Graphene-Conductive Ink Coated Laser Engraved Kapton Electrochemical Biosensor for the Detection of Dopamine and Interleukin 6

A novel electrochemical biosensor platform based on graphene conductive polyaniline ink and laser-engraved Kapton sensor has been developed for the detection of dopamine and IL-6. Dopamine is an important catecholamine neurotransmitter, and the abnormal concentration of dopamine has been linked to several neurological diseases. IL-6 acts as an important biomarker for prostate cancer detection. We have developed graphene-conductive Polyaniline ink (G-PANI) and laser-engraved Kapton sensor in this work. For the fabrication of the laser engraved sensor, CAD design has been utilized and the parameter of the laser system has been modified. We have used silver ink as contact pads and Autolab Potentiostat for the electrochemical analysis. Due to the superior electrical conductivity, graphene is an appealing sensing material. Conductive Polymers coupled with graphene exhibit better conductivity, tunable surface properties, superior biocompatibility, and stability. Polyaniline incorporated in graphene improves solubility in aqueous solutions and shows improved conductivity and stability. Doping with acids enhances and improves the electroactive behavior of Polyaniline, and so we have created a homogenous mixture of phytic acid, polyaniline, and graphene with a planetary mixer. The SEM images depict that the surface of G-PANI is smoother with the nanoporous structure with around 1 μm diameter. To evaluate the effectiveness of the developed electrode in detecting dopamine and IL-6, we have investigated electrochemical techniques (Cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS)) with Fe²⁺/Fe³⁺ redox pair. The Nyquist plots obtained from EIS are almost perfect semicircles (a characteristic of non-diffusion-limited electrochemical processes), with the diameter substantially dependent on charge transfer resistance(R_ct). The diameter of the Nyquist semicircle decreases with the increase of conductivity of the electrode surface and a shift to lower R_ct values. From the obtained equivalent circuit, G-PANI ink has a very low Rct value (13.5Ω), compared to the unmodified one (58.7 kΩ). We have analyzed the sensitivity of our proposed inks by using Cyclic Voltammetry with 3 µM dopamine in a basic medium (pH 7.4) with a scan rate of 0.08 V s^-1. The anodic peak current of the cyclic voltammograms (CVs) is 22.17 times higher than the unmodified laser-engraved Kapton sensor. The limit of detection (LOD) of the unmodified and modified sensor has been calculated over the range from 0.5 µM to 5µM dopamine. The G-PANI modified sensor has a much lower LOD (0.4084 µM) compared to the unmodified one (1.441 µM). The calibration curve shows a linear relationship (R²=0.99832 for G-PANI modified Kapton sensor) between the anodic peak current (I_PA) and dopamine concentrations. The sensor has been mildly oxidized by ozonolysis for about 30 sec to introduce -COO- groups for the immobilization. The equivalent circuit obtained from the EIS spectra has a higher Rct (1.87 kΩ) after ozonolysis, due to the inhibition of the electron transfer between the modified electrode and the negatively charged redox species. After IL-6 antibody immobilization, R_ct increased (12.5 kΩ) because IL-6 antibody film acts as a kinetic barrier for the electron transfer of the redox marker. Under optimal analysis settings, the analytical performance of the G-PANI modified Kapton sensor is tested in the presence of varying amounts of IL- 6 antigens utilizing EIS methods (frequency range 10 kHz to 10⁶ kHz). The limit of detection for IL-6 antigen detection was 62.1283 pg/ml. In the future, we will be working on developing flexible paper-based electrochemical sensors for environmental estrogen detection.