One-Dimensional Nanostructures: Microfluidic-Based Synthesis, Alignment and Integration towards Functional Sensing Devices

Microfluidic-based synthesis of one-dimensional (1D) nanostructures offers tremendous advantages over bulk approaches e.g., the laminar flow, reduced sample consumption and control of self-assembly of nanostructures. In addition to the synthesis, the integration of 1D nanomaterials into microfluidic chips can enable the development of diverse functional microdevices. 1D nanomaterials have been used in applications such as catalysts, electronic instrumentation and sensors for physical parameters or chemical compounds and biomolecules and hence, can be considered as building blocks. Here, we outline and critically discuss promising strategies for microfluidic-assisted synthesis, alignment and various chemical and biochemical applications of 1D nanostructures. In particular, the use of 1D nanostructures for sensing chemical/biological compounds are reviewed.

In situ synthesis of silver nanoparticle decorated vertical nanowalls in a microfluidic device for ultrasensitive in-channel SERS sensing

A microfluidic device with integrated novel silver nanoparticle (Ag NPs) decorated nanowall structures was fabricated via in situ electrodeposition of Cu-core/C-sheath nanowalls, followed by a facile in-channel silver galvanic replacement reaction method at room temperature. The integrated microfluidic devices with Ag NPs decorated nanowalls, serving as a highly active Raman substrate, were then applied for in-channel surface-enhanced Raman scattering (SERS) sensing using crystal violet as the model compound. The results show that the presence of a PDMS microfluidic channel does not significantly affect the Raman signal and crystal violet as low as 50 pM is prominently detected. The calculated apparent enhancement factor is 1.1 × 10(9), which allows for the ultra-sensitive detection of analytes in microfluidic devices. The superior enhancement of the in-channel Raman signal and excellent analyte sensitivity can be attributed to the synergistic effect of several distinct traits of the Ag NPs decorated nanowalls - a large available surface for analyte adsorption, a large number of nanocavities surrounded by nanowalls laterally confining the surface plasmons, and numerous "hot spots" resulting from close-contacted Ag NPs and/or the proximate edges of Ag decorated nanowalls. Because preparation of the active SERS substrate and subsequent finger-print SERS detection is completed within a microfluidic device, the developed method opens a new venue to integrate active SERS substrate within microfluidic channels and provides an excellent microfluidic SERS sensor platform for ultrasensitive and selective chemical and biological sensing.