Filtern
Dokumenttyp
- Zeitschriftenartikel (62)
- Vortrag (11)
- Beitrag zu einem Tagungsband (3)
- Posterpräsentation (2)
Schlagworte
- Fluorescence (33)
- Core-shell particles (12)
- Molecularly imprinted polymers (11)
- Microfluidics (7)
- Molecular imprinting (5)
- Multiplexing (5)
- Roughness (5)
- Smartphone (5)
- BODIPY (4)
- BODIPY dyes (4)
Organisationseinheit der BAM
- 1 Analytische Chemie; Referenzmaterialien (78) (entfernen)
Paper des Monats
- ja (3)
Eingeladener Vortrag
- nein (11)
Probe 1, which contains an anilinopyridine chromophore and an azaoxa macrocyclic subunit, presented an absorption band centered at 340 nm in acetonitrile. Addition of Fe(III), Cr(III) and Hg(II) induced the growth of a new absorption band at 430 nm (with color change from colorless to yellow), whereas in the presence of Cu(II), Zn(II) and Pb(II), less marked changes were observed. The color changes observed upon addition of Fe(III), Cr(III) and Hg(II) were ascribed to the formation of 1:1 stoichiometry complexes with probe 1. Coordination of Fe(III), Cr(III) and Hg(II) with the pyridine fragment of 1 induced an enhancement of the charge transfer character accompanied with a marked bathochromic shift that was reflected in a color change from colorless to yellow. The strength of the interaction between probe 1 and Fe(III) cation was modulated upon interaction with anions. Of all the anions tested, only cyanide was able to induce the bleaching of the yellow 1·Fe(III) complex solution. This bleaching was ascribed to
the formation of 1·Fe(III)-CN complex that restored, to some extent, the optical features of the free probe allowing the chromogenic sensing of cyanide. Besides, 1·Fe(III) complex was used to detect
cyanide in acetonitrile-water 90:10 v/v mixtures with good recoveries.
Small-molecule oxoanions are often imprinted noncovalently as carboxylates into molecularly imprinted polymers (MIPs), requiring the use of an organic counterion. Popular species are either pentamethylpiperidine (PMP) as a protonatable cation or tetraalkylammonium (TXA) ions as permanent cations. The present work explores the influence of the TXA as a function of their alkyl chain length, from methyl to octyl, using UV/vis absorption, fluorescence titrations, and HPLC as well as MD simulations. Protected phenylalanines (Z-L/D-Phe) served as templates/analytes. While the influence of the counterion on the complex stability constants and anion-induced spectral changes shows a monotonous trend with increasing alkyl chain length at the prepolymerization stage, the cross-imprinting/rebinding studies showed a unique pattern that suggested the presence of adaptive cavities in the MIP matrix, related to the concept of induced fit of enzyme−substrate interaction. Larger cavities formed in the presence of larger counterions can take up pairs of Z-X-Phe and smaller TXA, eventually escaping spectroscopic detection. Correlation of the experimental data with the MD simulations revealed that counterion mobility, the relative distances between the three partners, and the hydrogen bond lifetimes are more decisive for the response features observed than actual distances between interacting atoms in a complex or the orientation of binding moieties. TBA has been found to yield the highest imprinting factor, also showing a unique dual behavior regarding the interaction with template and fluorescent monomer. Finally, interesting differences between both enantiomers have been observed in both theory and experiment, suggesting true control of enantioselectivity. The contribution concludes with suggestions for translating the findings into actual MIP development.
2,4-D ist ein in der Landwirtschaft weitverbreitetes Pflanzenschutzmittel, das Grundwasser kontaminiert, sich innerhalb der Nahrungskette anreichert und Umwelt- und Gesundheitsprobleme verursachen kann. Hier stellen die Autoren ein mikrofluidisches Nachweissystem für die Echtzeitdetektion von 2,4-D in Grund- oder Oberflächenwasser vor. Es basiert auf der Kombination 2,4-D-selektiver, fluoreszierender, molekular geprägter Polymer-(MIP-)Mikropartikel mit einem 3D-mikrofluidischen Extraktions- und Detektionssystem. Messungen vor Ort sollen damit künftig möglich sein.
Microfluidic electrochemical immunosensor for the trace analysis of cocaine in water and body fluids
(2018)
Quick but accurate testing and on‐the‐spot monitoring of cocaine in oral fluids and urine continues to be an important toxicological issue. In terms of drug testing, a number of devices have been introduced into the market in recent decades, notably for workplace inspection or roadside testing. However, these systems do not always fulfill the requirements in terms of reliability, especially when low cut‐off levels are required. With respect to surface water, the presence of anthropogenic small organic molecules such as prescription and over‐the‐counter pharmaceuticals as well as illicit drugs like cannabinoids, heroin, or cocaine, has become a challenge for scientists to develop new analytical tools for screening and on‐site analysis because many of them serve as markers for anthropogenic input and consumer behavior. Here, a modular approach for the detection of cocaine is presented, integrating an electrochemical enzyme‐linked immunosorbent assay (ELISA) performed on antibody‐grafted magnetic beads in a hybrid microfluidic sensor utilizing flexible tubing, static chip and screen‐printed electrode (SPE) elements for incubation, recognition, and cyclic voltammetry measurements. A linear response of the sensor vs. the logarithm of cocaine concentration was obtained with a limit of detection of 0.15 ng/L. Within an overall assay time of 25 minutes, concentrations down to 1 ng/L could be reliably determined in water, oral fluids, and urine, the system possessing a dynamic working range up to 1 mg/L.
Highly emissive phenanthrene-fused boron–dipyrromethene (PBDP) dyes have been spectroscopically characterized in a series of solvents. The influence of different substituents (-H,
-I, -CN, -DMA or a 15C5-crown ether) in the para-position of a phenyl ring attached to the meso-position of the BODIPY core is discussed. This family of dyes has an intense emission at lambda > 630 nm, with fluorescence quantum yields between 0.7 and 1.0 in all solvents studied, except in the case of the dimethylamino-substituted
derivative, PBDP-DMA, which undergoes excited-state intramolecular charge transfer (CT), leading to broadband dual fluorescence in highly polar solvents. Introduction of a weaker electron donor such as a benzocrown to the meso-position is not able to trigger a second (charge or electron transfer) process and, interestingly, heavy atom (iodine, PBDP-I derivative) substitution at that moiety does also not have a relevant influence on the photophysics, i.e., enhanced intersystem crossing was not observed.
Electrochemical studies of PBDP-DMA complement the data reported and stress the fact that the decrease in fluorescence of PBDP-DMA in highly polar solvents is due to an excited-state CT process
rather than to a photoinduced electron transfer (PET).
Chemical functionalization for quantitative spectroscopic labeling on macroscopically flat surfaces
(2018)
This chapter highlights the application of chemical derivatization (CD) to facilitate the quantification of surface functional groups being an important issue for a wide field of applications. The selective attachment of a chemical label to a surface functional group being afterwards exclusively detectable by a highly sensitive technique overcomes the problem of characterizing low amounts of functional groups on macroscopically flat surfaces. The most frequently employed methods include CD X-ray photoelectron spectroscopy, ultraviolet/visible absorption, and fluorescence spectroscopy, as well as time-of-flight secondary ion mass spectrometry. Herein, the basic conditions for the different techniques regarding the specific surface functional group which need to be quantified are discussed. Additionally, the substrate highly influences the compatibility of the corresponding method. Because not just the quantification but also the preparation of the desired application is important, a summary of different preparation methods for glass, polymer and gold substrates is presented.
We introduce herein boron-dipyrromethene (BODIPY) dyes as a new class of fluorophores for the design of reporter dyes for supramolecular host–guest complex formation with cucurbit[7]uril (CB7). The BODIPYs contain a protonatable aniline nitrogen in the meso-position of the BODIPY chromophore, which was functionalized with known binding motifs for CB7. The unprotonated dyes show low fluorescence due to photoinduced electron transfer (PET), whereas the protonated dyes are highly fluorescent. Encapsulation of the binding motif inside CB7 positions the aniline nitrogen at the carbonyl rim of CB7, which affects the pKa value, and leads to a host-induced protonation and thus to a fluorescence increase. The possibility to tune binding affinities and pKa values
is demonstrated and it is shown that, in combination with the beneficial photophysical properties of BODIPYs, several new applications of host–dye reporter pairs can be implemented. This includes indicator displacement assays with favourable absorption and
emission wavelengths in the visible spectral region, fluorescence correlation spectroscopy, and noncovalent surface functionalization
with fluorophores.
Supramolecular chemistry, fluorescence detection, hybrid (nano)materials and device miniaturization are in themselves highly interesting areas of research, yet especially their combination paves the way to (bio)chemical analysis systems that show outstanding performance. The lecture gives an overview of the toolbox of single components developed in BAM’s Chemical and Optical Sensing Division over the years, and how their combination can result in powerful sensors, quick tests and assays. While at the core of a development is the analytical problem, that is, the determination of a certain analyte in a sample of interest with the required sensitivity and selectivity by a specific end user in a given setting, signaling mechanisms, recognition elements, signal transduction modes, materials functionalization, device design and system integration are adequately chosen, tailored and adapted. Examples including molecularly imprinted polymers, hybrid mesoporous nanomaterials, gated indicator release systems, microfluidic devices, test strips and smartphone-based analysis will be presented.
Molecularly Imprinted Polymers with Integrated Fluorescence as Versatile Biomimetic Sensing Matrices
(2018)
Molecularly imprinted polymers (MIPs) are an established, versatile and high-performance matrix for the selective separation or enrichment of (bio)chemical species, especially small molecules of biochemical or environmental relevance. MIPs are prepared through the polymerization of a mixture of functional monomers and cross-linkers in the presence of the template with subsequent extraction of the latter. Conceptionally, this process can be seen as mimicking in a strongly accelerated, though single-step manner a biological process such as antibody formation. Because the resulting MIPs contain cavities in their matrix that are complementary in size, shape and electronic/ electrostatic or hydrogen bonding demand to the imprinted target molecule or template, these polymers are frequently termed “artificial antibodies”. Compared to natural antibodies, they are chemically and physically much more robust. Regarding sensitivity and selectivity, however, there is still a gap to bridge before MIPs can fully compete with antibodies.
Another favorable aspect that distinguishes MIPs from antibodies is that they can be endowed with an explicit function, allowing the use of MIPs in applications that require more than only an efficient binder. For instance, if specifically designed and polymerizable fluorescent indicators are integrated as functional monomers into a MIP, direct fluorescence sensing can be accomplished. Because MIPs can be prepared in a variety of different formats, their combination with miniaturized or other specific analytical techniques or sensory devices is possible, especially when the transduction mode is light. This presentation will introduce basic design considerations, challenges, limitations and the potential that lies with such sensor materials with some recent examples of our group, targeting various organic oxoanions as analytes.
The detection of potential contaminants as early as possible and as close to their point of emission as well as immission is becoming increasingly important in contemporary environmental analytical chemistry. In addition, real-time monitoring of important chemical parameters for process control is strongly gaining relevance within the context of Industry 4.0. Not only is the development of powerful optical probes thus necessary but also their integration into a matrix and/or device that allows for the application of such systems in realistic measurement scenarios. Integrating fluorescent probes with sensing matrices, however, presents a major challenge because usually, when confined in a rather rigid matrix, fluorophores tend to behave completely different than for instance in the molecular state in solution. The present contribution will highlight recent examples of successful integration of BODIPY (boron–dipyrromethene) based probes with devices that have been developed in our group.
A simple system utilizing a test strip for direct readout with a conventional miniaturized camera as for instance routinely used in smartphones was recently devised by us for the determination of organophosphate nerve or chemical warfare agents (CWAs) Sarin (GB), Soman (GD), and Tabun (GA) in aqueous environments. Here, we coupled a reactive BODIPY to the inner and outer surface of mesoporous silica nanoparticles. In the presence of CWAs, the reactive BODIPY dye with an optimally positioned hydroxyl group undergoes an acylation reaction, yielding a bicyclic product that is non-emissive. The strong fluorescence quenching response allows reaching LODs in the pM range in natural waters.
Steric embedding, again relying on test strip analysis in combination with a smartphone-based readout and data processing, was sufficient to create a reusable optical pH stick. The family of pH-responsive fluorescent BODIPY probes used for this purpose has been designed in a rational manner with the aid of quantum chemistry tools. All the probes display very similar spectroscopic properties with ON−OFF fluorescence switching responses, being retained after embedding of the probes into hydrogel sensor spots on a plastic strip.
Dispensing with a matrix yet invoking microfluidic chips finally permits to use a highly sensitive boronic acid-functionalized BODIPY probe for in-line sugar analysis for instance in the beverage industry. Placement of an amino group in direct neighbourhood of the boronic acid moiety yielded a broad working range at neutral pH while meeting the desired sensitivity in the micro-molar range due to a pronounced analyte-induced fluorescence increase, guaranteeing the straightforward detection of sugar in (coloured) sodas without sample clean-up.