Electronic Spectra of Cs2NaYb(NO2)6: Is There Quantum Cutting?

The crystal structure and electronic spectra of the T h symmetry hexanitritoytterbate(III) anion have been studied in Cs2NaY0.96Yb0.04(NO2)6, which crystallizes in the cubic space group Fm3̅. The emission from Yb3+ can be excited via the NO2- antenna. The latter electronic transition is situated at more than twice the energy of the former, but at room temperature, one photon absorbed at 470 nm in the triplet state produces no more than one photon emitted. Some degree of quantum cutting is observed at 298 K under 420 nm excitation into the singlet state and at 25 K using excitation into either state. The quantum efficiency is ∼10% at 25 K. The energy level scheme of Yb3+ has been deduced from excitation and emission spectra and calculated by crystal field theory. New improved energy level calculations are also reported for the Cs2NaLn(NO2)6 (Ln = Pr, Eu, Tb) series using the f- Spectra package. The neat crystal Cs2NaYb(NO2)6 has also been studied, but results were unsatisfactory due to sample decomposition, and this chemical instability makes it unsuitable for applications.

Highly sensitive graphene-Pt nanocomposites amperometric biosensor and its application in living cell H2O2 detection.

A sensitive hydrogen peroxide (H2O2) sensor was constructed based on graphene-Pt (RGO-Pt) nanocomposites and used to measure the release of H2O2 from living cells. The graphene and Pt nanoparticles (Pt NPs) were modified on glassy carbon electrode (GCE) by the physical adsorption and electrodeposition of K2PtCl6 solution, respectively. Through characterization by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), it was observed that the electrodeposited Pt NPs were densely covered and well distributed on the entire graphene surface. Electrochemical study demonstrates that the RGO-Pt nanocomposites modified glassy carbon electrode exhibited a high peak current and low overpotential toward the reduction of H2O2. The relevant detection limit of H2O2 is ∼0.2 µM with a wide linear range from 0.5 µM to 3.475 mM, displaying a much higher sensitivity (459 ± 3 mA M(-1) cm(-2), n = 5) than that of Pt nanoparticles or graphene modified electrode. This novel biosensor can measure the H2O2 release from living cells because of its low detection limit, wide linear range, and higher sensitivity.

Simultaneous electrochemical measurement of metal and organic propellant constituents of gunshot residues.

The simultaneous electrochemical measurement of heavy-metal and organic propellants relevant to gunshot residues (GSRs) is demonstrated. Cyclic voltammetry (CV) and cyclic square-wave stripping voltammetry (C-SWV) are shown to detect, in a single run, common propellants, such as nitroglycerin (NG) and dinitrotoluene (DNT), along with the heavy metal constituents of GSR, antimony (Sb), lead (Pb), zinc (Zn) and barium (Ba). The voltammetric detection of the stabilizer diphenylamine (DPA) along with inorganic constituents has also been examined. The resulting electrochemical signatures combine -in a single voltammogram- the response for the various metals and organic species, based on the reduction and oxidation peaks of the constituents. Cyclic square-wave voltammetry at the glassy carbon electrode (GCE), involving an intermittent accumulation at the reversal potentials of -0.95 V (for Sb, Pb, DNT and NG) and -1.3 V (for Sb, Pb, Zn and DPA) is particularly useful to offer distinct electrochemical signatures for these constituents of GSR mixtures, compared to analogous cyclic voltammetric measurements. Simultaneous voltammetric measurements of barium (at thin-film Hg GCE) and DNT (at bare GCE) are also demonstrated in connection to intermittent accumulation at the reversal potential of -2.4 V. Such generation of unique, single-run, information-rich inorganic/organic electrochemical fingerprints holds considerable promise for 'on-the-spot' field identification of individuals firing a weapon, as desired for diverse forensic investigations.

A red-light-activated sulfonamide porphycene for highly efficient photodynamic therapy against hypoxic tumor.

Photodynamic therapy (PDT) is an emerging alternative cancer treatment modality that utilizes photo-sensitivity to cause cell death upon photo-irradiation. However, PDT efficiency has been hampered by tumor hypoxia, blue-shifted excitation wavelengths, and the high dark toxicity of photo-sensitizers. We designed and synthesized two novel porphycene-based photosensitizers (TBPoS-OH and TBPoS-2OH) with potent photo-cytotoxicity and a LD50 in the nM range under both normoxic and hypoxic conditions in a variety of cell types after photo-irradiation (λ = 640 ± 15 nm). Further studies showed fast-cellular uptake for TBPoS-OH that localized lysosomes and subsequently induced cell apoptosis via the lysosomal-mitochondrial pathway. Moreover, TBPoS-OH significantly reduced tumor growth in two xenografted mouse models bearing melanoma A375 and B16 cells. Finally, TBPoS-OH exhibited no obvious immunogenicity and toxicity to blood cells and major organs in mice. These data demonstrated that these two porphycene-based photosensitizers, especially TBPoS-OH, could be developed as a potential PDT modality.

Energy Transfer between Tb3+ and Eu3+ in LaPO4: Pulsed versus Switched-off Continuous Wave Excitation.

The energy transfer (ET) between Tb3+ and Eu3+ is investigated experimentally and with available theoretical models in the regime of high Tb3+ concentrations in ≈30 nm LaPO4 nanoparticles at room temperature. The ET efficiency approaches 100% even for lightly Eu3+-doped materials. The major conclusion from the use of pulsed laser excitation and switched-off continuous wave laser diode excitation is that the energy migration between Tb3+ ions, situated on La3+ sites with ≈4 Å separation, is not fast. The quenching of Tb3+ emission in singly doped LaPO4 only reduces the luminescence lifetime by ≈50% in heavily doped samples. Various theoretical models are applied to simulate the luminescence decays of Tb3+ and Tb3+, Eu3+-doped LaPO4 samples of various concentrations and the transfer mechanism is identified as forced electric dipole at each ion.

Massive Stokes shift in 12-coordinate Ce(NO2)63-: crystal structure, vibrational and electronic spectra.

The Ce3+ ion in Cs2NaCe(NO2)6 (I), which comprises the unusual Th site symmetry of the Ce(NO2)63- ion, demonstrates the largest Ce-O Stokes shift of 8715 cm-1 and the low emission quenching temperature of 53 K. The activation energy for quenching changes with temperature, attributed to relative shifts of the two potential energy curves involved. The splitting of the Ce3+ 5d1 state into two levels separated by 4925 cm-1 is accounted for by a first principles calculation using the crystal structure data of I. The NO2- energy levels and spectra were investigated also in Cs2NaLa(NO2)6 and modelled by hybrid DFT. The vibrational and electronic spectral properties have been thoroughly investigated and rationalized at temperatures down to 10 K. A comparison of Stokes shifts with other Ce-O systems emphasizes the dependence upon the coordination number of Ce3+.

Accelerated direct electrochemistry of hemoglobin based on hemoglobin-carbon nanotube (Hb-CNT) assembly.

In this study, we have demonstrated that hemoglobin can be coupled to acid-treated multiwall carbon nanotubes in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and assembled as hemoglobin-carbon nanotube (Hb-CNT) composites. Our observations of the electrochemical studies demonstrate that the electrochemical response of Hb-CNT assembled in the presence of EDC is much higher than that in the absence of EDC. It is evident that the direct electron transfer of hemoglobin could be effectively accelerated in the Hb-CNT assembly by using EDC on a glassy carbon electrode (GCE), and the relative electron transfer rate constant K(s) is found to be 1.02+/-0.05 s(-1). The results of our studies illustrate that the assembly of hemoglobin-multiwall carbon nanotubes using EDC could provide a novel strategy to effectively facilitate the direct electrochemistry of heme-containing proteins, which could be further utilized as a promising biosensor for some specific biological substrate and related biological process.

Dependency of copper toxicity to polychaete larvae on algal concentration.

Algae are often used as food in aquatic metal toxicity tests to maintain the well-being of test animals. Such food addition may change metal bioavailability because of the reduction of aqueous metal concentration and the increase in particle-bound metal concentration. While the importance of aqueous exposure pathway is widely recognized, few studies have determined the contribution of the dietary pathway to the overall metal toxicity to aquatic invertebrates. In this study, we determined the toxicity of both algal-bound copper alone and copper solution containing algae to the larvae of marine polychaete Hydroides elegans. Algae that had been pre-exposed to copper at up to 1024 microg l(-1), when fed to the larvae, did not cause significant abnormal larval development. However, when larvae were exposed to algal-copper mixture, percentage of normal larvae could be modeled as a logistic function of aqueous copper concentration, with a 48-h EC(50) (mean +/- S.E.) of 64.9 +/- 4.8 microg Cul(-1). When the toxicity was expressed using total copper concentration, the EC(50) ranged from 58.4 +/- 4.5 microg l(-1) in the control to 121.9 +/- 9.9 microg l(-1) in the 10(6) cells ml(-1) algal treatment. This study highlights the dependency of copper toxicity on the aqueous exposure pathway in this polychaete and the importance of considering algal binding of the metal in larval toxicological tests.

Ultrasensitive electrochemical detection of miRNA-21 by using an iridium(III) complex as catalyst.

The ultrasensitive electrochemical detection of miRNA-21 was realized by using a novel redox and catalytic "all-in-one" mechanism with an iridium(III) complex as a catalyst. To construct such a sensor, a capture probe (CP) was firstly immobilized onto the gold electrode surface. In the presence of miRNA-21, a sandwiched DNA complex could form between CP and a methylene blue (MB) labeled G-rich detection probe modified onto a gold nanoparticle (AuNP) surface (DP-AuNPs). Upon addition of K(+), the structure of DP changed to a G-quadruplex. Then, the iridium(III) complex could selectively interact with the G-quadruplex, catalyzing the reduction of H2O2, which was accompanied by an electrochemical signal change using MB as an electron mediator. Under optimal conditions, the electrochemical signal of MB reduction peak was proportional to miRNA concentration in the range from 5.0 fM to 1.0 pM, with a detection limit of 1.6 fM. In addition, satisfactory results were obtained for miRNA-21 detection in human serum samples, indicating a potential application of the sensor for bioanalysis.

pH-Dependent Cancer-Directed Photodynamic Therapy by a Water-Soluble Graphitic-Phase Carbon Nitride-Porphyrin Nanoprobe.

Theranostic photodynamic nanomaterials suffer from poor water solubility and nontargeted toxicity. A water-soluble graphitic-phase carbon nitride-based material (g-C3 N4 ) conjugated to a positively charged porphyrin P2 (conjugating concentration: 60 µm mg-1 mL-1 ) is shown to be a new concept of photodynamic therapeutic agent (g-C3 N4 -P2). The pH-sensitive emission of g-C3 N4 is the driving force for the generation of 1 O2 from g-C3 N4 -P2. The amount of 1 O2 /light generated from a photosensitizer porphyrin can be controlled by the pH-sensitive emission of g-C3 N4 at acidic pH (pH 4-6), especially under acidic conditions mimicking those of tumor tissue, and thus has the potential to be utilized as a cancer-selective PDT agent.

Spontaneous Deposition of Prussian Blue on Multi-Walled Carbon Nanotubes and the Application in an Amperometric Biosensor.

A simple method has been developed for the spontaneous deposition of Prussian blue (PB) particles from a solution containing only ferricyanide ions onto conducting substrates such as indium tin oxide glass, glassy carbon disk and carbon nanotube (CNT) materials. Formation of PB deposits was confirmed by ultraviolet-visible absorption spectrometry and electrochemical techniques. The surface morphology of the PB particles deposited on the substrates was examined by atomic force microscopy and scanning electron microscopy. CNT/PB composite modified glassy carbon electrodes exhibited an electrocatalytic property for hydrogen peroxide reduction. These modified electrodes exhibited a high sensitivity for electrocatalytic reduction of hydrogen peroxide at -0.05 V (vs. Ag|AgCl), probably due to the synergistic effect of CNT with PB. Then, CNT/PB modified electrodes were further developed as amperometric glucose biosensors. These biosensors offered a linear response to glucose concentration from 0.1 to 0.9 mM with good selectivity, high sensitivity of 0.102 A M-¹ cm-2 and short response time (within 2 s) at a negative operation potential of -0.05 V (vs. Ag|AgCl). The detection limit was estimated to be 0.01 mM at a signal-to-noise ratio of 3.

Layer-by-layer assembly of Prussian blue and carbon nanotube composites with poly(diallyldimethylammonium chloride) for the sensitive detection of hydrogen peroxide.

Prussian blue (PB) was deposited on multi-walled carbon nanotubes (MWCNT) in an aqueous solution. Multi-layer composites of the MWCNT-PB hybride material were obtained by layer-by-layer assembly with poly(diallyldimethylammonium chloride) (PDDA). The resulting {PDDA/MWCNT-PB}(n) multilayer films immoblized on glassy carbon electrodes showed sensitive detection for the reduction of hydrogen peroxide. A sensor based on the {PDDA/MWCNT-PB}(n) multilayer structure was fabricated and showed excellent sensitivity to the electrochemical reduction of hydrogen peroxide. Its response sensitivity increased with the number of the multilayers. A high response sensitivity of 0.83 mA M(-1) cm(-2) was obtained for a seven-layer sensor. This redox active multilayer structure offers potential applications in the development of high performance biosensors and biofuel cells.

Electron-transfer properties of different carbon nanotube materials, and their use in glucose biosensors.

Different types of carbon nanotube material (single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) of different internal diameter) have been used for preparation of CNT-modified glassy-carbon electrodes. Redox reactions involving ferricyanide and hydrogen peroxide were examined at the CNT-modified electrodes. Electrodes modified with SWCNTs usually had better electron-transfer properties than MWCNT-modified electrodes. Glucose biosensors were also prepared with electropolymerized polyphenylenediamine films, CNT materials, and glucose oxidase. Amperometric behavior in glucose determination was examined. SWCNT-modified glucose biosensors usually had a wider dynamic range (from 0.1 to 5.5 mmol L-1) and greater sensitivity in glucose determination. The detection limit was estimated to be 0.05 mmol L-1.

Scanning tunneling microscopic and voltammetric studies of the surface structures of an electrochemically activated glassy carbon electrode.

The microscopic surface structures of electrochemically activated glassy carbon have been examined by scanning tunneling microscopy. Experimental results demonstrate that there are two different types of electrode surface sites, corresponding to the bundles and bundle edges of the fibrous graphite microcrystallities. Electrochemical activation results in the formation of new void spaces of different sizes, and the structures are affected by the electrochemical activation procedures employed. The void volume resulting from cyclic polarization is usually smaller than that obtained by potentostatic activation. Electrochemical behaviors of the activated electrode are related to both the new void structures and the size of the electroactive species employed. On the basis of the STM voltammetric results, the microscopic structure of the activated electrode is proposed.