Use of a scanning near-field optical microscope architecture to study fluorescence and energy transfer near a metal

Fluorescence intensity depends strongly on the distance between the emitting molecule and a metallic interface. We show that a scanning near-field optical microscope (SNOM) is a simple and versatile tool for studying such an effect. The fluorescent molecules are embedded in a layer upon a silica substrate, and metal is coated on the SNOM tip. We present variations of fluorescence intensity versus tip-sample distance from 800 to ~80 nm . A simple model is used to explain the experimental results. The proposed setup could be used to study nonradiative transfer at a nanometric scale. It could also yield to a new type of optical near-field profiler that uses fluorescent signal.     

Gold/Silica biochips: Applications to Surface Plasmon Resonance and fluorescence quenching

We report Gold/Silica biochips for low cost biosensor devices. Firstly, the study of biochemical interactions on silica by means of Surface Plasmon Resonance (SPR) is presented. Secondly, Gold/Silica biochips are employed to reduce the strong quenching that occurs when a fluorophore is close to the gold surface. Furthermore, the control of the Silica-like thickness allows optimizing the distance between the metallic surface and the fluorophore in order to enhance the fluorescent signal. These results represent the first steps towards highly sensitive, specific and low cost biosensors based, for example, on Surface Plasmon Coupled Emission (SPCE) techniques.     

Low-cost fibered fluorescence spectroscopic probe designed for biomolecular film characterization

We present a new combination of a fluorescent film deposited onto a chip and a new kind of low-cost optical fluorescence probe. The probe consists of an optical fiber which guides the excitation beam to the chip and a second one which collects the fluorescence light toward a spectrometer slotted into a PC. The resulting data are then processed to extract the pertinent information. This system is designed for the detection of DNA but, at present, we have achieved the detection of functionalized lipidic vesicles and studied the photobleaching process of such films.     

Mössbauer effect study of relaxation mechanism in57Fe-doped ammonium alum

The Mössbauer spectra of the ammonium alum doped with approximately 1% of⁵⁷Fe for T. 80K have been considered. The characteristics of the spectra have been reproduced by taking into account that the parameter λ of the spin Hamiltonian is different from zero and that the spin-spin interaction couples the states of each one of the Kramers doublets corresponding to S_z+1/2 and ·S_z±3/2.     

Low-temperature anharmonic vibrations in the cuprates: a bipolaron model

Il Nuovo Cimento D - Starting from the recent experiments that have revealed large-amplitude anharmonic vibrations in the cuprates, the possibility of formation of bipolarons has been investigated....