Metal ion detection using a fluorogenic ‘click’ reaction

A Rhodamine-coumarin Triazole Conjugate as a Fluorescent Chemodosimeter for Cu(II) Detection and its Application in Live Cell Bioimaging

A rhodamine-triazole fluorescent probe bearing a coumarin moiety RTC was synthesized using the Cu(I)-catalyzed click reaction. The rhodamine-triazole conjugate was highly selective to Cu2+ among other metal ions, including Ca2+, Co2+, Cu2+, Cd2+, Mg2+, Fe2+, Fe3+, Hg2+, Zn2+, Ni2+, Pd2+ and Pb2+ in physiological conditions. Upon the addition of Cu2+, the colorless RTC solution turned pink and exhibited a significant fluorescence emission centered at 578 nm. The binding of Cu2+ induced a hydrolysis reaction, leading to a release of the coumarin unit from the rhodamine probe, as confirmed by mass spectrometric data. From the fluorescence titration, the detection limit of RTC for Cu2+ was determined to be 21 nM (1.3 ppb). The sensor was responsive to Cu2+ in a wide pH range and successfully applied to monitor Cu2+ in HEK293T cells by confocal fluorescence imaging.

From Bench to Cell: A Roadmap for Assessing the Bioorthogonal "Click" Reactivity of Magnetic Nanoparticles for Cell Surface Engineering

In this work, we report the use of bioorthogonal chemistry, specifically the strain-promoted click azide-alkyne cycloaddition (SPAAC) for the covalent attachment of magnetic nanoparticles (MNPs) on living cell membranes. Four types of MNPs were prepared, functionalized with two different stabilizing/passivation agents (a polyethylene glycol derivative and a glucopyranoside derivative, respectively) and two types of strained alkynes with different reactivities: a cyclooctyne (CO) derivative and a dibenzocyclooctyne (DBCO) derivative. The MNPs were extensively characterized in terms of physicochemical characteristics, colloidal stability, and click reactivity in suspension. Then, the reactivity of the MNPs toward azide-modified surfaces was evaluated as a closer approach to their final application in a living cell scenario. Finally, the DBCO-modified MNPs, showing superior reactivity in suspension and on surfaces, were selected for cell membrane immobilization via the SPAAC reaction on the membranes of cells engineered to express azide artificial reporters. Overall, our work provides useful insights into the appropriate surface engineering of nanoparticles to ensure a high performance in terms of bioorthogonal reactivity for biological applications.

Reaction pathway engineering converts a radical hydroxylase into a halogenase

Fe^II/α-ketoglutarate (Fe^II/αKG)-dependent enzymes offer a promising biocatalytic platform for halogenation chemistry owing to their ability to functionalize unactivated C-H bonds. However, relatively few radical halogenases have been identified to date, limiting their synthetic utility. Here, we report a strategy to expand the palette of enzymatic halogenation by engineering a reaction pathway rather than substrate selectivity. This approach could allow us to tap the broader class of Fe^II/αKG-dependent hydroxylases as catalysts by their conversion to halogenases. Toward this goal, we discovered active halogenases from a DNA shuffle library generated from a halogenase-hydroxylase pair using a high-throughput in vivo fluorescent screen coupled to an alkyne-producing biosynthetic pathway. Insights from sequencing halogenation-active variants along with the crystal structure of the hydroxylase enabled engineering of a hydroxylase to perform halogenation with comparable activity and higher selectivity than the wild-type halogenase, showcasing the potential of harnessing hydroxylases for biocatalytic halogenation.

Click chemistry as a tool in biosensing systems for sensitive copper detection

Copper detection for diagnostic purposes is an appealing field due to the important biological role copper plays as a trace metal. A convenient strategy for sensing copper is to utilize its catalytic ability. Therefore, this review summarizes approaches for copper determination by Cu^I-catalyzed azide/alkyne cycloaddition (CuAAC). The concept was introduced in 2006 and all contributions made up to the middle of 2020 are covered in this review. The issue is divided into three categories: electrochemical, visual, and fluorescence-based methods. The advantages, as well as the disadvantages, of every group, are discussed in detail. The methodology which allows for the determination of copper content in water and human biological samples from 5 s up to 48 h without complex instrumentation are discussed. The reported range of limit of detection (LOD) was 0.38 aM-20 μM, with 1-10 nM being the typical range. The most successful strategies involved using DNA chains or enzymes in the sensing systems.

The screening of metal ion inhibitors for glucose oxidase based on the peroxidase-like activity of nano-Fe3O4

In this study, a colorimetric method is proposed based on the peroxidase-like activity of Fe₃O₄magnetic nanoparticles for screening metal ion inhibitors for glucose oxidase activity.

Coumarin heterocyclic derivatives: chemical synthesis and biological activity

This review highlights the broad range of science that has arisen from the synthesis of coumarin-linked and fused heterocycle derivatives. Specific topics include their synthesis and biological activity.

Discrimination of colon cancer stem cells using noncanonical amino acid

Cancer stem cells (CSCs) may be responsible for tumor recurrence. Metabolic labelling of newly synthesized proteins with non-canonical amino acids allows us to discriminate CSCs in mixed populations due to the quiescent nature of these cells.

A benzothiazole alkyne fluorescent sensor for Cu detection in living cell

A new type of alkyne dye, 6-dimethylaminobenzothiazole alkyne (1), was developed for Cu sensing in biological system. Dye (1) offered excellent selective over a panel of ions, only Cu(I) could change the fluorescence of dye (I) by forming copper acetylide between the terminal alkyne and Cu(I). Its potential of detecting Cu in biological system was demonstrated in cell culture.

Quantum dot-based "turn-on" fluorescent probe for detection of zinc and cadmium ions in aqueous media

Health or environmental issue caused by abnormal level of metal ions like Zn(2+) or Cd(2+) is a worldwide concern. Developing an inexpensive and facile detection method for Zn(2+) and Cd(2+) is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn(2+) and Cd(2+) in aqueous media was reported. The proposed probe worked in fluorescence "turn-on" mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S(2-)). The presence of Zn(2+) (or Cd(2+)) can "turn-on" the weak fluorescence of QDs quenched by S(2-) due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn(2+) (or Cd(2+)) could be obtained in the range from 1.6 to 35 μM (1.3-25 μM for Cd(2+)). The limit of detection (LOD) for Zn(2+) and Cd(2+) were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn(2+) and Cd(2+) over other metal ions and was successfully used in the detection of Zn(2+) or Cd(2+) in real water samples.