Potentially a new approach in cancer diagnosis: development of lanthanide-loaded nanoparticle-based biosensors for determining telomerase levels

Abstract A key focus in cancer biomarker research is the quantification of telomerase-related signatures. In this study, we developed Eu 3 ⁺-doped silica nanoparticle immunoprobes for fluorescence-based quantification of telomerase reverse transcriptase (TERT) protein level as a proof-of-concept nanobiosensing platform. Biocompatible silica nanoparticles were functionalized with N-methacryloyl-L-aspartic acid (MAAsp) and Eu 3 ⁺ to promote ligand-assisted sensitization (antenna effect), followed by surface amination and covalent antibody immobilization to enhance specificity toward TERT. The materials were characterized by FT-IR, zeta potential analysis, SEM, TEM, UV-visible spectrometry, fluorescence spectrometry, and gel electrophoresis, confirming successful surface modification and probe formation. The nanoparticles exhibited an average hydrodynamic size of approximately 120 nm, consistent across sizing methods. Antibody immobilization showed a minimum immobilization efficiency of 88.42 ± 0.92% estimated by a UV-spectrometric mass-balance (A280) approach. The sensing capability was evaluated using commercial TERT antigen standards and cell lysates derived from HeLa and MCF-7 tumor cell lines, yielding concentration-dependent fluorescence responses and enabling calibration-based estimation of TERT-equivalent levels in cell-derived samples. When compared under the same gel-imaging conditions, the Eu 3 ⁺-based immunoprobes produced sharp and readily detectable signals relative to the commercial Cy2 dye. Although the present work does not include enzymatic telomerase activity assays (e.g., TRAP), normal controls, biological fluids, clinical specimens, or serum/plasma stability and biocompatibility assessments, the results support the analytical feasibility of Eu 3 ⁺-doped silica immunoprobes as fluorescent labels for TERT protein-level readout and motivate further validation in clinically relevant matrices. Graphical abstract