Utilizing an appropriate enzyme immobilization strategy is crucial for designing enzyme-based biosensors. Plant virus-like particles represent ideal nanoscaffolds for an extremely dense and precise immobilization of enzymes, due to their regular shape, high surface-to-volume ratio and high density of surface binding sites. In the present work, tobacco mosaic virus (TMV) particles were applied for the co-immobilization of penicillinase and urease onto the gate surface of a field-effect electrolyte-insulator-semiconductor capacitor (EISCAP) with a p-Si-SiO2-Ta2O5 layer structure for the sequential detection of penicillin and urea. The TMV-assisted bi-enzyme EISCAP biosensor exhibited a high urea and penicillin sensitivity of 54 and 85 mV/dec, respectively, in the concentration range of 0.1–3 mM. For comparison, the characteristics of single-enzyme EISCAP biosensors modified with TMV particles immobilized with either penicillinase or urease were also investigated. The surface morphology of the TMV-modified Ta2O5-gate was analyzed by scanning electron microscopy. Additionally, the bi-enzyme EISCAP was applied to mimic an XOR (Exclusive OR) enzyme logic gate.

Acetoin and diacetyl have a major impact on the flavor of alcoholic beverages such as wine or beer. Therefore, their measurement is important during the fermentation process. Until now, gas chromatographic techniques have typically been applied; however, these require expensive laboratory equipment and trained staff, and do not allow for online monitoring. In this work, a capacitive electrolyte–insulator–semiconductor sensor modified with tobacco mosaic virus (TMV) particles as enzyme nanocarriers for the detection of acetoin and diacetyl is presented. The enzyme acetoin reductase from Alkalihalobacillus clausii DSM 8716T is immobilized via biotin–streptavidin affinity, binding to the surface of the TMV particles. The TMV-assisted biosensor is electrochemically characterized by means of leakage–current, capacitance–voltage, and constant capacitance measurements. In this paper, the novel biosensor is studied regarding its sensitivity and long-term stability in buffer solution. Moreover, the TMV-assisted capacitive field-effect sensor is applied for the detection of diacetyl for the first time. The measurement of acetoin and diacetyl with the same sensor setup is demonstrated. Finally, the successive detection of acetoin and diacetyl in buffer and in diluted beer is studied by tuning the sensitivity of the biosensor using the pH value of the measurement solution.

Silicon sensors can be fabricated as small, rugged and reliable chip devices with a broad field of applications in medicine, biotechnology, food analysis and environmental monitoring. Thus, there is an increasing demand in realizing such sensors for the determination of, e.g. chemical and biological quantities in aqueous solutions. By developing semiconductor-based field-effect structures, moreover, their main advantage is due to the combination of both the physical effect as the transducer principle and the deposition of the sensitive layers directly onto the silicon chip. In this work, different sensor types that are originated from the field effect are presented: The capacitive ElS (electrolyte-insulator-semiconductor) sensor is suitable for the pH detection using the capacitance/voltage technique. By immobilizing an additional enzyme layer, e.g. of penicillinase, a biosensor has been realized. Both sensors can be integrated as an EIS sensor array. The utilization of the porous silicon technology offers the possibility of a further miniaturization. The LAPS (light-addressable potentiometric sensor) is based on the identical ElS structure. Here, each measuring point on the surface can be arbitrarily addressed by a probing light. The resulting photocurrent is generated as the sensor signal. This arrangement also allows a two-dimensional mapping of the spatial distribution of ions or molecules.

Despite the importance of cell characterization and identification for diagnostic and therapeutic applications, developing fast and label-free methods without (bio)-chemical markers or surface-engineered receptors remains challenging. Here, we exploit the natural cellular response to mild thermal stimuli and propose a label-and receptor-free method for fast and facile cell characterization. Cell suspensions in a dedicated sensor are exposed to a temperature gradient, which stimulates synchronized and spontaneous cell-detachment with sharply defined time-patterns, a phenomenon unknown from literature. These patterns depend on metabolic activity (controlled through temperature, nutrients, and drugs) and provide a library of cell-type-specific indicators, allowing to distinguish several yeast strains as well as cancer cells. Under specific conditions, synchronized glycolytic-type oscillations are observed during detachment of mammalian and yeast-cell ensembles, providing additional cell-specific signatures. These findings suggest potential applications for cell viability analysis and for assessing the collective response of cancer cells to drugs.

No abstract

Sensor systems for multi-parameter detection in fluidics usually combine different sensors, which are designed to detect only one physical or (bio-)chemical parameter. In the present work, an ISFET (ion-sensitive field-effect transistor), which is well known as a (bio-)chemical sensor, is utilised for the flow velocity and flow direction measurement for the first time. The proposed flow sensor presents a chemical sensor-actuator system and consists of a H + -ion generator and a pH ISFET that detects the in-situ electrochemically generated H + ions. By measuring the time of flight, the flow velocity can be determined. Since this measuring method represents a dynamic method, a calibration of the sensor usually is not required, because only relative changes in the sensor output signal are of interest. Moreover, sensor´s drift, temperature instability and sensitivity discrepancy between the various ISFETs are not relevant. The experimental results show good linearity between the measured flow velocity with the ISFET and the delivered flow rate of the pump. Due to the fast response of the ISFET (usually in the millisecond range), an ISFET-based flow sensor is suitable for the measurement of the flow velocity in a wide range. The results of the flow direction measurement with two ISFETs are presented, too.

Lead and nickel, as heavy metals, are still used in industrial processes, and are classified as “environmental health hazards” due to their toxicity and polluting potential. The detection of heavy metals can prevent environmental pollution at toxic levels that are critical to human health. In this sense, the electrolyte–insulator–semiconductor (EIS) field-effect sensor is an attractive sensing platform concerning the fabrication of reusable and robust sensors to detect such substances. This study is aimed to fabricate a sensing unit on an EIS device based on Sn3O4 nanobelts embedded in a polyelectrolyte matrix of polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) using the layer-by-layer (LbL) technique. The EIS-Sn3O4 sensor exhibited enhanced electrochemical performance for detecting Pb2+ and Ni2+ ions, revealing a higher affinity for Pb2+ ions, with sensitivities of ca. 25.8 mV/decade and 2.4 mV/decade, respectively. Such results indicate that Sn3O4 nanobelts can contemplate a feasible proof-of-concept capacitive field-effect sensor for heavy metal detection, envisaging other future studies focusing on environmental monitoring.

A thin-film amorphous silicon (a-Si) deposited on a glass substrate was employed as a semiconductor material for the chemical imaging sensor, which can visualize the distribution of ion concentration in a solution. The sensing properties and the spatial resolution of the a-Si sensors were investigated. Nearly-Nernstian pH sensitivities and submicron resolution were demonstrated, which suggests the superior performance of the chemical imaging sensor based on thin-film a-Si.