**4. Conclusions**

In this work, three Nbs for NOD-R were selected from a Bactrian camel phage display library, and N56 showed high stability and good affinity. Then, an ic-ELISA method for NOD-R detection was established, with a LOD lower than 1.0 μg/L, the generally reference value for cyanobacteria toxins. In a thorough comparison with UPLC–MS/MS, the ic-ELISA method exhibited good accuracy and reliability, which suggests its potential for the development of a rapid detection kit for the safety detection of toxins based on N56.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/foods10112758/s1, Figure S1: Comparison of the expression levels of three nanobodies (Nb-T3-15, Nb-56, Nb-3F9) by SDS-PAGE; Figure S2: Results of ethical review of animal experiments. (**a**) Original copy. (**b**) English translation; Table S1: Abbreviation list.

**Author Contributions:** Conceptualization, J.Y. and R.S.; methodology, G.W., R.S. and R.F.; validation, H.W. and R.S.; resources, H.L., F.L., J.Y. and Q.Z.; data curation, Y.W., G.W. and R.S.; writing-original draft preparation, G.W., R.S. and R.F.; writing—review and editing, J.Y., F.W., H.W.; supervision, H.W. and Y.S.; project administration, H.W. and J.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the National Key R&D Program of China (2019YFE0116600), Natural Science Foundation of China (31972157), Key-Area Research and Development Program of Guangdong Province (2019B020211002), Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (2017), Lingnan Modern Agricultural Science and Technology Guangdong Laboratory independent scientific research project (NZ2021032).

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by Experimental Animal Ethics Committee of South China Agricultural University (protocol code 2020F061, 5 August 2020) (Figure S2).

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