Increasing demand for timely and accurate environmental pollution monitoring and control requires new sensing techniques with outstanding performance, i.e., high sensitivity, high selectivity, and reliability. Metal–organic frameworks (MOFs), also known as porous coordination polymers, are a fascinating class of highly ordered crystalline coordination polymers formed by the coordination of metal ions/clusters and organic bridging linkers/ligands. Owing to their unique structures and properties, i.e., high surface area, tailorable pore size, high density of active sites, and high catalytic activity, various MOF-based sensing platforms have been reported for environmental contaminant detection including anions, heavy metal ions, organic compounds, and gases. In this review, recent progress in MOF-based environmental sensors is introduced with a focus on optical, electrochemical, and field-effect transistor sensors. The sensors have shown unique and promising performance in water and gas contaminant sensing. Moreover, by incorporation with other functional materials, MOF-based composites can greatly improve the sensor performance. The current limitations and future directions of MOF-based sensors are also discussed.

In this study, we designed a fluorescence resonance energy transfer system containing gold nanorods (AuNRs) and fluorescein (FAM) for the detection of hepatitis B virus DNA sequences. AuNRs were synthesized according to the seed-mediated surfactant-directed approach, and the surface of the AuNRs was wrapped with a thin layer of cetyltrimethylammonium bromide (CTAB), resulting in the AuNRs being positively charged. When FAM-tagged single-stranded DNA (FAM-ssDNA) was added into the AuNRs suspension, it was adsorbed onto the surface of the positively charged AuNRs and formed a FAM-ssDNA-CTAB-AuNRs ternary complex, the resulting structure led to a fluorescence resonance energy transfer (FRET) process from FAM to AuNRs and the fluorescence intensity of FAM was consequently quenched. When complementary target DNA was added to the FAM-ssDNA-CTAB-AuNRs complex solution, a further decrease in fluorescence intensity was observed because of an increased FRET efficiency. Under optimal conditions, the decline of the fluorescence intensity of FAM (ΔF) was linear with the concentration of the complementary DNA from 0.045 to 6.0 nmol L(-1) and the detection limit was as low as 15 pmol L(-1) (signal/noise ratio of 3). When this fluorescent DNA sensor was used to detect the polymerase chain reaction product of hepatitis B virus gene extracted from a positive real sample, a positive response was obtained. Impressively, the biosensor exhibits good selectivity, even for single-mismatched DNA detection.

Rapid determination of trace antibiotics is critical for environmental monitoring and the ecosystem. In this study, a sensitive and selective electrochemical sensor for ciprofloxacin (Cip) detection by anodic stripping voltammetry of Cu2+ is designed. Zr­(IV)-based metal–organic framework (MOF) NH2–UiO-66 and reduced graphene oxide (RGO) composites are used as working electrodes, which have a large surface area with porous structure and high electrical conductivity. Because Cip can form a stable composite with Cu2+ due to the complexation reaction, the anodic stripping voltammetry method is used for Cip determination with Cu deposition on the NH2–UiO-66/RGO-modified electrode. When Cip is present, the oxidization current of Cu2+ decreases significantly due to the formation of Cu2+–Cip complex. The prepared NH2–UiO-66/RGO sensor can detect trace levels of Cip down to 6.67 nM with a sensitivity of 10.86 μA μM–1, and a linear working range from 0.02 to 1 μM, which is superior to other electrochemical Cip sensors reported previously. The sensor also shows high selectivity, reproducibility, and stability in Cip sensing. Meanwhile, the electrochemical sensor is capable to detect Cip in real water samples with satisfactory recoveries. The ultrasensitivity, rapid detection, and easy operation of the reported sensors present significant potentials for real-time analysis and monitoring of trace antibiotic contaminants in water.