Key Findings
The PPG-MN sensor successfully tracks glucose dynamics in Epipremnum aureum (pothos) over a 14-hour diurnal cycle, measuring concentrations between 10 and 80 millimolar. In spike-and-recovery validation, the device returned recoveries of 98.5% to 103.0% with relative standard deviations below 3.5%. Additionally, the sensor functions as a chemiresistive ammonia gas detector for industrial deliming processes in leather factories. In antimicrobial tests, the sensor reduced bacterial survival of Staphylococcus aureus to 0.76% and Escherichia coli to 2.83%.
Technical Details
The device consists of a polyvinyl alcohol hydrogel network interpenetrated with conductive polyaniline and doped with phytic acid, with immobilized glucose oxidase for specificity. The array features conical tips 1000 micrometers long, a base diameter of 390 micrometers, and a tip spacing of 1000 micrometers. Fabrication involves a low-temperature process where a 25% polyvinyl alcohol solution is cooled to 3–4 °C, followed by polymerization and three freeze-thaw cycles at −20 °C and 25 °C.
- Mechanical Strength: Withstood 0.8 newtons per needle without failure.
- Sensitivity: Maintained 95.4% sensitivity after leaf insertion, with a linear current response from 10 to 100 millimolar (y = 0.0218x + 3.8128).
- Response Time: Under 30 seconds.
- Material Properties: Swelling ratio reached 94.7%, and the water contact angle dropped from 69.5° to 50.7°.
Background & Context
Phytic acid serves three roles: acting as a proton reservoir for electrical conductivity and crosslinking, promoting hydrophilic dispersion of polyaniline, and suppressing bacterial contamination via chelation of divalent metal ions and maintaining a localized pH below 5. To account for temperature-dependent enzyme activity, the team calibrated the sensor between 10 and 40 °C to derive a temperature-adjusted correction equation.
Significance & Outlook
The PPG-MN sensor provides a non-destructive method to monitor plant health and metabolism in real time. By integrating glucose sensing with ammonia detection, the technology offers a versatile tool for both agricultural research and industrial safety monitoring in tanneries.
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