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Highly stable and photoluminescent methylammonium lead halide perovskite quantum dots (MAPbBr3 PQDs) have been synthesized and applied for the fluorescence quenching detection of clothianidin in fruit and vegetable samples. Characterizations using different techniques, including photoluminescence (PL), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and time-resolved PL (TRPL), show that static quenching is the dominant fluorescence quenching mechanism of MAPbBr3 PQDs with clothianidin. Hydrogen bonds or van der Waals forces play major roles in the MAPbBr3 PQDs–clothianidin interaction. Under optimized conditions, the relative PL intensity of MAPbBr3 PQDs is linear to the concentration of clothianidin in the 0.0 and 20.0 mg/L range with a detection limit of 0.17 μg/kg. Excellent recoveries of 79.5–115.4% were acquired for radish and banana samples with a relative standard deviation below 9.4%. These results indicate that PQDs can be used for qualitative and quantitative identification of clothianidin, providing an effective detection method for risk prevention and control of neonicotinoid pesticide residues in agricultural products. [ABSTRACT FROM AUTHOR]

We report the development of nanoprobes that exploit the surface-enhanced Raman scattering (SERS) from nonaggregated, hollow, gold nanospheres (HGNSs). The homogeneity of the HGNSs leads to a nearly 10-fold improvement in signal consistency over standard silver SERS substrates, which translates into a significant increase in sensitivity and dynamic range for the model application of pH sensing. Moreover, the small size (30-nm diameter) of these SERS-active nanoparticles represents a major step in advancing sensing technology based on SERS, making this technology more amenable to intracellular sensing.

A study of a series of monomeric, homobimetallic, and heterobimetallic complexes with M(bpy)(sub 2)Cl-based moieties (M = Ru(super II) and Os(super II)) and ethynyl-and butadiynyl-bridged polyphosphines, using redox characteristics, electronic absorption, steady-state emission, nanosecond laser flash photolysis, and femtosecond laser spectroscopic is presented. The results show that electronic communication through polyphosphine/polyyne spacers is found to decrease upon increase of the carbon chain length.

A method of synthesis of colloidal glutathione and cysteine capped AG(sub2)S is reported.

A study was conducted to analyze electronic relaxation, rotational diffusion and vibrational relaxation in all-trans-1,8-diphenyl-1,3,5,7-octatetraene (DPO). DPO was prepared by recrystallization from ethanol. A pump-probe apparatus was utilized for the transient absorption measurements, and was based on a Ti:sapphire laser system. Results indicated fast photophysical processes and a solvent dependence that does not correlate to an energy gap law.

A study examined for the first time the photoexcited charge carriers in the nanoparticles of two forms of iron oxides, gamma-Fe2O3 and alpha-Fe2O3. Findings revealed that the photoexcited electrons are characterized by short lives and mainly nonradiative decay. Based on a power-dependency analysis, the relaxation mechanism for the early time decay is quite distinct from that observed in other semiconductor nanoparticles. The results have implications in the application of iron oxide nanoparticles in photocatalysis and magnetooptical devices.

Characterization of the photochemical reaction process and molecular structure of 1',3',3'-trimethyl-6-hydroxyspiro(2H-1-benzopyran-2,2'-indoline) in solution using picosecond and femtosecond transient electronic absorption spectroscopy was presented. Data revealed that the dissociation and subsequent re-formation of the C-O bond occurred in less than 100 and 200 femtoseconds, respectively. Also, the vibrational relaxation and isomerization times of the nascent adduct lasted in the picosecond range.

The method of sacrificial galvanic replacement of cobalt nanoparticles was used to synthesize nearly nondisperse hollow gold nanospheres (HGNs) with tunable interior and exterior diameters. The HGNs so synthesized show great potential for chemical and biological sensing applications, especially those requiring nanostructures with near-IR absorption.

The electronic conductivity of PbS and CdTe nanoparticle monolayers was examined voltammetrically by using interdigitated array (IDA) electrodes at the air/water interface. The conductivity of the final interfinger deposits was about two orders of magnitude smaller than that for pure metallic lead, indicating some surface contamination and/or less than perfect crystalline structure.

A study was conducted by using near infrared optical absorption methods on gold nanoparticle aggregates. The results show that the optical resonances in the visible are due to the gold surface plasma which are a function of the geometry of the particles.

The report describes the synthesis of PbS nanoparticles of different shapes and sizes with different surface capping using polymers including DNA. Pbs nanoparticles may find interesting applications in areas such as optical switching.

We report on the synthesis of semiconductor nanocrystals of PbS, ZnS, CdS, and MnS through a facile and inexpensive synthetic process. Metal-oleylamine complexes, which were obtained from the reaction of metal chloride and oleylamine, were mixed with sulfur. The reaction mixture was heated under appropriate experimental conditions to produce metal sulfide nanocrystals. Uniform cube-shaped PbS nanocrystals with particle sizes of 6, 8, 9, and 13 nm were synthesized. The particle size was controlled by changing the relative amount of PbCl[sub 2] and sulfur. Uniform 11 nm sized spherical ZnS nanocrystals were synthesized from the reaction of zinc chloride and sulfur, followed by one cycle of size-selective precipitation. CdS nanocrystals that consist of rods, bipods, and tripods were synthesized from a reaction mixture containing a 1:6 molar ratio of cadmium to sulfur. Spherical CdS nanocrystals (5.1 nm sized) were obtained from a reaction mixture with a cadmium to sulfur molar ratio of 2:1. MnS nanocrystals with various sizes and shapes were synthesized from the reaction of MnCl[sub 2] and sulfur in oleylamine. Rod-shaped MnS nanocrystals with an average size of 20 nm (thickness) × 37 nm (length) were synthesized from a 1:1 molar ratio of MnCl[sub 2] and sulfur at 240 °C. Novel bullet-shaped MnS nanocrystals with an average size of 17 nm (thickness) × 44 nm (length) were synthesized from the reaction of 4 mmol of MnCl[sub 2] and 2 mmol of sulfur at 280 °C for 2 h. Shorter bullet-shaped MnS nanocrystals were synthesized from a 3:1 molar ratio of MnCl[sub 2] and sulfur. Hexagon-shaped MnS nanocrystals were also obtained. All of the synthesized nanocrystals were highly crystalline. [ABSTRACT FROM AUTHOR]

A new and simple method has been developed to synthesize large quantities of highly monodisperse tetragonal zirconia nanocrystals. In this synthesis, a nonhydrolytic sol-gel reaction between zirconium(IV) isopropoxide and zirconium(IV) chloride at 340 °C generated 4 nm sized zirconia nanoparticles. A high-resolution transmission electron microscopic (HRTEM) image showed that the particles have a uniform particle size distribution and that they are highly crystalline. These monodisperse nanoparticles were synthesized without any size selection process. X-ray diffraction studies combined with Rietveld refinement revealed that the ZrO[sub 2] nanocrystals are the high-temperature tetragonal phase, and very close to a cubic phase. When zirconium(IV) bromide is used as a precursor instead of zirconium chloride, zirconia nanoparticles with an average size of 2.9 nm were obtained. The UV-visible absorption spectrum of 4 nm sized zirconia nanoparticles exhibited a strong absorption starting at around 270 nm. A fluorescence spectrum with excitation at 300 nm showed a broad fluorescence band centered around 370 nm. FTIR spectra showed indication of TOPO binding on the ZrO[sub 2] nanoparticle surface. These optical studies also suggest that the nanoparticles are of high quality in terms of narrow particle size distribution and relatively Iow density of surface trap states. [ABSTRACT FROM AUTHOR]

We report the first direct observation of the ultrafast electronic relaxation and coherent vibrational oscillation of strongly interacting gold nanoparticle aggregates measured by femtosecond laser spectroscopy. The electronic relaxation, reflected as a fast decay component with a time constant of 1.5-2.5 ps, becomes faster with decreasing pump power, similar to earlier observations of isolated gold nanoparticles. Surprisingly, periodic oscillations have been observed in the transient absorption/bleach signal and have been attributed to the coherent vibrational excitation of the gold nanoparticle aggregates. The oscillation period has been found to depend on the probe wavelength. As the probe wavelength is varied from 720 to 850 nm, the period changes from 37 to 55 ps. This suggests that the broad extended plasmon band (EPB) contains contributions from gold nanoparticle aggregates with different sizes and/or different fractal structures. Each of the different probe wavelengths therefore interrogates one subset of the aggregates with similar size or structure. Interestingly, the observed oscillation period for a given aggregate size determined by dynamic light scattering is longer than that predicted based on a elastic sphere model. One possible explanation is that the actual size of the aggregates is larger than what was observed from dynamic light scattering. An alternative, perhaps more likely, explanation is that the vibration of the aggregates is "softer" than that of hard spherical gold nanoparticles possibly because the longitudinal speed of sound is lower in the aggregates than in bulk gold. Persistent spectral hole burning was performed and yielded a hole in the nanoparticle aggregate's extended plasmon band, further supporting that the near-IR band is composed of absorption subbands from differently sized/structured aggregates. [ABSTRACT FROM AUTHOR]