Despite the unique advantages of nanochannels imparted by their small size, their utility is limited by the lack of affordable and versatile fabrication methods. Moreover, nanochannel-incorporated fluidic devices require micro-sized conduit integration for efficient access of liquid samples. In this study, a simple and cost-effective fabrication method for mixed-scale channel networks via hot-embossing of poly(methyl methacrylate) (PMMA) using a carbon stamp is demonstrated. Due to its high rigidity, PMMA ensures collapse-free channel fabrication. The carbon stamp is fabricated using only batch microfabrication and has a convex architecture that allows the fabrication of a complex channel network via a single imprinting process. In addition, the microchannels are connected to nanochannels via three-dimensional (3D) microfunnels that serve as single-particle-entrapment chambers, ensuring smooth transport of samples into the nanochannels. Owing to the 3D geometry of the microfunnels and the small size of the nanochannels, a solute gradient can be generated locally at the microfunnel. This local solute gradient enables the entrapment of microparticles at the microfunnels via diffusiophoresis, which can manipulate the particle motion in a controllable manner, without any external equipment or additional electrode integration into the channels. To the best of our knowledge, this is the first report of diffusiophoresis-based single-particle entrapment.
The demand for power‐efficient micro‐and nanodevices is increasing rapidly. In this regard, electrothermal nanowire‐based heaters are promising solutions for the ultralow‐power devices required in IoT applications. Herein, a method is demonstrated for producing a 1D nanoheater by selectively coating a suspended pyrolyzed carbon nanowire backbone with a thin Au resistive heater layer and utilizing it in a portable gas sensor system. This sophisticated nanostructure is developed without complex nanofabrication and nanoscale alignment processes, owing to the suspended architecture and built‐in shadow mask. The suspended carbon nanowires, which are batch‐fabricated using carbon‐microelectromechanical systems technology, maintain their structural and functional integrity in subsequent nanopatterning processes because of their excellent mechanical robustness. The developed nanoheater is used in gas sensors via user‐designable localization of the metal oxide semiconductor nanomaterials onto the central region of the nanoheater at the desired temperature. This allows the sensing site to be uniformly heated, enabling reliable and sensitive gas detection. The 1D nanoheater embedded gas sensor can be heated immediately to 250 °C at a remarkably low power of 1.6 mW, surpassing the performance of state‐of‐the‐art microheater‐based gas sensors. The presented technology offers facile 1D nanoheater production and promising pathways for applications in various electrothermal devices.
In this study, we present a highly responsive room-temperature resistive humidity sensor based on a shellac-derived carbon (SDC) active film deposited on sub-micrometer-sized carbon interdigitated electrodes (cIDEs). This monolithic carbon-based sensor demonstrates an excellent linear relationship with humidity and ohmic contact between the active carbon film and carbon electrodes, which results in low noise and low power consumption (∼1 mW). The active SDC film is synthesized by a single-step thermal process, wherein the temperature is found to control the amount of oxygen functional moieties of the SDC film, thereby providing an efficient means to optimize the sensor response time, recovery time, and sensitivity. This SDC–cIDEs-based humidity sensor exhibits an excellent dynamic range (0%–90% RH), a large dynamic response (50%), and high sensitivity (0.54/% RH). In addition, the two-dimensional feature (thickness ∼10 nm) of the SDC film enables a swift absorption/desorption equilibrium, leading to fast response (∼0.14 s) and recovery (∼1.7 s) under a humidity range of 0%–70% RH. Furthermore, the thin SDC-based sensor exhibited excellent selectivity to humidity from various gases, which in combination with its fast response/recovery promises its application for an instant calibration tool for gas sensors.
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