Optical Properties of Porphyrin: Graphene Oxide Composites

In this work we aim to (via a non-invasive functionalization approach) tune and alter the intrinsic features of optically “transparent” graphene, by integrating water-soluble porphyrin aggregates. We explore the potential to combine porphyrin aggregates and graphene oxide to assess the advantages of such as a composite compared to the individual systems. We apply a range of optical spectroscopy methods including photo-absorption, fluorescence assess ground-state and excited state interactions. Our studies show that comparing resonant Raman scattering with optical transmission and fluorescence microscopy that the presence of influences the microscopic structures of the resulting composites

Single-Molecule Nonresonant Wide-Field Surface-Enhanced Raman Scattering from Ferroelectrically Defined Au Nanoparticle Microarrays

Single-molecule detection by surface-enhanced Raman scattering (SERS) is a powerful spectroscopic technique that is of interest for the sensor development field. An important aspect of optimizing the materials used in SERS-based sensors is the ability to have a high density of "hot spots" that enhance the SERS sensitivity to the single-molecule level. Photodeposition of gold (Au) nanoparticles through electric-field-directed self-assembly on a periodically proton-exchanged lithium niobate (PPELN) substrate provides conditions to form well-ordered microscale features consisting of closely packed Au nanoparticles. The resulting Au nanoparticle microstructure arrays (microarrays) are plasmon-active and support nonresonant single-molecule SERS at ultralow concentrations (<10-9-10-13 M) with excitation power densities <1 × 10-3 W cm-2 using wide-field imaging. The microarrays offer excellent SERS reproducibility, with an intensity variation of <7.5% across the substrate. As most biomarkers and molecules do not support resonance enhancement, this work demonstrates that PPELN is a suitable template for high-sensitivity, nonresonant sensing applications.Science Foundation IrelandUCD School of PhysicsSwedish Scientific Research CouncilADOPT Linnaeus Centre for Advanced Optics and Photonics in Stockhol

Photoinduced Enhanced Raman from Lithium Niobate on Insulator Template

© 2018 American Chemical Society. Photoinduced enhanced Raman spectroscopy from a lithium niobate on insulator (LNOI)-silver nanoparticle template is demonstrated both by irradiating the template with 254 nm ultraviolet (UV) light before adding an analyte and before placing the substrate in the Raman system (substrate irradiation) and by irradiating the sample in the Raman system after adding the molecule (sample irradiation). The photoinduced enhancement enables up to an ∼sevenfold increase of the surface-enhanced Raman scattering signal strength of an analyte following substrate irradiation, whereas an ∼threefold enhancement above the surface-enhanced signal is obtained for sample irradiation. The photoinduced enhancement relaxes over the course of ∼10 h for a substrate irradiation duration of 150 min before returning to initial signal levels. The increase in Raman scattering intensity following UV irradiation is attributed to photoinduced charge transfer from the LNOI template to the analyte. New Raman bands are observed following UV irradiation, the appearance of which is suggestive of a photocatalytic reaction and highlight the potential of LNOI as a photoactive surface-enhanced Raman spectroscopy substrate.Science Foundation Irelan

Graphene oxide intercalation into self-assembled porphyrin J-aggregates

Studies are undertaken to examine graphene oxide intercalation into self-assembled J-aggregate porphyrin structures. Fluorescence lifetime and fluorescence anisotropy imaging were applied along with scanning electron microscopy to study the structure and optical properties of a graphene oxide/TMPyP hybrid composite material. It was seen that the presence of graphene oxide alters the macroscale and nanoscale self-assembled structures of TMPyP in addition graphene oxide also alters the optical activity reducing the emission intensity and exciton recombination lifetime. Evidence exists to support a model where planer-symmetric graphene oxide and TMPyP co-operate in the formation of self-assembled macro and nanostructures forming a composite with strong graphene oxide/TMPyP interaction

Graphene oxide intercalation into self-assembled porphyrin J-aggregates

Studies are undertaken to examine graphene oxide intercalation into self-assembled J-aggregate porphyrin structures. Fluorescence lifetime and fluorescence anisotropy imaging were applied along with scanning electron microscopy to study the structure and optical properties of a graphene oxide/TMPyP hybrid composite material. It was seen that the presence of graphene oxide alters the macroscale and nanoscale self-assembled structures of TMPyP in addition graphene oxide also alters the optical activity reducing the emission intensity and exciton recombination lifetime. Evidence exists to support a model where planer-symmetric graphene oxide and TMPyP co-operate in the formation of self-assembled macro and nanostructures forming a composite with strong graphene oxide/TMPyP interaction

Single-Molecule Nonresonant Wide-Field Surface-Enhanced Raman Scattering from Ferroelectrically Defined Au Nanoparticle Microarrays

Single-molecule detection by surface-enhanced Raman scattering (SERS) is a powerful spectroscopic technique that is of interest for the sensor development field. An important aspect of optimizing the materials used in SERS-based sensors is the ability to have a high density of “hot spots” that enhance the SERS sensitivity to the single-molecule level. Photodeposition of gold (Au) nanoparticles through electric-field-directed self-assembly on a periodically proton-exchanged lithium niobate (PPELN) substrate provides conditions to form well-ordered microscale features consisting of closely packed Au nanoparticles. The resulting Au nanoparticle microstructure arrays (microarrays) are plasmon-active and support nonresonant single-molecule SERS at ultralow concentrations (<10^–9–10^–13 M) with excitation power densities <1 × 10^–3 W cm^–2 using wide-field imaging. The microarrays offer excellent SERS reproducibility, with an intensity variation of <7.5% across the substrate. As most biomarkers and molecules do not support resonance enhancement, this work demonstrates that PPELN is a suitable template for high-sensitivity, nonresonant sensing applications

Micro- or nanorod and nanosphere structures derived from a series of phenyl-porphyrins

We examine here a series of meso-phenyl porphyrin micro- and nanostructures. Optical absorption and emission spectroscopy imaging and atomic force microscopy are used to investigate the effect of peripheral groups in nano- and microstructures of 5,10,15,20-tetraphenylporphyrin (H2TPP) compared to three other phenylporphyrins, i.e. 5,10,15-triphenylporphyrin (H2-Tri-PP), 5,10-diphenylporphyrin (H25,10-BPP) and 5,15-diphenylporphyrin (H25,15-BPP) molecules. We show that nanospheres and nanorods are formed, the occurrence and properties of which are influenced by the number and position of the phenyl substituents

Fractal structures in n-phenyl-porphyrin J-aggregate films

Studied here are thin films of a series of phenyl-porphyrins. The effect of the phenyl number and positioning on the porphyrin core is shown to have a significant impact on the ability of phenyl-porphyrins to produce aggregates. When four phenyl groups (H2TPP) and three phenyl groups are present (H2-Tri-PP) a strong aggregate film forms with fractal like structure. When two phenyl groups are present little evidence for aggregation can be determined, however fractal structure persists