Construction principles to modify responsive performance of fluorescent receptors: From background clearance to signal enhancement

"Covalent-Disassembly"-Based Approaches For Sensing Applications

The detection of analytes with small molecular probes is crucial for the analysis and understanding of chemical, medicinal, environmental and biological situations as well as processes. Classic detection approaches rely on the concept of molecular recognition and bond formation reactions. Bond breakage reactions have been less explored in similar contexts. This concept article introduces metal-salen and metal-imine complexes as "covalent-disassembly"-based (DB)-probes for detecting polyoxophosphates, thiols, amino acids, HCN and changes in pH. It discusses the roles, importance and combinations of structurally functionalized molecular building blocks in the construction of DB-probes. Applications of optimized DB-probes for analyte detection in live cells and foodstuff are also discussed. Furthermore, the mechanism of the disassembly of a Fe(III)-salen probe upon pyrophosphate binding is presented. Extraordinary selectivity for this analyte was achieved by a multistep disassembly sequence including an unprecedented structural change of the metal complex (i. e. "induced-fit" principle). Design principles of probes for sensing applications following the "covalent-disassembly" approach are summarized, which will help improving current systems, but will also facilitate the development of new DB-probes for challenging analytic targets.

Imaging of a novel ratio γ-glutamyl transpeptidase fluorescent probe in living cells and biopsies

Herein, a novel fluorescent probe, GTP, was developed for monitoring the GGT (γ-glutamyl transpeptidase) level in living cells and biopsies. It consisted of the typical recognition group γ-Glu (γ-Glutamylcysteine) and the fluorophore (E)-4-(4-aminostyryl)-1-methylpyridin-1-ium iodide. With a ratio response between the signal intensity at 560 nm and 500 nm (R_I560/_I500), it could be important complement for the turn-on ones. With the linear range of 0-50 U/L, the limit of detection was calculated as 0.23 μM. The detection system showed the strongest response near pH 7.4, and exhibited steady fluorescence signals for at least 48 h. With high selectivity, good anti-interference and low cytotoxicity, GTP was suitable for physiological applications. By monitoring the GGT level with the ratio values in the green and blue channels, the probe GTP could distinguish cancer cells from normal cells. Furthermore, in the mouse tissues and humanization tissue samples, the probe GTP could also recognize the tumor tissues from the normal ones.

An α-naphtholphthalein-derived colorimetric fluorescent chemoprobe for the portable and visualized monitoring of Hg2+ by the hydrolysis mechanism

An ɑ-naphtholphthalein-derived colorimetric fluorescent chemoprobe was elaborately designed for the portable and visual monitoring of Hg2+ in environmental and biological samples.

A turn on fluorescent assay for γ-glutamyltransferase activity and its application in biological imaging

γ-glutamyltransferase (GGT) is widely presented in living cells and overexpressed in many tumor tissues. Therefore, it is generally considered as an important biomarker for the detection of tumor, especially for liver cancer. Accurate determination of its activity is helpful for early diagnosis and treatment of related diseases. In this work, a "turn on" fluorescent probe NSA-GGT for the detection of GGT activity based on glutamine bond was designed and synthesized by employing dansylamino as fluorophore. The probe shows good water solubility and can be well dispersed in aqueous buffer. After incubated with GGT in phosphate buffer, the fluorescence of NSA-GGT centered at ∼523 nm increased over 25-fold. This sensing pattern exhibits an intriguing sensing sensitivity for GGT, and has good performance on intracellular GGT staining, serving as a promising candidate for GGT measurement. Subsequent biological experiments showed that probe NSA-GGT could also be used for fluorescent imaging of GGT activity in living cells and animal tissues.

AND-Logic Strategy for Accurate Analysis of Alzheimer's Disease via Fluorescent Probe Lighted Up by Two Specific Biomarkers

Alzheimer's disease (AD) has become a global threat to the elderly health with a short survival time after diagnosis. Due to the asymptomatic stage during the early development, patients are usually diagnosed at the middle or late stage. Therefore, an efficient tool for AD early diagnosis deserves considerable attention, which could make a significant contribution to the treatment intervention. A fluorescent probe has been widely applied for detecting and visualizing species of interest in vitro and in vivo, and the proper reaction between the probe and analytes is responsible for the fluorescence change to provide a lighting-on or ratiometric responsive pattern with satisfactory sensing behavior. In this work, we report the first attempt to build up an AND-logic probe P2 for AD accuracy diagnosis taking butyrylcholinesterase (BChE) and reactive oxygen species (ROSs) as dual targets. Upon the co-stimulation by these two factors through enzymatic hydrolysis and redox reaction, the NIR emission could be readily turned on. This AND sensing pattern avoided the false-positive response effectively, and other diseases sharing one biomarker could hardly induce a NIR fluorescence response. The sensing assay has also been confirmed to be feasible in vitro and in vivo with good sensibility and selectivity. It is worth mentioning that the probe structure has been optimized in terms of the linkage length. This study shows that probe P2 with a connecting arm of medium length (one methylene, n = 1) has superior sensing performance, promising to provide a reference for the relative structure design.

A berberrubine-derived fluorescent probe for hydrazine and its practical application in water and food samples

In this work, we attempted to develop a fluorescent probe for hydrazine in real samples. Accordingly, we designed BER9-HZ to fulfill the set rules as solubility, anti-interference capability and functional compatibility. The selected reporting group BER9 dissolved 100% within 10 min, which indicated much better solubility than Berberine. The 615 nm reporting signal was in the Near-Infrared region. BER9-HZ presented advantages including wide linear range (0-20 equivalent), high sensitivity (detection limit 0.076 μM), steadiness (pH 7.0-13.0, temperature 25-45 °C), rapid response (within 20 min) and high selectivity in both independent and co-existing systems. Significantly, BER9-HZ could work steadily in real environmental, plant and food samples, thus be used in the detection of hydrazine (directly incubated or pre-treated with real sample) in living cells. Therefore, this work marched one step further to the systematic managing of hydrazine in real samples, and raised useful information for future investigations on Nitrogen circulation.

Fluorescent Determination of Butyrylcholinesterase Activity and Its Application in Biological Imaging and Pesticide Residue Detection

Butyrylcholinesterase (BChE) is an essential human cholinesterase relevant to liver conditions and neurodegenerative diseases, which makes it a pivotal biomarker of health. It therefore remains challenging and highly desired to elaborate efficient chemical tools for BChE with simple operations and satisfactory working performance. In this work, a background-free detection strategy was built by virtue of the judicious coupling of a specific BChE-enzymatic reaction and in situ cyclization. High sensitivity with a low limit of detection (LOD) of 0.075 μg/mL could be readily achieved from the blank background and the as-produced emissive indicators, and the specific reaction site contributed to the high selectivity over other bio-species even acetylcholinesterase (AChE). In addition to the multifaceted spectral experiments to verify the sensing mechanism, this work assumed comprehensive studies on the application. The bio-investigation ranged from cells to an organism, declaring a noteworthy prospect in disease diagnosis, especially for Alzheimer's disease (AD), a common neurodegenerative disease with over-expressed BChE. Moreover, its excellent work for inhibition efficacy elucidation was also proved with the accuracy IC₅₀ of tacrine for BChE (8.6 nM), giving rise to an expanded application for trace pesticide determination.