Dual-site fluorescent probe for highly selective and sensitive detection of sulfite and biothiols

A dual-site fluorescent probe that could discriminatively respond to Cys and HSO^3- through two emission channels was reported, and it could further applied in imaging biothiols in living cells.     

一种基于查尔酮衍生物的荧光探针对巯基氨基酸的检测及细胞成像

生物硫醇(如半胱氨酸(Cys)、同型半胱氨酸(Hcy)及谷胱甘肽(GSH))与生物体和细胞中的许多生理和病理过程密切相关。荧光探针是对生物硫醇灵敏检测与成像的有力工具。本文合成了一种可检测生物硫醇的基于2′-羟基查尔酮荧光团开启型荧光探针1。探针中的2,4-二硝基苯磺酸酯基团既作为反应识别基团,又作为荧光猝灭基团。在DMSO/Tris(体积比8/2,pH=8.4)中,探针1与生物硫醇反应后释放出前体化合物3,3具有激发态分子内质子转移(ESIPT)和聚集诱导发光(AIE)特性,从而导致长波长荧光发射及较大的斯托克斯位移。探针1具有合成简单、灵敏度高、选择性高、细胞毒性低等优点,可以方便地检测溶液和活细胞中的生物硫醇。     

A sensitive and selective detection method for thiol compounds using novel fluorescence probe

In this work, a sensitive and selective detection method based on fluorescence resonance energy transfer (FRET) was developed for analyzing thiol compounds by using a novel fluorescent probe. The new fluorescent probe contains a disulfide bond which selectively reacts with nucleophilic thiolate through the thiol-disulfide exchange reaction. An obvious fluorescence recovery can be observed upon addition of the thiol compound in the fluorescent probe solution due to the thiol-disulfide exchange reaction and the destruction of FRET. This novel probe was successfully used to determine dithiothreitol (DTT), glutathione (GSH) and cysteine (Cys). The limits of detection (LOD) were 2.0 μM for DTT, 0.6 μM for GSH, and 0.8 μM for Cys. This new detection method was further investigated in the analysis of compound amino acid injection.     

A label-free DNA reduced graphene oxide-based fluorescent sensor for highly sensitive and selective detection of hemin

G-quadruplex structure aptamer (PS2.M) can capture acridine orange (AO) from reduced graphene oxide (rGO). When the AO-PS2.M/rGO mixture is incubated with hemin, the specific binding of hemin with PS2.M results in a release of AO from PS2.M and return of AO back to rGO. Based on the quenching of fluorescence, the target hemin was detected sensitively and selectively, giving a detection limit of 50 nM.     

Fluorescent probes for detection of biothiols based on “aromatic nucleophilic substitution-rearrangement” mechanism

“Aromatic nucleophilic substitution-rearrangement (SNAr-rearrangement)” mechanism provided a powerful tool to design fluorescent probes for the discrimination between biothiols.     

Highly sensitive fluorescent probe for detection of alkaloids

A new fluorescent probe, based on an amphiphilic Schiff-base zinc(II) complex, 1, for the sensitive detection of some important classes of alkaloids is presented. It exhibits optical absorption changes and fluorescence enhancement upon formation of 1:1 1·alkaloid adducts. Four diverse classes of alkaloids, represented by their basic structures and related representative prototypes, are investigated, through the study of optical and binding properties of 1·alkaloid adducts. It is found that the chromogenic and fluorogenic complex 1 is selective between these classes of alkaloids in the micromolar range, with a limit of quantification of 0.40 μM for nicotine and 0.43 μM for cinchonine.     

Highly sensitive fluorescent probe for selective detection of Hg2+ in DMF aqueous media

A highly sensitive fluorescent probe 1 for selective detection of Hg ion in mixed N,N-dimethylformamide aqueous media was designed and prepared by incorporating the well-known Rhodamine 6G fluorophore and a carbohydrazone binding unit into one molecule. The fluorescent probe 1 can detect the parts per billion level of HgII in a mixed aqueous environment and displays a highly selective response of fluorescence enhancement toward HgII.     

A novel AIEE and EISPT fluorescent probe for selective detection of cysteine

We designed and synthesized a simple and readily available fluorescent probe 3 for cysteine (Cys) based on naphthalene derivative. The probe is composed of a new class of aggregation-induced emission enhancement (AIEE) active dye 2 based on excited-state intramolecular proton transfer (ESIPT) and an acrylate group as the Cys recognition unit as well as the ESIPT blocking agent, which can be cut off by Cys from the probe in aqueous solution with mild conditions. The probe had great sensitivity and selectivity for the detection of Cys over homocysteine (Hcy) and glutathione (GSH) with a detection limit of 0.05 µM. In addition, we have successfully applied the probe for bioimaging studies of Cys in living cells, indicating that the probe holds great potential for biological applications.     

A selective coumarin-based “turn-on” fluorescent sensor for the detection of cysteine and its applications for bioimaging

A coumarin-based compound (1) was designed and synthesized as a new turn-on fluorescent probe for the detection of cysteine. The in vivo imaging of Hi5 cell and Caenorhabditis elegans had further confirmed the cysteine detection by compound 1.     

Reversible fluorescent probe for highly selective and sensitive detection of mercapto biomolecules

A coumarin-derived complex, Hg(2)L(2), was reported as a highly sensitive and selective probe for the detection of mercapto biomolecules in aqueous solution. The addition of Cys to a 99% aqueous solution of Hg(2)L(2) resulted in rapid and remarkable fluorescence OFF-ON (emission at 525 nm) due to the ligand-exchange reaction of Cys with L coordinated to Hg(2+). The increased fluorescence can be completely quenched by Hg(2+) and recovered again by the subsequent addition of Cys. Such a fluorescence OFF-ON circle can be repeated at least 10 times by the alterative addition of Cys and Hg(2+) to the solution of Hg(2)L(2), indicating that it can be used as a convertible and reversible probe for the detection of Cys. The interconversion of Hg(2)L(2) and L via the decomplexation/complexation by the modulation of Cys/Hg(2+) was definitely verified from their crystal structures. Other competitive amino acids without a thiol group cannot induce any fluorescence changes, implying that Hg(2)L(2) can selectively determine mercapto biomolecules. Using confocal fluorescence imaging, L/Hg(2)L(2) as a pair of reversible probes can be further applied to track and monitor the self-detoxification process of Hg(2+) ions in SYS5 cells.     

A turn-on fluorescent probe for selective and sensitive detection of hydrogen sulfide

An imidazolethione based turn-on fluorescent probe was synthesized for the detection of hydrogen sulfide, a biologically relevant molecule and an important air pollutant. The probe rapidly and selectively reacted with hydrogen sulfide to produce a strongly fluorescent product, resulting in the fluorescence enhancement of the system. The detection limit was determined to be 30 nM at the probe concentration of 1.0 μM. An indicating paper for visual detection of hydrogen sulfide gas has been fabricated by immobilizing the probe on a piece of appropriate paper substrate, and the detection limit of the visual method reached as low as 0.7 ppm. Moreover, the fluorescence turn-on/off of the system showed good reversibility when exposed alternately to hydrogen sulfide and mercuric ion, which was utilized to make an INHIBIT logic circuit for the presence of the two species.     

Graphene oxide-based biosensor for sensitive fluorescence detection of DNA based on exonuclease III-aided signal amplification

Based on the super fluorescence quenching efficiency of graphene oxide and exonuclease III aided signal amplification, we develop a facile, sensitive, rapid and cost-effective method for DNA detection. In the presence of target DNA, the target-probe hybridization forms a double-stranded structure and exonuclease III catalyzes the stepwise removal of mononucleotides from the blunt 3′ termini of probe, resulting in the recycling of the target DNA and signal amplification. Therefore, our proposed sensor exhibits a high sensitivity towards target DNA with a detection limit of 20 pM, which was even lower than previously reported GO-based DNA sensors without enzymatic amplification, and provides a universal sensing platform for sensitive detection of DNA.     

Highly selective and sensitive detection of Cu2+ with lysine enhancing bovine serum albumin modified-carbon dots fluorescent probe

Based on the ability of lysine (Lys) to enhance the fluorescence intensity of bovine serum albumin modified-carbon dots (CDs-BSA) to decrease surface defects and quench fluorescence of the CDs-BSA-Lys system in the presence of Cu(2+) under conditions of phosphate buffer (PBS, pH = 5.0) at 45 °C for 10 min, a sensitive Lys enhancing CDs-BSA fluorescent probe was designed. The environment-friendly, simple, rapid, selective and sensitive fluorescent probe has been utilized to detect Cu(2+) in hair and tap water samples and it achieved consistent results with those obtained by inductively coupled plasma mass spectroscopy (ICP-MS). The mechanism of the proposed assay for the detection of Cu(2+) is discussed.     

An ESIPT-based fluorescent probe for sensitive and selective detection of Cys/Hcy over GSH with a red emission and a large Stokes shift

An ESIPT-based fluorescent probe (Probe 1) using acrylate as recognition group for the selective and sensitive detection of cysteine/homocysteine (Cys/Hcy) has been developed. In the presence of Cys/Hcy, this probe was transformed into 1,3-bis(bispyridin-2ylimino)isoindolin-4-ol (dye 4) which displayed red fluorescence with a large Stokes shift (217 nm) when excited. The detection limits are as low as 5.4 nM and 7.0 nM for Cys and Hcy respectively (based on S/N = 3). Importantly, this probe has been successfully demonstrated for the detection of intracellular Cys/Hcy in living cells.     

Highly selective fluorescent recognition of glutathione by using a water soluble binaphthyl aldehyde

A water soluble binaphthyl-based aldehyde was designed and synthesized. This compound in combination with Zn(OAc)₂ is found to exhibit greatly enhanced fluorescence in the presence of GSH in aqueous solution (pH = 7.5) but give little or no fluorescence enhancement in the presence of cysteine, homocysteine and other amino acids. This remarkable selectivity makes this probe potentially useful for the analysis of the biologically important GSH.     

Highly selective separation and detection of cyromazine from seawater using graphene oxide based molecularly imprinted solid‐phase extraction

A novel molecularly imprinted polymer based on graphene oxide was prepared as a solid‐phase extraction adsorbent for the selective adsorption and extraction of cyromazine from seawater samples. The obtained graphene oxide molecularly imprinted polymer and non‐imprinted polymer were nanoparticles and characterized by scanning electron microscopy. The imprinted polymer showed higher adsorption capacity and better selectivity than non‐imprinted polymer, and the maximum adsorption capacity was 14.5 mg/g. The optimal washing and elution solvents for molecularly imprinted solid phase extraction procedure were 2 mL of acetonitrile/water (80:20, v/v) and methanol/acetic acid (70:30, v/v), respectively. The recoveries of cyromazine in the spiked seawater samples were in the range of 90.3–104.1%, and the relative standard deviation was <5% (n = 3) under the optimal procedure and detection conditions. The limit of detection of the proposed method was 0.7 μg/L, and the limit of quantitation was 2.3 μg/L. Moreover, the imprinted polymer could keep high adsorption capacity for cyromazine after being reused six times at least. Finally, the synthesized graphene oxide molecularly imprinted polymer was successfully used as a satisfied sorbent for high selectivity separation and detection of cyromazine from seawater coupled with high‐performance liquid chromatography.     

Highly selective two-photon fluorescent probe for imaging of nitric oxide in living cells简

A new two-photon fluorescent probe, ADNO, for nitric oxide （NO） based on intramolecular photoinduced electron transfer （PET） mechanism d/splays a rapid response to NO with a remarkable fluorescent enhancement in PBS buffer. The excellent chemoselectivity of ADNO for NO over other ROS/RNS （reactive oxygen species or nitrogen species） and common metal ions was observed. Moreover, ADNO has been successfully applied in fluorescence imaging of NO of living cells using both one-photon microscopy （OPM） and two-~hoton microscopy （TPM）,     

Size separation of graphene oxide using preparative free‐flow electrophoresis

Graphene oxide nanosheets often bear a wide size distribution. However, it is critical to have nanosheets with narrow size distribution for their unique size‐dependent physiochemical properties, and nanosheets with a narrow size distribution are the cornerstones for application. Therefore, efficient separation methods of graphene nanosheets have been given considerable attention in many scientific areas recently. Free‐flow electrophoresis is extensively used in the separation and purification of biological molecules with continuous flow separation. The charged graphene oxide nanosheets to some extent are very close in size to biological molecules and share similarity in motion behavior in an electric field. Thus, in the present work, we present a new and simple means to separate graphene oxide nanosheets into more mono‐dispersed size groups by using the free‐flow electrophoresis technique. By optimizing the separation conditions, we were able to obtain graphene oxide sheets with narrow size distribution. The separated samples were characterized by atomic force microscopy, and the size measurements were made by using the software “Image Pro Plus.” In addition, a brief discussion is also given into the theoretic background of the separation of graphene oxide according to the size by the technique of preparative free‐flow electrophoresis.     

Toehold-mediated nonenzymatic amplification circuit on graphene oxide fluorescence switching platform for sensitive and homogeneous microRNA detection

A novel graphene oxide (GO) fluorescence switch-based homogenous system has been developed to solve two problems that are commonly encountered in conventional GO-based biosensors. First, with the assistance of toehold-mediated nonenzymatic amplification (TMNA), the sensitivity of this system greatly surpasses that of previously described GO-based biosensors, which are always limited to the nM range due to the lack of efficient signal amplification. Second, without enzymatic participation in amplification, the unreliability of detection resulting from nonspecific desorption of DNA probes on the GO surface by enzymatic protein can be avoided. Moreover, the interaction mechanism of the double-stranded TMNA products contains several single-stranded toeholds at two ends and GO has also been explored with combinations of atomic force microscopy imaging, zeta potential detection, and fluorescence assays. It has been shown that the hybrids can be anchored to the surface of GO through the end with more unpaired bases, and that the other end, which has weaker interaction with GO, can escape GO adsorption due to the robustness of the central dsDNA structures. We verified this GO fluorescence switch-based detection system by detecting microRNA 21, an overexpressed non-encoding gene in a variety of malignant cells. Rational design of the probes allowed the isothermal nonenzymatic reaction to achieve more than 100-fold amplification efficiency. The detection results showed that our strategy has a detection limit of 10 pM and a detection range of four orders of magnitude.     

A new ESIPT-based fluorescent probe for highly selective and sensitive detection of HClO in aqueous solution

A new ESIPT-based fluorescent probe, PHC2, for the detection of hypochlorous acid has been rationally designed and developed. Endowed by the specific reaction between hypochlorous acid and phenyl azo group, PHC2 features high degree of selectivity and sensitivity for HClO with a low detection limit (13.2 nM) under physiological conditions in neutral aqueous solution.