Advantages of highly luminescent semiconductor nanodots and nanorods

Highly luminescent semiconductor nanodots and nanorods seem naturally as alternatives to fluorescent organic dyes. Among the most advanced features of inorganic nanoparticles are:

The narrow spectral width of emission. Bandwidth as small as 20 nm may be achieved, though typical synthesis produces nanoparticles with emission linewidths of 25-35 nm. As compared to 50-100 nm linewidth of usual fluorescent dyes the utilization of nanodots and nanorods as fluorescent markers allows to recognize and distinguish signals from much more labels in the same spectral range, than with organic dyes.

The excellent photostability of nanodots. Presence of epitaxial surface shell protects nanodots and nanorods cores from photobleaching usually observed due to the photochemical reactions with surrounding molecules. Even in the quite aggressive biological conditions (aerated aqueous solution, low, or high pH, high temperature) the core-shell nanoparticles preserve their high emission quantum yield and the narrow spectral width for a prolonged time. The core-shell nanodots and nanorods have been found to be several hundred times more photostable than the most advanced organic dyes.

High photoluminescence quantum yield. Typically, the photoluminescence quantum yield of our hydrophobic nanodots is nearly 70% and is guaranteed as >50% at room temperature which is comparable to the best organic fluorescent dyes.

Superior brightness. Large magnitudes of extinction coefficients accompanied by high fluorescence quantum yield results in superior brightness of nanodots which significantly exceeds the brightness of organic dyes.

The broad excitation region. All nanodots and nanorods possess very broad excitation spectra of the emission which extend from their absorption edge to deep UV. Therefore, a single light source may be utilized to excite effectively nanodots with different emission color.

The easy tunability of the emission color (spectral position of emission peak) through entire near-UV, visible, near- and mid-IR regions by changing the size and composition of nanoparticles. Due to the so-called "quantum confinement effect" the decrease in size of nanoparticles typically below 10 nm results in the spectral shift of the absorption and emission peaks from red to green and blue. Therefore, any desirable emission color from the available range may be achieved simply by controlling the final size of nanoparticle during the synthesis. Additionally, using the alloyed nanodots and nanorods, like Zn_1-xCd_xSe, allows covering the borderline spectral regions.

Great potential for multiplex labeling applications. Absorption spectra of nanodots and nanorods with different emission wavelengths significantly overlap in UV and "blue" spectral range thus providing simultaneous excitation of ALL nanoparticles with single light source (for instance, mercury or xenon lamp). Narrow spectral bandwidths of nanoparticle emission (~25-30 nm) give opportunity to use, for example, at least 5 different fluorescent labels (nanodots and/or nanororods) in one experiment for the spectral region of 525-650 nm.

Nearly 100% polarized photoluminescence of our nanorods made them unique materials for advanced applications in biomedical labeling, fabrication of LCD displays, solar cells and in optoelectronics.