Preparation, characterization, and application in biosensors of functionalized platforms with poly(4-aminobenzoic acid)

Electropolymerization of 4-aminobenzoic acid (4-ABA) on graphite electrodes (GEs) was investigated for the development of electrochemically functionalized platforms applied to the immobilization of biomolecules. The electrogeneration of 4-ABA was carried out in perchloric acid solutions using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. In the case of CV studies, the GEs were modified by applying 100 consecutive potential cycles, while, in the case of CA studies, the electrodes were modified at different potentials (E/V vs. Ag/AgCl): 0.95, 1.05, and 1.15. The modified GEs were characterized in HClO₄ solutions in the presence and absence of the ferricyanide/ferrocyanide redox couple (redox probe) using the CV and electrochemical impedance spectroscopy techniques. Scanning electron microscopy was used for morphological characterization. In the case of CA, the best electrochemical activities for the electropolymerization reaction are in the following order of performance: 1.05 > 1.15 > 0.95 V. The poly(4-ABA) platforms were investigated for the immobilization and direct detection of purine bases (adenine and guanine), where higher values of the anodic peak current (I _p,a) were observed for the transducers electroformed using CV. In the case of immobilization of poly(GA) oligonucleotides, as well as for the recognition of the hybridization event with the complementary target poly(CT), methylene blue (MB) and ethidium bromide (EB) were used as the indicator and intercalator, respectively. MB was reduced at −0.26 V resulting in the cathodic peak current (I _p,c) for the ssDNA, while EB was oxidized at +0.58 V yielding the higher anodic peak current (I _p,a) for the dsDNA. The platforms were also evaluated for immobilization of the DD K peptide, with the antibacterial activity and biological recognition being verified using the complementary (phospholipid 1-palmitoyl-2-oleoyl phosphatidylcholine—POPC) and noncomplementary (phospholipid POPC + cholesterol) targets. The recognition mechanism was monitored from impedance measurements, with a good interaction of the DD K peptide with the POPC mimetic membrane being verified. In addition, the interaction was affected by the presence of cholesterol, revealing that the use of poly(4-ABA) platforms is very promising for the development of biosensors.