Spectroscopic analysis of different body fluids has been realized by using tapered flat silver halide fiber elements as infrared biosensors. Here, a specially functionalized sensor is presented, which had been prepared by an Nhydroxysuccinimide (NHS) ester derivative containing a reactive thiol group. NHS esters are often used as coupling agents to covalently bind amine-containing biomolecules (e.g., enzymes, antibodies or peptides) for the preparation of bioanalytical sensors of high selectivity. Recently, an immuno-infrared-sensor for Alzheimer disease (AD) screening has been presented based on infrared ATR-measurements with antibody-immobilized Ge-element surfaces for the extraction and analysis of Amyloid-beta (Aβ)-monomers, oligomers, and fibrils from blood plasma and cerebrospinal fluid (CSF). Thereby the biomarker amide I maximum frequency was used for AD classification. Here, for functionalizing the silver halide surfaces different procedures have been investigated, which consider the exchange reaction of the halogen atoms by the thiol-group as one option. Other preparation methods use the chemical reduction of silver ions, either from aqueous salt solutions or of the fiber material itself. A further method uses a first printing of silver nanoparticles on top of the flattened fiber sections. The combination of specific protein immobilization via functionalized silver halide fibers with recently introduced quantum cascade laser spectrometers is very promising for device miniaturization suited for implementation into hospital laboratories or general practitioners’ offices.
We demonstrate the suitability of two cost efficient technologies, namely roll-to-roll hot embossing and laser-assisted hot embossing, to fabricate arrays of structures in the microscale down to the sub-100 nm range. We therefore employ polymers with a relatively moderate glass transition temperature, e.g., cyclic olefin copolymer (COC) and polystyrene (PS). We compare the two replication processes regarding their precision and cost using different 1D and 2D nanostructure gratings and microfluidic channels. All nickel shims used for the replication are fabricated in combination of electron beam or UV lithography and nickel electroforming. The replicated structures are used in different applications. The nanopillar arrays are coated with gold and integrated in the hot embossed microfluidic channels for lab-on-a-chip (LoC) surface-enhanced Raman analysis. We evaluate the as-fabricated 2D nanopillar arrays for surface-enhanced Raman spectroscopy (SERS) using solutions of rhodamine 6G as exemplary analytes. The influence of the geometrical parameters like diameter and pitch of the polymer structures as well as the influence of the gold layer thickness are discussed. 1D-gratings will be used as resonators for organic distributed feedback (DFB) lasers. Both elements, the SERS chips and the organic DFB lasers as tunable excitation source can be combined in the future to form one Raman-on-Chip optofluidic platform for sensitive detection of low-concentrated analytes in water.
The individualized functionalization of mass-produced microstructures is still challenging for the process technology. Here, a rroll-to-roll based process hot embossing is presented for the production of microfluidic structures by means of hot embossing is presented. The resulting microfluidic channels are functionalized modified with different materials. Thereby, digital printing technologies such as aAerosoljet or inkjet are used. This approach allows for mass production of microfluidic channels and their the individualized individual functionalizationfunctionalization of mass produced microfluidic channels. The encapsulation of the channels also takes placeis realized in an R2R-based thermal bonding process without adding any solvent or adhesive.
Taking account ofUsing this approach, several sensor systems for gas and / or fluid detection could be demonstrated. Surface -eEnhanced Raman Scattering scattering (SERS) with amplification enhancement factors of up to 107 [1] is demonstrated by printing gold nanoparticles into the microfluidic channel. We evaluate the printed SERS structures using solutions of rhodamine 6G and adenosine as exemplary analytes.
Furthermore, these channels could be functionalized with different fluorescent organic semiconductors. Their fluorescence intensity is quenched in the presence of a nitroaromatic compounds. By using different materials simultaneously, we are able to measure a fingerprint like pattern of different analytes, which we evaluated by means ofusing pattern recognition algorithms. This method can be used both in the gas phase (electronic nose) and in fluids (electronic tongue) for the detection of nitroaromatic compounds [2,3]. With the opto-electronic nose, we were able to reach detections limits below 1ppb.
[1] A. Habermehl et al, Sensors 17, 2401 (2017).
[2] N. Bolse et al, Flexible and Printed Electronics 2, 024001 (2017)
[3] N. Bolse et al, ACS Omega 2 (10), 6500-6505 (2017)
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.
KEYWORDS: Sensors, Explosives detection, Chemical analysis, Luminescence, Biological and chemical sensing, Printing, Polymers, Explosives, Data modeling, Cameras, Visualization
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.
For single photon experiments or research on novel hybrid structures consisting of several colloidal quantum dots (Qdots) and plasmonic nanoparticles both the precise localization and the optical behavior of the emitters need to be correlated. Therefore, the gap between the high spatial resolution topography information that provides detailed localization of single Qdots and the diffraction limited fluorescence image needs to be overcome. In this paper, we demonstrate the combination of atomic force microscopy (AFM) with wide-field fluorescence microscopy improved by superresolution optical fluctuation imaging (SOFI). With this approach the topography and the superresolution image can be overlaid with sub-diffraction precision. Consequently, we discriminate between single Qdots that are optically active and dark ones. Additionally, the optical time-dependent behavior of molecular emitters can be selectively investigated. This method is, furthermore, useful for an advanced manipulation and characterization toolbox of Qdots in general. In summary, our findings represent an easily adaptable, highly reproducible and comparatively cheap subdiffraction limit imaging method and they facilitate the efficient selection of bright Qdots in a standard lab environment for proof-of-principle nanostructures containing Qdots and for nanomanipulation experiments.
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