Shakiba Tolou-Shikhzadeh-Yazdi - Department of Biology, Faculty of Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Niloofar Shakibapour - Department of Biology, Faculty of Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Sare Hosseini - Cancer Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
Parisa Mokaberi - Department of Biology, Faculty of Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Bizhan Malaekeh-Nikouei - Nanotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran
Jamshidkhan Chamani - Department of Biology, Faculty of Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran

Objective(s): In this work, we propose an efficient preparation process for the synthesis of natural carbon quantum dots (NCQDs) by the usage of orange pericarp as the carbon natural resource, which is performed through hydrothermal treatment and top-down approaches.Materials and Methods: The structural, morphological, average size, and optical properties of synthesized NCQDs were investigated via dynamic light scattering (DLS), transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), field emission scanning electron microscope (FESEM), energy dispersive x-ray spectroscopy (EDX), ultraviolet-visible spectroscopy (UV-Vis), and fluorescence PL spectra.Results:  The shape of obtained NCQDs was observed to be spherical in the results of TEM analysis with an average size of ۶–۷ nm which confirms NCQDs essence. The signs of a strong peak (absorption) at around ۲۸۲ nm throughout the UV-vis spectrum have been detected. The provided FTIR spectroscopy confirmed the existence of functional groups above the NCQDs surface. Furthermore, the surface charge of -۱۱ mV through the obtained zeta potential regarding the synthesized NCQDs has been identified. MTT assay on mouse colon carcinoma cells (C۲۶) demonstrated the lack of any signs of toxicity in NCQDs. Conclusion: The obtained NCQDs contain high photo-stability, excellent PL activity, and efficient fluorescent emission based on excitation. The results of kinetic studies revealed the ability of NCQDs to inhibit trypsin activity in a non-competitive model, which qualifies them as potent inhibitors and quenchers of trypsin. It can be suggested that the synthesized NCQDs have the potential of functioning as a sustainable and eco-friendly source for various applications such as sensors for detecting Ca۲+ and Zn۲+ and trypsin biosensor for determining enzyme activity.

Carbon quantum dots, Enzyme activity, FESEM, Hydrothermal method, Ions detection, Orange pericarp