Plasma Assisted Control of Nanoparticle Distribution for Enhancing the Electrochemical Activity of Electrodes

Abstract

Introduction The performance of the biosensor is the reflection of the optimization of its attributes, such as selectivity, sensitivity, stability, and reproducibility. The enhancement in the sensitivity can be achieved by increasing the active surface area using nanoparticle (NP)-functionalized electrodes. NP-functionalized electrodes exhibit higher electric field intensities [1]. The surface architecture of these surface functionalized electrodes impacts on the response of the electrochemical biosensors. The sensor response depends on the size, shape, and surface attachment of nanoparticles [2]–[4]. In most of the sensing methods, the use of high-density NP causes polydispersity, and different orientations on the electrode surface conceal the effects of these factors[5], [6]. Hence to understand the effects of NP architecture on electrode response, the electrochemical performance of gold nanoparticles (Au NPs) deposited electrodes with drop casting, aerosolized deposition, and plasma assisted aerosolized deposition techniques are studied in this work. Methods Gold electrodes on Si/SiO2 substrate are fabricated using the evaporation technique. Au NPs of an average size of 20 nm, purchased from Sigma Aldrich are then deposited on fabricated electrodes to enhance the response due to the increase in surface area. Three different methods of nanoparticle deposition that were used are drop casting, aerosolized and plasma assisted aerosolized deposition[7]. The schematics of deposition techniques can be seen in figure 1. Figure 1a shows the drop casting deposition, 11b shows the aerosolized deposition, and 1c shows plasma set up. Cyclic voltammetry responses of gold electrodes with and without surface modification were recorded using CHI 1023 Instrument and were obtained in cyclic voltammogram obtained in 5mM [Fe (CN)6]3−/4−, as shown in figure 1. Results and Conclusions The peak current in cyclic voltammetry responses (figure1 d, 1e and, 1f) is enhanced 1.07 folds after drop cast gold NPs deposition, ~1.5 folds after aerosolized deposition, and ~3 folds after plasma assisted aerosolized deposition. The peak current is proportional to the electrochemically active surface area; hence, the surface area increase factor for plasma assisted aerosolized electrodes is ~3, as shown in fogure1. The separation between anodic and cathodic peaks (ΔE) for drop casted gold NPs deposited electrode is 60 mV, for aerosolized deposition is 395 mV and for plasma assisted aerosolized deposition is 561 mV. This decrease in separation between Faradaic peak potential after the NP deposition indicates that the electron transfer reaction is kinetically and thermodynamically favored at the electrode surface. The Au anodic and cathodic peaks are suppressed after NP deposition. The enhancement in the overall response of the electrode and the active surface area were achieved. This enhancement was achieved because of comparatively even distribution of nanoparticles during aerosolized and plasma assisted deposition than drop casted. The nanoparticles were sonicated properly during deposition using nebulizer in aerosolized deposition technique assembly. The plasma provided the surface excitation and surface charge tuning during plasma assisted deposition. The promising results have shown in this work will help improve the reproducibility of the sensors by quantifying the NP coverage on the electrode surface. The supervised interparticle and NP-electrode interaction will improve biosensing by demonstrated work with desired surface architecture during optimization of the sensing process. The issues caused by the random orientation of NPs will be resolved with understanding their effects with the optimized process. It will make the data interpretation easier using the presented work.