title: Studying capacitive field-effect biosensors modified with tobacco mosaic virus particles as enzyme nanocarriers
title: Untersuchung kapazitiver Feldeffekt-Biosensoren, modifiziert mit Tabakmosaikvirus-Partikeln als Enzymnanoträger
titleType: AlternativeTitle
Creators: name: Welden, Melanie Nicole
Publisher: name: Philipps-Universität Marburg
Year: 2024
Subjects: Pharmacology &amp; therapeutics, prescription drugs
Pharmakologie, Therapeutik

description: Electrochemical biosensors based on enzymatic reaction mechanisms have the potential to enable precise and selective detection of analytes. This is achieved by converting biological interactions into electrical output signals. Here, the selection of an appropriate enzyme immobilization strategy is of great importance for the functionality of such sensors. For a number of years, tobacco mosaic virus (TMV) particles have been the subject of investigation as an attractive nanoscaffold for enzyme immobilization on biosensors due to their definable nanostructure. The objective of this work was, therefore, to study and optimize the modification of electrolyte-insulator-semiconductor (EISCAP) biosensors with TMV particles as enzyme nanocarriers for the detection of various analytes.
The TMV-immobilization protocol was examined on Ta2O5 (and SiO2) transducer surfaces of EISCAP sensors. On Ta2O5, an increase in TMV density on the sensor surface was observed with an increase in the concentration of the TMV solution from 0.005 to 0.1 μg/μL. Higher concentrations (0.16 μg/μL and 0.32 μg/μL) resulted in a reduction in density, which is likely attributable to side-to-side aggregation of the viral particles. The alteration in the sensor’s surface charge, resulting from TMV immobilization, was effectively demonstrated by capacitive field-effect measurements, which revealed a concentration-dependent shift in the sensor signal following the TMV-immobilization procedure. Additionally, it was established that tailoring of the TMV immobilization on Ta2O5 surfaces enables completion within one hour.
The potential for label-free detection of TMV particles through their intrinsic molecular charge was explored on EISCAP sensors with a SiO2-transducer layer. The sensor demonstrated a sensitivity of about 13 mV/dec to varying TMV concentrations, revealing an increasing TMV-surface density with rising particle concentrations between 0.001 μg/μL and 0.2 μg/μL. Furthermore, the impact of ionic strength on the sensor signal was examined. It was observed that the sensor signal exhibited a decline with an increase in ionic strength.
Moreover, the feasibility of employing a single TMV-modified Ta2O5-EISCAP biosensor for the detection of different analytes was investigated. In a first set of experiments, the enzymes urease and penicillinase were immobilized individually on TMV-modified EISCAP sensors and characterized for the detection of their corresponing analytes (i.e., urea and penicillin). Subsequently, both enzymes were co-immobilized on a single sensor chip, thereby retaining their respective activities, which serves to illustrate the considerable potential of TMV nanocarriers for multi-analyte sensing. Additionally, this type of multi-enzyme biosensor was employed to successfully mimic a XOR-enzyme logic gate.
The potential of TMV-based biosensors for quality control within food industry was studied by TMV-modified EISCAP sensors, functionalized with the enzyme acetoin reductase that catalyzes the reduction of diacetyl to (R)-acetoin and the reduction of racemic acetoin to (R,R)- and meso-2,3-butanediol. The biosensor demonstrated the ability to detect acetoin and diacetyl in beer and wine samples. The sensitivity/selectivity of the sensor towards both substrates was successfully controlled individually by tuning the pH value of the analyte solution, to adjust the enzyme’s pH optimum for the particular conversion of acetoin and diacetyl, respectively. 
Moreover, to demonstrate a typical “lab on chip” microfluidic application, a TMV-modified light-addressable potentiometric sensor (LAPS) was combined together with a light-addressable electrode (LAE) as an actuator; in this experiment, penicillinase served as a model enzyme. Here, the activity of penicillinase could be regulated by locally modifying the pH value (using the LAE) within the microfluidic channel, thereby enabling a flexible control of the enzymatic reaction.
Finally, the TMV density on the sensor surface was further improved by the introduction of an intermediate layer comprising the positively charged polyelectrolyte poly(allylamine hydrochloride). This modification resulted in both a notable increase in TMV density on the sensor surface and an enhancement in sensitivity.
The results evidenced the great potential of TMV particles as enzyme nanocarriers for the development of highly sensitive capacitive field-effect biosensors for different fields of application.