FRET-based modified graphene quantum dots for direct trypsin quantification in urine.

A versatile nanoprobe was developed for trypsin quantification with fluorescence resonance energy transfer (FRET). Here, fluorescence graphene quantum dot is utilized as a donor while a well-designed coumarin derivative, CMR2, as an acceptor. Moreover, bovine serum albumin (BSA), as a protein model, is not only served as a linker for the FRET pair, but also a fluorescence enhancer of the quantum dots and CMR2. In the presence of trypsin, the FRET system would be destroyed when the BSA is digested by trypsin. Thus, the emission peak of the donor is regenerated and the ratio of emission peak of donor/emission peak of acceptor increased. By the ratiometric measurement of these two emission peaks, trypsin content could be determined. The detection limit of trypsin was found to be 0.7 µg/mL, which is 0.008-fold of the average trypsin level in acute pancreatitis patient's urine suggesting a high potential for fast and low cost clinical screening.

Selective tracking of lysosomal Cu2+ ions using simultaneous target- and location-activated fluorescent nanoprobes.

Levels of lysosomal copper are tightly regulated in the human body. However, few methods for monitoring dynamic changes in copper pools are available, thus limiting the ability to diagnostically assess the influence of copper accumulation on health status. We herein report the development of a dual target and location-activated rhodamine-spiropyran probe, termed Rhod-SP, activated by the presence of lysosomal Cu(2+). Rhod-SP contains a proton recognition unit of spiropyran, which provides molecular switching capability, and a latent rhodamine fluorophore for signal transduction. Upon activation by lysosomal acidic pH, Rhod-SP binds with Cu(2+) by spiropyran-based proton activation, promoting, in turn, rhodamine ring opening, which shows a "switched on" fluorescence signal. However, to protect Rhod-SP from degradation and interference by the physiological environment, it is engineered on mesoporous silica nanoparticles (MSNs), and the surface of Rhod-SP@MSNs is further anchored with ß-cyclodextrin (ß-CD) to enhance the solubility and bioavailability of Rhod-SP@MSN-CD. Next, to enhance cell specificity, a guiding unit of c(RGDyK) peptide conjugated adamantane (Ad-RGD) as prototypical system, is incorporated on the surface of Rhod-SP@MSN-CD to target integrin αvß3 and αvß5 overexpressed on cancer cells. Fluorescence imaging showed that both Rhod-SP@MSN-CD and Rhod-SP@MSN-CD-RGD were suitable for visualizing exogenous and endogenous Cu(2+) in lysosomes of living cells. This strategy addresses some common challenges of chemical probes in biosensing, such as spatial resolution in cell imaging, the solubility and stability in biological system, and the interference from intracellular species. The newly designed nanoprobe, which allows one to track, on a location-specific basis, and visualize lysosomal Cu(2+), offers a potentially rich opportunity to examine copper physiology in both healthy and diseased states.

A coumarin-based fluorescent probe for recognition of Cu(2+) and fast detection of histidine in hard-to-transfect cells by a sensing ensemble approach.

A coumarin-based fluorescent chemosensor CAQA has been synthesized. It can selectively and sensitively recognize Cu(2+) in aqueous acetonitrile solutions. Using the Cu-containing complex CAQA-Cu(2+) as a sensing ensemble, the device demonstrates highly selective recognition of His/biothiols and was applied in fluorescence imaging of histidine in hard-to-transfect living cells.

Ultrasound, pH, and magnetically responsive crown-ether-coated core/shell nanoparticles as drug encapsulation and release systems.

Core@shell nanoparticles with superparamagnetic iron oxide core, mesoporous silica shell, and crown ether periphery were fabricated toward drug delivery and tumor cell imaging. By the concept of nanovalve based on supramolecular gatekeeper, stimuli-responsive drug delivery nanosystems Fe3O4@SiO2@meso-SiO2@crown ethers were synthesized by (i) modified solvothermal reaction; (ii) sol-gel reaction; and (iii) amide coupling reaction. The successful coupling of the dibenzo-crown ethers onto the mesoporous silica shell was confirmed by thermogravimetric analysis and Infrared spectroscopy. In this system, the "ON/OFF" switching of the gatekeeper supramolecules can be controlled by pH-sensitive intramolecular hydrogen bonding or electrostatic interaction (such as metal chelating). Biological evaluation of the nanoparticles renders them noncytotoxic and can be uptaken by L929 cells. In this work, the antitumor drug (doxorubicin) loading and release profiles which were studied by the UV/visible absorption spectroscopy. The mechanism involves the best-fit binding of crown ethers with cesium or sodium ions at different pH values with ultrasonic wave in phosphate buffered saline (PBS). Magnetic resonance imaging analysis of the particles reveals a high relaxivity, rendering them potentially useful theranostic agents.

N-Acetyl-l-cysteine capped quantum dots offer neuronal cell protection by inhibiting beta (1-40) amyloid fibrillation.

This is the first work that revealed the neuro-protective effect of functionalized quantum dots against the cytotoxicity induced by beta-amyloid peptides. This study gives insight into the future treatment of Alzheimer's disease. It opens many avenues for the development of the next generation nanotechnology for biomedical and therapeutic applications.

Effect of surface-functionalized nanoparticles on the elongation phase of beta-amyloid (1-40) fibrillogenesis.

The influence of nanoparticles of various sizes and surface functionalities on the self-assembling fibrillogenesis of beta-amyloid (1-40) peptide was investigated. Functionalized nanoparticles including quantum dots and gold nanoparticles were co-incubated with monomeric Aß(1-40) peptides under seed-mediated growth method to study their influences on the elongation phase of the fibrillogenesis. It is observed that charge-to-surface area ratio of the nanoparticles and the functional moiety and electrostatic charges of the conjugated ligands on the particle surfaces took crucial regulatory role in the Aß(1-40) fibrillogenesis.

Chiral sulfonimide as a Brønsted acid organocatalyst for asymmetric Friedel-Crafts alkylation of indoles with imines.

Binaphthyl-based chiral sulfonimide (CSI) is demonstrated for the first time to be an efficient, strong Brønsted acid in asymmetric organocatalysis. A series of CSIs were synthesized and screened in the asymmetric Friedel-Crafts alkylation of indoles with imines. Good to excellent yields and enantioselectivities have been achieved. It was proved that it was crucial to wash the CSI catalyst with HCl before use.

Anthracene capped isobenzofuran: a synthon for the preparations of iptycenes and iptycene quinones.

Anthracene capped isobenzofuran 5 (5,6-(9,10-dihydroanthracen-9,10-yl)isobenzofuran) was synthesized for the first time. It is a highly reactive and versatile synthon for the synthesis of iptycene derivatives via Diels-Alder reactions. Cycloadducts 10 could be readily deoxygenated to iptycenes 11. Two new reactions of PhI(OAc)(2)/TfOH have been explored. Endoxides 10 were directly oxidized to iptycene quinones 12, and isobenzofuran 5 was conveniently converted to triptycene dialdehyde 16. H-shaped centrally extended pentiptycene quinones 13 and 14 were also synthesized.

An easy assembled fluorescent sensor for dicarboxylates and acidic amino acids.

Two mesitylene based neutral receptors 1 and 2 bearing two thiourea binding sites were constructed as fluorescent probes for sensing dicarboxylates. Their binding affinities toward dicarboxylates, aspartate and glutamate have been investigated in acetonitrile solution by fluorescence titration experiments. Both fluorescent sensors exhibited some ability to discriminate the antipodal forms of aspartate and glutamate.

Ratiometric fluorescent probe for enantioselective detection of D-cysteine in aqueous solution.

A ratiometric fluorescent probe based on a Cd(2+)-ACAQ complex was designed and demonstrated for the chemo- and enantioselective detection of cysteine in 99:1 buffered HEPES:ACN solutions. Under the measuring conditions, the sensor demonstrates high selectivity toward Cys against Hcy and GSH, and an enantioselectivity of 3.35 can be achieved for antipodal forms of Cys.

Oxadisilole fused triptycene and extended triptycene: precursors of triptycyne and extended triptycyne.

With benzobisoxadisilole 1 as a 1,4-benzdiyne equivalent, oxadisilole fused triptycene 5 and extended triptycene 6 were synthesized. Triptycenes 5 and 6 are new precursors of triptycyne 7 and extended triptycyne 8 respectively via the phenyliodination/fluoride induced elimination protocol. Using these two arynes, a series of triptycene derivatives were synthesized.

A colorimetric and fluorescent turn-on chemosensor operative in aqueous media for Zn2+ based on a multifunctionalized spirobenzopyran derivative.

By conjugating spiropyran chloride 8 with 2-amino-N-(quinolin-8-yl)acetamide (5), multifunctionalized spirobenzopyran derivative SPQN was designed and synthesized as a water soluble colorimetric and fluorescent turn-on chemosensor for Zn(2+). In 50% aqueous ethanol buffer solution, SPQN displayed a selective chelation fluorescence enhancement (16-fold) at 650 nm and visible color change (from colorless to red) with Zn(2+) among the metal ions examined. In addition, as the third channel to display the metal binding characteristics of SPQN, operating on an efficient FRET process between the quinoline and the merocyanine moiety of the sensor, ratiometric determination of Zn(2+) can be realized.

Spiropyran-based fluorescent anion probe and its application for urinary pyrophosphate detection.

In recent decades, numerous spiropyran derivatives have been designed and utilized for optical sensing of metal ions. However, there is still less research on spiropyran-based anion sensors. In this work, a new spiropyran compound (L) appended with a pendant bis(2-pyridylmethyl)amine was synthesized and used in fluorescent sensing of pyrophosphate ion (PP(i)) in aqueous solution. The molecular recognition and signal transduction are based on the cooperative ligation interactions and the ligation-induced structural conversion of the spiropyran, which leads to a significant change in the photophysical property of the spiropyran. In an ethanol/water solution (30:70, v/v) at pH 7.4, ligation of L with Zn(2+) causes an intense fluorescence emission at 620 nm at the expense of the original fluorescence at 560 nm. Once PP(i) was introduced, interaction between PP(i) and the L-Zn(2+) complex leads to full quenching of the 620 nm band emission which was concomitant with recovery of the 560 nm band emission, and the fluorescence intensity ratio, F(560)/F(620), is proportional to the PP(i) concentration. Under the optimum condition, the L-Zn(2+) complex responds to PP(i) over a dynamic range of 1.0 x 10(-6) to 5.0 x 10(-4) M, with a detection limit of 4.0 x 10(-7) M. The fluorescence response is highly selective for PP(i) over other biologically related substrates, especially the structurally similar anions, such as phosphate and adenosine triphosphate. The mechanism of interaction among L, Zn(2+), and PP(i) was primarily studied by (1)H NMR, (31)P NMR, and HRMS. To demonstrate the analytical application of this approach, the PP(i) concentration in human urine was determined. It was on the order of 3.18 x 10(-5) M, and the mean value for urinary PP(i) excretion by three healthy subjects was 62.4 micromol/24 h.

Quantum dot-mediated photoproduction of reactive oxygen species for cancer cell annihilation.

While semiconductor quantum dots produce little singlet oxygen, they may undergo Type I photoreactions to produce other reactive oxygen species (ROS) to kill cells. CdTe quantum dots coated with thioglycolic acid were used to test that possibility. Some thiol ligands were purposely removed to regenerate the surface electron traps that were passivated by the ligand. This allowed photoinduced electrons to dwell on the surface long enough to be gathered by nearby oxygen molecules to produce ROS. The photocytotoxicity of these quantum dots was tested on nasopharyngeal carcinoma cells. Photokilling was shown to be drug and light dose dependent. Using 0.6 mum quantum dots for incubation and 4.8 J cm(-2) for irradiation, about 80% of the cells were annihilated. These quantum dots promised to be potent sensitizers for photoannihilation of cancer cells.

Inhibition of beta 1-40 amyloid fibrillation with N-acetyl-L-cysteine capped quantum dots.

One of the primary factors that induce Alzheimer's disease (AD) is the deposition of beta-amyloid (Abeta). The Abeta molecules can self-assemble to form neurotoxic aggregates with various morphologies, such as dimers, oligomers, protofibrils and fibrils. For this aspect, we demonstrated that the amyloid fibrillation can be inhibited by quenching the nucleation and elongation processes with a low concentration of water dispersed N-acetyl-L-cysteine capped quantum dots (NAC-QDs). Based on the concentration dependence of NAC-QDs on the seeded fibril growth, there is a remarkable inhibition effect when the NAC-QDs concentration is increased by 100-fold from 10(-9) to 10(-7) M. The NAC-QDs concentration required to show inhibition effect is much lower than that of the amyloid peptide concentration (50 microM). The step-like change suggests that the inhibition effect of NAC-QDs displays a threshold response. The inhibition is likely due to the intermolecular attractive interactions such as the hydrogen bonding between NAC-QDs and amyloid fibrils resulting in the blockage of the active elongation sites on the fibrils.

Design of bis-spiropyran ligands as dipolar molecule receptors and application to in vivo glutathione fluorescent probes.

Despite considerable efforts toward the development of various sophisticated spiropyrans for metal ion sensing, less attention has been paid to organic molecule sensing. One of the major difficulties for detection of organic molecules using a spiropyran is the weak and nonspecific interaction between the spiropyran and the target. Here, we report the synthesis and molecular recognition characterization of two bis-spiropyrans for dipolar molecules and their application to in vivo glutathione (GSH) fluorescent probes. Unlike the mono-spiropyrans, the newly designed bis-spiropyran molecules feature a rigidly maintained molecular cleft and two spiropyran units as binding modules. The molecular recognition is based on multipoint electrostatic interactions and structure complementarity between the opened merocyanine form of the spiropyran and the analyte. It was observed that the spiropyran 1a binds GSH in aqueous solution with high affinity (K = (7.52 +/- 1.83) x 10(4) M(-1)) and shows strong fluorescence emission upon binding. Remarkably, fluorescence output of 1a is not significantly affected by other amino acids and peptides, especially, structurally similar compounds, such as cysteine and homocysteine. Furthermore, fluorescence anisotropy and confocal fluorescent microscopy confirmed that spiropyran 1a is a comparatively good candidate for intracellular delivery and can be accumulated intensively into cells. Thus, 1a can be utilized in vivo as a GSH probe or as a marker to show the level of intracellular GSH.

Spiropyran-based optical approaches for mercury ion sensing: improving sensitivity and selectivity via cooperative ligation interactions using cysteine.

Spiropyrans are an attractive starting point in design of optical approaches for metal ions sensing. However, the high background in aqueous solution and non-specific chelation of the spiropyran with heavy metal ions has hindered their application as reliable sensors for environmental and biological species. Here, we report on a new spiropyran-based approach for sensitive and selective sensing of Hg(2+) in aqueous solution, based on cooperative ligation interactions among the spiropyran probe, an intermediate, cysteine, and the metal ion. To test the feasibility of this design, three spiropyran scaffolds, L1-L3, with different ligation functions at the 8'-position were examined as model systems. The results demonstrate that by using cysteine, a potential ligand of Hg(2+), the spiropyran could detect 1.0x10(-7) M Hg(2+) in aqueous solution. Due to the specific metal-amino acid interaction, the approach exhibits selective response toward Hg(2+) over other metal ions and anions, although possible interference from Cu(2+) has to be considered at the high level of the metal ion. This approach has been used for the determination of Hg(2+) in water samples containing potential interferents with satisfactory recovery.

Camphor sulfonyl hydrazines (CaSH) as organocatalysts in enantioselective Diels-Alder reactions.

Cyclic sulfonyl hydrazine was demonstrated for the first time as a new functionality for organocatalysis. A series of six-membered cyclic hydrazines derived from camphor sulfonic acid were synthesized. With trichloroacetic acid as cocatalyst, they are efficient organocatalysts for enantioselective Diels-Alder reactions with good chemical yields and up to 96% ee. The reactions took place in brine at 0 degrees C to room temperature.

Cholic acid-based fluorescent probes for enantioselective recognition of trifunctional amino acids.

The ditopic fluorescent photoinduced electron transfer (PET) amino acid sensory probes and were designed and synthesized from cholic acid. To confer the probes with specific binding ability, an amidothiourea moiety and a cyclic diamino-chiral receptive site were introduced on the C17 side chain and the C7 and C12 hydroxyl pendants, respectively. In acetonitrile, the probes demonstrated differential binding toward trifunctional amino acids like serine, lysine, threonine and tyrosine against other simple amino acids. Enantioselectivities (KD/KL) of up to 8.9 and sensitivities in the micromolar range with the probes were observed for trifunctional amino acids.