PORTLAND, Ore.—The crown for the world's brightest nanoparticles has been claimed by the inventor of mesoporous silicon-dioxide (silica) nanoparticles, which have proven to be 34-times brighter than the brightest quantum dots—previously the world's brightest nanoparticles. The transparent silicon-dioxide hulls harbored fluorescent nanoparticles inside—rather than use quantum-confinement like quantum dots—enabling much brighter operation, according to their inventors at Clarkson University (Potsdam, New York).
The mesoporous silica nanoparticles have potential applications in medicine, biology, material science, and environmental protection, according to Clarkson University Physics professor Igor Sokolov, who claims that his brighter particles will allow much finer detection of environmental pollutants, biosensors and homeland defense detectors.
Fluorescent nanoparticles work by absorbing light of one wavelength, the emitting it at another. By functionalizing the particles so that they fluoresce only when in the presence of the substance to be detected, ultra-sensitive nanoparticles can detect smaller amounts of the pollutant or toxin that would otherwise be possible. To date, quantum dots were the world's brightest nanoparticles, but Clarkson University now claims that its mesoporous silica nanoparticles have won that crown.
Sokolov’s process securely seals a large number of organic fluorescent molecules inside nanoporous silicon dioxide hulls, which can range from 20 to 50 nanometers in diameter. As an example of their brightness, Sokolov claims that nanoparticles of just 40 nanometers in diameter are brighter than 25-30 nanometer water-dispersible quantum dots—the brightest reported quantum dots to date.
The ultra-bright particles were synthesized with the help of postdoctoral fellows Shajesh Palantavida and Eun-Bum Cho (now an assistant professor at Seoul National University of Science and Technology) along with a doctoral candidate at Clarkson, Dmytro Volkov.
Funding for the project was provided by the National Science Foundation and the U.S. Army Research Laboratory's Army Research Office.
Transmission electron microscopy (TEM) image of an ultrabright fluorescent mesoporous silica nanoparticle (image colored artificially to match the actual color of the dye in the particles).
I would just add that quantum dots have a number of issues which organic dyes do not. For example, toxicity, blinking, fast degradation in aqueous media, etc. Thus, the dyes are preferable in a number of applications.
Yes, you are absolutely right. We will try to make it smaller. Although it may already be used in a number of applications. The sizes are not far from water dispersable quantum dots (coated), which are 15-25nm.
Thank you for your interest. If you email me, I can send you a PDF copy of the paper. As to your note, brightness is a well defined quantity. It is proportional to the quantum yield and (!important) the cross-section of absorption (or absorptivity). Just quantum yield does not tell your much. For example, the brightest quantum dots have the quantum yield not more than ~20%, whereas 20 times dimmer dye molecules have almost 100% q. yield..
These researchers are not using quantum dots, but instead are using traditional organic fluorescent dyes--but packing then more tightly than is possible without the channels inside their silica shells. I asked them about quantum dots, but they said they could get a wider gamut of colors by using different combinations of colored organic dyes.
The positive impact from improved sensetivity (smaller number of indicators needed to create a given visual response) should be significant. Size does matter though and even 20nm particles might be too much for some (many?) applications.
I checked with the researchers, and they say that the fluorescent dyes inside are not quantum dots, but conventional organic marker-dyes already used in biomedical applications. The reason they can make conventional fluorescent marker-dyes brighter than quantum dots, is that their silicon dioxide shells are porous--thus they can pack more dye into its internal channels. Usually you can't pack the dyes together tightly, because they clump, degrading fluorescence, but by packing them in separate internal channels, the mesoporous silica shells allow more dye per unit area.
The researchers started with ultra-bright but micron-sized silica particles in 2007, and since then have been working to downsize them to the nanoscale. At first brightness suffered from the downsizing, but now they are going public because they claim to have succeeded in making ultra-bright, yet very small, fluorescent nanoparticles.
If i go by the logic that the bigger the size of porous SiO2 nanoparticle the higher the number of fluorescent organic molecules trapped into it, then why the brightness is only 34 times than that of quantum dot? Are they comparing the same size particles and dots or is there any limit on the size of produced SiO2 nanoparticles?
If i understood the news correctly then large number of fluorescent organic molecules are trapped into nanoporous SiO2, which has higher brightness than a quantum dot. Although each organic fluorescent molecules is a quantum dot, nanoporous SiO2 is acting as a medium only to confine all the molecules at one place. So it is not SiO2 which is fluorescent. And the higher brightness is due to the higher number of the organic molecules (quantum dots).
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