A novel metal‐organic framework (MOF) assembled by a semi‐rigid tricarboxylate, namely, 5‐(3,4‐dicarboxylphenoxy) nicotic acid (H3L) has been solvothermally synthesized: [Zn3(L)2(H2O)2] ⋅ 3H2O 1. Single‐crystal X‐ray diffraction analysis indicates that MOF 1 shows 2‐D layer with quadrangle channels along the a axis (ca. 7.0×8.3 Å2). The 2‐D layer self‐assembles into a final 3‐D supramolecular network via the interlayer π⋯π interactions. The photoluminescence investigations indicate that 1 can selectively and sensitively detect acetylacetone (acac) with high KSV value of 3.597×104 M−1 and low limit of detection (LOD) of 50.77 ppb. Further mechanism studies have shown that static photo‐competitive absorption, photoinduced electron transfer and H‐bonding interaction between chemosensor and the analyte may be the primary causes of the fluorescence quenching effect for acac.

The colorimetric signal readout method is widely used in visualized analyses for its advantages, including visualization of test results, simple and fast operations, low detection cost and fast response time. Gold nanoparticles (Au NPs), which not only exhibit enzyme-like activity but also have the advantages of tunable localized surface plasmon resonance (LSPR), high stability, good biocompatibility and easily modified properties, provide excellent platforms for the construction of colorimetric sensors. They are widely used in environmental monitoring, biomedicine, the food industry and other fields. This review focuses on the chromogenic mechanisms of colorimetric sensors based on Au NPs adopting two different sensing strategies and summarizes significant advances in Au NP-based colorimetric sensing with enzyme-like activity and tunable LSPR characteristics. In addition, the sensing strategies based on the LSPR properties of Au NPs are classified into four modulation methods: aggregation, surface modification, deposition and etching, and the current status of visual detection of various analytes is discussed. Finally, the review further discusses the limitations of current Au NP-based detection strategies and the promising prospects of Au NPs as colorimetric sensors, guiding the design of novel colorimetric sensors.

Alkaline phosphatase (ALP) is among the most studied enzymes by far, playing an important role in the metabolism of organisms and the regulation of protein activity. Herein, a label-free composite nanoprobe is constructed by combining inorganic nanomaterials and aggregation-induced emission (AIE) molecule to achieve highly sensitive and selective detection of ALP. Negatively charged 9,10-bis [2-(6-sulfonatopropoxyl) naphthylethenyl] anthracene (BSNVA) molecule is synthesized, which has the AIE performance and can be assembled on the surface of amino–SiO2 nanoparticles through electrostatic interaction for fluorescence enhancement. MnO2 nanosheets are rich in negative charges, enabling them to be wrapped on the surface of the amino–SiO2 nanosphere to shield the positive charge on its surface, making it impossible for BSNVA to accumulate on the surface and then weakening the bio-fluorescence of the system. Furthermore, with catalyzed substrates induced by ALP, generating ascorbic acid and the redox reaction between ascorbic acid and MnO2, the nanoprobe helps in realizing the high-sensitivity detection of ALP with a detection limit of 0.38 mU/mL. The proposed strategy requires no complex cleaning and modification processes and can overcome the quenching effect caused by the aggregation of traditional organic dyes, proving to be a simple, low-cost and “turn-on” fluorescent detection method for ALP.