Novel Materials for Urban Farming

Scarcity of natural resources, shifting demographics, climate change, and increasing waste are four major challenges in the quest to feed the exploding world population. These challenges serve as the impetus to harness novel technologies to improve agriculture, productivity, and sustainability. Urban farming has several advantages over conventional farming: higher productivity, improved sustainability, and the ability to provide fresh food all year round. Novel materials are key to accelerating the evolution of urban farming - with their ability to facilitate controlled release of nutrients and pesticides, improved seed health, substrates with better water retention capability, more efficient recycling of agricultural waste, and precise plant health monitoring. Materials science enables environmental sustainability and higher harvest yields in urban farms. Here, Singapore is used as an example of a land-scarce city where urban farming may be the solution for future food production. Potential research directions and challenges in urban farming are highlighted, and how material optimization and innovation drive the development of urban farming to meet national and global food demands is briefly discussed. This review serves as a guide for researchers and a reference for stakeholders of urban farms, policy makers, and other interested parties.

Augmenting the living plant mesophyll into a photonic capacitor

Living plants provide an opportunity to rethink the design and fabrication of devices ordinarily produced from plastic and circuit boards and ultimately disposed of as waste. The spongy mesophyll is a high -surface area composition of parenchyma cells that supports gas and liquid exchange through stomata pores within the surface of most leaves. Here, we investigate the mesophyll of living plants as biocompatible substrates for the photonic display of thin nanophosphorescent films for photonic applications. Size-sorted, silica-coated 650 ± 290 -nm strontium aluminate nanoparticles are infused into five diverse plant species with conformal display of 2-μm films on the mesophyll enabling photoemission of up to 4.8 × 10¹³ photons/second. Chlorophyll measurements over 9 days and functional testing over 2 weeks at 2016 excitation/emission cycles confirm biocompatibility. This work establishes methods to transform living plants into photonic substrates for applications in plant-based reflectance devices, signaling, and the augmentation of plant-based lighting.

Persistent drought monitoring using a microfluidic-printed electro-mechanical sensor of stomata in planta

Stomatal function can be used effectively to monitor plant hydraulics, photosensitivity, and gas exchange. Current approaches to measure single stomatal aperture, such as mold casting or fluorometric techniques, do not allow real time or persistent monitoring of the stomatal function over timescales relevant for long term plant physiological processes, including vegetative growth and abiotic stress. Herein, we utilize a nanoparticle-based conducting ink that preserves stomatal function to print a highly stable, electrical conductometric sensor actuated by the stomata pore itself, repeatedly and reversibly for over 1 week. This stomatal electro-mechanical pore size sensor (SEMPSS) allows for real-time tracking of the latency of single stomatal opening and closing times in planta, which we show vary from 7.0 ± 0.5 to 25.0 ± 0.5 min for the former and from 53.0 ± 0.5 to 45.0 ± 0.5 min for the latter in Spathiphyllum wallisii. These values are shown to correlate with the soil water potential and the onset of the wilting response, in quantitative agreement with a dynamic mathematical model of stomatal function. A single stoma of Spathiphyllum wallisii is shown to distinguish between incident light intensities (up to 12 mW cm^-2) with temporal latency slow as 7.0 ± 0.5 min. Over a seven day period, the latency in opening and closing times are stable throughout the plant diurnal cycle and increase gradually with the onset of drought. The monitoring of stomatal function over long term timescales at single stoma level will improve our understanding of plant physiological responses to environmental factors.