of slit width for both excitation and emission. We investigated the fluorescence variations in BPEI CD-based CDs in 2 mL solutions containing Cd2+, Co2+, Cu2+, Ni2+, and Pb2+ metal ions at various concentrations. Amongst these metal ions, the most pronounced sensitivity was noted for Cu2+ ions with a limit of detection (LOD) value of 0.39 ppm. For BPEI CDs created with BPEI:CA ratios of 0.5:1, 1:1, and 2:1 w/w, the sensitivity to Cu2+ ions increased with a higher BPEI ratio, with a LOD value of 0.30 ppm recorded for BPEI2 CDs. Moreover, Cu2+ ion solutions were prepared from various salts, including chloride, acetate, nitrate, and sulfate; aside from some fluorescence variation observed for BPEI0.5 CDs, no significant difference in BPEI CD fluorescence change was observed with the use of the various salt solutions of Cu2+ ion. In quenching experiments conducted on mixtures of Cd2+, Co2+, Cu2+, Ni2+, and Pb2+ metal ions with Cu2+, it was noted that BPEI CDs displayed selectivity for Cu2+ ions. Furthermore, the structures of BPEI CDs have been effectively utilized in real water samples, such as tap water and seawater, demonstrating a quenching capability of over 65% in the presence of 50 ppm Cu2+ ions.
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    Characterization of branched and linear polyethyleneimine by trapped ion mobility-time of flight-mass spectrometry
    (Elsevier B.V., 2026) Atakay, Mehmet; Demirci, Sahin; Sahiner, Nurettin; Salih, Bekir
    Background: Polyethyleneimine (PEI) is a common polyelectrolyte that is used in many areas, such as drug delivery, gene therapy, and water treatment. This is because it has a highly branched structure, functional amine groups in its repeating unit, and a high cationic charge density. To understand the behavior and function of PEI, it is important to accurately describe its structure. The ion mobility-mass spectrometry method is expected to yield structural insights into PEI's molecular architecture, encompassing variations in branching patterns, chain conformations, and the potential presence of isomeric forms. Results: The difference in zeta potential values between B-PEI and L-PEI can be attributed to the distinct types of functional amine groups present in their structures. The trapped ion mobility-time of flight-mass spectrometry (TIMS-ToF-MS) technique was used in this study to elucidate the molecular architecture of linear and branched PEI with varying polymeric distributions of ion series and end groups, concentrating on its dimensions, morphology, conformational variations, variable cationic adducts (Na+, K+, Li+, and Ag+), and charge states (+1 and + 2). The singly charged ions, like those in the main series and fragment series of PEI, are more compact than doubly charged ions because of the change in charge repulsion. TIMS, in conjunction with mass spectrometry, facilitated high-resolution separation of PEI conformers according to their collision cross-section (CCS) values and charge states. Significance: The findings indicated that PEI displays a wide range of both compact and extended molecular conformations at various m/z ratios, with specific populations associated with varying branching levels, cationic adducts, and charge distribution. The influence of various metal ions on PEI conformation was examined, indicating substantial alterations in CCS values under diverse conditions of analysis. Hyphenated TIMS and MS technologies make a strong analytical platform for studying polymer structures in depth. © 2026
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    Modification of cyclodextrin-based microgels with 2-hydroxymethyl-12-crown ether-4 for higher and selective Li+ ion adsorption from aqueous medium
    (Taylor & Francis Inc, 2026) Demirci, Sahin; Salih, Bekir; Sahiner, Nurettin
    The cyclodextrin (CD) oligosaccharides derived materials, e.g., p(alpha-CD), p(beta-CD), and p(gamma-CD) microgels were used in Li + ion adsorption studies, which revealed 55.4 +/- 3.9, 85.1 +/- 3.8, and 117.8 +/- 4.9 mg Li+/g, respectively, in 12 h from 500 mg/L 100 mL aqueous solutions. The Li+ ion adsorption by p(CD)-based microgels is best described by pseudo-first-order adsorption kinetics and Freundlich adsorption isotherms, with higher R-2 values. There is no significant selectivity observed for any microgels to Li + ions in the presence of Na+, K+, and Ca2+ ions. However, the relative selectivity (kl) calculation among the adsorbents revealed that p(beta-CD) microgels afforded higher selectivity than p(alpha-CD) and p(gamma-CD) microgels, with kl values greater than 1. Therefore, to further increase selectivity, p(beta-CD) microgels were modified (M-p(beta-CD)) with 2-hydroxymethyl-12-crown ether-4, known for its specificity for Li + ion. The adsorbed amount of Li+ ions by M-p(beta-CD) microgels was determined as 91.9 +/- 1.9 mg Li+/g, a slight increase with respect to the unmodified microgel upon 12 h contact time. Interestingly, the selectivity of M-p(beta-CD) microgels toward Li+ ion for Li+/Na+, Li+/K+, and Li+/Ca2+ was measured as 3.1, 4.5, and 5.1-fold higher, respectively, than bare p(beta-CD) microgels. Also, M-p(beta-CD) microgels retained >80% adsorption capacity of Li+ ions after 5 consecutive uses. Microgels employing cyclodextrin, particularly beta-CD systems demonstrated an effective and reusable adsorption capability for Li+, and the selectivity is markedly enhanced amid competing ions via the functionalization with crown ethers. [GRAPHICS]
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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.