Smart red berry-derived carbon nanofiber-polyethylene imine beads for controlled urea release, amoxicillin encapsulation and digital image colorimetry in soil by fast microwave method.

Abstract

A novel dual-mode optical sensor and controlled-delivery hydrogel system (CNF-PEI-AMX-Urea) was successfully engineered using biomass-derived carbon nanofibers (CNFs) decorated with active functional groups and co-entrapped with urea and amoxicillin (AMX). Morphological and structural evaluations confirmed an interconnected fibrous network with ultrafine widths ranging tightly between 2.40-4.76 nm and an amorphous-to-nanocrystalline sp2-hybridized graphitic framework. FTIR spectroscopy verified an intensely hydrophilic boundary layer rich in amine (3471 cm-1), hydroxyl (3372 cm-1), carbonyl (1669 cm-1), and graphitic carbon (1408 cm-1) functional groups, achieving a high operational degree of substitution of 0.52. The fabricated platform demonstrated striking dual-mode optical performance, functioning simultaneously as a daylight halochromic sensor exhibiting pronounced color difference (ΔE) values reaching 4.50 at pH 3 and 8.08 at pH 9 for blank beads, and 2.54 (pH 3) and 3.15 (pH 9) for the urea-loaded test system and as a pH-responsive fluorogenic probe under UV illumination with distinct emission shifts across acidic, neutral, and alkaline conditions. Furthermore, in vitro release studies conducted at a simulated soil pH of 6 demonstrated a slow, sustained, and diffusion-controlled delivery profile governed closely by the Higuchi model (R 2 = 0.9747 for urea, R 2 = 0.9811 for AMX), avoiding burst release and achieving 24-hour cumulative releases of 4.08% for urea and 15.58% for AMX. Overall, this multifunctional hybrid platform successfully unifies smart optical pH sensing with regulated agricultural delivery, presenting exceptional potential for intelligent real-time environmental monitoring and sustainable agricultural applications.

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