Fluorescence turn-on immunosensing of HE4 biomarker and ovarian cancer cells based on target-triggered metal-enhanced fluorescence of carbon dots

Rapid and sensitive detection of tumor biomarkers and cancer cells is of crucial importance for the early diagnosis and prognosis prediction of cancer. The present report describes a target-induced fluorescence enhancement immunosensor that utilizes the optical property of carbon dots (CDs) and the metal-enhanced fluorescence effect (MEF) property of silver nanoparticles (AgNPs) for the sensitive detection of the cancer biomarker human epididymis protein 4 (HE4) and ovarian cancer cells. Nitrogen and sulfur co-doped CDs with a quantum yield of 85.6% were prepared and served as the fluorophore in MEF. The HE4 antibody (Ab) specific to the HE4 antigen was linked covalently to the surface of the synthesized CDs as the capture. The HE4 Ab-conjugated AgNPs (AgNPs-Ab) were prepared and utilized as signal amplification elements. In the presence of the target HE4, composite sandwich structures were formed between the labeled CDs-Ab and AgNPs-Ab, which brought the CDs and AgNPs into proximity, resulting in the fluorescence of CDs enhancement owing to MEF. The intensity of fluorescence enhancement was positively correlated with the HE4 concentration in the clinically important range of 0.01-200 nM with a limit detection of 2.3 pM. Moreover, the immunosensor was also successfully applied to specific fluorescence labeling and quantitative determination of HE4-positive ovarian cancer cells. The proposed target-triggered MEF sensor platform demonstrated high sensitivity, excellent anti-interference ability, along with successful validation in complex biological matrices, providing a new approach for HE4 detection in early diagnosis and therapeutic monitoring.