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%.
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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