A NIR fluorescence probe for monitoring Cys upregulation induced by balsam pear polysaccharide and imaging in zebrafish

In this work, we introduced the acrylate recognition group into dicyanoisophorone derivative DCI-C-OH to construct the NIR fluorescent probe DCI-C-Cys with a large Stokes shift (240 nm). DCI-C-Cys could specifically respond to Cys, resulting in a 22-fold increase in fluorescence intensity at 702 nm. Meanwhile, the probe has the advantages of good water solubility, high sensitivity (93 nM), and excellent biocompatibility. Moreover, DCI-C-Cys successfully monitored endogenous and exogenous Cys in HepG2 cells and zebrafish. Most importantly, we found that balsam pear polysaccharide could lead to the increase of intracellular Cys levels, which might be conducive to the further study of the antioxidant mechanism of balsam pear polysaccharide.

Genetic regulatory element based whole-cell biosensors for the detection of metabolic disorders

Clinicians require simple, and cost-effective diagnostic tools for the quantitative determination of amino acids in physiological fluids for the detection of metabolic disorder diseases. Besides, amino acids also act as biological markers for different types of cancers and cardiovascular diseases. Herein, we applied an in-silico based approach to identify potential amino acid-responsive genetic regulatory elements for the detection of metabolic disorders in humans. Identified sequences were further transcriptionally fused with GFP, thus generating an optical readout in response to their cognate targets. Screening of genetic regulatory elements led us to discover two promoter elements (pmetE::GFP and ptrpL::GFP) that showed a significant change in the fluorescence response to homocysteine and tryptophan, respectively. The developed biosensors respond specifically and sensitively with a limit of detection of 3.8 μM and 3 μM for homocysteine and tryptophan, respectively. Furthermore, the clinical utility of this assay was demonstrated by employing it to identify homocystinuria and tryptophanuria diseases through the quantification of homocysteine and tryptophan in plasma and urine samples within 5 h. The precision and accuracy of the biosensors for disease diagnosis were well within an acceptable range. The general strategy used in this system can be expanded to screen different genetic regulatory elements present in other gram-negative and gram-positive bacteria for the detection of metabolic disorders.

Fluorescein propiolate: a propiolate-decorated fluorescent probe with remarkable selectivity towards cysteine

A fluorescent probe decorated with an alkynyl ester unit (e.g. propiolate) displayed a selective turn-on type fluorescent response towards cysteine.

Chemosensors for biogenic amines and biothiols

There is burgeoning interest among supramolecular chemists to develop novel molecular systems to detect biogenic amines and bio-thiols in aqueous and non-aqueous media due to their potential role in biological processes. Biogenic amines are biologically important targets because of their involvement in the energy metabolism of human biological systems and their requirement is met through food and nutrition. However, the increasing instances of serious health problems due to food toxicity have raised the quality of food nowadays. Biogenic amines have been frequently considered as the markers or primary quality parameters of foods like antioxidant properties, freshness and spoilage. For instance, these amines such as spermine, spermidine, cadavarine, etc. may originate during microbial decarboxylation of amino acids of fermented foods/beverages. These amines may also react with nitrite available in certain meat products and concomitantly produce carcinogenic nitrosamine compounds. On the other hand, it is also well established that biothiols, particularly, thiol amino acids, provide the basic characteristics to food including flavor, color and texture that determine its acceptability. For instance, the reduction of thiol groups produces hydrogen sulfide which reduces flavour as in rotten eggs and spoiled fish, and the presence of hydrogen sulfide in fish is indicative of spoilage. Thus, biogenic amines and bio-thiols have attracted the profound interest of researchers as analytical tools for their quantification. Much scientific and technological information is issued every year, where the establishment of precise interactions of biogenic amines and bio-thiols with other molecules is sought in aqueous and non-aqueous media. This review summarizes the optical chemosensors developed for the selective detection of biogenic amines and bio-thiols.

A near-infrared fluorescent probe based on chloroacetate modified naphthofluorescein for selectively detecting cysteine/homocysteine and its application in living cells

We have prepared a near-infrared (NIR) turn-on fluorescent probe (NFC) based on chloroacetate modified naphthofluorescein for specific detection of cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) and other amino acids (AAs) with the detection limits of 0.30 μM and 0.42 μM, respectively. The fluorescence intensity of the naphthofluorescein (NF) chromophore is modulated by an internal charge transfer (ICT) process. The probe NFC is readily available and weakly fluorescent, but of observably enhanced fluorescence after reacting with Cys or Hcy. We assumed and then demonstrated that the fluorescence off-on process involves a conjugate nucleophilic substitution/cyclization sequence. Furthermore, the probe has been successfully applied for detecting the total content of Cys and Hcy in human plasma and imaging in living cells with low toxicity.

Enhanced Doubly Activated Dual Emission Fluorescent Probes for Selective Imaging of Glutathione or Cysteine in Living Systems

The development of novel fluorescent probes for monitoring the concentration of various biomolecules in living systems has great potential for eventual early diagnosis and disease intervention. Selective detection of competitive species in biological systems is a great challenge for the design and development of fluorescent probes. To improve on the design of fluorescent coumarin-based biothiol sensing technologies, we have developed herein an enhanced dual emission doubly activated system (DACP-1 and the closely related DACP-2) for the selective detection of glutathione (GSH) through the use of one optical channel and the detection of cysteine (Cys) by another channel. A phenylselenium group present at the 4-position completely quenches the fluorescence of the probe via photoinduced electron transfer to give a nonfluorescent species. Probes are selective for glutathione (GSH) in the red region and for cysteine/homocysteine (Cys/Hcy) in the green region. When they were treated with GSH, DACP-1 and DACP-2 showed strong fluorescence enhancement in comparison to that for closely related species such as amino acids, including Cys/Hcy. Fluorescence quantum yields (Φ_F) increased for the red channel (<0.001 to 0.52 (DACP-1) and 0.48 (DACP-2)) and green channel (Cys) (<0.001 to 0.030 (DACP-1) and 0.026 (DACP-2)), respectively. Competing fluorescent enhancements upon addition of closely related species were negligible. Fast responses, improved water solubility, and good cell membrane permeability were all properly established with the use of DACP-1 and DACP-2. Live human lung cancer cells and fibroblasts imaged by confocal microscopy, as well as live mice tumor model imaging, confirmed selective detection.

Nitroolefin-modified cyclometalated iridium(iii) complexes for tunable detection of biothiols with deep-red emission

Two nitroolefin-modified cyclometalated iridium(iii) complexes were employed as turn-on probes for the rapid (1 min) detection of biothiols with tunable emission.

A mitochondria-targeted turn-on fluorescent probe for the detection of glutathione in living cells

A novel turn-on red fluorescent BODIPY-based probe (Probe 1) for the detection of glutathione was developed. Such a probe carries a para-dinitrophenoxy benzyl pyridinium moiety at the meso position of a BODIPY dye as self-immolative linker. Probe 1 responds selectively to glutathione with the detection limit of 109nM over other amino acids, common metal ions, reactive oxygen species, reactive nitrogen species, and reactive sulfur species. A novel electrostatic interaction to modulate the SNAr attack of glutathione was believed to play significant role for the observed selective response to glutathione. The cleavage of dinitrophenyl ether by glutathione leads to the production of para-hydroxybenzyl moiety which is able to self-immolate through an intramolecular 1,4-elimination reaction to release the fluorescent BODIPY dye. The low toxic probe has been successfully used to detect mitochondrial glutathione in living cells.

Rapid and selective detection of cysteine over homocysteine and glutathione by a simple and effective coumarin-based fluorescent probe

A fluorescent probe, with coumarin as the fluorophore, is capable of detecting cysteine over other biothiols, such as homocysteine and glutathione.

Dual emission channels for sensitive discrimination of Cys/Hcy and GSH in plasma and cells

A new selective fluorescent and colorimetric chemosensor for the detection of GSH was developed. The discrimination of GSH from Cys and Hcy is achieved through two emission channel detection. The detection limit of probe 1 for GSH reached 10 nM (3 ppb). The excellent sensitivity and selectivity of probe 1 allow the selective detection of GSH over Cys and Hcy, which can be visualized colorimetrically and/or fluorescently. The sensitive detection of GSH allowed for convenient measurement of the GSH content in human plasma. The presence of GSH in cells was demonstrated through cell imaging.

Design strategies of fluorescent probes for selective detection among biothiols

Simple thiol derivatives, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play key roles in biological processes, and the fluorescent probes to detect such thiols in vivo selectively with high sensitivity and fast response times are critical for understanding their numerous functions. However, the similar structures and reactivities of these thiols pose considerable challenges to the development of such probes. This review focuses on various strategies for the design of fluorescent probes for the selective detection of biothiols. We classify the fluorescent probes for discrimination among biothiols according to reaction types between the probes and thiols such as cyclization with aldehydes, conjugate addition-cyclization with acrylates, native chemical ligation, and aromatic substitution-rearrangement.

A water soluble glucopyranosyl conjugate as a selective and reactive probe for cysteine in a buffer and its application to living cells

A water soluble and biocompatible glucopyranosyl conjugate (L) has been synthesized, characterized and shown to be selective to Cys among the naturally occurring amino acids. TheLshows green fluorescence upon reaction with –SH containing molecules present in biological cells and hence provides cell imaging.

Sensitive and regenerable organochalcogen probes for the colorimetric detection of thiols

Isothiazolone and isoselenazolone based colorimetric probes for the detection of thiols have been reported. A regenerable probe for the detection of organothiols is developed from isoselenazolone. Both of these probes possess higher selectivity for aromatic thiols, cysteine and glutathione.

Extremely selective fluorescence detection of cysteine or superoxide with aliphatic ester hydrolysis

A novel fluorescence probe modality demonstrated with fluorescein affords a highly selective aqueous-based detection of cysteine over other biothiols,e.g.homocysteine, with a limit of detection of 11.3 μM.