An ethanol gas sensor based on carbon nanofibers (CNFs) with various densities and nanoparticle functionalization was investigated. The CNFs were grown by means of a Plasma-Enhanced Chemical Vapor Deposition (PECVD), and the synthesis conditions were varied to obtain different number of fibers per unit area. The devices with a larger density of CNFs lead to higher responses, with a maximal responsivity of 10%. Furthermore, to simultaneously improve the sensitivity and selectivity, CNFs were decorated with gold nanoparticles by an impaction printing method. After metal decoration, the devices showed a response 300% higher than pristine devices toward 5 ppm of ethanol gas. The morphology and structure of the different samples deposited on a silicon substrate were characterized by TEM, EDX, SEM, and Raman spectroscopy, and the results confirmed the presence of CNF decorated with gold. The influence of operating temperature (OT) and humidity were studied on the sensing devices. In the case of decorated samples with a high density of nanofibers, a less-strong cross-sensitivity was observed toward a variation in humidity and temperature.

A method is presented to directly measure the mass output of an impaction printer coupled with a spark ablation generator. It is based on a quartz crystal microbalance and shown to be reliable in quantifying mass deposition rate. Here, the method is demonstrated with an Au nanoparticle aerosol synthesized under several spark ablation and deposition settings. Changes in the deposition rate in response to changed synthesis conditions follow the spark ablation models on generation rate made in previous studies, validating this novel measurement method. In combination with the volume of a deposit, a good estimate of the film porosity can be made. The Au nanoparticle films synthesized here have a low porosity of 0.18 due to extensive restructuring and compaction on impact with the substrate. The porosity is found to be insensitive to deposition settings and is constant throughout the film. The simplicity and low cost of a quartz crystal microbalance setup make this an accessible method to determine porosity in porous thin films.

Continuous monitoring of tissue microphysiology is a key enabling feature of the organ-on-chip (OoC) approach for drug screening and disease modeling. Sensing charged species in OoC tissue microenvironments is thereby essential. However, the inherently small (i.e., cm) size of OoC devices poses the challenging requirement to integrate miniaturized and highly sensitive in situ charge sensing components to maximize signal extraction from small volumes (nL to µL range) of media used in these devices. Here we meet this need by presenting a novel dual-gate field-effect transistor-based charge sensor integrated within an optically transparent microelectromechanical (MEM) OoC device. Post-process mask-less decoration of Ti sensing electrodes by spark-ablated Au nanoparticle films significantly increases the effective electrode surface area and thus sensor sensitivity while retaining the CMOS-compatibility of the wafer-level fabrication process. We validate the biocompatibility of the sensor and its selective response to poly-D-lysine and KCl, and provide a perspective on monitoring cultures and differentiation of hiPSC-derived cortical neurons on our OoC device.

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The precise control of patterned arrays of carbon nanofibers (CNFs) is an issue of interest in a wide range of applications. In the present work, we report the synthesis of CNFs grown by plasma-enhanced CVD (PECVD) from a Ni catalyst patterned via aerosol printing of nanoparticles (NPs) by a spark ablation technique. The printing speeds were adjusted to vary the catalyst density and characterize the CNFs distribution in the pre-patterned lines. Depending on the printing speed, different CNFs distributions are obtained, ranging from dense vertically-aligned CNFs (VACNFs) to sparse individual CNFs.