Desenvolvimento de tintas condutivas para eletrodos impressos e sua aplicação em imunossensor eletroquímico para Sars-Cov-2

Abstract

Despite the potential of printed electrodes for low-cost diagnostics, their performance is still limited by the ink formulation, which affects film stability and the connectivity between conductive particles. In this research, conductive ink based on the copolymer VINNOL® H 15/50 and carbon fillers were developed and optimized. This ink was then used to fabricate an electrochemical immunosensor for the detection of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Spike protein. The most efficient ink formulation combined 2.5 g of VINNOL® H 15/50, 3.5 g of graphite, and 1.5 g of carbon black (33.3 % binder in the solid phase; 70:30 graphite to carbon black ratio), producing homogeneous films with an electrical resistance close to 5 Ω. The characterization of the ink confirmed the biphasic nature of the composite and the percolation network. Fourier Transform Infrared (FTIR) Spectroscopy identified C=O and C–O–C from the acetate segment and C–Cl from the chloride segment. Raman Spectroscopy preserved the D/G/2D modes of graphite with moderate disorder. Thermogravimetric Analysis (TGA) in N₂ showed four degradation events with a high carbonaceous residue. X-ray Diffraction (XRD) maintained the graphite reflections, and Scanning Electron Microscopy (SEM) revealed nanometric porosity favorable for electrolyte infiltration. Electrochemically, the unmodified electrode showed a quasi-reversible response in Cyclic Voltammetry (CV) and a charge transfer resistance of 127 Ω (Randles–CPE fit). The immunosensor was constructed by EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide) and NHS (N-hydroxysuccinimide) activation, immobilization of anti-S Immunoglobulin G (IgG), and blocking with bovine serum albumin (BSA). In Differential Pulse Voltammetry (DPV), it operated in a signal-off mode, with a current drop proportional to the antigen concentration. The analytical curve (100–700 ng mL⁻¹) was linear (R2= 0.983; slope −0.03194 μA·(ng mL⁻¹)⁻¹) and the limit of detection was 82.6 ng mL⁻¹. The method was identified as simple, reproducible, and scalable, indicating its potential for printed electrode-based rapid diagnostic platforms.