A DNA functionalized porphyrinic metal-organic framework as a peroxidase mimicking catalyst for amperometric determination of the activity of T4 polynucleotide kinase

An electrochemical biosensor for T4 polynucleotide kinase activity identification according to host-guest recognition among phosphate pillar[5]arene@palladium nanoparticles@reduced graphene oxide nanocomposite and toluidine blue

T4 polynucleotide kinase (T4 PNK) helps with DNA recombination and repair. In this work, a phosphate pillar[5]arene@palladium nanoparticles@reduced graphene oxide nanocomposite (PP5@PdNPs@rGO)-based electrochemical biosensor was created to identify T4 PNK activities. The PP5 used to complex toluidine blue (TB) guest molecules is water-soluble. With T4 PNK and ATP, the substrate DNA, which included a 5'-hydroxyl group, initially self-assembled over the gold electrode surface by chemical adsorption of the thiol units. Strong phosphate-Zr4+-phosphate chemistry allowed Zr4+ to act as a bridge between phosphorylated DNA and PP5@PdNPs@rGO. Through a supramolecular host-guest recognition connection, TB molecules were able to penetrate the PP5 cavity, where they produced a stronger electrochemical response. With a 5 × 10-7 U mL-1 detection limit, the electrochemical signal is linear in the 10-6 to 1 U mL-1 T4 PNK concentration range. It was also effective in measuring HeLa cell lysate-related PNK activities and screening PNK inhibitors. Nucleotide kinase-target drug development, clinical diagnostics, and screening for inhibitors all stand to benefit greatly from the suggested technology, which offers a unique sensing mechanism for kinase activity measurement.

Design and Application of Electrochemical Sensors with Metal-Organic Frameworks as the Electrode Materials or Signal Tags

Metal-organic frameworks (MOFs) with fascinating chemical and physical properties have attracted immense interest from researchers regarding the construction of electrochemical sensors. In this work, we review the most recent advancements of MOF-based electrochemical sensors for the detection of electroactive small molecules and biological macromolecules (e.g., DNA, proteins, and enzymes). The types and functions of MOF-based nanomaterials in terms of the design of electrochemical sensors are also discussed. Furthermore, the limitations and challenges of MOF-based electrochemical sensing devices are explored. This work should be invaluable for the development of MOF-based advanced sensing platforms.

Porphyrin-Based Metal-Organic Frameworks for Biomedical Applications

Porphyrins and porphyrin derivatives have been widely explored for various applications owing to their excellent photophysical and electrochemical properties. However, inherent shortcomings, such as instability and self-quenching under physiological conditions, limit their biomedical applications. In recent years, metal-organic frameworks (MOFs) have received increasing attention. The construction of porphyrin-based MOFs by introducing porphyrin molecules into MOFs or using porphyrins as organic linkers to form MOFs can combine the unique features of porphyrins and MOFs as well as overcome the limitations of porphyrins. This Review summarizes important synthesis strategies for porphyrin-based MOFs including porphyrin@MOFs, porphyrinic MOFs, and composite porphyrinic MOFs, and highlights recent achievements and progress in the development of porphyrin-based MOFs for biomedical applications in tumor therapy and biosensing. Finally, the challenges and prospects presented by this class of emerging materials for biomedical applications are discussed.

A Long-Term Stable Sensor Based on Fe@PCN-224 for Rapid and Quantitative Detection of H2O2 in Fishery Products

Hydrogen peroxide (H2O2) has been reported to be used for the illegal treatment of fishery products in order to obtain "fake" freshness. Residues of H2O2 in food may be of toxicology concern. In this study, a nonenzymatic sensor was developed based on Fe@PCN-224 metal-organic frameworks wrapped by Nafion to detect H2O2 concentration. The hybrid structure of Fe@PCN-224 was fabricated by incorporated free FeIII ions into the center of PCN-224, which was ultra-stable due to the strong interactions between Zr6 and the carboxyl group. Scanning electron spectroscopy images exhibited that Nafion sheets crossed together on the surface of Fe@PCN-224 nanoparticles to form a hierarchical and coherent structure for efficient electron transfer. Electrochemical investigations showed that the Fe@PCN-224/Nafion/GCE possessed good linearity from 2 to 13,000 μM (including four orders of magnitude), low detection limits (0.7 μM), high stability in continuous monitoring (current remained nearly stable over 2300 s) and in long-term measurement (current decreased 3.4% for 30 days). The prepared nanohybrid modified electrode was effectively applied to H2O2 detection in three different fishery products. The results were comparable to those measured using photometrical methods. The developed electrochemical method has a great potential in detecting the illegal management of fishery products with H2O2.

Synthesis, anti-ovarian cancer activity evaluation and docking studies of pyran derivatives

The synthesis and characterization of new pyran derivatives (1–3) were realized by means of infrared spectroscopy (IR), 1H nuclearmagnetic resonance spectroscopy (1H NMR), high resolution mass spectrum (HRMS) and single crystal X-ray crystallography. The anti-proliferation activity of compounds 1–3 was investigated against human ovarian cancer cells CAOV3 by Cell Counting Kit-8 (CCK-8) assay. The RT-PCR assay was performed to detect the relative expression level of the Foxm1b in the CAOV3 cell line after treated with compounds 1–3. Furthermore, molecular docking studies supported the biological assay data and suggested that compared with compounds 1 and 3, compound 2 has stronger interaction with protein.

Exonuclease III-assisted signal amplification strategy for sensitive fluorescence detection of polynucleotide kinase based on poly(thymine)-templated copper nanoparticles

A sensitive and label-free fluorometric method has been developed for the determination of polynucleotide kinase (PNK) activity, by employing exonuclease III (Exo III)-assisted cyclic signal amplification and poly(thymine)-templated copper nanoparticles (polyT-CuNPs). In the presence of PNK, cDNA with 5'-hydroxyl termini was phosphorylated and then hybridized with tDNA to form the cDNA/tDNA duplex, which subsequently triggered the λ exonuclease cleavage reaction, eventually resulting in the release of tDNA. The released tDNA could unfold the hairpin structure of HP DNA to generate partially complementary duplex (tDNA/HP DNA), wherein the HP DNA possessed T-rich sequences (T30) and tDNA recognition sequence. With the help of Exo III digestion, the tDNA was able to initiate the cycle for the generation of T-rich sequences, the template for the formation of fluorescent CuNPs. Conversely, the cDNA could not be cleaved by λ exonuclease without PNK and individual HP DNA could not be hydrolyzed by Exo III. The T-rich sequence was caged in HP DNA, resulting in a weak fluorescence signal. Under optimized conditions, the fluorescence intensity was linearly correlated to a concentration range of 0.001 to 1 U mL-1 with a low detection limit of 2 × 10-4 U mL-1. Considering the intriguing analytical performance, this approach could be explored to screen T4 PNK inhibitors and hold promising applications in drug discovery and disease therapy.

A nanoplatform based on metal-organic frameworks and coupled exonuclease reaction for the fluorimetric determination of T4 polynucleotide kinase activity and inhibition

A nanoplatform based on metal-organic frameworks (MOFs) and lambda exonuclease (λ exo) for the fluorimetric determination of T4 polynucleotide kinase (T4 PNK) activity and inhibition is described. Fe-MIL-88 was selected as the nanomaterial because of its significant preferential binding ability to single-stranded DNA (ssDNA) over double-stranded DNA (dsDNA) and its quenching property. The synthesized Fe-MIL-88 was characterized by transmission electron microscope, scanning electron microscope, and X-ray photoelectron spectroscopy. In the presence of T4 PNK, FAM-labeled dsDNA (FAM-dsDNA) is phosphorylated on its 5'-terminal. λ exo then recognizes and cleaves the phosphorylated strand yielding FAM-labeled ssDNA (FAM-ssDNA). The fluorescence of the produced FAM-ssDNA is quenched due to Fe-MIL-88's absorbing on FAM-ssDNA. On the contrary, in the absence of T4 PNK, the phosphorylation and cleavage processes cannot take place. Therefore, the fluorescence of FAM-dsDNA still remains. The fluorescence intensity is detected at the maximum emission wavelength of 524 nm using the maximum excitation wavelength of 488 nm. The assay of T4 PNK based on the fluorescence quenching of FAM-ssDNA achieves a linear relationship in the range 0.01-5.0 U mL^-1 with a detection limit of 0.0089 U mL^-1 in buffer. The assay exhibits excellent performance for T4 PNK activity determination in a complex biological matrix. The results also reveal the ability of the assay for T4 PNK inhibitor screening. Graphical abstract Schematic presentation of a nanoplatform based on Fe-MIL-88 and coupled exonuclease reaction for the fluorimetric determination of T4 polynucleotide kinase activity. FAM-ssDNA, FAM-labeled single-stranded DNA; cDNA, complementary DNA; λ exo, lambda exonuclease;T4 PNK, T4 polynucleotide kinase.

Aptamer-based colorimetric determination of early-stage apoptotic cells via the release of cytochrome c from mitochondria and by exploiting silver/platinum alloy nanoclusters as a peroxidase mimic

An enzyme-free aptameric nanosensor is presented for apoptosis assay. The method exploits the peroxidase-mimicking property of silver/platinum alloy nanoclusters (Ag/Pt NCs) and uses a Cyt c binding ssDNA aptamer. An extra-strand polycytosine (C₁₄) aptamer was designed as a template for synthesis of the Ag/Pt NCs. If cell lysate or purified Cyt c is placed in a polystyrene microplate, Cyt c will bind to the surface of the wells of a microtiterplate. On addition of Apt@Ag/PtNCs, it will associate with Cyt c and then catalytically oxidize colorless tetramethylbenzidine (TMB) in the presence of H₂O₂ to give a blue colored oxidation product (TMB_ox) due to the peroxidase-mimicking property of the Ag/Pt NCs. Under optimal conditions, the absorbance of TMB at 660 nm is linearly enhanced as the concentration of Cyt c increases from 50.0 fM to 500 nM, and the detection limit is ~10 pM. The assay is simple, sensitive and cost effective in that it is enzyme-free, antibody-free and label-free. Graphical abstractSchematic diagram of the apoptosis assay on the basis of microplate well-coated mitochondrial cytochrome c releasing by using Aptamer@Ag/Pt NCs.