Betul Ari

Background/Objectives: Carbon dots (CDs) are fluorescent carbon-based nanomaterials attracting considerable attention recently because of their high photostability, tunable luminescence characteristics, low toxicity, and versatile surface chemistry. In this study, Hematoxylin (HT), a naturally occurring phenolic aromatic compound used as a histological staining dye, abundant in hydroxyl functional groups, was selected as a sustainable precursor for CD synthesis. The intrinsic fluorescence and favorable carbonization characteristics of HT are also value-added advantages for CDs. Methods: The use of citric acid (CA) during synthesis improves fluorescence behavior, colloidal stability, and biological performance of CDs. HT-based CDs prepared via the bottom-up synthesis method employing the hydrothermal technique as multifunctional fluorescent materials were also evaluated for potential bioimaging and light-activated antimicrobial applications. Results: The obtained HT-based CDs displayed good aqueous dispersion properties. HT CDs had a hydrodynamic diameter of 115 ± 1 nm and showed a fluorescence emission intensity of 5181 a.u. at λ_em = 329 nm when excited at λ_ex = 300 nm. In contrast, HT:CA CDs prepared at a 1:1 HT-CA weight ratio had a hydrodynamic diameter of 310 ± 19 nm and exhibited a significantly higher fluorescence emission intensity, e.g., 31,840 a.u. at λ_em = 332 nm when excited at λ_ex = 300 nm. Antioxidant studies of HT CDs and HT CDs using four different assays revealed that the antioxidant capacity of HT was partially retained and exhibited a concentration-dependent response. Notably, HT:CA CDs demonstrated significantly enhanced antimicrobial performance under UV-A irradiation compared to HT CDs, with bacterial cell viability calculated as 13 ± 4% for HT:CA CDs and 59 ± 2% for HT CDs. Moreover, HT CDs and HT:CA CDs demonstrated significantly enhanced cytocompatibility on the L929 fibroblast cell line, high cell viability up to 200 μg/mL, versus toxic HT molecules even at 100 μg/mL. Conclusions: HT-based CDs, particularly HT:CA CDs, demonstrated favorable fluorescence, antioxidant, antimicrobial, and cytocompatibility properties, supporting their potential application as multifunctional fluorescent materials for bioimaging and light-activated antimicrobial applications.

Here, cryogels of cellulose derivatives, carboxymethylcellulose (CMC) with varying degrees of substitution (DS) of 0.7, 0.9, and 1.2 denoted as CMC ^0.7 , CMC ^0.9 , and CMC ^1.2 , and hydroxypropyl methylcellulose (HPMC) were prepared at cryogenic conditions, − 20 °C. The cryo-crosslinking reaction using divinylsulfone (DVS) as crosslinking at 100 mol% ratio cellulose-derivates (based on the repeating CMC and HPMC unit) is accomplished. The S–O peaks about 1100 and 1250 cm ⁻¹ wavelength in FT-IR spectra of cryogels and interconnected super pores in 50–500 µm size ranges from SEM images confirmed the chemical crosslinked CMC and HPCM cryogel synthesis. The DS of CMC influenced the swelling, degradation, and blood compatibility results of CMC-based cryogels. The CMC ^0.7 cryogel showed the highest swelling ratio%, 1991 ± 23% in PBS and highest hydrolytic degradation%, with 24 ± 4.8% weight loss within 7 days among all CMC-based cryogels. Additionally, all cellulose derivative cryogels were found to be hemocompatible with less than 3% hemolysis and more than 80% blood clotting index values and exhibited nontoxicity with more than 95% cell viability on L929 fibroblast even at high concentration, 1 mg/mL concentration. These findings indicate that these cryogels are excellent materials for tissue engineering and regenerative medicine as the porosity and degradation parameter can be readily controlled to promote cell proliferation and nutrient diffusion for different cells and tissues.

A facile and single-step synthesis of poly(L-Cysteine) (p(L-Cys)) particles through microemulsion polymerization using tetrakis(hydroxymethyl) phosphonium chloride (THPC) as crosslinker is accomplished for the first time. The L-Cys:THPC ratio in p(L-Cys) particles was calculated as 80:20% (by weight) with elemental analyses, and the generation of p(L-Cys) particles was confirmed. SEM imaging revealed a popcorn-like morphology of the p(L-Cys) particles with a 1–20 µm particle size range. The isoelectric point of p(L-Cys) particles was determined at pH 1.15 via zeta potential measurements. The hydrolytic degradation of p(L-Cys) particles was determined as about 85% within 3 h (by weight). The p(L-Cys) particles displayed excellent blood compatibility with a hemolysis % ratio of E. coli (Gram-negative, ATCC 8739) and a 2-fold reduction against S. aureus (Gram-positive, ATCC 6538). Additionally, the antioxidant capacity of p(L-Cys) particles was retained somewhat, measured as 0.14 ± 0.01 µM versus 2.25 ± 0.03 µM Trolox equivalent/g for L-Cys. Therefore, p(L-Cys) particles are versatile and offer a unique avenue for immense biomedical use.

Carbon dioxide (CO₂), one of the primary greenhouse gases, plays a key role in global warming and is one of the culprits in the climate change crisis. Therefore, the use of appropriate CO₂ capture and storage technologies is of significant importance for the future of planet Earth due to atmospheric, climate, and environmental concerns. A cleaner and more sustainable approach to CO₂ capture and storage using porous materials, membranes, and amine-based sorbents could offer excellent possibilities. Here, sucrose-derived porous carbon particles (PCPs) were synthesized as adsorbents for CO₂ capture. Next, these PCPs were modified with branched- and linear-polyethyleneimine (B-PEI and L-PEI) as B-PEI-PCP and L-PEI-PCP, respectively. These PCPs and their PEI-modified forms were then used to prepare metal nanoparticles such as Co, Cu, and Ni in situ as M@PCP and M@L/B-PEI-PCP (M: Ni, Co, and Cu). The presence of PEI on the PCP surface enables new amine functional groups, known for high CO₂ capture ability. The presence of metal nanoparticles in the structure may be used as a catalyst to convert the captured CO₂ into useful products, e.g., fuels or other chemical compounds, at high temperatures. It was found that B-PEI-PCP has a larger surface area and higher CO₂ capture capacity with a surface area of 32.84 m²/g and a CO₂ capture capacity of 1.05 mmol CO₂/g adsorbent compared to L-PEI-PCP. Amongst metal-nanoparticle-embedded PEI-PCPs (M@PEI-PCPs, M: Ni, Co, Cu), Ni@L-PEI-PCP was found to have higher CO₂ capture capacity, 0.81 mmol CO₂/g adsorbent, and a surface area of 225 m²/g. These data are significant as they will steer future studies for the conversion of captured CO₂ into useful fuels/chemicals.

Here, super-macroporous cryogel from a natural polysaccharide, pullulan was synthesized using a cryo-crosslinking technique with divinyl sulfone (DVS) as a crosslinker. The hydrolytic degradation of the pullulan cryogel in various simulated body fluids (pH 1.0, 7.4, and 9.0 buffer solutions) was evaluated. It was observed that the pullulan cryogel degradation was much faster in the pH 9 buffer solution than the pH 1.0 and 7.4 buffer solutions in the same time period. The weight loss of the pullulan cryogel at pH 9.0 within 28 days was determined as 31% ± 2%. To demonstrate the controllable drug delivery potential of pullulan cryogels via degradation, an antibiotic, ciprofloxacin, was loaded into pullulan cryogels (pullulan-cipro), and the loading amount of drug was calculated as 105.40 ± 2.6 µg/mg. The release of ciprofloxacin from the pullulan-cipro cryogel was investigated in vitro at 37.5 °C in physiological conditions (pH 7.4). The amount of drug released within 24 h was determined as 39.26 ± 3.78 µg/mg, which is equal to 41.38% ± 3.58% of the loaded drug. Only 0.1 mg of pullulan-cipro cryogel was found to inhibit half of the growing Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) colonies for 10 min and totally eradicated within 2 h by the release of the loaded antibiotic. No significant toxicity was determined on L929 fibroblast cells for 0.1 mg drug-loaded pullulan cryogel. In contrast, even 1 mg of drug-loaded pullulan cryogel revealed slight toxicity (e.g., 66% ± 9% cell viability) because of the high concentration of released drug.

Here, nitrogen-doped carbon dots (N-doped CDs) were synthesized by the hydrothermal method embedded within poly(lactic acid-co-glycolic acid) ((PLGA)) films at different amounts. The N-doped CDs (or CD) that possess fluorescence properties also have antimicrobial properties against S. aureus and E. coli microorganisms, determined by the disc diffusion method with 19 ± 2 and 18 ± 1 mm zone diameters, respectively. The CD embedded PLGA films (CD@PLGA) with different CD contents revealed an increased fluorescence intensity with the increased amount of CD. Moreover, the antibacterial potency of 50% CD containing PLGA (50-CD@PLGA) films (by weight) against S. aureus and E. coli microorganisms was examined and the zone diameters were found to be 14 ± 1 and 13 ± 1 mm, respectively. In addition, CD release studies from different amounts of CD (2.5–50 by weight) containing composite films showed that 50-CD@PLGA film released 127 ± 16 mg/g CD dots, which is 38 ± 5% of the embedded CDs in about 12 days, suggesting their potential application in food packing and wound dressing. Moreover, all CD@PLGA films were found to be blood compatible via hemolysis and blood clotting index tests with 90% blood clotting indices regardless of their CD content.

The biocompatible, viscoelastic properties of poly(vinyl alcohol) (PVA) in combination with the antimicrobial and antioxidant natural polyphenolic, tannic acid (TA), and the natural flavonoid and antioxidant curcumin (Cur), were used in the preparation of PVA:TA and PVA:TA:Cur cryogel composites using cryotropic gelation to combine the individually beneficial properties. The effect of TA content on the antioxidant and antimicrobial activities of PVA:TA cryogel composites and the antioxidant activities of PVA:TA:Cur cryogel composites was determined using Trolox equivalent antioxidant capacity (TEAC) and total phenol content (TPC) assays, and were compared. The PVA:TA:Cur cryogel composite showed the highest antioxidant activity, with a TEAC value of 2.10 ± 0.24 and a TPC value of 293 ± 12.00. The antibacterial capacity of the PVA:TA and PVA:TA:Cur 1:1:0.1 cryogel composites was examined against two different species of bacteria, E. coli and S. aureus. It was found that the minimum inhibition concentration (MIC) value of the PVA:TA:Cur 1:1:0.1 cryogel composites varied between 5 and 10 mg/mL based on the type of microorganism, and the minimum bactericidal concentration (MBC) value was 20 mg/mL irrespective of the type of microorganism. Furthermore, the hemocompatibility of the PVA:TA cryogel composites was evaluated by examining their hemolytic and coagulation behaviors. PVA:TA 1:1 cryogels with a value of 95.7% revealed the highest blood clotting index value amongst all of the synthesized cryogels, signifying the potential for blood contacting applications. The release of TA and Cur from the cryogel composites was quantified at different pH conditions, i.e., 1.0, 7.4, and 9.0, and additionally in ethanol (EtOH) and an ethanol–water (EtOH:Wat) mixture. The solution released from the PVA:TA cryogels in PBS was tested for inhibition capability against α-glucosidase (E.C. 3.2.1.20). Concentration-dependent enzyme inhibition was observed, and 70 µL of 83 µg/mL PVA:TA (1:1) cryogel in PBS inhibited α-glucosidase enzyme solution of 0.03 unit/mL in 70 µL by 81.75 ± 0.96%.

Cryogels attained from natural materials offer exceptional properties in applications such as tissue engineering. Moreover, Halloysite Nanotubes (HNT) at 1:0.5 weight ratio were embedded into CS cryogels to render additional biomedical properties. The hemolysis index of CS cryogel and CS:HNT cryogels was calculated as 0.77 ± 0.41 and 0.81 ± 0.24 and defined as non-hemolytic materials. However, the blood coagulation indices of CS cryogel and CS:HNT cryogels were determined as 76 ± 2% and 68 ± 3%, suggesting a mild blood clotting capability. The maximum% swelling capacity of CS cryogel was measured as 3587 ± 186%, 4014 ± 184%, and 3984 ± 113%, at pH 1.0, pH 7.4 and pH 9.0, respectively, which were reduced to 1961 ± 288%, 2816 ± 192, 2405 ± 73%, respectively, for CS:HNT cryogel. It was found that CS cryogels can hydrolytically be degraded 41 ± 1% (by wt) in 16-day incubation, whereas the CS:HNT cryogels degraded by 30 ± 1 wt %. There is no chelation for HNT and 67.5 ± 1% Cu(II) chelation for linear CS was measured. On the other hand, the CS cryogel and CS:HNT cryogel revealed Cu(II) chelating capabilities of 60.1 ± 12.5%, and 43.2 ± 17.5%, respectively, from 0.1 mg/mL Cu(II) ion stock solution. Additionally, at 0.5 mg/mL CS, CS:HNT, and HNT, the Fe(II) chelation capacity of 99.7 ± 0.6, 86.2 ± 4.7% and only 11.9 ± 4.5% were measured, respectively, while no Fe(II) was chelated by linear CS chelated Fe(II). As the adjustable and controllable swelling properties of cryogels are important parameters in biomedical applications, the swelling properties of CS cryogels, at different solution pHs, e.g., at the solution pHs of 1.0, 7.4 and 9.0, were measured as 3587 ± 186%, 4014 ± 184%, and 3984 ± 113%, respectively, and the maximum selling% values of CS:HNT cryogels were determined as 1961 ± 288%, 2816 ± 192, 2405 ± 73%, respectively, at the same conditions. Alpha glucosidase enzyme interactions were investigated and found that CS-based cryogels can stimulate this enzyme at any CS formulation.

Methyldopa is one of the important drugs used in the treatment of high blood pressure (hypertension). In addition to various methods such as chromatographic and spectrophotometric methods, electrochemical methods are used for the determination of methyldopa. However, poly (p-aminobenzene sulfonic acid), pen-tip graphite electrode (PGE) study was not found in the literature search. Modified electrodes are important because they increase the sensitivity of the analysis. Furthermore, electrochemical methods have advantages such as being faster and cheaper than other instrumental analysis methods, being more sensitive, not requiring long pretreatments in the preparation of samples. In this study, the glassy carbon electrode (GCE) was modified with poly(p-aminobenzene sulfonic acid) to prepare poly (p-aminobenzene sulfonic acid) -modified glassy carbon electrodes. Cyclic voltammetry (CV) technique was used for the electropolymerization process. Methyldopa was selected in various concentrations of phosphate pH 7.40 buffer, anodic and cathodic voltamograms were taken and oxidation and reduction properties were investigated. Measurements were taken at different scanning rates by CV technique and the current type of methyldopa was determined. Peak flow-concentration graphs were drawn from the measurements taken by Differential Pulse Voltammetry (DPV) technique and the linearity range was 0.020- 2.500 µM for modified-GCE and 0.020-2.820 µM for PGE. The limit of detection (LOD) was calculated as 0.006 µM for modified-GCE, 0.012 µM for PGE. The limit of quantification (LOQ) was calculated as 0.020 µM for modified-GCE and 0.040 µM for PGE.

In this study, dextran (DEX) cryogels were prepared using 50% divinyl sulfone (DVS) crosslinker based on the repeating unit of DEX, under cryogenic conditions via cryogellation technique. It was shown that DEX cryogels can be used as column fillers to remove toxic substances such as organic dye, methylene blue (MB), pesticide, and paraquat (PQ) which are harmful to the environment and human health. The maximum absorption capacity of 15 mg DEX cryogels was determined as 10.69±0.14 mg/g using 5 mL of 100 ppm MB dye in about seven minutes, and as 2.87±0.33 mg/g from 5 mL of 40 ppm PQ pesticide in about ten minutes. The reusability of DEX cryogel for MB was also examined. In the consecutive use of DEX cryogel weighing ~30 mg, initially cryogel absorbed 6.43±0.15 mg MB/g cryogel from 20 ppm 30 mL MB dye, but this value decreased to 4.71±0.48 mg MB/g cryogel after the fifth use. The same cryogel released the same amount of MB dye after the first use of 3.78±0.33 mg MB/g cryogel, but after the fifth use the release amount decreased to 0.92±0.38 mg MB/g cryogel upon treatment with 1 M 30 mL HCl solution. The adsorption kinetics of DEX cryogel for MB were also examined and the Langmuir isotherm model with a correlation coefficient of 0.9983 and the KL value of 0.36, representing the best fit amongst the other well-known models such as the Freundlich isotherm, Temkin, Elovich and Dubinin-Radushkevich.