Sequential Ag+/biothiol and synchronous Ag+/Hg2+ biosensing with zwitterionic Cu2+-based metal-organic frameworks

Recent Advancements in Sensing of Silver ions by Different Host Molecules: An Overview (2018-2023)

The chemosensors act as powerful tool in the detection of metal ions due to their simplicity, high sensitivity, low cost, low detection limit, rapid photophysical response, and application to the environmental and medical fields. This review article presents an overview for the chemosensing of Ag+ ions based on Calix, MOF, Nanoparticle, COF, Calix, Electrochemical chemosensor published from 2018 to 2023. Here, we have reviewed the sensing of Ag+ ions and summarised the binding response, mechanism, LOD, colorimetric response, adsorption capacity, technique used. The purpose of this review article to provide a detailed summary of the performance of different host chemosensors that are helpful for providing future direction to researchers on Ag+ ion detection and provides path to design effective chemsosensor (simple to synthesize, cost effective, high sensitivity, with more practical application). While studying the related article literature, we came across some challenges and that has been discussed lastly and provided solutions for them.

Selective and Sensitive Detection of Hg2+ and Ag+ by a Fluorescent and Colorimetric Probe with Large Stokes Shift

Development of fluorescent sensors with large Stokes shift for selective detection of heavy metals is of great importance. A novel fluorescent probe with extremely large Stokes shift (212 nm) was synthesized for selective and simultaneous detection of Hg2+ and Ag+ ions. The deep yellow probe turned colorless or pale yellow after addition of Hg2+ or Ag+. The new probe could be utilized for absorption spectral detection of Hg2+ and Ag+ both in ethanol and aqueous solution. Addition of Hg2+ and Ag+ ions caused significant decrease in the fluorescence intensity of the new probe and the selective recognition of Hg2+ and Ag+ was not interfered by common competitive metal ions including Li+, Na+, K+, Cu2+, Fe2+, Zn2+, Co2+, Ni2+, Mn2+, Sr2+, Ca2+, Mg2+, Al3+, Cr3+ and Fe3+. The detection limit for Hg2+ and Ag+ was calculated to be 4.68 μM and 4.29 μM, respectively. Application of the new probe for quantitative determination of Hg2+ and Ag+ concentrations in real water samples was accomplished.

Nanoscale Two-Dimensional FeII- and CoII-Based Metal-Organic Frameworks of Porphyrin Ligand for the Photodynamic Therapy of Breast Cancer

The delivery of biocompatible reagents into cancer cells can elicit an anticancer effect by taking advantage of the unique characteristics of the tumor microenvironment (TME). In this work, we report that nanoscale two-dimensional Fe^II- and Co^II-based metal-organic frameworks (NMOFs) of porphyrin ligand meso-tetrakis (6-(hydroxymethyl) pyridin-3-yl) porphyrin (THPP) can catalyze the generation of hydroxyl radicals (•OH) and O₂ in the presence of H₂O₂ that is overexpressed in the TME. Photodynamic therapy consumes the generated O₂ to produce a singlet oxygen (¹O₂). Both •OH and ¹O₂ are reactive oxygen species (ROS) that inhibit cancer cell proliferation. The Fe^II- and Co^II-based NMOFs were non-toxic in the dark but cytotoxic when irradiated with 660 nm light. This preliminary work points to the potential of porphyrin-based ligands of transition metals as anticancer drugs by synergizing different therapeutic modalities.

Detection of Pb2+ in Tea Using Aptamer Labeled with AIEgen Nanospheres Based on MOFs Sensors

Tea is an important economic crop and health beverage in China. The presence of heavy metal ions in tea poses a significant threat to public health. Here, we prepared an aptamer biosensor labelled with AIEgen nanospheres to detect Pb²⁺ in tea. The dsDNA modified by amino and phosphoric acid was combined with the carboxylated AIEgen NPs to form AIEgen-DNA with a fluorescence group, which was then fixed to the surface of Zr-MOFs to quench the fluorescence of AIEgen NPs. At the same time, PEG was added to remove nonspecific adsorption. Then Pb²⁺ was added to cut the DNA sequences containing the cutting sites, and AIEgen NPs and part of the DNA sequences were separated from the Zr-MOFs surface to recover the fluorescence. By comparing the fluorescence changes before and after adding Pb²⁺, the detection limit of Pb²⁺ can reach 1.70 nM. The fluorescence sensor was applied to detect Pb²⁺ in tea, and the detection results showed that the tea purchased on the market did not contain the concentration of Pb²⁺ within the detection range. This study provides new insights into monitoring food and agriculture-related pollutants based on fluorescent biosensors.

Incorporation of perovskite nanocrystals into lanthanide metal-organic frameworks with enhanced stability for ratiometric and visual sensing of mercury in aqueous solution

In-situ growth of CsPbBr₃ nanocrystal into Eu-BTC was realized for synthesis of dual-emission CsPbBr₃@Eu-BTC by a facile solvothermal method, and a novel ratiometric fluorescence sensor based on the CsPbBr₃@Eu-BTC was prepared for rapid, sensitive and visual detection of Hg²⁺ in aqueous solution. The transmission electron microscopy (TEM), X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analysis were used to verify the successful incorporation of CsPbBr₃ into the Eu-BTC. Meanwhile, the CsPbBr₃@Eu-BTC nanocomposite maintained high fluorescence performance and stability in aqueous solution. After adding Hg²⁺, the green fluorescence of CsPbBr₃ was quenched and the red fluorescence of Eu³⁺ remained unchanged, while the color changed from green to red obviously. The occurrence of dynamic quenching and electron transfer were verified by fluorescence lifetime, Stern-Volmer quenching constant and XPS analysis. The ratiometric fluorescence sensor shows high analytical performance for Hg²⁺ detection with a wide linear range of 0-1 μM and a low detection limit of 0.116 nM. In addition, it also shows high selectivity for the detection of Hg²⁺ and can be successfully applied to detect Hg²⁺ in environmental water samples. More importantly, a novel paper-based sensor based on the CsPbBr₃@Eu-BTC ratiometric probe was successfully manufactured for the visual detection of Hg²⁺ by naked eyes. This new type of ratiometric fluorescent sensor shows great potential for applications in point-of-care diagnostics.

New NIR spectroscopic probe with a large Stokes shift for Hg2+ and Ag+ detection and living cells imaging

A new near-infrared (NIR) probe based on a coumarinyl ligand (CL) was designed and synthesized. The probe CL can be used for simultaneous fluorescent turn-on and colorimetric detection of Hg²⁺ and Ag⁺ in ethanol/water medium. Colorless solution of probe CL changed to light yellow or dark yellow after addition of Hg²⁺ or Ag⁺ ions. Meanwhile the maximum absorption band shifted from 379 nm to 404 nm and the intensity increased enormously (for Hg²⁺) or moderately (for Ag⁺). Probe CL displayed an extraordinarily large Stokes shift of 316 nm and addition of Hg²⁺ or Ag⁺ to probe CL induced enhancement in the intensity of fluorescence emission at 695 nm by 15 or 8 fold. The detection limit of CL for Hg²⁺ and Ag⁺ ions is 0.83 and 8.8 μM, respectively. The applicable pH for sensing Hg²⁺ by probe CL is in a broad range of 2-12. Application of probe CL for in vitro U87MG cell imaging to detect Hg²⁺ ions was confirmed.

Connectivity Replication of Neutral Eu3+- and Tb3+-Based Metal-Organic Frameworks (MOFs) from Anionic Cd2+-Based MOF Crystallites

Neutral three-dimensional Eu³⁺- and Tb³⁺-based metal-organic frameworks (MOFs) with 4-fold interpenetration can be produced by seeding with anionic Cd²⁺-based MOF crystallites of identical connectivity. In the absence of these crystallites, two-dimensional networks are formed.

Metal-organic frameworks of linear trinuclear cluster secondary building units: structures and applications

Secondary building units (SBUs) in metal-organic frameworks (MOFs) are essential from both a structural and performance perspective. While a variety of SBUs, such as paddlewheel CuII2, triangular CrIII3, tetrahedral ZnII4, and octahedral ZrIV6 have been extensively studied, the linear trinuclear SBUs (herein denoted as M₃), though frequently encountered, are rarely discussed as a class. A literature survey reveals that M₃ clusters are ubiquitous in discrete molecular entities as well as in MOFs. Unlike most other cluster types, however, they have an unprecedented metal diversity and ligand tolerance. The single-crystals of some M₃-based MOFs are also sufficiently robust upon guest removal and exchange or multi-step post-modifications to enable catalytic mechanism elucidation. Some of these M₃-based SBUs endow MOFs with stability under demanding conditions necessary, for example, in flue gas separation. Herein we review MOFs sustained by this common but under-appreciated class of SBUs and discuss applications of the resulting MOF motifs.

High Catalytic Activity of Fluorophore-Labeled Y-Shaped DNAzyme/3D MOF-MoS2NBs as a Versatile Biosensing Platform for the Simultaneous Detection of Hg2+, Ni2+, and Ag+ Ions

In this study, we have designed a three-fluorophore-labeled Y-shaped DNAzyme with a high catalytic cleavage activity and a three-dimensional (3D) MOF-MoS₂NB (metal-organic framework fused with molybdenum disulfide nanobox), which was synthesized as an efficient quencher of the fluorescent biosensor. The synthesized porous 3D MOF-MoS₂NBs and Y-shaped DNAzyme exhibited a good analytical response toward the simultaneous multiple detections of Hg²⁺, Ni²⁺, and Ag⁺ ions over the other coexisting metal ions. More specifically, the three kinds of enzyme aptamer and substrate aptamer (SA) were hybridized and annealed to form the Y-shaped DNAzyme structure and labeled with three different fluorophores such as FAM, TAMRA, and ROX over the 3'-end of SA. When the targets were induced, the DNAzyme was triggered to cleave the fluorophore-labeled SAs. Then, the cleaved SAs (FAM-SA, TAMRA-SA, and ROX-SA) were adsorbed on the 3D MOF-MoS₂NB surface to quench the fluorescence signal due to a noncovalent interaction (van der Waals and π-π stacking interaction), which transmuted the fluorescence on-state to off-state. As a result, the fluorescence assay confiscated the high selectivity and sensitivity for the target analytes of Hg²⁺, Ni²⁺, and Ag⁺ ions achieved for the detection limits of 0.11 nM, 7.8 μM, and 0.25 nM, respectively. Accordingly, the sensitivity of the developed sensor was explored with a better lower detection limit than the previously reported biosensors. The utility of the designed Y-shaped DNAzyme may find a broad field of application in real water sample analysis with interfering contaminants.

Progress in Metal-Organic Frameworks Facilitated Mercury Detection and Removal

Metal Organic Frameworks (MOFs) are noted as exceptional candidates towards the detection and removal of specific analytes. MOFs were reported in particular for the detection/removal of environmental contaminants, such as heavy metal ions, toxic anions, hazardous gases, explosives, etc. Among heavy metal ions, mercury has been noted as a global hazard because of its high toxicity in the elemental (Hg0), divalent cationic (Hg2+), and methyl mercury (CH3Hg+) forms. To secure the environment and living organisms, many countries have imposed stringent regulations to monitor mercury at all costs. Regarding the detection/removal requirements of mercury, researchers have proposed and reported all kinds of MOFs-based luminescent/non-luminescent probes towards mercury. This review provides valuable information about the MOFs which have been engaged in detection and removal of elemental mercury and Hg2+ ions. Moreover, the involved mechanisms or adsorption isotherms related to sensors or removal studies are clarified for the readers. Finally, advantages and limitations of MOFs in mercury detection/removal are described together with future scopes.

Exploratory studies of a multidimensionally talented simple MnII-based porous network: selective “turn-on” recognition @ cysteine over homocysteine with an indication of cystinuria and renal dysfunction

Selective and real field detection of biothiols (Cys and Hcy) from aqueous and extra bio-matrices by a simple Mn^II-MOF.