Bacterial infection is one of the major causes of human death worldwide. To prevent bacterial infectious diseases from spreading, it is of critical importance to develop convenient, ultrasensitive, and cost-efficient methods for bacteria detection. Here, an electrochemical detector of a functional two-dimensional (2D) metal–organic framework (MOF) nanozyme was developed for the sensitive detection of pathogenic Staphylococcus aureus. A dual recognition strategy consisting of vancomycin and anti-S. aureus antibody was proposed to specifically anchor S. aureus. The 2D MOFs with excellent peroxidase-like activity can efficiently catalyze o-phenylenediamine to 2,2-diaminoazobenzene, which is an ideal electrochemical signal readout for monitoring the bacteria concentration. Under optimal conditions, the present bioassay provides a wide detection range of 10–7.5 × 107 colony-forming units CFU/mL with a detection limit of 6 CFU/mL, which is better than most of the previous reports. In addition, the established electrochemical sensor can selectively and accurately identify S. aureus in the presence of other bacteria. The present work provides a new pathway for sensitive and selective detection of S. aureus and presents a promising potential in the realm of clinical diagnosis.

Here, the effect of morphology on the electrocatalytic activity of metal–organic framework (MOF) was investigated. Post synthetic gold (Au) insertion was done into hollow PCN-222 (HPCN-222) and solid PCN-222 (SPCN-222) frameworks by a simple hydrothermal method. The crystalline nature, chemical composition, and morphologies of the synthesized MOFs were characterized by PXRD, XPS, and TEM. Electrochemical characterizations were done by cyclic voltammetry and electrochemical impedance spectroscopy. The excellent electrocatalytic activity of highly small-sized Au(0) with the enhancement of electrical conductivity through a hopping mechanism combined with a hollow structure and high surface area in the HPCN-222 MOF hugely alters the electrochemical properties. Overall, a better electrocatalytic surface area, charge transfer coefficient, and catalytic activity were generated at the modified electrode. The hollow structure MOF showed better electrocatalytic activity than solid structured MOF. The AuHPCN-222 modified glassy carbon electrode (AuHPCN-222/GCE) electrochemical sensor was employed for the analytical analysis of estradiol (ED) in an optimum experimental condition. AuHPCN-222 showed selective and better electrocatalytic activity toward ED than GCE. The differential pulse voltammetric measurements by the fabricated sensor showed two linear determination ranges for ED; those are 0.01–1 and 1–220 μM. The measured limit of detection (m-LOD) was found to be 0.5 nM with the highest sensitivity of 2.2 μA μM cm–2. The analytical performances for the detection of ED in human urine and serum samples were done with reasonable recoveries (98%–103%) using the standard addition method. Also, the sensor showed better reproducibility and repeatability with stability.

In this work, a nanocomposite of Zr-trimesic acid MOF (MOF-808) with carbon nanotube (CNT) was synthesized through an in situ formation of MOF-808 on the activated CNT. The synthesized materials were characterized by powder X-ray diffraction, transmission electron microscopy, X-ray photoluminescence spectroscopy, Brunauer–Emmett–Teller, Fourier transform infrared spectroscopy, and Raman spectroscopy. The protein compatible nature with high surface area and electrocatalytic ability of MOF-808 was utilized to construct an immunosensor for ultra low-level detection of the ovarian cancer biomarker, carbohydrate antigen 125 (CA 125). The mutual benefit of each constituent of the MOF-808/CNT composite was capable of producing highly enhanced electrochemical properties. A glassy carbon electrode modified with MOF-808/CNT was used as a platform to fabricate a label-free electrochemical immunosensor. The antibody binding sites of MOF-808/CNT were enriched by functionalization with streptavidin. The immunosensor exhibited two linear determination ranges of 0.001–0.1 and 0.1–30 ng·mL–1, and the calculated limit of detection was 0.5 pg·mL–1 (S/N 3). The immunosensor showed excellent reproducibility and selectivity. The patient serum sample analysis was cross-verified with the electrochemiluminescence method with a relative error of 105–110%.

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Despite having the potential to synthesize stable metal−organic frameworks (MOFs), rare earth metal-based MOFs have not been exploited extensively. Owing to the high coordination numbers, the MOFs can generate a suitable coordination environment for various applications. Herein, samarium (Sm)-based MOFs were synthesized with three different organic linkers, namely, trimesic acid (TMA), meso-tetra(4carboxyphenyl)porphine (TCPP), and 1,3,6,8-tetra(4-carboxylphenyl) pyrene(TBPy) by the solvothermal approach. The morphologies of Sm-TMA MOF, Sm-TCPP MOF, Sm-TBPy MOF were rod-shaped, cubic consisting of stacked 2D layers, and spherical made of small cubic structures, respectively. After the electrochemical properties of the synthesized MOFs were investigated, the MOFs were used to fabricate immunosensors for detection of carcinoembryonic antigen using a label-free signaling strategy. The immunosensors exhibited a wide linear detection range and a lower detection limit. The exhibited reproducibility and selectivity of the immunosensors were within the tolerable limits. The established label-free immunosensor has been successfully applied for detection of carcinoembryonic antigen in human serum samples, demonstrating that the rare earth metal-based MOFs are promising for construction of biosensors for medical diagnosis.

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