**4. Conclusions**

The electrode modification with PPy-NTs/AuNPs has shown to be rapid, straightforward, and reliable for the construction of biosensors. This hybrid material was used as a platform for SAM layers, followed by the anchoring of different biomolecules, indicating a potential application in different types of biosensors and recognition elements. All characterization experiments corroborated the influence of the nanometric architecture on the electrochemical response for the detection and quantification of different analytes, with the RCT parameter showing the most sensible response for the biological recognition of the biological markers. The nanostructures also are responsible for the possibility of detection in the range of femtomolar to picomolar, corroborating the great sensitivity achieved by the combination of the nanostructures, specific adsorption, and impedance technique.

**Author Contributions:** Conceptualization, A.E.D., J.V. and A.L.S.; methodology, A.E.D. and J.V.; validation, A.E.D. and A.L.S.; investigation, A.E.D., J.V., D.E.P.S. and M.V.; data curation, A.E.D., J.V. and J.G.A.R.; writing—original draft preparation, A.E.D.; J.V. and D.E.P.S.; writing—review and editing, A.E.D. and M.V.; supervision, D.E.P.S. and M.V.; project administration, D.E.P.S. and M.V.; funding acquisition, D.E.P.S. and M.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by CAPES (Finance Code 001), FAPESP (grant no. 2014/50867-3), and CNPq (grant no. 465389/2014-7).

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

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank Centro de Microscopia Eletrônica da UFPR for microscopic analysis.

**Conflicts of Interest:** The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

**Figure A1.** EDS spectra were obtained for the characterization of the electrode modified with PPy (**A**) and the electrode modified with PPy/AuNPs (**B**).

**Figure A2.** Characterization of the PPy/AuNPs-based biosensor construction steps for the Avidin-HRP/Biotin couple. Cyclic voltammograms (**A**,**B**) show the characterization of different steps in the construction of the platform-based biosensor, and the Nyquist diagram (**C**) is for the same characterization.


**Table A1.** Parameters' values obtained by EIS to PPy e PPy/AuNPs, in electrode modification steps.

**Table A2.** Parameters' values obtained by EIS to PPy e PPy/AuNPs for stabilization tests using 0.001 pmol L<sup>−</sup>1.


**Figure A3.** Adsorption test of different antibody concentrations (0.001, 0.67, 3.30, and 6.60 pmol L<sup>−</sup>1), using a modified electrode only with PPy. Cyclic voltammograms (**A**), Nyquist diagram (**B**).

#### **References**

