Fluorescent Protein-Based Turn-On Probe through a General Protection-Deprotection Design Strategy

Recent advances in fluorescent materials for mercury(ii) ion detection

Invading mercury would cause many serious health hazards such as kidney damage, genetic freak, and nerve injury to human body. Thus, developing highly efficient and convenient mercury detection methods is of great significance for environmental governance and protection of public health. Motivated by this problem, various testing technologies for detecting trace mercury in the environment, food, medicines or daily chemicals have been developed. Among them, the fluorescence sensing technology is a sensitive and efficient detection method for detecting Hg2+ ions due to its simple operation, rapid response and economic value. This review aims to discuss the recent advances in fluorescent materials for Hg2+ ion detection. We reviewed the Hg2+ sensing materials and divided them into seven categories according to the sensing mechanism: static quenching, photoinduced electron transfer, intramolecular charge transfer, aggregation-induced emission, metallophilic interaction, mercury-induced reactions and ligand-to-metal energy transfer. The challenges and prospects of fluorescent Hg2+ ion probes are briefly presented. We hope that this review can provide some new insights and guidance for the design and development of novel fluorescent Hg2+ ion probes to promote their applications.

Genetic encoding of ε-N-L-lactyllysine for detecting delactylase activity in living cells

Lysine ε-N-L-lactylation is a newly discovered post-translational modification. Herein we present the genetic encoding of ε-N-L-lactyllysine in bacterial and mammalian cells, allowing the preparation of site-specifically ε-N-L-lactylated recombinant proteins and the construction of fluorescent and luminescent probes for detecting delactylases in living cells. Using these probes, we demonstrate sirtuin 1 as a potential delactylase for non-histone proteins.

Dual-channel colorimetric fluorescent probe for determination of hydrazine and mercury ion

Hydrazine and mercury (Hg) poisoning represented a serious hazard to human health. So, developing method to detect and recognize them is highly desirable. Here, we prepared a multifunctional colorimetric and fluorescent probe (PI-Rh) consisting of a phenanthroimidazole (PI) dye conjugated with a Rhodamine (Rh) group for the effective recognition of hydrazine and Hg²⁺, induvidually and collectively, with different colorimetric and fluorescence outputs. Probe PI-Rh displays low detection limits measured to be 0.0632 μM (~2 ppb) and 0.0101 μM (~2 ppb) respectively for hydrazine and Hg²⁺ with high selectivity and excellent sensitivity. Moreover, the experimental results indicated that the superiority of this probe lied in its wide applications, for example, successful response in real water, and soil analysis. Interestingly, an visual, rapid, and real-time detection of gaseous hydrazine can be realized with 0.2793 μM detection limit using the facile PI-Rh-impregnated test paper.

Genetically encoding thyronine for fluorescent detection of peroxynitrite

Peroxynitrite is a highly reactive oxidant effecting cell signaling and cell death. Here we report a fluorescent protein probe to selectively detect peroxynitrite. A novel unnatural amino acid, thyronine (Thy), was genetically encoded in E. coli and mammalian cells by evolving an orthogonal tRNA^Pyl/ThyRS pair. Incorporation of Thy into the chromophore of sfGFP or cpsGFP afforded a virtually non-fluorescent reporter. Upon treatment with peroxynitrite, Thy was converted into tyrosine via O-dearylation, regenerating GFP fluorescence in a time- and concentration-dependent manner. Genetically encoded thyronine may also be valuable for other redox applications.

Design of fluorescent protein-based sensors through a general protection-deprotection strategy

Engineered fluorescent proteins have been extensively used in biological research for the study of gene expression, protein function and trafficking, and protein-protein interactions. In addition, fluorescent proteins have also been engineered to act as biosensing agents to detect intracellular signaling molecules and other small-molecule metabolites. Although they have been engineered extensively to achieve novel properties, fluorescent proteins are traditionally modified using the 20 canonical amino acids. This limits the number of functional groups that are available to the design and construction of novel fluorescent proteins. The expansion of the genetic code through the incorporation of noncanonical amino acids presents an opportunity to add new functionalities with the intent of modifying chemical and physical properties of fluorescent proteins. Herein we provide a general procedure for the site-specific incorporation of noncanonical amino acids into fluorescent proteins in live cells. We will also discuss a noncanonical amino acid-containing fluorescent protein sensor that is based on a general protection-deprotection design strategy, for the selective detection and quantification of Hg²⁺.

Mechanochemical Synthesis of a Fluorescein-Based Sensor for the Selective Detection and Removal of Hg2+ Ions in Industrial Effluents

Environmentally benign mechanochemistry-assisted high-yielding synthesis of fluorescein-phenylalaninol (FPA) conjugates as a Schiff base receptor is reported herein. This newly synthesized fluorescent probe is found to be most exciting and efficient because of its simultaneous detection and removal of mercury ions (Hg²⁺) in aqueous medium and industrial effluents through precipitate formation. The receptor successfully worked as a chemosensor in selectively sensing the Hg²⁺ ion through the rapid transition from yellow to pink in the colorimetric as well as quenching of fluorescence intensity in the fluorometric assay. The removal of mercury ions was confirmed by the inductively coupled plasma analysis of the supernatant. The lower detection limit of Hg²⁺ ions for the receptor FPA is 1.65 and 0.34 μM as determined through absorption and fluorescence spectroscopic methods, respectively. The high removal efficiency (∼98%) of the mercury ions is promising and could be achieved via the formation of the complex in a 1:1 stoichiometric ratio of receptor to Hg²⁺ ions. Furthermore, this probe may be a practical alternative for use in a paper-based portable device for achieving on-site detection of mercury ions in solid, solution, and vapor phases.

Coumarin Thiourea-Based Fluorescent Turn-on Hg2+ Probe That Can Be Utilized in a Broad pH Range 1-11

A novel coumarin-thiourea conjugate was synthesized facilely. It served as a fluorescent turn-on chemosensor for selective detection of Hg²⁺ ion over other common competitive metal ions including Li⁺, Na⁺, K⁺, Ag⁺, Cu²⁺, Fe²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺, Ca²⁺, Mg²⁺, Al³⁺, Cr³⁺ and Fe³⁺ ions based on the Hg²⁺-promoted desulfurization and cyclization reactions. Addition of Hg²⁺ ion to the sensor solution in 2:8 EtOH/H₂O induced a hypsochromic shift of the UV-Vis absorption band from 360 nm to 340 nm accompanying distinct enhancement in the absorption intensity while addition of other metal ions failed to bring about substantial change in the absorption spectra. Addition of Hg²⁺ to the sensor solution also caused marked increase in the fluorescence emission intensity and most common competitive metal ions did not interfere with the selective sensing of Hg²⁺ ion by the sensor. The detection limit of Hg²⁺ ion by the probe was calculated to be 1.46 × 10^-7 M and the probe could be utilized for selective detection of Hg²⁺ ion by fluorescence turn-on mode over a broad pH range of 1-11.

A nanomolar detection of mercury(II) ion by a chemodosimetric rhodamine-based sensor in an aqueous medium: Potential applications in real water samples and as paper strips

A new promising rhodamine based colorimetric and fluorometric chemosensor, RDV has been designed and synthesized for specific detection of Hg²⁺ ion. It acts as highly selective "turn-on" fluorescent chemosensor for Hg²⁺ ion without interference from other competitive metal ions in aqueous acetonitrile medium. The drastic color change with addition of Hg²⁺, from colorless to pink, indicates RDV can acts as "naked-eye" indicator for Hg²⁺. The Hg²⁺ promoted selective hydrolysis of appended vinyl ether group in RDV followed by Hg²⁺ chelated complex formation with concomitant opening of spirolactam ring is the plausible sensing mechanism. The detailed absorption, fluorescence, ¹H NMR, ¹³C NMR and mass spectrometry confirms the proposed sensing mechanism. The limit of detection (LOD) of Hg²⁺ by RDV is 136 nM indicating the high sensitivity towards Hg²⁺. The RDV shows consistent spectroscopic response in biological pH range 4-10. In addition to explore practical applicability of RDV, its paper strips have been made and used to detect Hg²⁺ in pure water solution up to 10 ppm level. Furthermore, the potential application of RDV for the sensing of Hg²⁺ in real water samples (tap water and drinking waters from different sources) were also monitored and demonstrated.

On/Off Fluorescent Chemosensor for Selective Detection of Divalent Iron and Copper Ions: Molecular Logic Operation and Protein Binding

Here, naphthalene diamine-based β-diketone derivative (compound LH) was successfully used as a dual signaling probe for divalent cations, Fe2+ and Cu2+ ions, in bimodal methods (colorimetric and fluorometric). It showed fluorescent enhancement for Fe2+ ion by photoinduced electron transfer mechanism and fluorescence quenching for Cu2+ ion by charge-transfer process. Binding stoichiometry for [LH-(Fe2+)2] and [LH-(Cu2+)2] was found to be 1:2 by Job's plot method and, the binding constants were calculated as 1.6638 × 1010 and 9.22929 × 108 M-1, respectively. Compound LH exhibited OR and XOR logic gate behavior with H+, Fe2+, and Cu2+ as inputs. Further, the compound LH and bovine serum albumin binding interaction showed quenching of fluorescence by Förster resonance energy-transfer mechanism.

Playing with the Molecules of Life

Our understanding of the complex molecular processes of living organisms at the molecular level is growing exponentially. This knowledge, together with a powerful arsenal of tools for manipulating the structures of macromolecules, is allowing chemists to to harness and reprogram the cellular machinery in ways previously unimaged. Here we review one example in which the genetic code itself has been expanded with new building blocks that allow us to probe and manipulate the structures and functions of proteins with unprecedented precision.

A thiocoumarin-based colorimetric and ratiometric fluorescent probe for Hg2+ in aqueous solution and its application in live-cell imaging

A new intramolecular charge transfer (ICT) based colorimetric and ratiometric fluorescent chemodosimeter for the detection of Hg²⁺ has been rationally designed and developed.

A novel ESIPT-based fluorescent chemodosimeter for Hg2+ detection and its application in live-cell imaging

A novel ESIPT-based fluorescent chemodosimeter for the detection of Hg²⁺ has been rationally designed and developed.

Genetically encoded fluorescent sensors for measuring transition and heavy metals in biological systems

Great progress has been made in expanding the repertoire of genetically encoded fluorescent sensors for monitoring intracellular transition metals (TMs). This powerful toolkit permits dynamic and non-invasive detection of TMs with high spatial-temporal resolution, which enables us to better understand the roles of TM homeostasis in both physiological and pathological settings. Here we summarize the recent development of genetically encoded fluorescent sensors for intracellular detection of TMs such as zinc and copper, as well as heavy metals including lead, cadmium, mercury, and arsenic.