A novel ratiometric dual-emission fluorescence magnetic nanohybrid for HIgG immunoassay

Abstract

In this work, we designed a novel ratiometric dual-emission fluorescence magnetic nanohybrid. Carbon-coated magnetic composite nanoparticles (Fe₃O₄@C NPs) were prepared through the poly-condensation reaction of glucose under hydrothermal conditions. With appropriate hydrothermal time, temperature and glucose concentration, the glucose was polymerized and carbonized. Then, carbon dots were in situ-synthesized in the carbon shell that gave blue fluorescence due to surface energy trap emission. Furthermore, the surface of Fe₃O₄@C NPs was endowed with positive charges through modification with poly(diallyldimethylammonium chloride) (PDDA), and the electrostatic forces could bind electronegative CdTe quantum dots (QDs) on the Fe₃O₄@C NP surface (Fe₃O₄@C@QDs). The carbon shell preserves the stability of internal Fe₃O₄ NPs and inhibits the quenching of CdTe QD photoluminescence. To further demonstrate the performance of the nanohybrid as an immunosensor, HIgG was employed as a model target. In a competitive immunoassay, Fe₃O₄@C@QDs were coated with anti-human IgG. After binding HIgG, HIgG–Au NPs were captured by the remaining unreacted site of anti-human IgG on the Fe₃O₄@C@QDs nanohybrid surface and quenched the fluorescence of CdTe QDs via fluorescence resonance energy transfer (FRET). The proposed ratiometric dual-emission (carbon dots and QDs) fluorescence magnetic nanohybrid displayed excellent analytical performance for the detection of HIgG in the range of 0.005–100 ng mL⁻¹ with a lower detection limit of 0.0025 ng mL⁻¹.