**4. Conclusions**

This study provided an effective strategy to prepare SeCS using CS as a stabilizing agent. Using the reaction system at reaction conditions of a Na2SeO3:Vc ratio of 1:8, 0.1 mg/mL CS,a3hreaction time and a 25 ◦C reaction temperature could generate spherical SeCS nanoparticles of 131.3 ± 4.4 nm in diameter with a high selenium entrapment efficiency (33.18%). These amorphous SeNPs were suggested to interact with CS via physical adsorption, and exhibited pH stability (pH > 8) and storage stability at 4 ◦C for 28 days. Moreover, SeCS exerted a stronger in vitro antioxidant capacity than SeNPs and CS. These results confirmed the higher stability and the improved antioxidant properties of SeNPs capped with CS compared to SeNPs. Taken together, SeCSs have the potential to further develop a dietary supplement to apply in the prevention and alleviation of oxidative stress-related diseases.

**Author Contributions:** J.C. and X.C. designed the experiment and wrote the paper. X.C., J.L., B.L. and T.F. performed the experiments. J.C. and X.C. analyzed the data. R.L., X.L., B.S., X.J. and S.Z. participated in experimental design and contributed regents and materials. J.C. and S.Z. coordinated the studies. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Key-Area Research and Development Program of Guangdong Province (grant number: 2020B1111030004), Guangdong Basic and the Applied Basic Research Foundation (grant number: 2020A1515010860 and 2021A1515012455), the Guangdong Ocean University Innovation Program (grant number: 230419100), the Nanhai Youth Scholar Project of Guangdong Ocean University (grant number: QNXZ201909), the Project of Science and Technology of Zhanjiang

City (grant number: 2020A01034), the Scientific Research Foundation of Guangdong Ocean University (grant number: R17034), the Guangdong Province ordinary universities characteristic innovation project (grant number: 2020KTSCX051), and the Guangdong Provincial Department of Education and the Innovative Team Program of High Education of the Guangdong Province (grant number: 2021KCXTD021).

**Institutional Review Board Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **References**

