The hydrothermal method, a quick, easy, and economical way to synthesize nanoparticles, was used to synthesize the CDs by precursors from the extract solution of coriander leaves and CaCl2.

The dynamic light scattering (DLS) analysis result (Fig. 2a, b) illustrates how CDs are monodispersed, with hydrodynamic particle sizes of about 6 nm and zeta potentials of around − 10.8 mV. The SEM and TEM images demonstrated that the spherical CDs, with a particle size of about 6 nm, were effectively synthesized (Fig. 2c, d).

DLS shows that (a) particle size is monodisperse and around 6 nm. (b) The Zeta potential of the nanoparticle is negative and around − 10.8 mV. (c) TEM and (d) SEM images of synthesized CDs show spherical morphology with good dispersion and homogeneous particles

The surface elemental analysis of CDs was performed using energy-dispersive X-ray spectroscopy (EDS) with elemental mapping (Fig. 3). It demonstrates that the O, C, N, Ca, Mg, K, Cl, and Na make up the majority of the CDs’ surface. The most important minerals in the coriander are O, C, N, Ca, Mg, K, and Na; these elements are transferred to the CD’s structure following the synthesizing process and CDs have been able to inherit the characteristics of the original source very well [32, 33]. In addition, since the CaCl2 is used as a precursor in CDs, the Cl is also doped to the structure as well; This result shows that the Ca successfully doped to the structure.

To determine the chemical components, functional groups, and surface composition of the extracted coriander leaves and synthesized CDs, Fourier transform infrared (FT-IR) spectra were employed (Fig. 3a). The results show the presence of a variety of functional groups as is common in plant extracts.

Both spectra have large peaks around 3423 cm− 1 and 3436 cm− 1 (synthesized carbon dots); they are indicative of the existence of O-H and N-H stretching vibrations, which are frequently found in amines, phenols, and alcohols. The 1622 cm− 1 and 1051 cm− 1 peaks in the coriander leaves that are moved in the synthesized carbon dots to 1635 cm− 1 and 1073 cm− 1 respectively (potential C-O and C = O stretching), indicating that these groups play a role in CD synthesis.

The synthesized carbon dots exhibit peaks at 1145, 1452, and 1565 cm− 1, indicating the presence of additional peaks not clearly seen in the coriander leaf spectrum that indicate the emergence of new bands. While the FTIR signal from the coriander leaves, at 1397 cm− 1, reveals C-H bonds, the synthesized carbon dots exhibit additional peaks at 1386 cm− 1, suggesting changes or new functional groups due to the synthesis process. In coriander leaves, the Mg-N stretching in chlorophyll has a pronounced peak around 500–700 cm− 1; in synthesized carbon dots, this peak is nearly absent, indicating that the structure of the chlorophyll has changed after the synthesized process. This outcome aligns with the Excitation and Emission result (Fig. 4), which shows that following the CD synthesizing procedure, the coriander leaves’ red chlorophyll emission changed to blue under the UV lamp. Overall, the comparison of the FTIR spectra shows that some of the original functional groups from the coriander leaves have been maintained in the synthesized carbon dots from the leaves and that the synthesis process has either introduced new bonds or made them more apparent.

According to the XRD results (Fig. 3d), the examined nanoparticle has an almost amorphous overall structure. The broad peak is around 25˚, which is equivalent to a 0.34 nm lattice spacing; such a hump has been frequently seen in amorphous carbon XRD patterns. The XRD pattern that was observed also roughly matched the standard diffraction pattern [Ref. Code 96-201-0755] [50].

(a) FT-IR spectrum of CDs. (b) CD elemental mapping images showing the distribution and presence of the generally distributed elements C, O, N, Ca, Mg, Cl, and Ca. (c) EDS spectra for CDs. (d) XRD diffraction pattern of CDs

According to Uv-vis absorption (Fig. 4), the peaks that have been observed within the range of 240–300 nm and 300–390 nm are associated with π → π* and n → π* transitions of C = C, C − C, and C = O [51]. The peak between 300 and 390 nm altered in the CD-dCDs, indicating that the synthesis was successful. This finding is consistent with the FTIR data, which indicate that the predominant stretching involved in the synthesis of carbon nanoparticles was in the functional bands of C = O and C-O.

The CDs have a maximum excitation of around 360 nm, according to the PL spectra (Fig. 4), and the emission peak is red-shifted to around 500 nm when the excitation wavelength is raised from 320 nm to 400 nm. In the meanwhile, the peak emission occurs at 480 nm is inside the visible blue light spectrum. As a result, we see the quantity of blue emission from CD nanoparticles under the gel doc (Fig. 4e); whereas, the Corriador extract’s red emission under gel doc is caused by the presence of chlorophyll which this finding indicates that the synthesis of carbon dots was successful and the raw Corriador extract’s structure changed during the synthesis process. The distribution of surface states of nanoparticles with varying energy levels is linked to the excitation-dependent emission performance of CDs whereas CDs emit blue light. The quantum yield was determined to be 15% based on the research presented by Williams et al. [52] and the excitation and emission of CD nanoparticles.

(a) Uv − vis results in different wavelengths (from 300 to 1000) for Coriander leaf extracts and CDs. (b) Excitation of the CDs. (c) Emission spectra of CDs at different excitation wavelengths. (d) emission of Coriander leaf extracts and CD samples under the gel doc

A variety of CD concentrations (5%, 10%, and 15% of the CS weight) were used as a crosslinking agent in this study, and a range of BEX concentrations (10%, 20%, and 40% of the CS weight) were added to the CS matrix via the simple casting method. When the various concentrations of doped carbon dots were compared, the CDs 10% made good cross-link in CS, the optimal balance between strength and ductility (Fig. 5), and resulted in a stable structure with maximum uptake of BEX. In the higher concentration of CDs, the uptake of BEX decreased and the structure was so rough with low flexibility which is consistent with the results of the SEM (Fig. 6) and force-extension curve (Fig. 5). The maximum concentration of uptake BEX was 40% which in the higher concentrations than 40% the amount of sediment showed after the synthesizing process indicates the limitation of BEX uptake, so the final film produced based on CDs 10% and BEX 40%. Because of its plasticizing and bioactive properties, glycerol was also used in the formation of the nanohydrogel film.

The force-extension curves for the CS film, CS/CD 5%, CS/CD 10%, and CS/CD 15% are displayed in Fig. 5. Each sample has an initial linear section that displays a forced rise that is proportionate to extension, illustrating elastic behaviour. The yield point and Ultimate Tensile Strength (UTS) in the blank film are lower than in crosslinked films, and it shows some plastic deformation before breaking, suggesting moderate ductility. CS films that have CDs incorporated as crosslinkers exhibit a notable improvement in their mechanical features, including yield strength, stiffness, and UTS. Strength and ductility have a trade-off; greater CD concentrations make films stronger but may also make them less flexible. The 10% CD concentration seems to give an excellent balance between strength and ductility, making it perhaps the best choice for applications requiring both features. Over-crosslinking (e.g., 15% CDs) might lead to increased fragility, which might not be desired for all applications.

(a) Stress, (b) elongation at break, and (c) tensile strength of the CS, CS/CD with different CDs

The SEM pictures of the blank, CS/CD 10%, and final film are shown in Fig. 6. According to the SEM pictures, the surface morphology of every film is consistent; yet, the surface morphology of the nanocomposite was somewhat altered to a rougher state by adding CDs and BEX which this result is consistent with the tensible result.

The UV-visible absorbance result (Fig. 6b) shows absorbance across the entire unvisible spectrum by the blank film. After cross-linking the film by CDs, an absorption peak around 280 nm with a peak around 320 nm, potentially from n-π* transitions in aromatic compounds (likely from carbon dots) [25, 51, 53]. The final film absorbance is similar to the CS/CD 10% around 280–320 nm; however, there is an additional peak around 500 nm which aligns with the previous studies and the UV-visible absorbance result of the Bistorta family [54]. All things considered, this outcome demonstrates the final film’s successful synthesis.

(a) FTIR results for Cs film (blank), CS/CD 10%, and final film. (b) Uv − vis results in different wavelengths (from 200 to 1000) for blank, CS/CD 10%, and final film, (c) The swelling ratio in PBS (pH 7.4) at 37 °C for the CS, CS/CD 10%, and final film, and (d) SEM result of blank, CS/CD 10%, and final film

The FT-IR spectra of CS, CS & CDs 10%, and the final film are considered to have demonstrated the effective construction of the nanohydrogel film and the comprehension of the chemical interactions and alterations in the film structure (Fig. 6).

All three films show prominent peaks in the regions around 3400 cm− 1, 1600 cm− 1, 1400 cm− 1, and 600 cm− 1. These peaks typically indicate the presence of O-H and N-H stretching vibrations, C = O stretching vibrations, C-O stretching vibrations in the carboxylate group stretching vibrations, and N-H stretching vibrations in primary amine groups (NH₂) in out-of-plane bending vibrations, respectively. CS’s hydroxyl functional and amine groups can form hydrogen bonds and electrostatic interactions, respectively, with the carboxylate functional groups in the CDs [55].

The 1100–1000 cm− 1 region is indicative of C-O stretching vibrations in blank film, characteristic of polysaccharides which is almost constant in CD 10% and final film.

Unique peaks in the final film at 1078 cm− 1 and 978 cm− 1, and variations in peak intensities even in the common peaks, suggest different chemical interactions or additional functional groups present in the final film compared to the other samples which these differences reflect the structural modifications and new interactions introduced by the CDs or BEX in the CS matrix.

The films’ swelling behavior in PBS (pH 7.4) at 37 °C is shown in Fig. 6c. The produced nanohydrogel films’ capacity to absorb wound moisture is directly correlated with the swelling findings. It was demonstrated that when immersion time increased, the swelling ratio increased considerably. By adding CDs and BEX to the CS polymeric matrix, the swelling ratio is reduced which may be according to the crosslinking of the CS that resulted in increasing the hydrogel network’s hardness [56]. Moreover, incorporating BEX could make the film more robust and decrease the swelling rate. The polyphenols, tannins, and other bioactive substances in BEX can create additional crosslinks within the film, improving its overall stability [45, 46, 49] which is consistent with the SEM results (Fig. 6d).

The blood clotting capacity is an essential feature of biomaterials-based wound dressings. Figure 7 displays the blood clotting study’s findings the results show that adding 10% of CD in films has improved its blood clotting capacity. These results could be due to the inheritance of calcium from the coriander as well as additionally calcium doped into the CDs’ structure (32, 33). After incorporating BEX, the blood clotting ability of the CS film significantly increased and matched the effectiveness of commercial gauze and other studies [18, 27].

The hemolytic effects were respectively increased by the hemolysis rate to 8.96% with crosslinking the film with CDs in the formulation process and the increase continues with the addition of BEX to 18.22%. The majority of the hemolysis often occurred after the extract was added; however, the final film hemolysis was less than 20% (Fig. 7). Additionally, the optical picture in Fig. 7 showed the treated films’ supernatant containing red blood cells which is insignificant when compared to the negative control (PBS). With its exceptional blood clotting index, the synthesized film is the preferred option for use as a wound application.

The cytotoxicity of the CS, CS/CD 10%, and final film on HFF-1 cell lines was tested using the MTT method (Fig. 7) and even after 48 h, nearly 80% of the samples’ cell viability was maintained.

The results indicate that the cytotoxicity of hydrogels was slightly enhanced with treatment time and the amount of CDs and BEX in the nanohydrogel. So there is a direct correlation between the concentration of these substances employed in nanohydrogel films and the toxicity of the films. This good result and low toxicity are due to the use of biological precursors in film synthesis [7, 39]. Based on the findings, produced films could offer an effective and safe basis for wound dressing.

The antibacterial activity of the produced films was investigated using disc diffusion techniques against microorganisms S. aureus and E. coli (the most popular gram-positive and gram-negative bacteria) in order to explain their antibacterial performance [57, 58] (Fig. 7).

(a) Hemolysis rate, (b) Blood clotting index (c) Cell viability of Blank, CS/CD 10%, and final films after incubation with human blood and human red blood cells (erythrocytes). Images of the antibacterial inhibition zones for CS, CS/CD 10%, and final film against (d) E.Coli and (e) S.Aureus

Figure 7 displays that after cross-linking with CDs and adding the BEX into the structure, the antibacterial property of the film has significantly increased (especially against E.Coli) compared to the blank CS film, which is a sign of the antibacterial property of the precursors used and is consistent with the previous studies [34, 39].