Kompakte Abfrageeinheit auf Basis einer Doppelphotodiode für die spektraloptische Sensorik

Spektraloptische Sensoren erfassen physikalische als auch (bio-)chemische Messgrößen hochempfindlich und robust auf Grundlage von definierten spektralen Eigenschaftsänderungen - Wellenlängenverschiebung oder Änderung des Intensitätsverhältnisses zweier Spektrallinien - des Messwandlers. Die aufwändige Spektrenaufnahme des Sensorsignals mittels voluminösen Spektrometern oder durchstimmbaren Laser und die sich daraus ergebende komplexe Signalauswertung schränkt jedoch derzeit ihre industriellen Einsatzmöglichkeiten erheblich ein. In der vorliegenden Arbeit wird eine neuartige, miniaturisierte Auswerteeinheit mit einer Doppelphotodiode vorgestellt, die durch ihren Stapelaufbau aus zwei unterschiedlich spektralempfindlichen Photodiodenschichten gleichzeitig spektralselektives Element und Detektor ist. Statt wie bisher die spektrale Information aus einem Spektrum zu extrahieren, wird der Schwerpunkt der spektralen Gesamtverteilung anhand des gemessenen Verhältnisses der beiden wellenlängenabhängigen Photoströme echtzeitfähig ausgewertet. Der Ansatz vereinigt die Einfachheit einer intensitätsbasierten Messung mit der Robustheit einer spektralen Auswertung, wodurch sich völlig neue Systemkonzepte für die spektraloptische Sensorik eröffnen. Die Leistungsfähigkeit der onlinefähigen Signalauswertung mittels der Doppelphotodiode wird an einer brechzahlsensitiven nanoplasmonischen Goldschicht sowie dem thermometrischen Leuchtstoffes NaYF4: Yb3+, Er3+ demonstriert

Aufbau und Biofunktionalisierung einer LSPR-Molekülsensorikeinheit

Der Gebrauch klassischer Oberflächenplasmonenresonanz-Sensoren ist derzeit aufgrund ihrer massiven und justageaufwendigen Bauweise auf den Laborbetrieb beschränkt. Am Fraunhofer IKTS wird gegenwärtig ein miniaturisiertes Sensorsystem entwickelt, dessen Messeffekt auf lokalisierter Oberflächenplasmonenresonanz basiert. Als zentrales Element steht dabei eine mit Fängermolekülen funktionalisierte nanostrukturierte Goldoberfläche in direktem Kontakt mit einem Photodiodenpaar. Bei einer Wechselwirkung des Analyten mit der biologischen Erkennungsstruktur und gleichzeitiger transmittiver Beleuchtung können die Signaländerungen anhand eines einfachen Photostromvergleiches ausgewertet werden –ganz ohne die Verwendung eines aufwendigen Spektrometers. Die vereinfachte und kompakte Bauweise dieses Sensorsystems soll in Zukunft eine Integration in Anlagen zur Online-Prozessüberwachung und Echtzeitdetektion von Biomolekülen erlauben. In diesem Beitrag wird der aktuelle Arbeitsstand des Sensoraufbaus sowie der Biofunktionalisierung dargestellt

Onlinefähige Signalauswertung für spektraloptische Sensoren mit einer Doppelphotodiode

Spectral-optical sensor technology records physical as well as (bio-)chemical measurands on the basis of specific spectral property changes of the transducer. In this article a signal evaluation with a double-layered photodiode (DPD) is presented, which is a spectrally selective element and detector at the same time due to its stack structure of two different spectrally sensitive photodiode layers. Instead of extracting the spectral information from a spectrum, the centroid of the overall spectral distribution is evaluated in real time on the basis of the measured ratio of the two wavelength-dependent photocurrents. The performance of the DPD is demonstrated by means of surface temperature measurements with the phosophor NaYF4:Yb3+,Er3+. It is shown that with an integratorbased readout electronics a max. measurement deviation for the centroid wavelength of 0.1 nm can be achieved. In sum, the online-capable signal processing and compact size of the double-layered photodiode foster the on-site applicability of spectral-optical sensors for the process industry, environmental monitoring and many others fields

A compact readout platform for spectral-optical sensors

The continuous monitoring of industrial and environmental processes is becoming an increasingly important aspect with both economic and societal impact. So far, spectral-optical sensors with their outstanding properties in terms of sensitivity and reliability have not been considered as a potential solution because of the cost-intensive and bulky readout hardware. Here we present a card-size, in expensive, and robust readout platform based on a wavelength-sensitive photodiode. In test and characterization experiments we achieved a wavelength shift resolution of better than 0.1 nm and a detection limit of 0.001 AU for ratiometric measurements. We furthermore discuss the capability and current limitations of our readout unit in context with interrogation experiments we performed with a photonic crystal-based fluid sensor. In sum we expect the presented readout platform to foster the exploitation of spectral-optical sensor technology for gas monitoring, chemical analytics, biosensing and many others fields

Plasmonic sensor system for on-site monitoring of diclofenac molecules

In previous studies, we applied a commercial surface plasmon resonance (SPR) sensor successfully to detect molecules of diclofenac in solutions simulating contaminated water sources. For such laboratory investigations, SPR sensors are well suited and, hence, they are established in the field of environmental and life sciences. However, they lack robustness which limits their applicability for on-site measurements, e.g. directly at water treatment plants. We therefore extended our study and set up a robust low-cost biosensor system. We used nanoimprint lithography to fabricate nanostructured gold surfaces which act as SPR transducers. For readout of the SPR signal the system is equipped with a novel photocur-rent read-out unit allowing to register changes in the SPR signal resulting from specific binding of anti-diclofenac anti-bodies to the diclofenac-functionalized gold surface. The observed shift in the optical transmittance spectra and changes in the photocurrents also proved that diclofenac molecules were successfully immobilized on the sensor substrate. The measurements also showed specific binding of anti-diclofenac antibody with subsequent regeneration

Fast response hydrogel-based plasmonic sensor substrate for the detection of ethanol

The inline monitoring of ethanol concentrations in liquids is a crucial part of process monitoring in breweries and distilleries. Current methods are based on infrared spectroscopy which are bulky and costly making them non-affordable for small and middle-sized companies. To overcome these problems, we present a small, compact and cost-effective sensing method, based on a nanostructured, plasmonically active sensor substrate. The sensor substrate is coated with a microstructured ethanol-sensitive acrylamide-bisacrylamide hydrogel which induces a change of the hydrogel’s refractive index in conjugation with the hydrogel swelling and shrinking. With such an approach, the ethanol concentration in liquids can be determined in a simple optical transmittance setup. In our study, we demonstrate the capability of the sensor principle for the detection of ethanol concentration ranging from 0 to 30 vol%. Furthermore, we determined the response time of the sensor substrate to be less than 10 seconds, which shows an enormous improvement compared to other hydrogel-based sensing methods. Finally, initial results for real sample measurements are presented

Hydrogel-based plasmonic sensor substrate for the detection of ethanol

The in-line monitoring of ethanol concentration in liquids is a crucial part of process monitoring in breweries and distilleries. Current methods are based on infrared spectroscopy, which is time-consuming and costly, making these methods unaffordable for small and middle-sized companies. To overcome these problems, we presented a small, compact, and cost-effective sensing method for the ethanol content, based on a nanostructured, plasmonically active sensor substrate. The sensor substrate is coated with an ethanol-sensitive hydrogel, based on polyacrylamide and bisacrylamide, which induces a change in the refractive index of the substrate surface. The swelling and shrinking of such hydrogels offer a means to measure the ethanol content in liquids, which can be determined in a simple transmittance setup. In our study, we demonstrated the capability of the sensor principle for the detection of ethanol content ranging from 0 to 30 vol% ethanol. Furthermore, we determined the response time of the sensor substrate to be 5.2 min, which shows an improvement by a factor of four compared to other hydrogel-based sensing methods. Finally, initial results for the sensor’s lifetime are presented

Detection of diclofenac molecules by planar and nanostructured plasmonic sensor substrates

Surface plasmon resonance (SPR) sensors are well-established and widely used in the field of environmental and life sciences. To overcome the limitation of SPR sensors to applications in the laboratory environment initial studies on a low-cost nanostructured sensor substrate fabricated by nanoimprint lithography for the development of a SPR-based on-site biosensor system were conducted. For this purpose, diclofenac molecules were successfully immobilized both on planar and nanostructured gold sensor substrates, which was proved by XPS and SPR measurements. For the latter substrates, a specific binding between an anti-diclofenac antibody and immobilized diclofenac can be observed in form of a localized surface plasmon resonance shift in the optical transmission spectrum. The results show that our low-cost sensor substrate is wellsuited as transducer element for future SPR-based biosensors