C•spec™ architecture combines the optical functionality of organic dyes with the chemical and mechanical robustness of amorphous silica to create materials that greatly exceed the capabilities of both parent materials. Dye encapsulation can enhance the brightness of individual fluorescent dye molecules as well as incorporate multiple dye molecules into a single particle to yield probes with exceptional brightness. Furthermore, the modular shell architecture and versatile chemistry of silica allow for the introduction of other functionalities for contrast agents, chemical delivery and biological targeting.
Brightness Enhancement - C•spec™ particles are significantly brighter and more stable than free dyes in aqueous solution. For example, for 30 nm C•spec™ particles, the brightness enhancement over free dyes is about 30x and approaches that of same sized, but toxic, quantum dots. Based on Fluorescence Correlation Spectroscopy (FCS) measurements, we have verified on numerous batches of various dyes that C•spec™ particles are one to two orders of magnitude brighter than free dye molecules, with the per-particle enhancements over free dye depending on the specific dye and the size of the particle. The quantum yield of fluorescent dyes is increased when they are encapsulated in the C•spec™ particles’ rigid silica matrix.
Increased Dye Concentration - The core-shell C•spec™ architecture enables an increase in fluorophore concentration above levels that would quench the emission of free dyes. The silica matrix surrounding each dye molecule separates it from others within the particle core and each core is separated from all other cores by the shell when collective behavior is required (e.g., for surface coatings). The separation of the dye molecules in the rigid core prevents intermolecular “stacking” or quenching interactions and allows higher spatial dye density than could be achieved with free dyes without quenching. This architecture leads to unprecedented brightness levels compared to free dyes.
Multifunctional Nanoparticles - The C•spec™ particles’ architecture is ideally suited to building particles that incorporate different functional building blocks. By varying the cores and layering multiple shells, it is possible to progress towards the next generations of highly functional “lab-on-a-particle” designs, which incorporate targeting, imaging, sensing and treatment in a single vehicle. This approach was explored by our collaborators at Cornell in a Chemical Society Reviews Cover Article in 2006. As shown in the Figure shown on the left, the lab-on-a-particle incorporates a core imaging dye, a gold nanoshell, a sensing layer and a mesoporous surface shell for controlled release of therapeutic agents.
Scanning Electron Microscopy images of C•spec™ particles from tens of nanometers in diameter (left) to hundreds of nanometers (center) to micron-sized particles (right), showing the low polydispersity of the particles.
This schematic showing an array of C•spec™particles on a surface illustrates the separation between the nanoparticle cores. This separation prevents inter-particle quenching, which allows a higher local concentration of fluorophores than is possible for individual dye molecules.
A schematic of a “lab-on-a-particle” architecture: a multi-shell, multi-component nanoparticle
