Scientists Are Searching for Biomedical Fluorescent Labels Already for Many Years. an Example

Summary

Scientists are searching for biomedical fluorescent labels already for many years. An example of these labels are the quantum dots. Quantum dots can absorb short wavelength, high-energy UV- light and emit at a longer wavelength low-energy visible light with a process called downconversion. These quantum dots have a number of disadvantages like photobleaching and leading to damage to the tissue, because of the need to use UV- light. A more recent example of fluorescent labels are upconversion nanoparticles. These particles can absorb a lower energy, longer wavelength of near-infrared light and with energy transfer of a neighboring ion emit higher energy, shorter wavelength visible light with a process called upconversion. These upconverting nanoparticles are much more resistant to photobleaching and give less damage to the tissue because they are irradiated with near-infrared light, which render them particularly useful for bio-imaging and bio-labeling applications. One of the holy grails, scientists are currently pursuing is to improve the emission performance of these upconversion nanoparticles. A promising routeappears to be the use of core/shell architectures.

In this report a comparison of the core and the core/shell structure is made by measuring the intensity and the wavelengths distribution of the emission. Also the size and morphology of the synthesized particles play an important role. They have been measured with TEM. The particles synthesized in this report are the -NaYF4 : Yb3+, Er3+ nanoparticles.The size of the synthesized particles is 10-20 nm for the core and 14-27 nm for the core/shell structure.

Comparing the emission spectra of the core and core/shell structure particles reveals that the peak positions remain the same.However, there is a dramatic difference between the two when the overall upconversion intensity and the relative green: red (G /R) emission ratio are compared. The relative G/R ratio for the core 1:2.6 while for the core/shell structure 1:1.8.

In this report an evolving existent synthetic approach is used to synthesize the upconverting nanoparticles (-NaYF4 : Yb3+, Er3+) [6]. During the synthesisvarious reaction parameters such as temperature, concentration, reaction time and the solvent have been changed. The reaction should be performed in a dry environment under nitrogen flow. The temperature influences the size and shape of the particles, the pretreatment time has influence on the certainty that all the water from the solvent is evaporated. The solvent makes sure that the particles will be separated from each other to avoid clustering. The concentration of the reactants determines the color of the emission from the nanoparticles.