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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.
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