Akin to constant concentration biological growth, a new ‘Extended LaMer’ method for reproducible and predictable synthesis of nanoparticles was developed.
Significance and Impact
This general approach allows systematic production of precise, monodisperse nanoparticles of any size in a scale-independent approach. Applications include quantum dots, metal nanoparticles, and magnetic particles, which all display size-dependent properties.
Using conventional reaction conditions, but in bio-inspired steady-state growth conditions (constant temperature, constant concentration) reproducible, constant particle growth occurs without ripening.
This is the only method known that allows systematic variation of size and size-dependent nanoparticle properties in a continuous, predictable manner.
Biology produces nanoparticles with exquisite control of size and crystallographic properties by growing crystals in controlled environments where critical parameters are held constant using the complex machinery of life. In contrast, the well-known methods of nanoparticle synthesis use wildly varying temperature (heating-up method) and concentration (hot-injection method) to produce nanoparticles. While these methods can yield highly crystalline, low size dispersity particles, reproducibility is challenging, and systematic size control is nearly impossible. These reactions are typically described by the “LaMer Mechanism” of growth where dramatic changes in concentration of the reactive species leads to extremely complex kinetics that are difficult to predict. We have developed a general methodology to produce nanoparticles that uses a biologically inspired approach, but conventional equipment and reaction conditions. By maintaining temperature constant throughout the reaction, and using a continuous addition of precursor to maintain reagent concentration constant (after a brief initial state of flux) we have demonstrated a dramatic improvement over conventional approaches. During the steady state regime (with constant temperature and concentration) of the “Extended LaMer” mechanism, particle growth is constant in time so particles may be grown to any size desired, in a way that is predictable by linear extrapolation. This approach is inherently scalable, as heat and mass-transport issues are minimized in a system without variations in temperature and concentration. This is a critical step to enable uniform, monodisperse nanoparticle scale-up for a range of electronic, magnetic, optical and thermal applications. Current applications being explored are the production of precisely tailored nanoparticles for biomedical imaging (on the multi-gram scale), as well as magnetic nanoparticles for high frequency, low loss inductors (on the multi-kg scale).