Copper and Palladium NWs for Hydrogen Peroxide detection

H2O2 is a wide used chemical in different field, like in paper and textile industries and pharmaceutical applications. Furthermore, H2O2 concentration in human body is related to glucose concentration because the reaction between glucose and glucosidase produce hydrogen peroxide [1] . Moreover, is used as a biomarker of oxidative stress, being an oxidative specie [2] . For all these reasons, researcher all over the world are working to develop new and novel strategies for in situ, non-invasive and fast detection of this chemical. One of these fields concern the electrochemical sensors, that are sensors with an electrical (current, potential, impedance) output. The surface area the electrodes in these kind of sensors is highly important being able to enhance the features of the sensor, mainly in terms of sensitivity [3] . Nanostructured electrodes made of Nanowires (NWs), Nanotubes (NTs) or Nanoparticles (NPs) are so perfect candidates as electrochemical sensors: the surface area can increase over 70 times.Furthermore, using nanostructures is possible to have miniaturized, portable, cheap and wearable sensors [5] . In this work we show the performances of a novel electrode of Pd-NWs, growth by galvanic deposition into the pores of a polycarbonate membrane, as sensor for hydrogen peroxide. Briefly, a polycarbonate membrane is sputtered with a thin film of gold, in order to make it conductive and then a 12µm copper current collector is electrodeposited on top of it. Using a conductive carbon paste, the current collector is electrically coupled with an aluminum tube and immersed in a solution containing Pd ions. In this way the galvanic reactions occurs dissolving the aluminum tube and depositing the Pd ions into the pores of the membrane. The polycarbonate membrane is then dissolved by etching in pure dichloromethane [6] . The effect of different parameters, like pH, anodic to cathodic area ratio and Pd concretions, was checked and the process has been optimized in order to have a reproducible and fast deposition. We obtained stable and self standing nanostructures with an average height of 5.1 µm after 40 mins of galvanic deposition. The electrodes were characterized by scanning electrode microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). These electrodes has been polarized at -0.2V vs Ag/AgCl in a solution of PBS 0.1M and ethanol increasing the H2O2 concertation over time, recording the output current. We found that the hydroalcholic solution is essential in order to improve the scarce wettability of the nanostructured electrode. We tested the effect of the surface area as well by testing a commercial Pd-thin film and self-made Pd-NWs electrodes with different length of NWs (obtained stopping the galvanic deposition at 10, 20 and 30 mins). We found that the sensitivity of the electrodes increase with the surface area, going from 0.0788 µA µM-1 cm-2 for the planar electrode to 0.368 µA µM-1 cm-2 using 5.1 µm NWs. With 40 mins of deposition we obtained a Limit of detection (LOD) of 13.3 µM and a linear range from 53 to 4400 µM. We also tested the reproducibility and the selectivity of the sensor. When the tested concentration is in the middle of the linear range the electrode is highly accurate and reproducible, with an error lower than 5%. Ascorbic acid (AA), Uretic Acid (UA), Glucose (GLU) and Potassium Oxalate (POX) were tested as interference chemicals and we found an excellent selectivity towards these chemicals with no appreciable changes, also in solutions containing H2O2 at concentration an order of magnitude lower than the interference species. Finally we checked the lifetime of the electrode: after 1 month of storage in PBS solution the sensitivity of the electrode decrease and a new calibration is necessary.