Electrochemiluminescence immunosensor based on graphene-CdS quantum dots-agarose composite for the ultrasensitive detection of alpha fetoprotein.

A novel strategy for the enhancement of electrochemiluminescence (ECL) was developed by combining CdS quantum dots (QDs), graphene (G) and agarose. This enhanced ECL was exploited to develop a label-free ECL immunosensor for the ultrasensitive detection of alpha fetoprotein (AFP). The novel G-CdS QDs-agarose composite was first coated on the glass carbon electrode surface to form a robust film, which exhibited high ECL intensity, good biocompatibility and high stability. After that 3-aminopropyl-triethoxysilane (APS), as a binding linker, was conjugated to the G-CdS QDs-agarose composite film on the electrode, the ECL signal was significantly enhanced. The fabrication of ECL immunosensor was successfully completed by immobilizing the AFP-antibody (Ab) onto the electrode through glutaric dialdehyde (GLD). The specific immunoreaction between AFP and antibody resulted in the decrease in ECL intensity and the intensity decreased linearly with the logarithm of AFP concentration in the range of 0.0005-50 pg mL(-1) with a detection limit of 0.2 fg mL(-1). The immunosensor exhibits high sensitivity, specificity, stability, reproducibility and good regeneration, thus has the potential to be used in clinical application. Besides, the highly enhanced ECL from the G-CdS QDs-agarose composite film opened new avenues to apply graphene and QDs ECL in analytical systems and ECL biosensors.