Multifunctional and eco-friendly nanofibrous based tools to control and reduce environmental impacts in agricultural systems

Abstract

My PhD research activity proposes some innovative strategies to improve the technological infrastructure of agriculture practices by combining the development of novel agricultural products and sensors based on nanostructured smart materials, keeping competitiveness of yields and farms while improving the protection of natural resources. Consequently, by exploiting the potentials of electrospinning technology, a series of nanofibrous and eco-compatible fabrics were designed and investigated with the aim of: i) providing nutrients to plants, specifically iron, firstly by loading Fe chelating agents like phytosiderophores (mugineic acid) and phenolic compounds (catechol) on suitable supports, then releasing them in the surroundings, in order to mobilize this micronutrient and make it absorbable by plants, thus playing the role of biostimulants; ii) delivering nutrients to plants by supporting the successful colonization of soil (rhizosphere) by the adhesion and growth of beneficial microorganisms (plant growth promoting rhizobacteria, PGPR) on suitable supports, thus acting as biostimulants; iii) designing and testing of selective nano-composite conductive sensors based on biodegradable and recyclable polymers, capable of detecting some biogenic gases and volatile compounds in traces released in the soil upon treatments and metabolic activities. The exceptional specific surface area of the nanofibrous scaffolds created on purpose, together with the employment of biodegradable and biocompatible materials, resulted in efficient, eco-friendly and safe products for agriculture. Biomaterials and biodegradable polymers like polyhydroxybutyrate (PHB) and polycaprolactone (PCL) were selected and properly processed into freestanding nanofibrous membranes. The effectiveness of two non-woven fabrics differently designed and arranged to provide iron to plants from insoluble sources in the environment (FeCl3) were tested in tomato (Solanum lycopersicum L. “Marmande") and duckweed (Lemna minor L.) plants grown in hydroponics and loading mugineic acid and catechol molecules, respectively. The resulting nanofibrous fabrics succeeded in providing iron to plants thus enabling them to recover the physiological and biometric features from previous Fe-deficiency conditions, thus acting as promising nanobiostimulants. A further approach concerned the investigation of PCL as a nanofibrous scaffold capable of hosting beneficial bacteria (Burkholderia terricola) to crop improving. The PCL nanofibrous scaffolds were inoculated with the bacteria cells and the dynamics of the consequent mechanisms involved in the specific adhesion of the cells to the nanofibers in both early and following stages of colonization were investigated in details. Since the nanofibrous framework was successful in enabling and stimulating the colonization by the plant growth promoting rhizobacteria (PGPR), then it could be suggested as a promising strategy for the creation of novel advanced nanobiostimulants for precision agriculture. To complete and maximize the expected benefits in an advanced and smart agricultural platform, miniaturized sensors based on similar nanofibrous and eco-friendly materials were also developed and investigated as selective and sensitive tools for monitoring biogenic gases and volatile organic compounds (VOCs) related to metabolic activities present in soils. In detail, conductive chemical sensors based on electrospun nanofibrous biodegradable (PHB) and recyclable (polystyrene, PS) polymers were arranged in both ternary and quaternary combinations with a conductive nanopowder of mesoporous graphene and a well-known sensing molecule (a free-base porphyrin, H2TPP). The resulting sensors were tested on biogenic gases and VOCs like amines, carboxylic acids, ketones, aromatic hydrocarbons, and nitrogen oxides. Their cost-effectiveness and ease of production, as well as reproducibility and environmental stability, confirmed that such sensors could be potentially used in monitoring soil in agro-ecosystems as well as in natural and perturbed conditions.