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An ideal sensor system is a combination of a selective receptor, an effective transducer, and a sensitive detector. To utilize molecularly imprinted polymers (MIPs) as responsive recognition phases in sensors, the employment of fluorescent molecules or nanoparticles (NPs) that show prominent changes in their spectroscopic properties after binding of the target molecule in the MIP’s cavity is particularly attractive. Such fluorescent MIPs (fMIPs) act through target-induced quenching, enhancement, or spectral shifts of the fluorescence. This contribution introduces different strategies of incorporation of fluorescent dyes, probes, and NPs into fMIPs. In addition, various sensing mechanisms are reviewed, and depending on the application of the sensor, the different deployable formats, their advantages, drawbacks, and impact will be presented and discussed.
Ammonia and its conversion product ammonium have a strong negative impact on human health and ecosystems. Most ammonia measurements in ambient air are performed in the molar fraction range (0.5 to 500) nmol/mol. There is a need for reliable traceable ammonia gas standards as well as in situ analytical procedures for the monitoring of ammonia in ambient air.
The permeation method is an effective tool for dynamically generating precise gas standards with a low uncertainty in the concentration range of a few nmol/mol to several µmol/mol in an inert carrier gas, e. g. pure nitrogen or purified ambient air. Here, we present our ammonia gas standard generator as well as results of the characterisation of its individual components supporting the uncertainty assessment according to GUM for stable gas concentrations in this range.
In order to detect ammonia in the nmol/mol-range, a suitable sensor has to be developed. In this contribution, we therefore additionally present first approaches on the development of such a sensor using optical fluorescence as transduction mechanism due to its intrinsically high sensitivity and high spatial resolution. Incorporation of a fluorescent dye, which shows fluorescence enhancement in the presence of ammonia, into a polymer matrix allows to reversibly recognize low amounts of ammonia. It can be concluded that fluorescence sensor is a robust tool for measurements of ammonia; however it needs calibration for the planed use.
Nonporous corundum powder, known as an abrasive material in the industry, was functionalized covalently with protein binders to isolate and enrich specific proteins from complex matrices. The materials based on corundum were characterized by TEM, ESEM, BET, DLS, and zeta potential measurements. The strong Al-O-P bonds between the corundum surface and amino phosphonic acids are used to introduce functional groups for further conjugations. The common cross-linker glutaraldehyde was compared with a hyperbranched polyglycerol (PG) of around 10 kDa. The latter is oxidized with periodate to generate aldehyde groups that can covalently react with the amines of the surface and the amino groups from the protein via a reductive amination process. The amount of bound protein was quantified via aromatic amino acid analysis (AAAA). This work shows that oxidized polyglycerol can be used as an alternative to glutaraldehyde. With polyglycerol, more of the model protein bovine serum albumin (BSA) could be attached to the surface under the same conditions, and lower nonspecific binding (NSB) was observed. As a proof of concept, IgG was extracted with protein A from crude human plasma. The purity of the product was examined by SDS-PAGE. A binding capacity of 1.8 mg IgG per g of corundum powder was achieved. The advantages of corundum are the very low price, extremely high physical and chemical stability, pressure resistance, favorable binding kinetics, and flexible application.
Besides the traditional areas of application such as separation and enrichment which made molecularly imprinted polymers (MIPs) very attractive, they have emerged as a valuable detection tool in the field of environmental analysis due to the low production costs, high stability, format adaptability and the possibility to imprint and thus specifically recognize a wide variety of target analytes. Regarding optical sensing, however, MIPs have only been used in considerably few applications, especially in fluorescence sensors, basically because of the challenge to incorporate a fluorescently responding moiety into a polymer matrix. One way to overcome this limitation is the coating of a thin MIP layer onto the surface of silica nanoparticles using tailor-made fluorescent indicator monomers or cross-linkers for direct transfer of the binding event into an optical signal.
Regarding sensors for environmental monitoring, microfluidic devices utilizing optical detection modules are especially appealing because of their versatility in terms of miniaturization and automation. So far, MIPs have only rarely been used in combination with microfluidic sensor devices.
Here, we present the hydrogen bond-mediated optical response of fluorescent MIP sensor particles against a typical small-molecule analyte 2,4-D (2,4-dichlorophen¬oxyacetic acid) which is an important herbicide widely used in agriculture and known to cause adverse health effects when ingested by contaminated water. By combining the sensor particles with droplet-based 3D microfluidics, a microfluidic phase-transfer assay was designed which enables the direct analysis of 2,4-D in river and lake water without sample pre-treatment or clean-up.
In the KonSens Project, sensor systems are developed, validated, and operated in form of functional models for the application areas Structure Integrated Sensors and Mobile Multi-gas Sensors. Key aspects are the detection and evaluation of corrosion processes in reinforced concrete structures as well as the detection and quantification of very low concentrations of toxic gases in air. The adaption of sensor principles from the lab into real-life application including appropriate communication techniques is a major task.
In recent years, Structural Health Monitoring have gained in importance, since growing age of buildings and infrastructure as well as increasing load requirements demand for reliable surveillance methods. In this regard, the project follows two strategies: First, the development and implementation of completely embedded sensor systems consisting of RFID-tag and in situ sensors, and their further application potential (e.g. for precast concrete elements, roadways, wind power plants, and maritime structures). Secondly, the development of a long-term stable, miniaturized, fiber optic sensor for a ratiometric and referenced measurement of the pH-value in concrete based on fluorescence detection as an indicator for carbonation and corrosion.
Environmental pollution through emission of toxic gases becomes an increasing problem not only in agriculture (e.g. biogas plants) and industry but also in urban areas. This leads to increasing demand to monitor environmental emissions as well as ambient air and industrial air components in many scenarios and in even lower concentrations than nowadays. The selectivity of luminescence-based sensors is enabled by the combination of the sensing dye and the material, which is used as accumulation medium for concentration of the analyte. This principle allows for developing gas sensors with high selectivity and sensitivity of defined substances. Additional benefits, particularly of fluorescence-based sensors, are their capability for miniaturization and potential multiplex mode. Objective is the development and implementation of sensors based on fluorescence detection for defined toxic gases (ammonia, hydrogen sulfide, ozone, and benzene) with sensitivity in the low ppm or even ppb range. Additionally, the integration of such sensors in mobile sensor devices is addressed.
In the present paper the development of a semi-automated device for long-term monitoring of gaseous ammonia is described. A sensor material was produced that changes its optical properties in the pres-ence of low concentrations of ammonia in air. The implementation into an electronic device enables precise, simple, economic and fast monitoring of low concentrations of harmful gases, like ammonia, and hence can help to improve the climate monitoring in livestock housing, barns or stables.
There is significant contamination of our water resources and an accelerating accumulation of hazardous species in the aquatic biosphere. Whether for instance mercury as a contaminant constantly released from a multitude of industrial processes or chemical warfare agents (CWAs) such as Tabun (GA), Sarin (GB) or Soman (GD) as highly toxic remnants of World War II, released from dumped containers upon their progressive corrosion, are concerned such hazards can cause serious problems to human health even at low concentration and monitoring them becomes increasingly essential. Conclusively, it is necessary to develop sensors for such hazards that combine high sensitivity, good selectivity, fast responses and can dispense with complex instrumentation.
Here, we present SBA-15-type mesoporous silica materials containing boron–dipyrromethene (BODIPY) probes in their pore systems that allow for the sensitive and selective detection of the two target analytes CWAs and Hg2+ in natural waters via a change in the optical properties. In case of Hg2+, the BODIPY dye is directly adsorbed on the (inner and outer) surface of the highly porous material and coordinates the metal ion, leading to an enhancement of fluorescence with a limit of detection (LOD) of 15 ppt. Using the same silica material but incorporating a covalently attached BODIPY dye, the CWAs GA, GD and GB can be detected via fluorescence quenching induced by an intraannular cyclization. The obtained LOD in natural waters is in the pM range and hence below the Maximum Permissible Concentrations for CWAs in drinking water. Aspects of system design as well as application in water and food analysis (fish extracts) will be presented.
There is significant contamination of our water resources and an accelerating accumulation of hazardous species in the aquatic biosphere. Whether for instance mercury as a contaminant constantly released from a multitude of industrial processes or chemical warfare agents (CWAs) such as Tabun (GA), Sarin (GB) or Soman (GD) as highly toxic remnants of World War II, released from dumped containers upon their progressive corrosion, are concerned such hazards can cause serious problems to human health even at low concentration and monitoring them becomes increasingly essential. Conclusively, it is necessary to develop sensors for such hazards that combine high sensitivity, good selectivity, fast responses and can dispense with complex instrumentation.
Here, we present SBA-15-type mesoporous silica materials containing boron–dipyrromethene (BODIPY) probes in their pore systems that allow for the sensitive and selective detection of the two target analytes CWAs and Hg2+ in natural waters via a change in the optical properties. In case of Hg2+, the BODIPY dye is directly adsorbed on the (inner and outer) surface of the highly porous material and coordinates the metal ion, leading to an enhancement of fluorescence with a limit of detection (LOD) of 15 ppt. Using the same silica material but incorporating a covalently attached BODIPY dye, the CWAs GA, GD and GB can be detected via fluorescence quenching induced by an intraannular cyclization. The obtained LOD in natural waters is in the pM range and hence below the Maximum Permissible Concentrations for CWAs in drinking water. Aspects of system design as well as application in water and food analysis (fish extracts) will be presented.
Mit Tröpfchen Spielen
(2018)
Mikrofluidische Systeme sind leistungsstarke analytische Tools mit attraktiven Eigenschaften wie miniaturisierter Größe, geringem Reagenzien und Probenverbrauch, schneller Ansprech- und kurzer Messzeit. Der Bedarf solcher leistungsstarken, miniaturisierten und direkt vor Ort anwendbaren Sensorsysteme steigt kontinuierlich, hauptsächlich durch das Bedürfnis der Gesellschaft, schneller, besser und umfassender über kritische Faktoren im Lebens- und Arbeitsumfeld sowie der Umwelt informiert zu sein.
Pollution through emission of toxic gases is of utmost environmental concern, raising the interest in developing reliable gas sensors. Exemplarily, ammonia and its conversion products can provoke considerable damage on human health and ecosystems. Hence, there is a need for reliable and reversible sensor materials to monitor traces of gaseous ammonia in ambient air, which at best can be used on-site for field measurements. Although various types of sensors such as potentiometric, amperometric, and biological sensors are available for detecting trace amounts of gases, fluorescent sensors have gained importance due to several advantages such as high sensitivity, possible miniaturization, as well as potential multiplexing. Herein, we present the development of a sensor material for gaseous ammonia in the lower ppm or even ppb range using optical fluorescence as transduction mechanism due to its intrinsically high sensitivity and high spatial resolution.[1] Therefore, a fluorescent dye, which shows reversible fluorescence enhancement in the presence of the analyte was incorporated into a polymer matrix, the latter to ensure the accumulation of ammonia. To calibrate the designed optical sensor system a gas standard generator was used, producing standard gas mixtures, which comply with the metrological traceability for ammonia gas standards in the desired environmentally relevant measurement range.[2] Beside the development of a highly sensitive, selective, and reversible sensor, the integration of such systems into mobile sensor devices is addressed. Therefore, a prototype of a miniaturized hand-held instrument was developed enabling a straightforward and long-term read-out of the measurement signal.