nanomaterials Article 3,4-Methylenedioxypyrovalerone (MDPV) Sensing Based on Electropolymerized Molecularly Imprinted Polymers on Silver Nanoparticles and Carboxylated Multi-Walled Carbon Nanotubes Rosa A. S. Couto 1 , Constantino Coelho 1 , Bassim Mounssef Jr. 2 , Sara F. de A. Morais 2 , Camila D. Lima 3 , Wallans T. P. dos Santos 4 ,Félix Carvalho 5 , Cecília M. P. Rodrigues 6 , Ataualpa A. C. Braga 2 , Luís Moreira Gonçalves 2, * and M. Beatriz Quinaz 1, *   Citation: Couto, R.A.S.; Coelho, C.; Mounssef, B., Jr.; Morais, S.F.d.A.; Lima,C.D.; dos Santos, W.T.P.; Carvalho, F.; Rodrigues, C.M.P.; Braga, A.A.C.; Gonçalves, L.M.; et al. 3,4-Methylenedioxypyrovalerone (MDPV) Sensing Based on Electropolymerized Molecularly Imprinted Polymers on Silver Nanoparticles and Carboxylated Multi-Walled Carbon Nanotubes. Nanomaterials 2021, 11, 353. https:// doi.org/10.3390/nano11020353 Academic Editor: Cosimino Malitesta Received: 22 December 2020 Accepted: 25 January 2021 Published: 1 February 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 REQUIMTE, LAQV, Laboratory of Applied Chemistry, Department of Chemical Sciences, Faculty of Pharmacy, University of Porto, 4050-213 Porto, Portugal; rcouto@ff.up.pt (R.A.S.C.); tino44coelho@gmail.com (C.C.) 2 Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo (USP), São Paulo, SP 05508-000, Brazil; bassim.mounssef@usp.br (B.M.J.); sara.famorais@usp.br (S.F.d.A.M.); ataualpa@iq.usp.br (A.A.C.B.) 3 Departamento de Química, Universidade Federal dos Vales do Jequitinhonha e Mucuri, Diamantina, MG 39100-000, Brazil; camila.lima@ufvjm.edu.br 4 Departamento de Farmácia, Universidade Federal dos Vales do Jequitinhonha e Mucuri, Diamantina, MG 39100-000, Brazil; wallanst@ufvjm.edu.br 5 REQUIMTE, UCIBIO, Laboratory of Toxicology, Department of Biological Sciences, Faculty of Pharmacy, University of Porto, 4050-213 Porto, Portugal; felixdc@ff.up.pt 6 Research Institute for Medicines (iMed.ULisboa), Faculty of Pharmacy, Universidade de Lisboa, 1649-003 Lisbon, Portugal; cmprodrigues@ff.ulisboa.pt * Correspondence: lmgoncalves@iq.usp.br (L.M.G.); bquinaz@ff.up.pt (M.B.Q.) Abstract: 3,4-methylenedioxypyrovalerone (MDPV) is a harmful and controlled synthetic cathinone used as a psychostimulant drug and as sport-enhancing substance. A sensor was developed for the direct analysis of MDPV by transducing its oxidation signal by means of an electropolymerized molecularly imprinted polymer (e-MIP) built in-situ on the screen-printed carbon electrode’s (SPCE) surface previously covered with multi-walled carbon nanotubes (MWCNTs) and silver nanoparticles (AgNPs). Benzene-1,2-diamine was used as the functional monomer while the analyte was used as the template monomer. Each step of the sensor’s development was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a solution containing ferricyanide, however no redox probe was required for the actual MDPV measurements. The interaction between the poly(o-phenylenediamine) imprinted polymer and MDPV was studied by density-functional theory (DFT) methods. The SPCE-MWCNT-AgNP-MIP sensor responded adequately to the variation of MDPV concentration. It was shown that AgNPs enhanced the electrochemical signal by around a 3-fold factor. Making use of square-wave voltammetry (SWV) the developed sensor provided a limit of detection (LOD) of 1.8 μmol L –1 . The analytical performance of the proposed sensor paves the way to the development of a portable device for MDPV on-site sensing to be applied in forensic and doping analysis. Keywords: analytical chemistry; ‘bath salts’; biomimetics; drug analysis; electropolymerization; elec- troanalysis; forensic chemistry; modified electrodes; new psychoactive substances (NPS); o-phenylenediamine 1. Introduction Methylenedioxypyrovalerone (MDPV), also known as “Magic”, “Vanilla Sky”, “Ivory Wave”, “Super Coke”, or “Energy 1” is one of the many synthetic cathinones intentionally Nanomaterials 2021, 11, 353. https://doi.org/10.3390/nano11020353 https://www.mdpi.com/journal/nanomaterials