Sub-millisecond microfluidic mixers coupled to time-resolved photonics to study ultra-fast reaction kinetics: the case of ultra-small gold nanoparticle synthesis

• Published in: Lab on a chip 2024-01, Vol.24 (2), p.327-338
• Main Authors: Ramamoorthy, Raj Kumar, Yildirim, Ezgi, Rodriguez-Ruiz, Isaac, Roblin, Pierre, Lacroix, Lise-Marie, Diaz, Ana, Parmar, Rohan, Teychené, Sébastien, Viau, Guillaume
• Format: Article
• ISSN: 1473-0197; 1473-0189
• DOI: 10.1039/d3lc00778b

We report a continuous microreactor platform achieving sub-millisecond homogeneous reagent mixing (∼300 μs) for a time-resolved study on the synthesis of ultra-small gold nanoparticles (NPs). The microreactor (coupled with small angle X-ray scattering, UV-vis, and X-ray absorption spectroscopy for in situ and in operando characterizations), operates within mixing time frames below system characteristic times, providing a unique opportunity to deepen the comprehension of reaction and phase transition pathways with unprecedented details. The microreactor channel length can be approximated to a given reaction time when operated in continuous mode and steady state. As a result, the system can be statically investigated, eliminating technique-dependent probing time constraints and local inhomogeneities caused by mixing issues. We have studied Au(0) NP formation kinetics from Au( iii ) precursors complexed with oleylamine in organic media, using triisopropylsilane as a reducing agent. The existence of Au( iii )/Au( i ) prenucleation clusters and the formation of a transient Au( i ) lamellar phase under certain conditions, before the onset of Au(0) formation, have been observed. Taking advantage of the high frequency time-resolved information, we propose and model two different reaction pathways associated with the presence or absence of the Au( i ) lamellar phase. In both cases, non-classical pathways leading to the formation of NPs are discussed. We report a continuous microreactor platform achieving sub-millisecond homogeneous reagent mixing (∼300 μs) for a time-resolved study on the synthesis of ultra-small gold nanoparticles (NPs).