Fe(III)-quenched cysteine-capped copper nanoclusters as a selective fluorescence turn-on sensor for valine: A potential cancer biomarker candidate.

This study introduces a fluorescence turn-on sensor for the selective detection of valine, an amino acid increasingly recognized as a potential biomarker in cancer diagnostics, using iron(III) (Fe3+) quenched L-cysteine capped copper nanoclusters (L-cys@CuNCs) based on the paramagnetic quenching mechanism of Fe3+. The L-cys@CuNCs, synthesized through a one-pot hydrothermal method, exhibit stable green fluorescence, high photostability and a detection limit of 3.00 µM for valine. Restoration of fluorescence upon interaction with valine enables a highly sensitive detection, with strong selectivity against other amino acids and ions. This specificity makes the sensor particularly promising for screening valine in biological samples, supporting its potential as a non-invasive cancer biomarker. To enhance practicality, a paper-based assay was developed, demonstrating its adaptability to point of care formats. Additionally, testing in human saliva and urine samples validated the probe's utility in real biological conditions, underscoring its potential in non-invasive cancer diagnostics. This biosensing platform offers a rapid, accessible tool for valine detection, contributing to early cancer detection and patient screening in clinical and resource limited settings.