Luminescent nanoparticles are gaining more and more interest in bio-labeling and bio-imaging applications, like for
example DNA microarray. This is a high-throughput technology used for detection and quantification of nucleic acid
molecules and other ones of biological interest. The analysis is resulting by specific hybridization between probe
sequences deposited in array and a target ss-DNA usually expressed by PCR and functionalized by a fluorescent dye.
These organic labels have well known disadvantages like photobleaching and limited sensitivity. Quantum dots may be
used as alternatives, but they present troubles like blinking, toxicity and excitation wavelengths out of the usual range of
commercial instruments, lowering their efficiency. Therefore in this work we investigate a different strategy, based on
the use of inorganic silica nanospheres incorporating standard luminescent dyes or rare earth doped nanocrystals. In the
first case it is possible to obtain a high luminescence emission signal, due to the high number of dye molecules that can
be accommodated into each nanoparticle, reduced photobleaching and environmental protection of the dye molecules
thanks to the encapsulation in the silica matrix. In the second case, rare earths exhibit narrow emission bands (easy
identification), large Stokes shifts (efficient discrimination of excitation and emission) and long luminescence lifetimes
(possibility to perform time-delayed analysis) which can be efficiently used for the improvement of signal to noise ratio.
The synthesis and characterization of good luminescent silica spheres either by organic dye-doping or by rare-earth-doping
are investigated and reported. Moreover, their application in the DNA microarray technology in comparison to
the use of standard molecular fluorophores or commercial quantum dots is discussed. The cheap and easy synthesis of
these luminescent particles, the stability in water, the surface functionalization and bio-compatibility makes them very
promising for present and future applications in bio-labeling and bio-imaging.
Luminescent nanoparticles are gaining more and more interest for
bio-sensing and bio-imaging applications. In
particular it is desiderable to work with cheap and non toxic materials which could be easily functionalized in their
surface. To these respects silica nanoparticles seem to be a very promising and interesting solution. The liquid synthesis
of silica spheres can be obtained by condensation of tetraethylortosilicate (TEOS) in basic or acid environment. Several
strategies have been developed to make them luminescent by the incorporation of organic or inorganic emission centres,
but often requiring multiple processing steps and use of expensive or toxic molecules. Moreover, common dyes suffer
disadvantages such as a broad spectral band, short fluorescent lifetime and photobleaching. In contrast, rare earths
exhibit narrow emission bands, large Stokes shifts and long luminescence lifetimes. In this work we focus our attention
on the synthesis and characterization of europium-doped silica spheres. Europium introduction in the spheres can be
interesting for biological applications to increase the signal to noise ratio due to the long luminescence lifetime
(possibility to perform time-delayed analysis) and to the good emission intensity. The obtained results are presented and
discussed, giving suggestions for the optimization of their morphological and optical properties. The possibility of
realizing good luminescent silica spheres by following the described procedure is shown and suggestions for future
development are given. The cheap and easy synthesis of these luminescent particles, the stability in water, the easy
surface functionalization and bio-compatibility makes them very attractive in biological imaging and other applications.
Double focal plane exposure technique has the property to increase greatly the depth of focus of a lithographic process and appears to be a solution to fulfil the requirements of the most aggressive lithographic targets. The purpose of this work is to investigate the performances of this technique and to understand its mechanisms, to be able to find the best conditions of use for a given process. A simple model based on aerial images considerations has been developed to determine the behaviors of the main lithographic parameters (DoFmax, Elmax, central dose, shape of the Bossung curves) for various values of the distance between the two focal planes. Comparisons with four experiments have been realized with different conditions (type of pattern, dimensions, wavelength, N.A. and coherence (sigma) ). The possibility to predict the best experimental conditions (trade-off between DoF, El, resolution and LER) has been verified.
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