Immersible SIlicon Photonic Sensors
One of the biggest challenges of humanity in the 21st century is to devise sustainable solutions to produce more food while minimising environmental impact. Hydroponics has emerged as one such solution, as it requires no arable land, reduces the usage of clean water and can be used in any urban setting. Within this framework, GOhydro aims at developing a cost-efficient smart-sensing ICT platform capable of monitoring the crops’ health and nutrient content of hydroponically cultivated microgreens in order to optimise the cultivation process and allow the harvest of the best possible products. GOhydro aspires to culminate in the production of a platform that will be a shifting paradigm of how AI-driven technological innovation can become an affordable, accessible-by-all tool applicable to all forms of urban farming. Towards this, the project will produce a multi-modal sensor kit driven by a thorough analysis of nutritional and lighting requirements of microgreens and combine it with a multi-model machine learning solution that will guide growers to optimise microgreens tending in accordance with the environment where their hydroponic unit is installed and operates. In a nutshell, the proposal aims at creating a form of an easy-to-use e-agronomist which will assist any grower to fine-tune and optimise her hydroponic production. The basic concept that underlies the entire GOhydro project is the development of an efficient and cost-efficient tool that can allow anyone to create his/her own hydroponic installation and have a personalized monitoring tool.
During the past two decades, the progress in micro/nano-fabrication techniques and in-depth understanding of photonic circuits have allowed the “transfer” of optical biosensing modules into Silicon-based photonic integrated circuits (PICs). The key driver for such a choice is the growing -but still unmet- need for practical biosensors satisfying the growing demand for effective medical diagnostic technologies. Silicon-based solutions take advantage of three major parameters: (1) due to the compatibility with complementary metal-oxide semiconductor (CMOS) foundry processes, silicon PICs can be manufactured with great efficiency at high volume and relatively-low cost; (2) the high refractive index contrast between silicon and silicon dioxide/silicon nitride, or other surrounding media, enables the development of miniaturized compact sensing devices, with the additional possibility of fabricating multiple sensors on one single chip; and (3) silicon photonics are excellent transducers for continuous and quantitative label-free biosensing, which can directly respond to affinity interactions between analyte and receptor molecules in real-time.Nonetheless, despite mpressive progress the existing Si PICs, these have not managed to escape the laboratory settings and satisfy the need for efficient point-of-interest solutions. The innovative photonic platform that is explored in this project consists of microfluidics-free, fully-immersible silicon photonic sensors. It is a portable, lightweight and easy-to-use platform that aspires to bring the analytical capabilities of a laboratory to the point of interest. In particular, in this project it is explored whether the dynamic spectral signals obtained by the PIC probes (without ANY surface activation) when immersed in the extracts of hydroponically-cultivated microgreens (and in particular basil varieties) can be correlated to the nutrient content of the plants in order to pinpoint the optimum time for harvest.
Despite the impressive progress the existing Si PICs have not managed to escape the laboratory settings and satisfy the need for efficient point-of-interest solutions. The reason is that Silicon inherently does not emit light and there is always the need to find a way to couple light in- and out-of-the PIC chips. Thus, even though the chips themselves are miniaturized and compact, the fact that their driving and readout system requires a laboratory setup makes the chip miniaturization and improved analytical performance almost seem futile and the use of PIC sensors in everyday life impractical. The need for large laboratory equipment gives rise to the so called “chip-in-a-lab dilemma” for PIC sensors. To transform them from laboratory-based demonstrations into practical devices that can be commercialized and used easily in everyday life, it is necessary to develop a compact PIC sensor system, where not only the sensor chip itself, but its readout system is also compact and easy to operate by a non-expert. In essence, the "big bet" of commercial photonic sensors is how they can escape the confines of the laboratory and become practical, cost-efficient and easy-to-deploy tools at the point of interest.
NCSR De has found a way out of the above dilemma by developing and patented (Patents: GR20160100552A; US2020064260A1; EPO: EP3532825A1) a way to transform the photonic chips into re-usable consumables that could be used in a similar manner to immunochromatographic strips. These was achieved in a two-fold way: (1) by appropriate photonic engineering of the PICs that allow their operation in a dip-stick manner and alleviate the need for microfluidic compartments, pumps and wires, and (2) by developing a new principle of operation, the so-called Broad-band Mach-Zehnder Interferometry (BB-MZI), which allows the system to function with a simple high-brightness LED and for each chip to be self-referenced. As a result, the system basically relies on coupling light to the photonic chip, which is used as an immersible probe, reading a spectrum with a portable spectrophotometer and analysing in real-time (a few minutes) the recorded spectra. The dynamic behaviour of the recorded spectra is directly related to the concentration of the targeted analyte upon customisable surface activation of the sensor surface with the appropriate probe molecules (allowing thus label-free detection formats). The platform has alreaqdy been successfully applied for the semi-quantitative detection of SARS-CoV-2 antibodies in hyman serum (Biosensors and Bioelectronics, in press) and is currently applied for the safety and quality monitoring of milk. The innovative approach that this technology wishes to follow in the GOhydro project is to employ the immersible photonic chips containing BB-MZIs without any surface activation and record the dynamically-evolving interferometric spectra that are created due to adhesion of the various molecules contained in a plant pulp. With the aid of the GOhydro AI component a correlation between the shape and time evolution of the spectra and the nutrient content or crop health of the microgreens may be established.
The TRL stage of the platform is currently at TRL6 with respect to the SARS-CoV-2 antibody detection and at TRL5 with regards to the detection of adulteration and harmful substances of goat milk. With reagrds to the GOhydro project, TRL is still at TRL3 since the project is ongoing. The first indications are that the photonic probes without any surface modification and without any algorithm applied yet can distinguish between the varieyt of basil microgreens. In order to improve our innovation, we are seeking for the niche application that could allow penetration to the market and attraction of VC funding. Our goal is to develop our own SME and to become the producers of the system. Interaction with potential end-users from the agri-food sector would enable us to better understand the needs and dvelop solutions that are critical to be obtained along the entire farm-to-fork chain
