ABSTRACT
An effective method for the production of surface enhanced Raman scattering (SERS) active substrates is presented. Nanostructured silver thin films are pulsed laser deposited in an argon atmosphere. The films consist of arrays of nanoparticles whose size is controlled by the Ar pressure. The surface morphology of the films can be tuned by the laser pulse number. Nanoparticle size is calculated by a phenomenological model taking into account the dynamics of the laser generated silver plasma. The SERS activity of the films is investigated by Raman scattering of adsorbed rhodamine 6G at different concentrations.
Subject(s)
Crystallization/methods , Lasers , Nanostructures/chemistry , Nanostructures/ultrastructure , Nanotechnology/methods , Silver/chemistry , Spectrum Analysis, Raman/methods , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Particle Size , Surface PropertiesABSTRACT
In this study we report on the application of an aperture near-field optical microscope for Raman imaging of organic materials. Spectral analysis and detailed Raman imaging are performed with integration times of 100 ms per point, without the aid of field enhancement effects. The studied samples consist of two high Raman-efficiency molecular samples: a 7,7',8,8'-tetracyanoquinodimethane crystal showing surface defects and a 7,7',8,8'-tetracyanoquinodimethane thin film characterized by the presence of submicrometre-sized organometallic copper-salt complexes. In the first case, the effect of the surface deformation was studied, whereas in the second sample we were able to chemically image the formation of salt complexes. Subdiffraction resolution was achieved in both studies.
Subject(s)
Microscopy, Scanning Probe , Spectrum Analysis, Raman/instrumentation , Crystallization , Crystallography , Models, Structural , Nitriles/analysis , Scattering, Radiation , Spectrum Analysis, Raman/methods , Time FactorsABSTRACT
Pseudo-first-order rate constants for the hydrolysis of acetylsalicylic acid as a function of temperature have been obtained by variable-temperature kinetic experiments. A method, based on a generalization of non-isothermal analysis, has been used that takes advantage of the capabilities of modern data collection and processing systems. Both spectrophotometric and, for the first time under non-isothermal conditions, fluorometric measurements have been carried out. The results obtained are identical to those obtained under the same conditions but using traditional constant-temperature kinetic runs. This provides the possibility of reducing the amounts of time and chemicals usually spent in collecting kinetic data in mechanistic studies in solution by an order of magnitude.
Subject(s)
Aspirin/chemistry , Fluorometry/methods , Hydrolysis , Spectrophotometry, Ultraviolet/methods , TemperatureABSTRACT
This paper deal with the spectroscopic analysis of proteins, i.e., human serum albumin (HSA) and bovine serum albumin (BSA). These two proteins present very similar UV absorption and fluorescence spectra. The UV-spectra of both proteins result from the sum of the absorption spectra of the aromatic amino acid, mainly tryptophan and tyrosine, present in the biological molecules. On the contrary, the fluorescence HSA and BSA spectra are not the sum of the emission fluorescence spectra of tyrosine and tryptophan, but they are mainly constituted by the tryptophan fluorescence with a poor contribution arising from tyrosine. This fact may be due to inter- and intramolecular quenching phenomena. Significant difference were recorder in the life time fluorescence decay of HSA and BSA, which showed tau values of 2.3 and 4.5 nanoseconds, respectively. The time-resolved fluorescence spectroscopy was performed with an experimental apparatus assembled in our laboratories, which is able of measuring the fluorescence decay in the range 2 x 10(-10)-2 x 10(-8) sec.