Nanofluidic Trapping of Faceted Colloidal Nanocrystals for Parallel Single-Particle Catalysis

Abstract

Catalyst activity can depend distinctly on nanoparticle size and shape. Therefore, understanding the structure sensitivity of catalytic reactions is of fundamental and technical importance. Experiments with single-particle resolution, where ensemble-averaging is eliminated, are required to study it. Here, we implement the selective trapping of individual spherical, cubic, and octahedral colloidal Au nanocrystals in 100 parallel nanofluidic channels to determine their activity for fluorescein reduction by sodium borohydride using fluorescence microscopy. As the main result, we identify distinct structure sensitivity of the rate-limiting borohydride oxidation step originating from different edge site abundance on the three particle types, as confirmed by first-principles calculations. This advertises nanofluidic reactors for the study of structure–function correlations in catalysis and identifies nanoparticle shape as a key factor in borohydride-mediated catalytic reactions.

Label-Free Imaging of Catalytic H2O2 Decomposition on Single Colloidal Pt Nanoparticles Using Nanofluidic Scattering Microscopy

“…Specifically, their arrival at the constriction is manifested as a distinct step in the time trace of the scattering intensity measured at the trap. This enables the detection of the arrival of single and multiple individual nanoparticles inside a single nanochannel in analogy to our previous work, however, here also for optically dark particles (Figure f). This is important to ensure that the desired number of particles inside each nanochannel can be verified prior to the catalysis experiments we discuss below, where we target a situation where as many channels as possible are functionalized with a single nanoparticle only.…”

“…The nanochannels are arranged in a set of 100 parallel channels, where each channel is 340 μm long and has a quadratic 150 nm × 150 nm crosssection (Figure 1b). To enable the trapping of colloidal nanoparticles according to the recipe we have recently established, 23 each nanochannel is equipped with a 120 nm high and 1 μm long constriction ("trap") in the center. When flushed through the nanochannel and arriving at that trap, particles with a diameter larger than the 30 nm gap between the trap and the nanochannel wall are captured, while substantial liquid flow through the channel is still enabled.…”

“…(b) Artists' rendition of the array of parallel nanochannels that is functionalized by a constriction ("trap") in the center region to enable trapping of colloidal nanoparticles flushed through the system, provided the particles are larger than the trap in one dimension. 23 (c) Dark-field optical microscopy image of an array of nanochannels with a nominal 150 nm × 150 nm cross-section. The trap region that is 1 μm long and 120 nm high appears as a darker area due to the smaller scattering cross-section of the nanochannel in this region.…”

“…To contribute to the quest of experimental method development that enables efficient and quantitative scrutiny of catalytic reactions on single nanoparticles, we have recently introduced the concept of nanofluidic reactors and used them in combination with plasmonic imaging and spectroscopy, together with mass spectrometry in the gas phase − and with fluorescence microscopy in the liquid phase, using both nanofabricated particles and individually trapped colloidal nanocrystals as the catalyst. , One of the key traits of this nanofluidic reactor platform is that it ensures identical reaction conditions for the individual particles during an experiment while isolating each of them in its own nanochannel. Thereby, it enables highly parallelized studies of tens of single nanoparticles in the same experiment, whereby it eliminates errors and uncertainties inherent to the subsequent experiments traditionally used.…”

DNA in nanochannels: theory and applications

“…We hope that this review will inspire researchers across disciplines to use nanofluidic devices for their research. Options are vast for DNA analysis, but the concepts can also be extended to other important topics, where recent examples in our group include analysis of biological nanoparticles (Friedrich et al ., 2017) and heterogeneous catalysis in the liquid phase (Levin et al ., 2019; Levin et al ., 2022).…”