Simple green routes for the customized preparation of sensitive carbon nanotubes/epoxy nanocomposite electrodes with functional metal nanoparticles Jose Mu ˜ noz, Julio Bastos-Arrieta, Maria Mu ˜ noz, Dmitri Muraviev, Francisco C ´ espedes and Mireia Baeza * In this communication, we report novel, simple and effective methodologies for the incorporation of functional metal nanoparticles in carbon nanotubes/epoxy nanocomposite electrodes. The incorporation of nanoparticles was obtained by three different routes: (a) in situ functionalization of carbon nanotube surfaces, (b) incorporation and dispersion into a composite matrix and (c) composite surface modification by drop-attachment. These techniques offer a customized route for the preparation of sensitive amperometric sensors. Independent of the route of noble metal nanoparticle incorporation, the final result is a significant enhancement of the electroanalytical response. Introduction Carbon nanotubes (CNTs) represent an important group of nanomaterials, which are used in different applications since their discovery because of their remarkable electrical, chemical, mechanical, thermal and structural properties. 1–3 Currently, signicant interest is focused on nanocomposites based on CNTs, especially in multiwalled carbon nanotubes (MWCNTs), because of their electrocatalytic activity. The unique qualities of MWCNTs make them highly attractive for the development of CNTs-based chemical (bio)sensors, in general, and electro- chemical detection, in particular. 4–8 Furthermore, CNTs can be considered as feasible supports for heterogeneous catalysts such as functional metal nanoparticles (FMNPs). 9–11 Recently, FMNPs have been used extensively in the elds of physical, chemical and material sciences because of their surface-volume ratio that provides them unique properties different from the analogous bulk material. 12–14 Modied-CNT electrodes combined with these nanoparticles have shown excellent electrocatalytic activity because of the fast electron transfer ability of CNTs, 15,16 as can be seen in the electrochemical detection of hydrogen peroxide and glucose. 17,18 Accordingly, FMNPs have received considerable attention for their catalytic and electrochemical features for the preparation of amperometric sensors and biosensors, 19–21 leading to an enhancement of the electron transfer between redox centers in the analyte and electrode, decreasing the overpotentials of several analytically important electrochemical reactions. 22,23 Despite these advantages, the surface modication of CNTs with nanocrystals as FMNPs usually involves thermal evapora- tion, 24 electroless deposition by galvanic replacement, 25 MNPs hydrosol absorption 26 or electrochemical deposition. 27 Greener synthesis routes have also been used for the preparation of FMNPs on CNTs, such as seed-mediated growth, 28,29 in which metal salt solutions can be reduced by a strong reducing agent (e.g. NaBH 4 ) at room temperature and in an aqueous solution. The possible aggregation of the FMNPs limits their application in electrochemical systems. Because of this fact, the preparation of FMNPs must provide an extra level of stability and a favour- able distribution in the nal nanocomposite material. 20 Regarding this, the intermatrix synthesis (IMS) technique becomes a valid FMNPs preparation methodology. IMS takes advantage of the ion-exchange properties of the support matrix (e.g. sulfonic resins, CNTs) for consecutive loading and reduc- tion processes during the synthesis of FMNPs with a favourable distribution in the nal composite material. 30,31 IMS is based on the following two sequential steps: i. Introduction of the FMNPs precursors into the polymer by loading their functional groups with the desired metal ions or metal complex precursors of the nanoparticles. ii.Their reduction to zero-valent state inside the support matrix is carried out by using an appropriate reducing agent such as NaBH 4 or ascorbic acid. Eqn (1) and (2) present the classical IMS on cationic exchangers (e.g. carboxylic functionality): 2[R–COO  H + ]+M 2+ / [R  COO  ] 2 M 2+ + 2H + (1) Departament de Qu´ ımica, Facultat de Ci` encies, Universitat Aut` onoma de Barcelona, Edici C-Nord, Cerdanyola del Vall` es (Bellaterra), Barcelona, 08193, Spain. E-mail: mariadelmar.baeza@uab.cat; Tel: +34 93581 4927 Cite this: RSC Adv. , 2014, 4, 44517 Received 18th July 2014 Accepted 27th August 2014 DOI: 10.1039/c4ra07294d www.rsc.org/advances This journal is © The Royal Society of Chemistry 2014 RSC Adv. , 2014, 4, 44517–44524 | 44517 RSC Advances PAPER