Hierarchical integration of nanopillars and nanochannels in a nanofluidic device for single-nanoparticle detection

Nanofluidics using 10-1000 nm nanochannels has been developed, and the analysis of single nanoparticles such as extracellular vesicles and macromolecules utilizing the smallness of nanospaces are expected. Electrical detection with resistive pulse sensing (RPS) using a channel comparable in size to the nanoparticle is effective even for non-fluorescent analytes, but integration of an ultra-small RPS nanochannel with other micro- and nanochannels for transport and chemical processing without clogging the channels is still a challenging. In the present study, a nanofluidic device with the function of single nanoparticle detection using RPS was developed. Considering 60 nm fluorescent nanoparticles as a model sample, we designed a nanofluidic device with a hierarchical structure of microchannels (depth: 8 μm) for sample injection, and a filtering nanochannel (depth: 400 nm) containing nanopillars and a downstream nanochannel (depth: 400 nm) which are connected by an RPS nanochannel with a diameter comparable to the nanoparticle size. A top-down fabrication process by electron beam lithography and dry etching was developed to realize the hierarchical structure with an RPS nanochannel of 90 nm width, 80 nm depth and 400 nm length, which is sufficiently small for the electrical detection, and the nanopillars of 90 nm spacing for filtering aggregated nanoparticles. Using the fabricated device, the electrophoretic transport, filtering and detection of a 60 nm fluorescent nanoparticle was demonstrated. An electrical signal peak with a current reduction of 5.3% was detected, in agreement with the designed value, when a nanoparticle passes through the RPS nanochannel. The developed device will contribute to the realization of single nanoparticle analysis by nanofluidics for biology and medicine.