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Abstract:

Biological receptors demonstrate a high affinity and selectivity towards their target, which is why they receive great interest for integration into biosensor applications. However, their instability in non-physiological conditions is a major drawback, which poses significant challenges. To address this, synthetic receptors have been developed that mimic these biological receptors. These so-called biomimetic receptors show a similarly high affinity and selectivity towards their target while also being very stable under non-physiological conditions. This work focuses on advancing two widely used transducer platforms for use with these biomimetic receptors. The first platform is electrochemical impedance spectroscopy (EIS). For medical diagnostics, food-safety analysis and detection of environmental pollutants, simultaneous detection and quantification of multiple target molecules would be a great advantage. Commonly implemented systems use non-faradaic impedance spectroscopy. Adding a redox potential probe, such as silver/silver chloride, as a reference electrode besides the standard working and counter electrodes allows for the use of faradaic impedance spectroscopy techniques using redox-active molecules such as ferricyanide, thereby extending the range of possible applications through increased sensitivity of the measurements. Also, the ability to perform differential measurements would allow using undiluted patient samples, which significantly simplifies sample preparation. The differential impedimetric sensor cell (DISC) system, which has been designed and constructed in this work, meets all of these requirements as it can quasi-simultaneously analyze up to eight different targets inside a single small liquid sample. Furthermore, it was validated against a high-resolution dielectric spectrometer (Novocontrol, Alpha analyzer) using well characterized samples at different temperatures (25, 30, 35, 37, and 40 °C) over its whole frequency range (10 Hz - 100 kHz). The second platform is a thermal technique based on the heat-transfer method (HTM). In this work, a novel biomimetic sensor based on this principle was designed, which allows for the sensitive and specific detection of Escherichia coli (E. coli) bacteria in a broad concentration range (1e2 - 1e6 CFU/mL) in buffer fluids as well as in relevant food samples (i.e., apple juice). Surface imprinted polymers (SIPs) were used as biomimetic receptors in this system. The increased sensitivity, which enables this low detection limit, originates from the planar meander heater element, which enables a more focused and efficient heat-flow through the system. Moreover, reference tests with other species of Enterobacteriaceae closely related to E. coli, show a very low cross-sensitivity: i.e., a sensor response at or below the noise level. Furthermore, the experiments performed in this part of the work show that the presence of bacteria enhances the thermal conductivity of a liquid. Both systems designed in this work use a flow-through cell, which enables easy exchange of sample and buffer liquids during measurements. This allows the experience acquired during the design of one system to be implemented during the design of the other system and vice versa, or even combining both transducer platforms into a single system.