## 4 Conclusions  
In this contribution, the amperometric CPE/MWCNTs/TYR/Nafion(r) biosensor behavior is demonstrated in the analysis of various kinds of berries. After several steps of optimization, the determination of TEAC in strawberries, blackberries, raspberries, blueberries, and cranberries was performed. The highest content of polyphenolic compounds expressed as TEAC values was found for cranberries (6378 mg/100 g) and raspberries (5317 mg/100 g) in dry matter and furthermore their pulp; cranberries (935 mg/100 g) and raspberries (793 mg/100 g). Contrary to this, the lowest TEAC value was found for strawberries in dry matter (1569 mg/100 g) and in pulp (133 mg/100 g). The obtained results were compared to the reference method of DPPH assay, as well as to the data of other methods (ORAC, TRAP, FRAP), based on the spectrophotometry taken from literature. It can be stated that our results from the presented TYR biosensor are in satisfactory correlation with above mentioned DPPH assay. For ORAC and TRAP assays, values of correlation coefficient higher than 0.9 can be achieved, excluding raspberries. It has to be mentioned that the results obtained by the biosensor exhibit a negative error, due to the presence of nonphenolic compounds, mainly AA. Therefore, TYR biosensor is suitable for determination of \"total phenolic content\" and \"total antioxidant capacity\" for samples with low content of non-polyphenolic antioxidants. It has also one disadvantage, namely its stability, which results from lifetime of present TYR enzyme; hence, the current response starts to decrease approximately after one week. The developed biosensor offers a portable device for rapid quality control of the foodstuff in terms of their freshness and nutritional value. It could bring some favorable features, like low costs, simple instrumentation, measuring of turbid samples, working with less hazardous chemicals, etc. It is by no means a replacement of spectrophotometric assays, but an alternative to them. The electrochemical approach could also serve as a complementary method to already established ones, which could bring additional information about analyzed samples, reflecting their electrochemical properties directly.  
The following are available online at [[http://www.mdpi.com/2076-3417/10/7/2497/s1](http://www.mdpi.com/2076-3417/10/7/2497/s1)]([http://www.mdpi.com/2076-3417/10/7/2497/s1](http://www.mdpi.com/2076-3417/10/7/2497/s1)). Figure S1: Effect of carbon nanotubes content in DMF dispersion on the anodic and cathodic peak potentials, Figure S2: Dependency of peak current on different volumes of MWCNTs, Figure S3: Typical amperometric responses of the CPE/MWCNTs/TYR/Nafion(r) biosensor, Scheme SI: Proposed mechanism of p-quinone reduction by ascorbic acid.  
Conceptualization, M.S., A.M.A., R.M.; methodology, M.S.; formal analysis, M.S., A.F., T.A.; electrodes characterisation, M.V.; authors of manuscript, M.S., A.F., A.M.A.; final correction, V.A., L.R. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Czech Science Foundation (project 19-03160S).  
This work was financially supported by the Czech Science Foundation (project 19-03160S).  
The authors declare no conflict of interest.