Highly Sensitive Label-Free Immunosensor based on 5-Sulfosalicylic Acid Doped Poly(2-chloroaniline) for Detection of CA72-4 in Gastric Cancer.

Gastric cancer (GC) is a leading cause of cancer-related deaths worldwide, highlighting the urgent need for sensitive and cost-effective diagnostic tools. In this work, a label-free electrochemical immunosensor (ECI) based on poly(2-chloroaniline) doped with 5-sulfosalicylic acid (dP2ClAn/SSA) was developed for the detection of cancer antigen 72-4 (CA72-4), a key biomarker for the early GC diagnosis. The incorporation of 3-aminopropyltriethoxysilane (APTES) as a linker agent facilitated the antibody immobilization, improved electron transfer, and promoted stable sensor performance. Detection of CA72-4 using differential pulse voltammetry (DPV) demonstrated a broad detection range of 0.001-500 U/mL, with the calculated limit of detection of 0.0053 U/mL (1 U = 1 ng). The sensor exhibited excellent selectivity, reproducibility, and stability over 28 days of storage. Validation with human serum samples confirmed its accuracy and reliability, with performance comparable to ELISA. With its simplicity, portability, and cost-effectiveness, this ECI represents a promising diagnostic tool for early GC detection and clinical point-of-care applications.