Capacitive Sensor to Monitor Enzyme Activity by Following Degradation of Macromolecules in Real Time

Cellulose acetate-coated capacitive sensor for determining carbon-cycle enzymes activity and as a microbial Indicator for soil health

This study demonstrates cellulose acetate (CA)-coated screen-printed carbon electrodes (SPCEs) for soil microbial activity detection. A capacitive sensor design utilizes a coated CA layer for effective insulation in electrolytes, eliminating the need for additional signal protection. Optimization involved comparing spin and dip coating methods, with a one-layer 10-second dip coating identified as the best balance between quality and yield. These CA/SPCEs exhibited remarkable stability over a month, suggesting their potential for long-term use in monitoring agricultural soils. Analysis of CA/SPCE profile and thickness provided insights into surface characteristics and the impact of the CA coating on electrode roughness. ATR-FTIR analysis, along with capacitive sensing, demonstrated superior sensitivity and precision for monitoring CA film degradation compared to mechanical gauges. Chemical degradation studies suggest CA's potential immunity in near-neutral environments, while enzymatic degradation investigations revealed dominance by enzymes, particularly in the initial stages. The CA/SPCE sensor responds to both enzymatic and chemical degradation, potentially serving as an indicator of total soil microbial activity. Soil experiments explored CA/SPCE with Cap-S for microbial activity sensing. Significant differences in the long-term degradation rate were observed in mycorrhizal fungi-enriched soil compared to controls, highlighting microbial influences. This study underscores the adaptability and versatility of this technology, particularly for assessing C-cycle microbial activity in agricultural fields.

Fabrication of a Label-Free Immunosensor Using Surface-Engineered AuPt@GQD Core-Shell Nanocomposite for the Selective Detection of Trace Levels of Escherichia coli from Contaminated Food Samples

Fabrication of label-free immunosensors is highly necessitated due to their simplicity, cost-effectiveness, and robustness. Herein, we report the facile development of a label-free, direct, rapid, capacitive immunosensor for ultrasensitive and rapid recognition of trace levels of Escherichia coli from contaminated food samples. This was achieved using gold platinum core-shell nanoparticles loaded with graphene quantum dots (AuPt@GQDs) that were utilized as electrode modifiers. The incorporation of GQDs to the surface of AuPt core-shell nanoparticles was performed using the "greener" probe-sonication method. The electrochemical properties of AuPt@GQDs, determined using cyclic voltammetry and electrochemical impedance spectroscopy, suggested the optimized loading concentration of AuPt to be 0.05% in the core-shell nanocomposite to exhibit the highest current response. Furthermore, immobilization of anti-E. coli monoclonal antibodies (anti-E. coli mAb) onto the surface of modified electrodes was performed using amine coupling. The high specific binding of E. coli cells onto the surface of the immuno-electrode was measured as a direct function of change in transient capacitance with time that was measured at low and high frequencies. The resultant immunosensor (bovine serum albumin/anti-E. coli mAb/AuPt0.05@GQDs/FTO) demonstrated a detection range (5 to 4.5 × 103 cells/mL), with the detection limit as low as 1.5 × 102 cells/mL, and an excellent sensitivity ∼171,281.40 μF-1 mL cells-1 cm-2 without the use of any labels (R2-0.99). These findings were further verified using real sample analysis wherein the immuno-electrode demonstrated outstanding sensitivity, the highest noticed so far. More interestingly, the high resuability ∼48 weeks (RSD-5.92%) and excellent reproducibility in detection results (RSD ∼ 9.5%) testify its potential use in a clinical setting. The results reveal the usefulness of the surface-engineered AuPt@GQDs core-shell nanocomposite as an electrode modifier that can be used for the development of newer on-site monitoring devices to estimate trace levels of pathogens present as contaminants in food samples.