Analytische Chemie
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Three fluorescent molecular rotors of 4-dimethylamino-4-nitrostilbene (4-DNS) were investigated for their potential use as viscosity probes to indicate the content of kerosene in diesel/kerosene blends, a wide-spread activity to adulterate fuel. In solvents with low viscosity, the dyes rapidly deactivate via a so-called twisted intramolecular charge transfer state, efficiently quenching the fluorescence. Measurements of diesel/kerosene blends revealed a good linear correlation between the decrease in fluorescence and the increase of the fraction of the less viscous kerosene in diesel/kerosene blends. Immobilization of the hydroxy derivative 4-DNS-OH in cellulose paper yielded test strips that preserve the fluorescent indicator's behavior. Combination of the strips with a reader based on a smartphone and a controlling app allowed to create a simple field test. The method can reliably detect the presence of kerosene in diesel from 7 to 100%, outperforming present standard methods for diesel adulteration.
The synthesis, characterization, and application of mesoporous materials containing boron–dipyrromethene (BODIPY) moieties that allow the sensitive and selective detection of HgII in aqueous environments by fluorescence enhancement is reported. For this purpose, BODIPY dye I containing a thia‐aza crown ether receptor as the fluorescent probe for the detection of HgII in aqueous environments is encapsulated into mesoporous materials to avoid self‐quenching or aggregation in water. Determination of HgII is accomplished within a few seconds with high selectivity and sensitivity, reaching a limit of detection of 12 ppt. The determination of trace amounts of HgII in natural waters and in fish extracts is demonstrated by using our sensing material. The incorporation of the material into several μ‐PAD strips yields a portable, cheap, quick, and easy‐to‐handle tool for trace HgII analysis in water.
Gasoline adulteration is a frequent problem world-wide, because of the chance of quick, maximized profits. However, addition of cheaper ethanol or hydrocarbons like kerosene does not only result in economic damage but also poses problems for vehicles and the environment. To enable law enforcement forces, customers or enterprises to uncover such a fraudulent activity directly upon suspicion and without the need to organize for sampling and laboratory analysis, we developed a simple strip-based chemical test. Key to the favorable performance was the dedicated materials tailoring, which led to test strips that consisted of a cellulose support coated with silica, passivated with hexamethyldisilazane and functionalized covalently with a molecular probe. The probe fluoresces brightly across a broad solvent polarity range, enabling reliable quantitative measurements and data analysis with a conventional smartphone. The assays showed high reproducibility and accuracy, allowing not only for the detection of gasoline adulteration but also for the on-site monitoring of the quality of commercial E10 gasoline.
In particular, the rapid development of lateral flow assays as indispensable tools for everyone to contain the SARS-CoV-2 pandemic has fuelled the global demand for analytical tests that can be used outside dedicated laboratories. In addition to their use in medical diagnostics, rapid tests and assays have become increasingly important in various fields such as food safety, security, forensics, and environmental management. The advantage is obvious: taking the assay directly to the sample minimizes the time between suspicion and decision-making, allowing faster action. Especially today, when mobile communication devices with powerful computing capabilities and built-in cameras are ubiquitous, more people than ever before around the world have the basic skills to operate a powerful detector at their fingertips. This sets the stage for a much wider use of analytical measurements in terms of prognosis and prevention, enabling professional laypersons in particular.
However, current strip-based systems are primarily focused on single parameter analysis, whether it is SARS-CoV-2 biomarkers, blood glucose levels, or lead concentrations in water samples. Industrial applications of such methods also often still rely on single-parameter assays, requiring multiple runs even for a limited number of key parameters. Overcoming these limitations depends on developing low-number multiplexing strategies that ensure robustness, reliability, speed, ease of use, and sensitivity.
This lecture will give an overview of several generic approaches developed in recent years to address these challenges. It will highlight how the synergy of supramolecular (bio)chemistry, luminescence detection, hybrid (nano)materials and device miniaturization can result in powerful (bio)analytical assays that can be used at a point-of-need.1-5 Selected examples will introduce key aspects of such systems that include tailored signaling mechanisms and recognition elements, materials functionalization and device integration, including hybrid nanomaterials, gated indicator release systems, strip modification, and smartphone-based analysis.