article · Scientific Reports
Water-soluble, fluorescent nitrogen-doped carbon quantum dots were successfully prepared using castor seeds as a sole precursor through a green hydrothermal process. The resulting nanoparticles are spherical and amorphous, with an average diameter of 6.57 nanometres and surface functional groups including carboxylic and hydroxyl moieties. These quantum dots display excitation-dependent blue fluorescence, strong photostability, and a quantum yield of approximately 9.6 percent. Their fluorescence intensity exhibits a sensitive linear response across acidic and basic pH ranges, enabling the creation of dual fluorescent pH sensors. Furthermore, the nanoparticles demonstrate notable aqueous stability with a negative zeta potential, antimicrobial activity, and low cytotoxicity toward WI-13 cells. The findings confirm that castor-seed-derived quantum dots offer practical utility in pH sensing and antimicrobial roles, while showing potential for biological cell imaging, optoelectronics, and thermal sensing.
Using agricultural precursors such as castor seeds offers an eco-friendly and cost-effective route to manufacture advanced nanomaterials. Because these quantum dots display low cellular toxicity alongside stable fluorescence and antimicrobial properties, they present safer alternatives to conventional heavy-metal quantum dots for monitoring biological environments and measuring pH fluctuations.
This work represents early-stage laboratory research demonstrating that castor seed biomass can be converted into functional nanomaterials. Potential applications include diagnostic reagents, laboratory pH sensors, and antimicrobial coatings. Developers of optical sensing devices, biotechnology firms, and medical researchers could benefit from this process, though real-world deployment will require further optimisation of quantum yield, toxicity validation, and industrial scale-up testing.
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Abstract Water-soluble fluorescent N-doped carbon quantum dots (N-CQDs) were hydrothermally prepared through a green synthesis route using castor seeds as a single precursor and a hydrothermal method. Several experimental techniques have been used to characterize synthesized N-CQDs to confirm their structure and to verify their applicability in cell imaging and pH sensing. The synthesized N-CQDs were found to have are characterized by amorphous nature with a spherical shape with an average particle size of 6.57 nm as revealed from XRD and TEM measurements. The FTIR results reveal the presence of carboxylic and hydroxyl functional groups on the surface of the CQDs, which was also confirmed by XPS analysis. The fluorescence characterization of the synthesized N-CQDs showed blue emission and excitation dependence with good photostability. It was found that the optimal excitation and emission wavelengths were (λ Ex = 360) and (λ Em = 432) nm, respectively. The fluorescence quantum yield (QY) of about 9.6% at the optimum excitation wavelength 360 nm. Moreover, the fluorescence intensity of N-CQDs showed good linear dependence with the pH values in ranges of 3.5 − 7.5 and 8 − 12 as well as high sensitivity for slight changes of pH values. According to these results, two fluorescent pH sensors were created based on acidic and basic media. The obtained N-CQDs have zeta potential of -21.86 mV and thus have excellent stability in water. Moreover, N-CQDs derived from the castor seeds have antimicrobial activity and exhibits low cytotoxicity to WI-13 cells with IC 50 = 394.4 ± 13.8 µg/mL. The results of this study demonstrated that the synthesized N-CQDs derived from castor seeds can be used as pH sensing and antimicrobial materials. On the other hand, they are also promising in applications in cell imaging, thermo-sensing and optoelectronics.
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DOI: 10.1038/s41598-024-78745-0
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