We report on a fluorescent optoelectronic nose for the trace detection of nitroaromatic explosive vapours. The sensor arrays, fabricated by aerosol-jet printing, consist of six different commercially available polymers as transducers. We assess the within-batch reproducibility of the printing process and we report that the sensor polymers show efficient fluorescence quenching capabilities with detection limits of a few parts-per-billion in air. We further demonstrate the nose's ability to discriminate between several nitroaromatics including nitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene at three different concentrations using linear discriminant analysis. Our approach enables the realization of highly integrated optical sensor arrays in optoelectronic noses for the sensitive and selective detection of nitroaromatic explosive trace vapours using a potentially low-cost digital printing technique suitable for high-volume fabrication.
Surface-enhanced Raman spectroscopy (SERS) combines the high specificity of Raman scattering with high sensitivity due to an enhancement of the electromagnetic field by metallic nanostructures. However, the tyical fabrication methods of SERS substrates suffer from low throughput and therefore high costs. Furthermore, point-of-care applications require the investigation of liquid solutions and thus the integration of the SERS substrate in a microfluidic chip. We present a roll-to-roll fabrication approach for microfluidics with integrated, highly efficient, surface-enhanced Raman scattering structures. Microfluidic channels are formed using roll-to-roll hot embossing in polystyrene foil. Aerosol jet printing of a gold nanoparticle ink is utilized to manufacture highly efficient, homogeneous, and reproducible SERS structures. The modified channels are sealed with a solvent-free, roll-to-roll, thermal bonding process. In continuous flow measurements, these chips overcome time-consuming incubation protocols and the poor reproducibility of SERS experiments often caused by inhomogeneous drying of the analyte. In the present study, we explore the influence of the printing process on the homogeneity and the enhancement of the SERS structures. The feasibility of aerosol-jet-modified microfluidic channels for highly sensitive SERS detection is demonstrated by using solutions with different concentrations of Rhodamine 6G and adenosine. The printed areas provide homogeneous enhancement factors of ~4 × 106. Our work shows a way towards the low-cost production of tailor-made, SERS-enabled, label-free, lab-on- chip systems for bioanalysis.
One of the primary challenges in explosive detection using fluorescence quenching is the identification and quantification of detected targets. In this work, we explore the reliability of aerosol jet printed sensor arrays for the discrimination of nitroaromatic traces using linear discriminant analysis (LDA). We varied the amount of the deposited material by controlling the printer’s shutter to investigate the impact on the detection reliability. For a twofold variation of the amount of the deposited material, we report excellent classification rates between 81 and 96% for the discrimination of nitrobenzene, 1,3-dinitrobenzene, and 2,4-dinitrotoluene at 1, 3, and 10 parts per billion in air, respectively. Our results close to the detection limits indicate a remarkable identification and quantification of explosive trace vapors because of high control of the printing process. This work demonstrates the high potential of digitally printed fluorescence quenching sensor arrays and the excellent capabilities of LDA as a simple supervised statistical learning technique.
Roll‐to‐roll hot embossing is exploited for the fabrication of 1D nanogratings and 2D nanopillar arrays. Critical structure diameters as low as 150 nm and distances down to 50 nm are replicated in a polystyrene foil using flexible nickel shims, which are made using electron beam lithography and subsequent electroplating. The high quality of the as‐fabricated structures is proven by their application in two key nanophotonic components. After evaporation of 250 nm of Alq3:DCM on 1D nanogratings using grating periods between 375 and 415 nm, we can realize tunable organic DFB lasers emitting between 604 and 665 nm. 2D nanopillar arrays are covered with a thermally evaporated Au layer and integrated in microfluidic chips for surface‐enhanced Raman measurements. High and homogeneous enhancement of the Raman signal is achieved using rhodamine 6G as exemplary analyte. For polystyrene nanopillar arrays with pillar diameters of 190 nm, a spacing of 50 nm, and a height of 100 mm coated with a 70 nm thick Au layer, an analytical enhancement factor of ≈4.3 × 104 is demonstrated. The presented work shows the versatility of roll‐to‐roll hot embossing for the low‐cost and large‐area fabrication of nanostructures.
We present the reduction of solution processed graphene oxide films by hydrogen iodide vapor. The films were studied by Raman spectroscopy and Fourier-transform infrared spectroscopy and its optoelectronic properties characterized. We obtained reduced graphene oxide films on polyethylene terephthalate flexible substrates with good electrical properties, 3.74×10 Ω·m, and high optical transmittance of 70% in the visible range. The fabricated layers contain graphene sheets with sizes up to ∼10 μm long and ∼6 μm wide. The presented solution, with highly concentrated processed graphene oxide, could be used as printing ink for manufacturing transparent and conductive electrodes on plastic substrates without the requirement of elevated temperatures.
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