The unique chemical and physical properties of metal−organic frameworks (MOFs) endow them with promising applications in the electrochemical sensing field. Herein, a novel label-free electrochemical sensing strategy for cardiac troponin I (cTnI) has been constructed on the basis of immunoaffinityinduced depression of the electrochemical signal of Cu-MOF-74. The electrochemical assay shows that the immunoaffinity reaction between cTnI and anti-cTnI on the electrode surface can effectively inhibit the electrochemical signal of electrode-confined Cu-MOF-74, suggesting that the Cu-MOF-74-based interface may find application in the label-free analysis of cTnI. Thus, Cu-MOF-74 acts as a bifunctional material in this strategy, namely, the immobilization matrix of probe molecules and the signal source of the sensing analysis. In addition, the reason for the electrochemical signal depression of Cu-MOF-74 induced by immunoaffinity reaction is attributed to the increase in the insulation layer and the blocking of the electrolyte diffusion from the bulk solution to the electrode surface. In this strategy, the analytical range of cTnI is from 0.01 pg mL −1 to 1.0 ng mL −1 and the detection limit is 4.5 fg mL −1 . The Cu-MOF-74-based sensing interface is also reliable for cTnI analysis in real serum samples, showing that the biosensor has promising application in point-of-care testing (POCT) of myocardial injury-related diseases.

Nitrogen reduction electrocatalysts are highly attractive for catalytic science. However, most electrocatalysts are limited by their low faradaic efficiency, poor ammonia yield, and tedious and costly catalyst synthesis process. In this work, Fe-based oxide composite nanoparticles with steady chemical states are prepared by a single-step green procedure under ambient conditions. The resulting FeÀ Fe 3 O 4 demonstrates remarkable activity and selectivity for nitrogen reduction reaction (NRR) with the highest faradaic efficiency of 53.2 � 1.8 % and NH 3 yield rate of 24.6 � 0.8 μg h À 1 mg cat.À 1 at À 0.4 V (vs. RHE) in 0.1 m Na 2 SO 4 electrolyte. Characterization experiments and theoretical calculation reveal that FeÀ Fe 3 O 4 exhibits significantly enhanced charge transfer capability and suppresses the competitive HER process.www.chemsuschem.org

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Titanium dioxide has recently received a lot of attention as a potential catalyst for the electrochemical nitrogen reduction reaction (NRR). However, the effect of surface reconstruction of titanium dioxide during the phase transition on electrocatalysis has attracted little attention. Here, we develop a facile one-pot phase-transition engineering strategy to implant defects in iron-doped titanium dioxide. Our engineering strategy shows advantages including a simple synthesis process, phasetransition efficiency, cost-effective materials, and scalability. The experimental results and density functional theory (DFT) calculations demonstrate that surface oxygen vacancies and doping Fe atoms play crucial roles as potential electrocatalytic sites for the NRR on Fe−TiO 2 catalysts, which enables efficient inhibition of the hydrogen evolution reaction (HER). A high NH 3 yield of 30.9 ± 0.4 μg h −1 mg cat.−1 and a Faradaic efficiency (FE) of 40.4 ± 1.1% at −0.4 V vs reversible hydrogen electrode are obtained for the NRR, outperforming most Ti-based catalysts reported previously. The formation and electrocatalytic NRR properties of Mn−TiO 2 , Co−TiO 2 , Ni−TiO 2 , and Cu−TiO 2 are also verified.

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