Quantum Dots for Life Sciences
Recent advances in nanotechnology have produced a new class of biological detection labels based on semiconductor quantum dots. There is a broad range of applications for this technology, including single molecule biophysics, biomolecular profiling, optical barcoding, and in vivo imaging. In comparison with organic dyes and fluorescent proteins, quantum dots have unique optical and electronic properties, including size-tunable light emission, improved signal brightness, resistance against photobleaching, and simultaneous excitation of multiple fluorescence colors. It has been estimated that CdSe quantum dots are about 20-40 times brighter depending on particle sizes and quantum yields, and 1,000s of times more stable against photobleaching than single dye molecules. Several unique advantages of quantum dots as fluorescent biomarkers are summarized by the following:
- Quantum dots have very large molar extinction coefficients on the order of 0.5-5 x 106 M-1cm-1, which increases the probe brightness under photon-limited conditions (where light intensities are severely attenuated by scattering and absorption). It will permit detection down to the single nanoparticle level, along with reliable quantification of binding and transport phenomena;
- Quantum dots’ high photostability allows imaging over prolonged periods;
- Quantum dots’ broad excitation spectrum allows the simultaneous excitation of quantum dots that can be used to image and analyze multiple molecular targets simultaneously;
- Quantum dots have a narrow emission band for multicolor labeling;
- Quantum dots’ longer excited state lifetimes provides a means for separating the quantum dot fluorescence from background autofluorescence typically seen in fixed tissue samples, a technique known as time-domain imaging;
- Quantum dots’ large Stokes shifts (the distance between the excitation and emission peaks) can be used to further improve detection sensitivity;
- Quantum dots have a high biochemical stability and specificity, low background, and adjustable stoichiometry (ligands/quantum dot);
- Quantum dots have a ligand compliance - the noninterference of quantum dots with the biochemical specificity of an attached ligand;
- Quantum dots have steric compatibility.
The above properties render quantum dots the ideal fluorophore for ultrasensitive, multiplexed, and quantitative fluoroimmunoassays. Challenge of the QDs for practical application is its high non-specific binding and chemical stability during the conjugation, storage, and targeting process. Ocean NanoTech is working on improving the inorganic core structure and surface organic layer coating to solve problems. Some progresses can be found in our recent publication in Small.
Some of the R&D projects at Ocean NanoTech are:
- Development of Cd-free QDs for the life sciences.
- Multiplex biomarker assays for simultaneous detection.
- Multiplex later-flow assays.
- Higher emission and brighter QDs for microarray development.
- Rapid and sensitive multiplex detection of bacteria, cells, proteins, DNA,a dn other biological materials.