Eu-MOF nanorods functionalized with large heterocyclic ionic liquid for photoelectrochemical immunoassay of α-fetoprotein

Abstract

An ionic liquid with a sizeable heterocyclic structure was successfully synthesized and used as a linker to coordinate with Eu3+ ions to provide metal-organic framework (Eu-MOF) nanorods. Gold nanoparticles-modified Eu-MOF nanocomposites (Eu-MOF@AuNPs) were synthesized by the in-situ reduction of chloroauric acid on the Eu-MOF nanorod surface. The outstanding conductivity and local surface plasmon resonance (LSPR) of Au-NPs and the distinct nature of MOFs worked together to enhance photoelectrochemical (PEC) performance by decreasing the recombination of photo-excited carriers and taking advantage of a broad absorption range for light harvesting. Under white light irradiation, the Eu-MOF@AuNPs nanocomposite had a better PEC performance than pure Eu-MOF. Therefore, a novel photoelectrochemical immunosensor was fabricated for alpha-fetoprotein (AFP) using Eu-MOF@AuNPs as the photoactive element. When the anti-AFP was attached to the Eu-MOF@AuNPs/GCE interface, the designed immunosensor exhibited a specific photocurrent response to AFP. The specific binding of AFP to anti-AFP can cause a significant steric hindrance, thus hinder the charge transfer and the separation of electron-hole pairs due to large molecular size and poor conductivity. As a result, the PEC immunosensing platform presented a decreasing trend on photocurrent intensity. Under the optimized conditions, the calibration plot showed a linearity with the logarithm of AFP concentration (0.002–15.0 ng mL−1), and a detection limit of 0.16 pg mL−1 was obtained (S/N = 3). Moreover, this immunosensor presented a brilliant selectivity, high reproducibility, and outstanding stability, which possesses remarkable potential applications in determining AFP in serum samples.