A dichromatic plasmonic ELISA CD81 protein sensor for ultrasensitive detection of preeclampsia

Preeclampsia (PE) seriously affects pregnant women and fetuses' health and causes maternal near-misses. CD81 has been confirmed to be a novel PE biomarker with great potential. Herein, a hypersensitive dichromatic biosensor based on the plasmonic enzyme-linked immunosorbent assay (plasmonic ELISA) is proposed initially for the application of CD81 in early screening for PE. In this work, a novel chromogenic substrate [(HAuCl₄)-(N-methylpyrrolidone)-(Na₃C₆H₅O₇)] is designed based on the H₂O₂ dual catalysis reduction pathway of Au ions. The two reduction pathways of Au ions are controlled by H₂O₂ which ensures that the synthesis and growth of AuNPs are sensitive to H₂O₂. The amount of H₂O₂ correlates with the concentration of CD81 and directs the production of different-sized AuNPs in this sensor. Blue solutions are generated when analytes are present. When analytes are absent, solutions turn red. Therefore, due to different absorption peaks in red and blue, bimodal detection can be performed, and then two detection signals can be generated, one on signal at 550 nm and another off signal at 600 nm. This method exhibits a linear response to the logarithmic CD81 concentrations in the range of 0.1-1000 pg mL^-1 with detection limits of 86 fg mL^-1 and 152 fg mL^-1 at two wavelengths. The false positive rate is low due to the nonspecific coloration caused by serum, which produces a more intense color contrast. The results indicate that the proposed dichromatic sensor could be used as a visual sensing platform for the direct detection of CD81 in biological samples and demonstrate its potential in preeclampsia diagnosis.