Nico Bolse

Lab-on-Chip, Surface-Enhanced Raman Analysis by Aerosol Jet Printing and Roll-to-Roll Hot Embossing

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.

A low-cost versatile fluorescence quenching detection system for liquid- and vapor-phase sensing

We report on the design and evaluation of a low-cost versatile optical sensor system to detect explosive traces by fluorescence quenching. In comparison to common detection systems, it allows to rapidly sample sensor arrays in various analyte carriers. Moreover, our work enables system development towards low-cost analysis and sensor testing solutions due to the simplicity of the approach. Therefore, we demonstrate the detection of nitroaromatic analytes in toluene, in water and in air by the application of transducing polymers. The results of the system demonstration indicate that the transduction strongly depends on the transducer state and on the analyte carrier.

Discrimination of trace nitroaromatics using linear discriminant analysis on aerosol jet printed fluorescent sensor arrays

In this work, we report on fluorescent sensor arrays fabricated by aerosol jet printing on glass substrates to detect explosives-related nitroaromatic species. The printed sensor arrays consist of six different fluorescent polymers responding to nitroaromatic vapors through a photo-induced electron transfer. This results in a quenched fluorescence proportional to the vapor concentration. Distinct fluorescence quenching patterns are detected for nitroaromatic species including nitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene. The detected fingerprints are evaluated at low concentrations of only 1, 3 and 10 parts-per-billion in air. Linear discriminant analysis is used to train each sensor array enabling the discrimination of the target analyte vapors. To investigate the reproducibility of multiple sensor arrays on a single substrate, the measured fluorescence quenching patterns are used to benchmark the linear discriminant models. For this purpose, the target analytes and vapor concentrations are predicted for each sensor array. On average, we report low and reproducible misclassification rates of about 4 % indicating excellent discriminatory abilities at low concentrations close to the detection limits. We conclude that digital printing of fluorescent polymers offers the potential to realize low-cost sensor arrays for a reliable detection of trace explosives.

Nitroaromatic explosive vapor detection using a digitally printed sensor array (Conference Presentation)

We report on a fluorescent optoelectronic nose for the trace detection of nitroaromatic explosive vapors. The sensor arrays, fabricated by aerosol-jet printing, consist of six different polymers as transducers. We 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 (LDA). 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. Our approach enables the realization of highly integrated optical sensor arrays in optoelectronic noses for the sensitive and selective detection of nitroaromatic explosive trace vapors using a potentially low-cost digital printing technique suitable for high-volume fabrication. An important challenge is temperature-dependence which is often neglected even though organic emitters are strongly affected by temperature. For some materials, even small changes of a few Kelvin can lead to large changes in the emission intensity making a temperature-control for sensing applications inevitable. Therefore, the temperature-dependence of these sensors is investigated via a heated transparent thin film on the back of such sensors allowing the active layer to be temperature controlled. All of these led to the development of a portable system.

Transient response of a microfibrous web array for the discrimination of nitroaromatic explosive vapors

We report on the transient response of a microfiber array for the detection of nitroaromatic trace explosives through fluorescence quenching by 1,3-dinitrobenzene, 2,4-dinitrotoluene and nitrobenzene. The sensor array was fabricated from polymer-coated microfibers. An in-house developed portable system was used to study the sensor array response when exposed to vapor concentrations between 1–10 parts-per-billion in air. We show that linear discriminant analysis can be used to discriminate explosives-related compounds close to the detection limits.