Novel hybrid fluorescent nanoparticles with outstandingly high light intensity
Researchers at the Karlsruhe Institute of Technology (KIT) have successfully developed low-cost, fluorescent dyes with especially high light intensities. These inorganic–organic hybrid dyes can be synthesized easily and isolated, stored and redispersed in common solvents (ethanol/water). They can be excited using blue light (UV or blue light from LED) and emit depending on their composition in the blue, green, red or infrared spectrum. Preferred are applications in the field of medical diagnostic and therapeutic, advertising material and safety equipment (fluorescent marker).
In the field of biology and medicine the advantage of the inventive fluorescent dyes are their sufficient biocompatibility and highly specific signals, that do not overlap with auto fluorescence of organs, cells and organelles. Thus the hybrid fluorescent dyes represent attractive alternatives to the widely used semiconductor quantum dots and rare earth doted oxides or fluorides.
Nanoscale fluorescent materials are of special interest as markers for medical diagnostics and therapeutics as well as security markers on or in paper or plastic.
For medical application, biocompatible compounds with high emission intensity, fast cell uptake and without inducing toxic or allergic reactions are of particular interest. In addition, it is necessary for fluorescent nanoparticles to have a diameter of less than 50 nm and to avoid agglomeration in order to allow for an easy cell uptake.
Because of their small size, fluorescent nanoparticles are not visible to the naked eye. They only become detectable through their emission upon excitation with a specific wavelength.
These characteristics designate them for an application as security marking in or on paper (for example bank notes, security papers) respectively in or on plastic (for example identity cards) as well as for advertising.
The step from innovation to market-ready products is hindered by the limited availability of suitable fluorescent nanoparticles. What is missing, are biocompatible fluorescent dyes with high light intensity (i.e. a large number of luminescence centers and a high quantum efficiency), good dispersibility and methods to manufacture such products efficiently and simply in technically relevant quantities.
Researchers at the Karlsruhe Institute of Technology (KIT) have successfully developed low-cost, biocompatible, inorganic–organic hybrid nanomaterials with very high light intensities. These hybrid fluorescent dyes can be excited via blue light (UV or blue-light LED) and emit depending on their composition in the blue, green, red or infrared spectrum.
The inorganic-organic hybrid fluorescent dyes with a general composition [ZrO] [dye phosphate] consist of inorganic [ZrO]2+-metal cations and organic fluorescent dye anions, which carry a phosphate group [dye phosphate]2- as functional group.
Fig. 1 shows representative examples and their emissions. The fabrication of inorganic-organic hybrid dyes involves a simple precipitation in an aqueous solution while considering particle nucleation and growth. The nanoparticles exhibit average diameters of 30 - 50 nm. They are colloidally stable in water respectively in physiological media (e.g. phosphate buffered saline) and can be modified by simple measures, for example dextran, to support cell penetration and uptake. By selecting an appropriate dye anion, it is possible to vary the emission wavelength from blue and green to yellow, red and infrared.
The excitation is preferentially achieved using blue light (350 to 500 nm) from an LED. The hybrid particles are amorphous and do not require any core-shell structure. They are easily and efficiently produced through precipitation in an aqueous solution and do not contain any toxic elements (e.g. Cd, Pb, Se, Te). First trials demonstrate a high level of biocompatibility and a complete decomposition within 3 to 4 days.
- Simple water-based synthesis of nanoscale
- HFM (10 - 50 nm) with narrow particle size distribution greater than or equal 20 %
- Excitation and emission wavelengths can be adjusted by selecting the appropriate dye anion
- Concentration of fluorescent dye can be varied (<1 mol% up to molar quantities, i.e. 100 %)
- High emission intensity despite amorphous structure
- Excitation of HFM in the visible (blue-light LED) to ultraviolet wavelength spectrum feasible
- Emission in the blue, green, yellow, red and infrared spectrum possible
- HFM from water and without the addition of stabilizers can be isolated and redispersed without agglomeration
- HFM is biocompatible compared to commonly used toxic CdSe or CdTe quantum dots
- HFM can be produced in a broad range of quantities (scale-up)
- Biocompatible fluorescence marker in diagnostic and therapeutic medicine
- Security markings in and on paper and plastic
- Promotional purposes through inclusion in paper or plastic products
Find out more
M. Roming, H. Lünsdorf, K. E. D. Dittmar, C. Feldmann,
"ZrO(HPO4)1−x(FMN)x: schnelle und einfache Synthese eines nanoskaligen Lumineszenzbiomarkers",
Angew. Chem. 2010, 122, 642 –647;
J. Heck, J. Napp, F. Alves, C. Feldmann, ... to be published soon.