Single atom-dispersed catalysts (SADCs) with highly exposed active sites can be used as sensitive signal probes because of their superior catalytic efficiency. However, the dispersed atoms tend to aggregate, restricting the loading capacity of metal atoms. Herein, the defective sites on Zr-oxo clusters of metal−organic frameworks (MOFs) UiO-66-NH 2 were modulated by excessive acetic acid and utilized for confining metal atoms with high loading capacity. To verify the feasibility of the designed strategy, the Co element was loaded onto MOFs UiO-66-NH 2 to prepare SADCs with desirable Fenton-like activity. The prepared Co SADCs at a low concentration of 1.0 μg mL −1 are found to boost chemiluminescent (CL) emission for 3700 times due to the significantly improved Co content of 5.55 wt %. The superior CL enhancement efficiency is ascribed to reactive oxygen species generated by the accelerated decay of H 2 O 2 . To verify the application potential in CL assay, they were used as signal probes to establish an immunoassay method for carbendazim with a dynamic range of 1.0 pg mL −1 to 25 ng mL −1 and a limit of detection of 0.33 pg mL −1 . This defective site modulation strategy paves an avenue for preparing SADCs with a high CL response by improving the loading capacity of metal atoms.

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A facile, one-step doping protocol was adopted to synthesize Co single atomic site catalysts (SASCs) in UiO-66 metal–organic frameworks. In view of highly uniform active sites of Co–O6 moieties, the SASCs specifically contribute to catalyzing the generation of a large amount of singlet oxygen instead of superoxide or hydroxyl radicals, which endows Co SASCs with a the remarkable enhancement effect (∼3775 times) on luminol chemiluminescent (CL) emission. Interestingly, monolayer titanium carbide MXenes can drastically quench the CL signal of the Co SASC-boosted luminol reaction by ∼94.6% as highly efficient luminescent absorbents. Furthermore, the emitter–quencher pair of Co SASCs and titanium carbide MXenes was successfully adopted to develop an immunoassay method for cardiac troponin I (cTnI) on an immunochromatographic test strip platform. With a sandwich immunoreaction mode, a titanium carbide MXene-labeled cTnI tracer antibody was captured on the test line of a test strip, which significantly inhibited the CL response of the Co SACs-boosted luminol system. The dynamic range for quantitating cTnI is 1.0–100 pg mL–1, with a detection limit of 0.33 pg mL–1 (3σ). The test strip was successfully used to detect cTnI in human serum samples collected from cardiopathy patients. This proof-of-principle work manifests both the CL enhancement of SASCs and the quenching behavior of MXenes, which shows the thrilling prospects of combinational usage of the two functionalized nanomaterials for tracking biological recognition events.

In view of the outstanding catalytic efficiency, single-atom catalysts (SACs) have shown great promise for the construction of sensitive chemiluminescent (CL) platforms. However, the low loading amount of active sites dramatically obstructs the improved catalytic activity of these metal SACs. Benefiting from the exceedingly unique catalytic properties of the metal–metal bonds, atomic clusters may give rise to enhancing the catalytic properties of SACs based on the synergistic effects of dual atomic-scale sites. Inspired by this, atomic Co3N clusters-assisted Co SACs (Co3N@Co SACs) were synthesized through a facile doping method. Through X-ray absorption spectroscopy, the active metal sites in the synergetic dual-site atomic catalysts of Co3N@Co SACs were confirmed to be Co–O4 and Co3–N moieties. Co3N@Co SACs served as a superior co-reactant to remarkably enhance the luminol CL signal by 2155.0 times, which was prominently superior to the boosting effect of the pure Co SACs (98.4 times). The synergetic dual-site atomic catalysts contributed to accelerating the decomposition of H2O2 into singlet oxygen as well as superoxide radical anions to display superb catalytic performances. For a concept employment, Co3N@Co SACs were attempted to utilize as CL probes for establishing a sensitive immunochromatographic assay to quantitate pesticide residues, in which imidacloprid was adopted as the model analyte. The quantitative range of imidacloprid was 0.05–10 ng mL–1 with a detection limit of 1.7 pg mL–1 (3σ). Furthermore, the satisfactory recovery values in mock herbal medicine samples demonstrated the effectiveness of the proposed Co3N@Co SAC-based CL platform. In the proof-of-concept work, synergetic dual-site atomic catalysts show great perspectives on trace analysis and luminescent biosensing.

As a multidrug-resistant pathogen, Acinetobacter baumannii has long been identified as one of the most common nosocomial bacteria. High-performance recognition probes for wide-spectrum detection of A. baumannii are highly desired to achieve efficient diagnosis and timely treatment of infectious diseases induced by this pathogen. An engineering tail fiber protein (ETFP) named as Gp50 encoded by lytic phage Abp9 was expressed in Escherichia coli and identified as a binding protein for A. baumannii. According to the results of genome sequencing of an A. baumannii wild strain and phage-resistant strains, the binding receptor of ETFP Gp50 is inferred to be a lipopolysaccharide distributed on the bacterial surface. The engineering protein did not show lytic activity to A. baumannii, which facilitates the development of reliable diagnosis kits and biosensors with high flexibility and low false-negative rate. The results of specificity study show that ETFP Gp50 is a species-specific binding protein with a recognition rate of 100% for all tested 77 A. baumannii strains, while that of the natural phage Abp9 is only 27.3%. With the engineering protein, a fluorescence method was developed to detect A. baumannii with a detection range of 2.0 × 10 2 to 2.0 × 10 8 cfu mL −1 . The method has been used for the quantification of A. baumannii in a diverse sample matrix with acceptable reliability. The work demonstrates the application potential of ETFP Gp50 as an ideal recognition probe for rapid screening of A. baumannii strains in a complicated sample matrix.