Europium (III)-salicylate embedded carboxymethyl cellulose thin film immunosensor for ultrasensitive detection of breast cancer biomarker CA15-3: comprehensive experimental and computational insights.

The accurate quantification of carbohydrate antigen 15-3 (CA15-3) is critically important for breast cancer diagnosis and monitoring. This study reports a novel luminescent thin-film immunosensor based on europium (III)-salicylate [Eu (sal)₃] embedded within an epichlorohydrin-crosslinked carboxymethyl cellulose (mCMC) matrix and functionalized with anti-CA15-3 antibodies. The sensor operates through antigen-antibody interaction-induced fluorescence quenching of the Eu (sal)₃ complex. The biosensor demonstrated a linear response range of 240-920 mU/mL with an ultra-low detection limit of 0.085 U/mL, significantly outperforming conventional immunoassay methods. The system exhibited excellent recoveries (86.6-154.5%) and precision (RSD < 0.59%). Complementary computational studies using DFT, TD-DFT, and molecular dynamics simulations provided mechanistic insights into the coordination geometry (Eu-O: 2.38-2.42 Å), electronic structure (HOMO-LUMO gap: 4.3 eV), photophysical properties (quantum yield: 86.6%, lifetime: 612 μs), and binding interactions with CA15-3 (K: 24.3 nM). This integrated approach establishes the immunosensor as a rapid, cost-effective, and ultrasensitive platform for clinical breast cancer diagnostics.