Electroactive biodegradable microneedles for minimally invasive real-time, in-situ plant physiological monitoring and industrial NH₃ sensing

Abstract

Real-time, in situ monitoring of plant physiological parameters and industrial toxic gas emissions is vital for advancing precision agriculture and ensuring environmental safety. Herein, we developed an electroactive biodegradable microneedle (PPG-MN) sensor enabling minimally invasive monitoring of interstitial glucose, ambient temperature, humidity, and environmental ammonia (NH₃) gas leakage. The sensor matrix was fabricated using a polyvinyl alcohol (PVA) network interpenetrated with conductive polyaniline (PANI) and doped with phytic acid (PA), while glucose oxidase (GOx) was immobilized for specificity. The resulting microneedle array exhibited sufficient mechanical strength to penetrate the plant epidermis, establishing a stable electrode–tissue interface via hydrogel swelling. The sensor demonstrated excellent environmental friendliness, featuring a pathogen inhibition rate exceeding 97% and complete soil biodegradation within 35 days. By integrating enzymatic sensing with a temperature and humidity compensation mechanism (effective across 25–50 °C and 25%–50% relative humidity (RH)), the PPG-MN achieved a rapid response time (< 30 s) and a wide linear detection range (1–100 mM). Furthermore, continuous in situ monitoring of Epipremnum aureum leaves over 14 h successfully tracked dynamic glucose fluctuations driven by photosynthesis and respiration. Additionally, leveraging the reversible doping/de-doping mechanism of the PA-doped PANI network, the hydrogel base acts as a highly sensitive chemiresistive gas sensor. The PPG-MN exhibited a strong linear response (R^² = 0.986) to NH₃ across a broad concentration range of 10 to 500 ppm, effectively encompassing the typical toxic emission levels encountered during leather deliming processes. These results indicate that the PPG-MN sensor is a promising, eco-friendly tool for both agricultural Internet of Things (IoT) systems and hazardous gas pre-warning in industries like leather processing.

Graphical Abstract

Keywords

Electronic microneedle / Plant physiological monitoring / Ammonia gas sensor / Biodegradable / In situ sensing / Environmental monitoring / Leather industry

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Funding

Key Research and Development Projects of Shaanxi Province(No. 2024SF-YBXM-586)

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