A facile green synthesis of photoluminescent carbon dots using Pumpkin seeds for ultra-sensitive Cu2+ and Fe3+ ions detection in living cells

Abstract

A facile and efficient green synthesis of photoluminescent carbon dots (CDs) was achieved using pumpkin seeds (PS) through the hydrothermal-carbonization method. Pumpkin seeds, well-known for their nutrient-rich composition, offer potential health benefits, including heightened fertility, enhanced heart health, and improved blood sugar regulation. The as-synthesized PS-CDs characterization through UV–vis, photoluminescence (PL), FTIR, XRD, and HR(TEM) analysis. The PL PS-CDs exhibited an excitation-dependent behavior, with the peak shifting from 410 nm to 475 nm under excitation wavelengths ranging from 270 nm to 400 nm. Notably, the synthesized PS-CDs displayed outstanding advantages, such as a high fluorescent quantum yield of 12.7 % with bright blue emissions when exposed to UV light at 365 nm. High-resolution TEM images revealed an average size of approximately 4.0 ± 0.2 nm for the synthesized PS-CDs, ranging from 2 to 7 nm with interlayer distance of 0.21 nm. PL spectra of PS-CDs solution, with an excitation wavelength of 338 nm and emission wavelength of 420 nm, were examined in the presence of various metal ions (50 μM). The fluorescence lifetime of the PS-CDs showed an exponential curve, with an average lifetime (τav) of 8.47 ns for Cu2+and 3.61 ns for Fe3+ ions, respectively, which is strongly indicates that quenching occurs through a static mechanism. The PS-CDs exhibited high sensitivity and selectivity towards Cu2+ and Fe3+ ions, with a linear relationship observed up to a concentration of 50 μM and detection limits of 0.43 and 0.11 μM (S/N = 3), respectively. Moreover, the low-toxicity and strongly fluorescent PS-CDs were successfully applied for cell imaging. The practical utility of the developed sensor was determined through the analysis of Cu2+ and Fe3+ ions in spiked water samples, highlighting its considerable analytical and bioanalytical applications.