Establishment of a Ca(II) ion-quantum dots fluorescence signal amplification sensor for high-sensitivity biomarker detection.

Quantum dots (QDs) have been considered as the promising fluorescent labeling material, which is expected to meet the requirement of high-sensitivity detection in clinical diagnostics. Some common metal ions are known to affect the stability and fluorescence properties of QDs, but scarcely any systematic research has been done about their impacts on QD-based bio-detection. By evaluating the effect of Ca2+ metal ions on the properties of aqueous QDs, a new metal ion-QD fluorescence signal amplification sensor (i.e., Ca2+-QD-fluorescence-linked immunosorbent assay, Ca2+-QD-FLISA) has been developed for the detection of inflammatory biomarkers with high sensitivity. Compared with the common QD-FLISA, the detection sensitivity for CRP of Ca2+-QD-FLISA was improved by a 4-fold of magnitude to 0.23 ng/mL, and this assay showed good selectivity, high accuracy, and excellent repeatability. The versatility of the QD-FLISA method were also validated by using different metal ion-QD probes (Ca2+, Mg2+, Ba2+, Fe2+, and Mn2+) to detect CRP, serum amyloid A (SAA), and procalcitonin (PCT). The significant improvement in detection sensitivity was achieved due to the crosslinking of aqueous QDs by Ca2+ ions to enhance fluorescence and at the same time promote antigen-antibody binding efficiency. The present study illustrates the versatility of metal ion-QD-FLISA as a simple and effective method to detect a wide range of biomarkers with high sensitivity and accuracy.