Miniaturized gas chromatography (µGC) systems hold potential for the rapid analysis of volatile organic compounds (VOCs) in an extremely compact and low-power enabled platform. Here, we utilize microfabrication technology to demonstrate the single chip integration of the key components of a µGC system in a two-step planar fabrication process. The 1.5 Â 3 cm microfluidic platform includes a sample injection unit, a micromachined semi-packed separation column (µSC) and a micro-helium discharge photoionization detector (µDPID). The sample injection unit consists of a T-shaped channel operated with an equally simple setup involving a single three-way fluidic valve, a micropump for sample loading and a carrier gas supply for subsequent analysis of the VOCs. The innovative sample injection technique described herein requires a loading time of only a few seconds and produces sharp and repeatable sample pulses (full width at half maximum of approximately 200 ms) at a carrier gas flow rate that is compatible with efficient chromatographic separation. Furthermore, our comprehensive characterization of the chip reveals that a wide variety of VOCs with boiling points in the range of 110-216°C can be analyzed in less than 1 min by optimizing the flow and temperature programming conditions. Moreover, the analysis of four VOCs at the concentration level of one part per million in an aqueous sample (which corresponds to a headspace concentration in the lower parts-per-billion regime) was performed with a sampling time of only 6 s. The µDPID has demonstrated a linear dynamic range over three orders of magnitude. The system presented here could potentially be used to monitor hazardous VOCs in real time in industrial workplaces and residential settings.
A wide range of applications rely on the ability to integrate electrically conductive microstructures with microfluidic channels. To bypass the planar geometric restrictions of conventional microfabrication processes, researchers have recently explored the use of “Direct Laser Writing (DLW)”—a submicron‐scale additive manufacturing (or “3D printing”) technology—for creating conductive microfeatures with fully 3D configurations. Despite considerable progress in the development of DLW‐compatible photomaterials, thermal post‐processing requirements to support electrical conductivity remain a critical barrier to microfluidics integration. In this work, novel graphene‐laden photocomposites are investigated to enable DLW‐based printing of true 3D conductive microstructures directly inside of enclosed microchannels (i.e., in situ). Photoreactive composite materials comprising reduced graphene oxide (rGO) particle concentrations of up to 10 wt% exhibited high compatibility with DLW, with minimal optical interference at critical wavelengths. Developed rGO‐photocomposites revealed an ultimate DC conductivity of 9.85 ± 0.48 × 10−5 S m−1. Experimental results for DLW of 3D microcoils (1 wt% rGO; wire diameter = 10 µm; coil diameter = 40 µm) revealed an impedance of 2.71 ± 0.12 MΩ at 2 MHz. In addition, results for in situ DLW of geometrically sophisticated rGO‐laden microstructures suggest utility of the presented approach for potential 3D microelectronics‐based microfluidic applications.
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