A selective fluorescent turn-on NIR probe for cysteine

A selective and sensitive turn-on fluorescent NIR probe for cysteine has been developed. Cleavage of 2,4-dinitrobenzenesulfonyl (DNBS) with thiols switches the weakly fluorescent aza-BODIPY dye (λ(em) = 734 nm, Φ(f) = 0.03) to a strongly fluorescent species in the NIR region (λ(em) = 755 nm, Φ(f) = 0.14).     

A turn-on two-photon fluorescent probe for ATP and ADP

An acedan derivative containing Zn(II)-DPA has been developed as a two-photon probe for nucleoside phosphates, which shows enhanced fluorescence toward ATP and ADP at physiological pH 7.4 among other competing anions including AMP; the probe is permeable to cell membranes and thus can be directly used for two-photon imaging of ATP and ADP in live cells.     

A highly selective colorimetric and turn-on fluorescent probe for cyanide anion

A new colorimetric and turn-on fluorescence chemosensor was developed for cyanide anion with high selectivity in the presence of other anions in an aqueous THF solution. The sensing mechanism is attributed to the interruption of π-conjugation by a nucleophilic addition of cyanide to the β-position of a dicyanoethylene unit.     

A selective turn-on fluorescent sensor for Fe and application to bioimaging

A novel compound FD1 was demonstrated as a turn-on fluorescent sensor for imaging of iron(III) ion in biological samples. Based on the spirolactam (nonfluorescence) to ring-open amide (fluorescence) equilibrium, FD1 exhibited high selectivity and sensitivity for Fe³⁺ over other metal ions. Moreover, fluorescent microscopy experiments further established that FD1 could be used for sensing Fe³⁺ within living cells.     

A selective turn-on fluorescent sensor for imaging copper in living cells

We present the synthesis, properties, and biological applications of Coppersensor-1 (CS1), a new water-soluble, turn-on fluorescent sensor for intracellular imaging of copper in living biological samples. CS1 utilizes a BODIPY reporter and thioether-rich receptor to provide high selectivity and sensitivity for Cu+ over other biologically relevant metal ions, including Cu2+, in aqueous solution. This BODIPY-based probe is the first Cu+-responsive sensor with visible excitation and emission profiles and gives a 10-fold turn-on response for detecting this ion. Confocal microscopy experiments further establish that CS1 is membrane-permeable and can successfully monitor intracellular Cu+ levels within living cells.     

A borondipyrrolemethene-based turn-on fluorescent probe for silver ion with high sensitivity and selectivity and its application in water samples and living cells

A borondipyrrolemethene-based compound (1) is synthesized and used as a “turn-on” fluorescent probe for silver ions (Ag⁺). The probe displays highly sensitive fluorescence response toward Ag⁺ with a 40-fold fluorescence enhancement when 60 μM of Ag⁺ is added. The fluorescence intensity of the probe is linearly dependent on Ag⁺ concentration ranging from 0.05 to 60 μM. And the detection limit (LOD) can reach 0.02 μM, which complies with the standard of World Health Organization (WHO) for drinking water (0.9 μM). Moreover, the probe shows remarkable selectivity for Ag⁺ over other metal ions. Furthermore, the response behavior of 1 toward Ag⁺ is pH independent in the neutral range from 6.0 to 8.0. The response of 1 toward Ag⁺ is fast (response time is less than 2 min) and reversible chemically. What’s more, the sensing mechanism of probe 1 toward Ag⁺ is verified by mass spectra (MS) and density functional theory (DFT) calculations. In particular, the probe is applied for detection of Ag⁺ in water samples and living cells successfully.     

A boradiazaindacene-based turn-on fluorescent probe for cyanide detection in aqueous media

Turn on events: A molecular probe consisting of a boradiazaindacene unit conjugated with a dicyano-vinyl group has been designed for the selective and sensitive detection of cyanide by strong fluorescence enhancement in aqueous media (see scheme).     

A turn-on fluorescent iron complex and its cellular uptake

In the treatment of chronic iron overload disorders, ligands capable of complexing so-called "labile" (nonprotein bound) Fe are required to enter iron-loaded cells, sequester excess Fe, and then exit the cell (and the body) as an intact Fe complex. Despite the emergence of several ligand families that show high activity in mobilizing intracellular Fe, the mechanism and the locations of these subcellular labile Fe pools are still poorly understood. Our previous studies have unearthed a class of heterocyclic hydrazine-based chelators (e.g., benzoyl picolinoyl hydrazine, H(2)BPH) that show excellent activity at mobilizing Fe from Fe-loaded cells. Herein, we have grafted a fluorescent tag (rhodamine B) onto H(2)BPH to generate a ligand (L(1)) that is nonfluorescent in its uncomplexed form but becomes strongly fluorescent in complex with Fe(III). The free ligand and its 1:2 Fe complex [Fe(III)(L(1))(2)](3+) have both been fully characterized spectroscopically and with X-ray crystallography. Confocal fluorescent microscopy of HeLa cells incubated with [Fe(III)(L(1))(2)](3+) shows that the complex rapidly enters HeLa cells and localizes within endosomes/lysosomes.     

A simple pyrene-based highly sensitive turn-on fluorescent chemodosimeter for Hg2+

A highly sensitive fluorescent turn-on probe specific for mercury ion has been developed on the basis of mercury ion-promoted hydrolysis of a pyrene-1-carbaldehyde hydrazone (1). The chemical conversion of 1, catalyzed by Hg²⁺ ions, was studied by using UV, fluorescence and ¹H NMR spectroscopy, which clearly showed the conversion of 1 to highly fluorescent compound 1-pyrenecarboxaldehyde (2).     

A new spirobifluorene-bridged bipolar system for a nitric oxide turn-on fluorescent probe

A new spirobifluorene-bridged bipolar molecule (EDADO) as a nitric oxide (NO) turn-on fluorescent probe was designed and synthesized. The fluorescence of EDADO is strongly quenched by photoinduced electron transfer (PET) from the electron-donating o-phenylenediamine-containing biphenyl branch to the orthogonally arranged electron-accepting 1,3,4-oxadiazole-containing conjugated oligoaryl system. Upon reacting with NO, EDADO is converted to EDADO-T, which exhibits strong fluorescence due to the suppression of PET.     

A highly selective turn-on fluorescent chemosensor for copper(II) ion

A new pyrene derivative (1) containing a diaminomaleonitrile moiety exhibits high selectivity for Cu²⁺ detection. Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu²⁺. However, the metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Fe²⁺, Fe³⁺, Hg²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in fluorescence values for the system. The apparent association constant (K_a) of Cu²⁺ binding in chemosensor 1 was found to be 5.55×10³ M⁻¹. The maximum fluorescence enhancement caused by Cu²⁺ binding in chemosensor 1 was observed over the pH range 5-7.5.     

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.     

Conjugated metallopolymers for fluorescent turn-on detection of nitric oxide

A series of eight pi-conjugated polymers (CPs) composed of phenylenevinylene, phenyleneethynylene, fluorene, and thiophene derivatives have been prepared with bipyridyl or terpyridyl substituents within the pi-conjugated backbone or at side-chain positions. These ligand-modified CPs serve as macromolecular scaffolds for conducting metallopolymers. The optical and photoluminescent properties of the polymers and corresponding copper(II) metallopolymers were investigated. Copper(II) is a highly efficient quencher of CP emission (75-100% quenching). CPs featuring bipyridyl units within the CP backbone are quenched more efficiently than those with terpyridyl units. The copper(II) metallopolymer undergoes reduction to the corresponding copper(I) species upon reaction with nitric oxide, with concomitant changes in integrated emission ranging from a 50% decrease to a 320% increase. The positive emission response is largest when Cu(II) was bound to the CP through bipyridyl units within the backbone, making these materials the best candidates for NO sensing by a turn-on emission mechanism.     

A colorimetric and fluorescent turn-on chemosensor for Zn based on an azobenzene-containing compound

This paper presents a new colorimetric reversible fluorescent turn-on chemosensor molecule for zinc ion based on an azobenzene derivative. The basal fluorescence intensity of the chemosensor molecule is little affected under physiological pH 5-9, whilst the excitation (507 nm) and emission (610 nm) wavelength of the molecular probe for zinc ion is in the visible range.     

A two-photon fluorescent probe with a large turn-on signal for imaging hydrogen sulfide in living tissues

A two-photon fluorescence turn-on H₂S probe GCTPOC–H₂S based on a two-photon platform with a large cross-section, GCTPOC, and a sensitive H₂S recognition site, dinitrophenyl ether was constructed. The probe GCTPOC–H₂S exhibits desirable properties such as high sensitivity, high selectivity, functioning well at physiological pH and low cytotoxicity. In particular, the probe shows a 120-fold enhancement in the presence of Na₂S (500 μM), which is larger than the reported two-photon fluorescent H₂S probes. The large fluorescence enhancement of the two-photon probe GCTPOC–H₂S renders it attractive for imaging H₂S in living tissues with deep tissue penetration. Significantly, we have demonstrated that the probe GCTPOC–H₂S is suitable for fluorescence imaging of H₂S in living tissues with deep penetration by using two-photon microscopy. The further application of the two-photon probe for the investigation of biological functions and pathological roles of H₂S in living systems is under progress.     

A colorimetric and fluorescent turn-on chemosensor for Al and its application in bioimaging

The sensing properties of a boron dipyrromethene derivative 1 containing a N,N-(dimethylamino)styryl group at its α-position and an aniline moiety at meso-position were investigated by steady-state UV-vis absorption and fluorescence spectroscopy, which were found to exhibit wavelength ratiometric and large fluorescence enhancement in the presence of Al³⁺ with specific selectivity over other metal ions in aqueous media. Furthermore, confocal fluorescence microscopy experiments demonstrated that 1 could be used as a fluorescent probe for Al³⁺ in living cells.     

A ratiometric fluorescent probe for alkaline phosphatase with high sensitivity

Alkaline phosphatase(ALP)is one of essential biomarkers in mammalian tissue.Here we report a ratiometric probe for ALP,which is rationally designed and synthesized by employing ESIPT fluorophore N-(3-(benzo[d]thiazol-2-yl)-4-hydroxyphenyl)benzamide(BTHPB).The enzymatic dephosphorylation converts the probe to BTHPB,which exhibits a large spectral red-shift(120 nm),allowing extremely high sensitivity of ALP sensing at 0.004 mU/mL.The probe also shows excellent biocompatibility and has been applied for monitoring the endogenic ALP in living cells.     

A 1,8-naphthalimide-derived turn-on fluorescent probe for imaging lysosomal nitric oxide in living cells

Nitric oxide has played an important role in many physiological and pathological processes as a kind of important gas signal molecules. In this work, a new fluorescent probe LysoNO-Naph for detecting NO in lysosomes based on 1,8-naphthalimide was reported. LysoNO-Naph has sub-groups of o-phenylenediamine as a NO reaction site and 4-(2-aminoethyl)-morpholine as a lysosome-targetable group. This probe exhibited good selectivity and high sensitivity (4.57 μmol/L) toward NO in a wide pH range from 4 to 12. Furthermore, LysoNO-Naph can be used for imaging NO in lysosomes in living cells.     

A novel HPQ-based turn-on fluorescent probe for detection of fluoride ions in living cells

2-(2′-Hydroxyphenyl)-4(3H)-quinazolinone (HPQ) has been reported as a precipitating fluorescent molecule with excellent optical properties, such as large Stokes shift and strong fluorescence intensity. HPQF, a novel HPQ-based turn-on probe for localizable detection of fluoride ions, was designed, synthesized and fully characterized by ¹H NMR, ¹³C NMR and HRMS. As a chemogenic fluoride probe, the tert-butyldiphenylsilane moiety of HPQF can be easily cleaved by fluoride. After spontaneous 1,6-elimination, HPQ molecule was generated to emit fluorescence under the excitation light. Further study shows that HPQF exhibited high selectivity and sensitivity for detection of fluoride. In addition, HPQF was utilized for the detection of fluoride in living cells.