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The repeated outbreaks of coronavirus disease 2019 (COVID-19) have seriously threatened human health and economic development. Therefore, it is still significant to explore an efficient method for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection. Herein, we designed a dual-mode colorimetric and fluorescent immunosensor based on Fe2+ doped ZIF-67 derivatives-based composites, Pt nanoparticles loaded on CoFe nanoparticles embedded porous carbon-nitrogen hexahedron (CoFe/NC@Pt), for detecting SARS-CoV-2 nucleocapsid protein. The doping of Fe2+ generated bimetallic CoFe nanoparticles and formed more defects after pyrolysis. Meanwhile, the peroxides-like activity significantly improved owning to the synergistic effect of Co and Fe nanoparticles. Furthermore, loaded Pt nanoparticles not only provided more active sites, but also could couple antibodies by modifying functional groups. CoFe/NC@Pt exhibited good peroxidase-like activity and could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxides in the presence of H 2 O 2 , generating visible color signals. While the oxTMB could quench the fluorescence of carbon dots through inner filter effect, thereby providing fluorescent signals. The limit of detection were 0.022 ng/mL (colorimetric) and 0.018 ng/mL (fluorescent). And the specificity of the immunosensor was verified by comparing with other interferents. Therefore, this dual-mode immunosensor with good performance provided a reliable strategy for diagnosis of COVID-19. [Display omitted] • A dual-mode colorimetric and fluorescent immunosensor based on CoFe/NC@Pt nanozyme. • CoFe/NC@Pt exhibited good peroxidase-like activity. • The quenching mechanism of CDs was inner filter effect. • The accuracy of the sensor was improved by mutual authentication of double signals. [ABSTRACT FROM AUTHOR]

A new furfuran-based rhodamine B fluorescent probe ( RBFF ) has been designed and synthesized, and its sensing behavior towards various metal ions was evaluated via UV–vis and fluorescence spectroscopic techniques. RBFF exhibits a highly sensitive and selective “turn-on” fluorescent response toward Fe 3+ ion and a fluorescence “turn-off” response when added B 4 O 7 2− to the RBFF -Fe 3+ in the EtOH/H 2 O solution (1:1, v/v, HEPES, 1 mM, pH 7.20). The detection limit of RBFF for Fe 3+ was calculated to be 0.025 μM. The fluorescence microscopy experiment suggested that RBFF could also be served as a biological fluorescence probe for the detection of Fe 3+ in human cervical carcinoma cells (HeLa). [ABSTRACT FROM AUTHOR]