Electrochemical characterization of mono- and multilayer DSPA films absorbed onto ITO

ALEXIS PECCI GENARO; VALERIA PFAFFEN; TOMÁS E. BENAVIDEZ; CANDELARIA I. CAMARA

Cordoba

Congreso; LI Reunión Anual de la Sociedad Argentina de Biofísica; 2023

Sociedad Argentina de Biofísica

In order to obtain biologically active surfaces, different modification techniques have been applied onto solid substrates (conductive materials, polymers, etc.) since the last decades of the 20th century. Immobilization methods driven by physical and chemical interactions were developed. Particularly, Langmuir-Blodgett deposition enable highly controlled lipidic films stabilized by film-substrate physical interactions. This means an interesting advantage when the modification process requires an accurate and controlled deposition. In this work, distearoylphosphatidic acid (DSPA) was used to modify ITO (Indium Tin-Oxide) substrates by the Langmuir-Blodgett technique. DSPA was deposited onto ITO at 40 mN.m-1 with a resulting transfer rate of 0.97 to finally obtain mono- and multilayered DSPA films. The DSPA films were then characterized by Cyclic Voltammetry, Electrochemical Impedance Spectroscopy, contact angle, and AFM. The electrochemical experiments were carried out in a 50 mmol.L-1 phosphate buffer solution containing 5 mmol.L-1 K3Fe(CN)6/K4Fe(CN)6 at pH = 7.6.Results: The experimental results shown that DSPA films were able to be adsorbed onto ITO electrodes.When a DSPA monolayer was obtained, the DSPA-modified ITO displayed an increased surface hydrophobicity (higher contact angle) and the electrode roughness (AFM) decreased considerably (ANOVA). In addition, DSPA monolayer was able to blocked partially the electrochemical behavior of Fe2+/Fe3+ couple. Accordingly, the 80% of the electrochemical active surface area was blocked. This blocking effect remained constant within the evaluated time range (50 h). According to EIS results, an increased impedance modulus was observed as well as the resistance of charge transfer (RCT). As DSPA deposition number increased (multilayered DSPA films), the blocking ratio reached about 95% and the Fe2+/Fe3+ behavior was almost completely inhibited. This effect was corroborated by the increased value of total impedance and the RCT as well. AFM images also demonstrated an increase of surface roughness and the contact angle analysis showed angle values higher than those observed by the monolayer.The experimental results demonstrated that DSPA was able to develop stable LB films onto hydrophilic substrates (ITO). Also, the electrochemical techniques were helpful tools to study DSPA layers adsorbed onto conducting materials. In this regard, DSPA films can be considered as stable modifying platforms to attach biological molecules like proteins (enzymes, SpA, antibodies) to then be applied in the development of biosensors.