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- 2017 (3) (entfernen)
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- Fluorescence (3)
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Eingeladener Vortrag
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The fluorescence properties of three molecular rotors, related to 4-dimethylamino-4-nitrostilbene (4-DNS), are studied versus different diesel/kerosene blends. In nonviscous solvents, these compounds can populate a twisted intramolecular charge transfer state which deactivates nonradiatively, successfully suppressing fluorescence emission. Solution experiments with diesel/kerosene blends showed a good linear correlation between the fluorescence intensity of the probe molecules and the diesel fraction of the blend. The dyes have been immobilized on paper, retaining their fluorescence behavior, i.e., negligible emission in the presence of nonviscous organic solvents and increasing fluorescence when the environment is increasingly viscous. When the impregnated paper is devised as a test strip, the latter is compatible with a newly designed smartphone reader system, which allows in-the-field measurements. The method can safely detect the presence of kerosene in diesel at ≥7%, which competes favorably with current standard methods for the detection of diesel adulteration.
Fluorescent sensory MIP (molecularly imprinted polymer) particles were combined with a droplet-based 3D microfluidic system for the sensitive and selective determination of 2,4-dichlorophenoxyacetic acid (2,4-D) in water samples. 2,4-D being an important and widely used herbicide to regulate plant growth, its extensive use leads to food or ground water contamination. Analytical assays based on MIP have emerged as a valuable tool in the field of environmental analysis thanks to low production costs, stability, format adaptability and their ability to recognize a wide variety of targets, such as the critical neutral organic molecules present in water: herbicides, pesticides, antibiotics, etc.
To accomplish this, a tailor-made fluorescent indicator cross-linker was designed that translates directly the binding event into an enhanced fluorescence signal. This phenoxazinone-type cross-linker was co-polymerized into a thin MIP layer grafted from the surface of silica microparticles. The latter was achieved by integration of the fluorescent core-shell MIP sensor particles into a modular microfluidic platform that allows for an in-line phase-transfer assay, extracting the analyte from aqueous sample droplets into organic phase droplets that contain the sensor particles.
This tool offering a novel simple and rapid way for the detection of herbicides, real-time fluorescence determination of 2,4-D down to 20 nM was realized with the system and applied for the analysis of worlwide surface water samples.
The identification and quantification of phosphorylated amino acids, peptides and proteins is one of the key challenges in contemporary bioanalytical research, noteworthy to diagnose and treat diseases at an early stage. Small sensing devices like microfluidic chips combined with “smart” detection chemistry and simple data assessment, processing and presentation are attractive in this regard. We developed novel synthetic probes, targeting phosphorylated amino acids, based on core-shell microparticles consisting of a silica core coated with a molecularly imprinted polymer shell (MIP). These “plastic antibodies” which are extremely robust, resist denaturing solvents and high temperatures, can be reproducibly produced at low cost, can potentially overcome many of the problems in the current detection strategies. The MIP layer, containing a fluorescent probe monomer, responds to phosphorylated amino acids such as phosphorylated tyrosine (pTyr) with a significant imprinting factor, i.e. selectivity, higher than 3.5, and a “lighting-up” of its fluorescence accompanied by the development of a strongly red-shifted emission band. The bead-based ratiometric detection scheme has also been successfully transferred to a microfluidic chip format to demonstrate its applicability to rapid assays. Such a device could yield an automated pTyr measurement system in the future. The setup was built by coupling a PDMS/Teflon/glass microfluidic chip with an optical setup for fluorescence measurements able to extract and monitor pTyr concentration from 0.5–200 μM.