Yukiyasu Kashiwagi

Imaging Mass Spectrometry with Silver Nanoparticles Reveals the Distribution of Fatty Acids in Mouse Retinal Sections

A new approach to the visualization of fatty acids in mouse liver and retinal samples has been developed using silver nanoparticles (AgNPs) in nanoparticle-assisted laser desorption/ ionization imaging mass spectrometry (nano-PALDI-IMS) in negative ion mode. So far, IMS analysis has concentrated on main cell components, such as cell membrane phospholipids and cytoskeletal peptides. AgNPs modified with alkylcarboxylate and alkylamine were used for nano-PALDI-IMS to identify fatty acids, such as stearic, oleic, linoleic, arachidonic, and eicosapentaenoic acids, as well as palmitic acid, in mouse liver sections; these fatty acids are not detected using 2,5-dihydroxybenzoic acid (DHB) as a matrix. The limit of detection for the determination of palmitic acid was 50 pmol using nano-PALDI-IMS. The nano-PALDI-IMS method is successfully applied to the reconstruction of the ion images of fatty acids in mouse liver sections. We verified the detection of fatty acids in liver tissue sections of mice by analyzing standard lipid samples, which showed that fatty acids were from free fatty acids and dissociated fatty acids from lipids when irradiated with a laser. Additionally, we applied the proposed method to the identification of fatty acids in mouse retinal tissue sections, which enabled us to learn the six-zonal distribution of fatty acids in different layers of the retina. We believe that the current approach using AgNPs in nano-PALDI-IMS could lead to a new strategy to analyze basic biological mechanisms and several diseases through the distribution of fatty acids.

The detection of glycosphingolipids in brain tissue sections by imaging mass spectrometry using gold nanoparticles

Glycosphingolipids (GSLs) are amphiphilic molecules consisting of a hydrophilic carbohydrate chain and a hydrophobic ceramide moiety. They appear to be involved primarily in biological processes such as cell proliferation, differentiation, and signaling. To investigate the mechanism of brain function in more detail, a more highly sensitive method that would reveal the GSL distribution in the brain is required. In this report, we describe a simple and efficient method for mapping the distribution and localization of GSLs present in mouse brain sections using nanoparticle-assisted laser desorption/ionization imaging mass spectrometry (IMS). We have developed and tested gold nanoparticles (AuNPs) as a new matrix to maximize the detection of GSLs. A matrix of AuNPs modified with alkylamine was used to detect various GSLs, such as minor molecular species of sulfatides and gangliosides, in mouse brain sections; these GSLs were hardly detected using 2,5-dihydroxybenzoic acid (DHB), which is the conventional matrix for GSLs. We achieved approximately 20 times more sensitive detection of GSLs using AuNPs compared to a DHB matrix. We believe that our new approach using AuNPs in IMS could lead to a new strategy for analyzing basic biological mechanisms and several diseases through the distribution of minor GSLs.

Novel photocatalytic function of porphyrin-modified gold nanoclusters in comparison with the reference porphyrin compound

The photocatalytic function of three-dimensional porphyrin monolayer-protected gold clusters (MPCs) with different chain lengths has been examined in photocatalytic reduction of hexyl viologen (HV2+) by 1-benzyl-1,4-dihydronicotinamide (BNAH) in comparison with that of the reference porphyrin compound without metal clusters. Both porphyrin monolayer-protected gold clusters and the reference porphyrin compound act as efficient photocatalysts for the uphill reduction of HV2+ by BNAH to produce 1-benzylnicotinamidinium ion (BNA+) and hexyl viologen radical cation (HV•+) in benzonitrile. In the case of porphyrin monolayer-protected gold clusters the quantum yield reaches a maximum value with an extremely low concentration of HV2+, which is larger than the corresponding value of the reference porphyrin compound. The dependence of quantum yields on concentrations of BNAH and HV2+ as well as the time-resolved single-photon-counting fluorescence and transient absorption spectroscopic results indicates that the ph...

Metal and size effects on structures and photophysical properties of porphyrin-modified metal nanoclusters

Three-dimensional (3D) porphyrin monolayer protected metal nanoclusters (MPCs) have been prepared to examine the effects of metal (Au, Ag, Au–Ag alloy, Pd and Pt) and size (1–3 nm) on the structures and photophysical properties. The quenching rate constants of the porphyrin excited singlet state by the surfaces of mono-metal nanoclusters and gold nanoclusters with different diameters are virtually the same. In contrast, the quenching rate constant of the gold–silver alloy nanocluster is half that of the corresponding mono-metal clusters (i.e. Au or Ag). This reveals that interaction between the surface of the gold–silver alloy and the porphyrin excited singlet state is attenuated as compared wtih the mono-metal systems. Thus, porphyrin metal alloy nanoclusters are potential candidates as a new type of artificial photosynthetic materials and photocatalysts.

A Variety of Silver Nanoparticle Pastes for Fine Electronic Circuit Pattern Formation

Metal powder-based thick-film pastes are limited to make the electronic circuit pattern on the refractory ceramics or glass, because of their firing temperature. In addition, the line width and space of the circuit pattern are limited over 50 mum. However, the electronic devices are recently demanded to be compact, lightweight and flexible. For this demand, recent progress of nanotechnology has accelerated to develop a new type of materials for electronic devices. From this point of view, much attention has been paid to metal nanoparticles with diameters ranging from several nanometers to tens of nanometers, which may be expected to be fired at low temperature less than 300degC based on their physical property. Using a series of silver nanoparticles, we have developed the low temperature firing silver nanoparticle pastes, including silver nanoparticles stabilized by a series of organic ligands. The silver contents of the manufactured silver nanoparticle pastes are easily controlled ranging from 50 to 90 wt%. The electronic circuit pattern can be formed on a polyimido film by screen printing technique and fired at low temperatures of 150 to 300degC. The formed conductive films exhibit the resistivity compared with that of bulk metal. The film thickness ranges from 2.6 to 30 mum and their resistivity is 2.46 to 40 muOmegacm. This paper describes a variety of silver nanoparticle pastes and the properties of their fired film.

An extremely long-lived charge-separated state of zinc tetraphenylporphyrin coordinated with pyridylnaphthalene-diimide

The nitrogen of pyridylnaphthalenediimide (PyNIm) coordinates to the metal center of zinc tetraphenylporphyrin (ZnTPP) to form a donor-acceptor complex: ZnTPP-PyNIm. Formation of the ZnTPP-PyNIm complex was probed by UV-vis, fluorescence and NMR spectra. The fluorescence of ZnTPP is strongly quenched and the fluorescence lifetime is shortened significantly in the complex. The transient absorption spectrum of the charge-separated state (ZnTPP•+-PyNIm•-) is successfully detected by laser flash photolysis measurements of the ZnTPP-PyNIm system in benzonitrile. The charge-separated state of the complex produced by the photoinduced electron transfer has the longest lifetime, (450 μs) at 288 K, ever reported for donor-acceptor systems linked covalently or non-covalently in solution. However, when benzonitrile is replaced by benzene, the triplet excited state (3ZnTPP*), rather than the charge-separated state, is formed upon laser excitation of the ZnTPP-PyNIm complex, due to the lower energy of (3ZnTPP*) compared to the charge-separated state in benzene.

Photoinduced electron transfer in a supramolecular triad system composed of ferrocene-zinc porphyrin-pyridylnaphtha-lenediimide

A supramolecular ferrocene-zinc porphyrin-pyridylnaphthalenediimide triad is formed by coordinating the pyridine entity of pyridylnaphthalenediimide with the zinc ion of a ferrocene-zinc porphyrin dyad in benzonitrile. The fluorescence of the zinc porphyrin moiety is efficiently quenched by photoinduced electron transfer from the singlet excited state of the zinc porphyrin moiety to the naphthalenediimide moiety. This is followed by subsequent electron transfer from the ferrocene moiety to the zinc porphyrin radical cation to produce the final charge-separated state, ferricenium ion-zinc porphyrin-naphthalenediimide radical anion, which is successfully detected as a transient absorption spectrum in the laser flash photolysis. The decay of the charge-separated state obeys first-order kinetics irrespective of the initial concentration of the charge-separated state to afford a long lifetime (320 μs). This is the first example of a supramolecular triad that has a long lifetime as compared with the charge-separated state lifetime of the component dyad.

Fine-Pitch Copper Wiring Formed with Super-Inkjet and Oxygen Pump

We have successfully printed wires of 5 µm line widths and spaces in copper nanoparticle ink with a super-inkjet printer. The wires show resistivity as low as 8.1 µΩcm after sintering at 250 °C in an extremely low oxygen atmosphere generated by an oxygen pump. To our knowledge, this is the first report of micron-scale copper wiring formed by a direct printing method without any masks or templates.

Multiple photosynthetic reaction centers composed of supramolecular assemblies of a zinc porphyrin dendrimer with pyridylnaphthalenediimide

Multiple photosynthetic reaction centers have successfully been constructed using a supramolecular complex of zinc porphyrin dendrimer [D(ZnP)16] with pyridylnaphthalenediimide (PyNIm) in benzonitrile. The apparent formation constant determined from the fluorescence quenching of the singlet excited state of porphyrin moieties by PyNIm is significantly larger than that determined from the UV-vis spectral change. This indicates that efficient energy migration occurs between the porphyrin units of the dendrimer prior to the electron transfer from the singlet excited state of zinc porphyrin to PyNIm. The charge-separated (CS) state has been successfully detected as the transient absorption spectrum in the laser flash photolysis. The CS lifetime of in the supramolecular complex of D(ZnP)16 with PyNIm was determined to be 0.83 ms at 298 K.

Size-controlled Synthesis of Gold Nanoparticles by Thermolysis of a Gold(I)-Sulfide Complex in the Presence of Alkylamines

A size-controlled synthesis of gold nanoparticles has been developed by the thermolysis of AuCl(SMe2) in the presence of alkylamines at 120 °C. In the procedure, the key intermediate was [Au(NH2R)2]Cl, detected by electrospray ionization (ESI) mass spectrometry. This thermally unstable intermediate was reduced by alkylamines under mild conditions to produce alkylamine-capped gold nanoparticles. The average diameters of the gold nanoparticles could be regulated in a range from 4.3 to 6.1 nm by applying primary alkylamines with alkyl chains of different lengths. Larger gold nanoparticles with diameters from 10 to 22 nm were prepared by a combination of alkylamines and alkylcarboxylic acids with various lengths of the alkyl chains. The gold nanoparticles were characterized by transmission electron microscopy (TEM), UV/Vis absorption spectroscopy, powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), gas chromatography/mass spectroscopy (GC/MS), and thermogravimetric and differencial thermal analyses (TG/DTA) Graphical Abstract Size-controlled Synthesis of Gold Nanoparticles by Thermolysis of a Gold(I)-Sulfide Complex in the Presence of Alkylamines