Toward an immobilization method for spore-based biosensors in oxidative environment

An Enzyme-Based Interdigitated Electrode-Type Biosensor for Detecting Low Concentrations of H2O2 Vapor/Aerosol

This work introduces a novel method for the detection of H2O2 vapor/aerosol of low concentrations, which is mainly applied in the sterilization of equipment in medical industry. Interdigitated electrode (IDE) structures have been fabricated by means of microfabrication techniques. A differential setup of IDEs was prepared, containing an active sensor element (active IDE) and a passive sensor element (passive IDE), where the former was immobilized with an enzymatic membrane of horseradish peroxidase that is selective towards H2O2. Changes in the IDEs’ capacitance values (active sensor element versus passive sensor element) under H2O2 vapor/aerosol atmosphere proved the detection in the concentration range up to 630 ppm with a fast response time (<60 s). The influence of relative humidity was also tested with regard to the sensor signal, showing no cross-sensitivity. The repeatability assessment of the IDE biosensors confirmed their stable capacitive signal in eight subsequent cycles of exposure to H2O2 vapor/aerosol. Room-temperature detection of H2O2 vapor/aerosol with such miniaturized biosensors will allow a future three-dimensional, flexible mapping of aseptic chambers and help to evaluate sterilization assurance in medical industry.

Assessment of Various Process Parameters for Optimized Sterilization Conditions Using a Multi-Sensing Platform

In this study, an online multi-sensing platform was engineered to simultaneously evaluate various process parameters of food package sterilization using gaseous hydrogen peroxide (H₂O₂). The platform enabled the validation of critical aseptic parameters. In parallel, one series of microbiological count reduction tests was performed using highly resistant spores of B. atrophaeus DSM 675 to act as the reference method for sterility validation. By means of the multi-sensing platform together with microbiological tests, we examined sterilization process parameters to define the most effective conditions with regards to the highest spore kill rate necessary for aseptic packaging. As these parameters are mutually associated, a correlation between different factors was elaborated. The resulting correlation indicated the need for specific conditions regarding the applied H₂O₂ gas temperature, the gas flow and concentration, the relative humidity and the exposure time. Finally, the novel multi-sensing platform together with the mobile electronic readout setup allowed for the online and on-site monitoring of the sterilization process, selecting the best conditions for sterility and, at the same time, reducing the use of the time-consuming and costly microbiological tests that are currently used in the food package industry.

Mechanical and Electronic Cell-Chip Interaction of APTES-Functionalized Neuroelectronic Interfaces

In this work, we analyze the impact of a chip coating with a self-assembled monolayer (SAM) of (3-aminopropyl)triethoxysilane (APTES) on the electronic and mechanical properties of neuroelectronic interfaces. We show that the large signal transfer, which has been observed for these interfaces, is most likely a consequence of the strong mechanical coupling between cells and substrate. On the one hand, we demonstrate that the impedance of the interface between Pt electrodes and an electrolyte is slightly reduced by the APTES SAM. However, this reduction of approximately 13% is definitely not sufficient to explain the large signal transfer of APTES coated electrodes demonstrated previously. On the other hand, the APTES coating leads to a stronger mechanical clamping of the cells, which is visible in microscopic images of the cell development of APTES-coated substrates. This stronger mechanical interaction is most likely caused by the positively charged amino functional group of the APTES SAM. It seems to lead to a smaller cleft between substrate and cells and, thus, to reduced losses of the cell's action potential signal at the electrode. The disadvantage of this tight binding of the cells to the rigid, planar substrate seems to be the short lifetime of the cells. In our case the density of living cells starts to decrease together with the visual deformation of the cells typically at DIV 9. Solutions for this problem might be the use of soft substrates and/or the replacement of the short APTES molecules with larger molecules or molecular multilayers.

Surface Functionalization of Platinum Electrodes with APTES for Bioelectronic Applications

The interface between electronic components and biological objects plays a crucial role in the success of bioelectronic devices. Since the electronics typically include different elements such as an insulating substrate in combination with conducting electrodes, an important issue of bioelectronics involves tailoring and optimizing the interface for any envisioned applications. In this paper, we present a method for functionalizing insulating substrates (SiO₂) and metallic electrodes (Pt) simultaneously with a stable monolayer of organic molecules ((3-aminopropyl)triethoxysilane (APTES)). This monolayer is characterized by high molecule density, long-term stability, and positive surface net charge and most likely represents a self-assembled monolayer (SAM). It facilitates the conversion of biounfriendly Pt surfaces into biocompatible surfaces, which allows cell growth (neurons) on both functionalized components, SiO₂ and Pt, which is comparable to that of reference samples coated with poly-L-lysine (PLL). Moreover, the functionalization greatly improves the electronic cell-chip coupling, thereby enabling the recording of action potential signals of several millivolts at APTES-functionalized Pt electrodes.

Combined calorimetric gas- and spore-based biosensor array for online monitoring and sterility assurance of gaseous hydrogen peroxide in aseptic filling machines

A combined calorimetric gas- and spore-based biosensor array is presented in this work to monitor and evaluate the sterilization efficacy of gaseous hydrogen peroxide in aseptic filling machines. H₂O₂ has been successfully measured under industrial conditions. Furthermore, the effect of H₂O₂ on three different spore strains , namely Bacillus atrophaeus, Bacillus subtilis and Geobacillus stearothermophilus, has been investigated by means of SEM, AFM and impedimetric measurements. In addition, the sterilization efficacy of a spore-based biosensor and the functioning principle are addressed and discussed: the sensor array is convenient to be used in aseptic food industry to guarantee sterile packages.