Developing a Millifluidic Platform for the Synthesis of Ultrasmall Nanoclusters: Ultrasmall Copper Nanoclusters as a Case Study

Abstract

The future of lab-on-a-chip devices for the synthesis of nanomaterials hinges on the successful development of high-throughput methods with better control over their size. While significant effort in this direction mainly focuses on developing "difficult to fabricate" complex microfluidic reactors, scant attention has been paid to the "easy to fabricate" and simple millifluidic systems that could provide the required control as well as high throughput. By utilizing numerical simulation of fluids within the millifluidic space at different flow rates, the results presented here show velocity profiles and residence time distributions similar to the case of microfluidics. By significantly reducing the residence time and residence time distribution, a continuous flow synthesis of ultrasmall copper nanoclusters (UCNCs) with exceptional colloidal stability is achieved. In-situ synchrotron-radiation-based X-ray absorption spectroscopy (XAS) reveal that the as-prepared clusters are about 1 nm, which is further supported by transmission electron microscopy and UV-vis spectroscopy studies. The clusters reported here are the smallest ever produced using a lab-on-a-chip platform. When supported on silica, they are found to efficiently catalyze C-H oxidation reactions, hitherto unknown to be catalyzed by Cu. This work suggests that a millifluidic platform can be an inexpensive, versatile, easy-to-use, and powerful tool for nanoparticle synthesis in general, and more specifically for ultrasmall nanoclusters (UNCs).

Green Route to Prepare Biocompatible and Near Infrared Thiolate-Protected Copper Nanoclusters for Cellular Imaging

“…1(e)], indicating the formation of Cu NCs. 40 The GSHÀCu NCs have a well-de¯ned excitation band with a peak at 480 nm in excitation spectrum (see Fig. S1).…”

Investigation of the synthesis and characterization of platinum-DMSA nanoparticles using millifluidic chip reactor

“…This indicated the spontaneous reduction of the H 2 PtCl 6 with DMSA at the beginning of the channel, therefore supporting the XANES analysis. In addition, the absence of plasmon peak at 260 nm can be attributed to the formation of Pt(DMSA) nanoparticles with diameter less than about 5 nm; since nanoparticles and atomically precise clusters lose their visible extinction features as they decrease in size [21][22][23][24][25][26][27][28][29][30]. A separate UV-Vis spectrum was obtained for the unquenched solution of Pt(DMSA) nanoparticles (zone 7) in order to determine any changes in their optical property.…”

Millifluidics for Chemical Synthesis and Time-resolved Mechanistic Studies

“…Conventionally, microfluidic systems are used for precise control and manipulation of fluids that are geometrically constrained to submillimeter scale. We have recently introduced the concept of chip-based millifluidics, which can be used for manipulation of fluids in channels in millimeter scale (either width or depth or both of the channels are at least a millimeter in size) [7][8][9] . Furthermore, the millifluidic chips are relatively easy to fabricate while offering similar control over flow-rates and manipulation of reagents.…”

“…As an example, we have recently demonstrated the synthesis of ultra-small copper nanoclusters and characterized them using in situ X-ray absorption spectroscopy as well as TEM. Ability to obtain small residence times within millifluidic channels in combination with the use of MPEG, which is very efficient bidentate PEGylated stabilizing agent for the formation of stable colloids of copper nanoclusters 7 .…”

“…In addition to the synthesis of chemicals and nanomaterials, the millifluidics could offer, due to higher volume and concentration at the probe area, a synthetic platform that is more generalized and efficient for time-resolved kinetic studies and also achieves better signal to noise ratio than microfluidic systems 7,10 . We show the use of millifluidic chip as an example for time resolved analysis of the growth of gold nanostructures from solution using in situ XAS with a time resolution as small as 5 msec 11 .…”