Development and characterization of hybrid films based on agar and alizarin red S for applications as non-enzymatic sensors for hydrogen peroxide

For the first time, the dye alizarin red S (ARS) was immobilized on indium tin oxide (ITO) electrodes via a layer-by-layer technique (LbL). This was achieved only when ARS was interspersed with the polymers agar (extracted from seaweed Gracilaria birdiae ) and PAH [poly(allylamine hydrochloride)]. ARS alone did not show electroactivity when adsorbed onto ITO. Single-walled carbon nanotubes (functionalized with COOH, denoted CNTs) were used to increase the electrochemical signal of the LbL system. Interactions at the molecular level between the CNTs and other materials used in the construction of the films accounted for a threefold increase in the current signal of ARS. The films were developed as trilayer films of agar/PAH/ARS or agar(CNT)/PAH(CNT)/ARS and characterized by differential pulse voltammetry (DPV) and UV–visible spectroscopy and scanning electron microscopy. From the results, it was also possible to calculate the energy diagram for both films. The results showed that the films are promising for applications as electrochemical sensors. Accordingly, the agar(CNT)/PAH(CNT)/ARS film was tested for the reduction of hydrogen peroxide (H 2 O 2 ). Under a constant potential of −0.5 V versus SCE (saturated calomel electrode), the film exhibited a rapid response for the reduction of peroxide (less than 5 s), and the current stabilized approximately at 30 s. The limit of detection for the amperometric sensor was approximately 0.15 µmol L −1 .