Development of graphite carbon nitride based fluorescent immune sensor for detection of alpha fetoprotein

A novel fluorescent immunosensor for determination of alpha fetoprotein (AFP) in serum samples has been developed based on the nano graphite carbon nitride (g-C₃N₄) as fluorophore and immunomagnetic beads (MBs) as separation material. The bulk g-C₃N₄ was obtained by thermal polymerization of melamine, and then carboxylated and exfoliated to acquire the carboxylated nano g-C₃N₄ (c-n-g-C₃N₄), which has been characterized and the results showed that it had excellent fluorescent properties. The antibodies of AFP (Ab₁, Ab₂) were conjugated to the MBs and the c-n-g-C₃N₄, respectively. In assay of AFP detection, the magnetic part of the immunosensor, MBs-Ab₁, would form the sandwich type complex with the signal part of the sensor, c-n-g-C₃N₄-Ab₂. The developed immunosensor could simplify the process of separation due to the MBs. The results illustrated that proposed approach held a good linearity between the fluorescence intensity of the sensor and the AFP concentration ranging from 5-600ng/mL with the limit of detection as low as 0.43ng/mL, and its spiking recoveries ranged from 98.2% to 105.9% with RSD from 2.1% to 3.5%. The fabricated fluorescent immunosensor possesses the merits of good sensitivity, excellent selectivity, high biocompatibility and low cost, and the results provide a novel clue to develop immunosensor for determination of the biomarkers in complex matrices.