Changlong Jiang

Real-Time Discrimination and Versatile Profiling of Spontaneous Reactive Oxygen Species in Living Organisms with a Single Fluorescent Probe.

Fluorescent probes are powerful tools for the investigations of reactive oxygen species (ROS) in living organisms by visualization and imaging. However, the multiparallel assays of several ROS with multiple probes are often limited by the available number of spectrally nonoverlapping chromophores together with large invasive effects and discrepant biological locations. Meanwhile, the spontaneous ROS profilings in various living organs/tissues are also limited by the penetration capability of probes across different biological barriers and the stability in reactive in vivo environments. Here, we report a single fluorescent probe to achieve the effective discrimination and profiling of hydroxyl radicals (•OH) and hypochlorous acid (HClO) in living organisms. The probe is constructed by chemically grafting an additional five-membered heterocyclic ring and a lateral triethylene glycol chain to a fluorescein mother, which does not only turn off the fluorescence of fluorescein, but also create the dual reactive sites to ROS and the penetration capability in passing through various biological barriers. The reactions of probe with •OH and HClO simultaneously result in cyan and green emissions, respectively, providing the real-time discrimination and quantitative analysis of the two ROS in cellular mitochondria. Surprisingly, the accumulation of probes in the intestine and liver of a normal-state zebrafish and the transfer pathway from intestine-to-blood-to-organ/tissue-to-kidney-to-excretion clearly present the profiling of spontaneous •OH and HClO in these metabolic organs. In particular, the stress generation of •OH at the fresh wound of zebrafish is successfully visualized for the first time, in spite of its extremely short lifetime.

Ratiometric fluorescence detection of mercuric ion based on the nanohybrid of fluorescence carbon dots and quantum dots

A novel nanohybrid ratiometric fluorescence probe comprised of carbon dots (C-dots) and hydrophilic CdSe@ZnS quantum dots (QDs) has been developed by simply mixing the blue-emission C-dots with red-emission carboxylmethyldithiocarbamate modified CdSe@ZnS QDs (GDTC-QDs). The nanohybrid ratiometric fluorescence probe exhibits dual emissions at 436 nm and 629 nm under a single excitation wavelength. Due to the strong chelating ability of GDTC on the surface of QDs to mercuric ion (Hg(2+)), the fluorescence of the GDTC-QDs in the nanohybrid system could be selectively quenched in the presence of Hg(2+) while the fluorescence of the C-dots remained constant, resulting in an obviously distinguishable fluorescence color evolution (from red to blue) of the nanohybrid system. The detection limit of this method was found to be as low as 0.1 μM. Furthermore, the recovery result for Hg(2+) in real samples including tap water and lake water by this method was satisfying, suggesting its potential application for Hg(2+) sensing.

Synthesis and characterization of ZnSe hollow nanospheres via a hydrothermal route

ZnSe hollow nanospheres have been hydrothermally synthesized at 140 °C for 24 h starting from the precursor ZnCl2(N2H4)2 and Na2SeO3 by using hydrazine hydrate (N2H4H2O) as the reducing agent. The sample was characterized by XRD, ICP-AES, FE-SEM, and TEM. The BET surface area of the obtained ZnSe hollow nanospheres is 77.13 m2 g−1. Both the transverse optic (TO) and longitudinal optic (LO) phonon peaks in Raman spectra of the ZnSe product showed a obvious shift to lower frequency compared to bulk values; a blue-shift () was observed in PL spectra. It appears that the hollow spheres might be formed by a soft-template of gas bubbles of N2 produced during the reaction.

Single clusters of self-assembled silver nanoparticles for surface-enhanced Raman scattering sensing of a dithiocarbamate fungicide

Hydrophobic silver (Ag) nanoparticles of ∼16 nm diameter were self-assembled as building blocks in an emulsion to form large spherical clusters upon the removal of organic solvents. The self-assembled clusters of Ag nanoparticles have diameters in the range 0.5–1.0 μm and are composed of thousands of densely packed Ag nanoparticles, leading to the generation of multiple active sites or hot spots for surface-enhanced Raman scattering (SERS) in a single cluster, as clearly observed using confocal Raman microscopy. Such single clusters of Ag nanoparticles show significant SERS activity for Rhodamine-6G and dithiocarbamates such as thiram. The enhancement factor for R6G was calculated to reach 1 × 109, which is possible for the observation of SERS signals of a single molecule of R6G according to literature reports. The as-prepared individual clusters of Ag nanoparticles have been demonstrated for the SERS detection of the agricultural chemical thiram. The results show that the detection limit for thiram is as low as 0.024 ppm, which is much lower than the maximal residue limit (MRL) of 7 ppm in fruit prescribed by U.S. Environmental Protection Agency (EPA). The system also possesses the ability to selectively detect dithiocarbamate compounds over other types of agricultural chemical. Furthermore, spiked and recovery tests show that the Ag nanoparticle clusters can be used to detect thiram in natural lake water and commercial apple juice without much interference.

Surface-enhanced Raman scattering sensor for theophylline determination by molecular imprinting on silver nanoparticles

A surface-enhanced Raman scattering (SERS)-based sensor for the determination of theophylline (THO) has been developed by imprinting the target molecules on the surface of silver nanoparticles. The desired recognition sites are generated after template removal and homogeneous distribution on the silver nanoparticles that have been incorporated within polymer matrix by the in situ reduction of theophylline-silver complexes, providing molecular recognition ability and SERS active surfaces. The theophylline molecules, complementary to the shape, size, and functionality of the recognition cavities, can selectively bind to the recognition sites at the surface of silver nanoparticles driven by the formation of hydrogen bonding and surface coordination. It has been demonstrated that the SERS signals of the theophylline molecules captured on the surface of the silver nanoparticles have a good reproducibility and a dose-response relationship to the target analytes, showing the potential for reliable identification and quantification of the bioactive compound. The molecular imprinting-based SERS sensor, like antibodies or enzymes, also possesses the ability to distinguish theophylline from the closely related structure caffeine due to the variations of molecular size and shape as well as the different affinity to silver ions.

Low-temperature solvothermal route to 2H–SiC nanoflakes

Silicon carbide nanoflakes have been synthesized through a one-step solvothermal route involving reaction of SiCl4 and CaC2 at 180°C for the first time. According to x-ray powder diffraction, infrared, and Raman spectra analysis, the obtained nanoflakes possess a crystalline structure of 2H–SiC. Electron microscopy investigations show that the nanoflakes have typical diameters of 200–500nm, thickness of ∼15nm, and grow along the [001] direction. The nanoflakes exhibit a new photoluminescence peak at ∼314nm, which is ascribed to defects in the SiOx. The possible growth mechanism of the nanoflakes is discussed.

Label-free surface-enhanced Raman scattering imaging to monitor the metabolism of antitumor drug 6-mercaptopurine in living cells.

The molecular processes of drugs from cellular uptake to intracellular distribution as well as the intracellular interaction with the target molecule are critically important for the development of new antitumor drugs. In this work, we have successfully developed a label-free surface-enhanced Raman scattering (SERS) technique to monitor and visualize the metabolism of antitumor drug 6-mercaptopurine in living cells. It has been clearly demonstrated that Au@Ag NPs exhibit an excellent Raman enhancement effect to both 6-mercaptopurine and its metabolic product 6-mercaptopurine-ribose. Their different ways to absorb at the surface of Au@Ag NPs lead to the obvious spectral difference for distinguishing the antitumor drug and its metabolite by SERS spectra. The Au@Ag NPs can easily pass through cell membranes in a large amount and sensitively respond to the biological conversion of 6-mercaptopurine in tumor cells. The Raman imaging can visualize the real-time distribution of 6-mercaptopurine and its biotransformation with the concentrations in tumor cells. The SERS-based method reported here is simple and efficient for the assessments of drug efficacy and the understanding of the molecular therapeutic mechanism of antitumor drugs at the cellular level.

A chemically reactive Raman probe for ultrasensitively monitoring and imaging the in vivo generation of femtomolar oxidative species as induced by anti-tumor drugs in living cells

A chemically reactive Raman probe has been developed for ultrasensitively monitoring and imaging the in vivo generation of femtomolar oxidative species as induced by anti-tumor drugs in living cells.

In situ loading of Ag nanocontacts onto silica nanospheres: a SERS platform for ultrasensitive detection

Analytical techniques based on surface-enhanced Raman scattering (SERS) suffer from a lack of reproducibility and reliability, thus hampering their practical applications. Herein, we have developed SiO2@Ag nanospheres as an effective SERS detection platform through in situ loading Ag nanocontacts onto the SiO2 nanospheres, the well-designed and uniform nanocomposites provide highly enhanced effects for the tremendous SERS signal amplification. The huge enhanced effect might originate from the hot spots generated from the nanocontacts among the silver nanoparticles loaded onto the silica nanosphere, and also possibly from the nanogaps among the neighboring silver nanoparticles between the two silica nanospheres. The SERS enhancement factor of the SiO2@Ag nanospheres substrate is as high as 1016. Moreover, the as-fabricated SERS substrate can be employed to enhance the Raman signals of some chemicals that are harmful to environment including thiram, melamine and ethyl-parathion. The detection limits with the SERS platform are several orders of magnitude lower than the maximal residue limit (MRL) in fruit prescribed by U.S. Environmental Protection Agency (EPA). Therefore the surface lifting spectroscopic technique based on the SiO2@Ag nanosphere SERS platform offers great practical potential for the on-site assessment and identification of harmful chemicals with ultralow concentrations in agricultural products and environments.

Controlled depositing of silver nanoparticles on flexible film and its application in ultrasensitive detection

Surface-enhanced Raman scattering (SERS) has been proven to be a powerful analytical tool for the detection of trace molecules because of its integration of high sensitivity, unique spectroscopic fingerprint, and non-destructive data acquisition. However, the lack of reliable, stable, well-defined, and uniform SERS substrates impedes their further practical applications. Herein, we have developed a SERS-active substrate based on a flexible and stable polymer (PDMS) film loaded with nanoparticles for ultrasensitive Raman signal readout and trace detection of pesticide residues in agricultural products and environments. By controlling the deposition of Ag nanoparticles, tremendous Raman enhancement can be achieved due to numerous hot spots generated among the Ag nanoparticles on the PDMS composite film. The flexible SERS film can be employed to detect rhodamine 6G (R6G) with an enhancement factor (EF) of 3.37 × 1011 and the pesticide thiram in commercial grape juice with a detection limit of as low as 0.1 μm (0.03 ppm), which is considerably lower than the maximum residue limit (MRL) of 7 ppm in fruit prescribed by the U.S. Environmental Protection Agency (EPA). Furthermore, spiked detection indicated that the AgNP–PDMS flexible film can be used to monitor thiram in commercial grape juice and natural lake water without further treatment. Therefore, the AgNP–PDMS flexible film enhanced Raman spectroscopic technique offers great potential for practical applications in the on-site monitoring and assessment of pesticide residues in agricultural products and environments.