# Measurement of Visible Radiation through a _Sansevieria cylindrica_-Based \"Living Sensor\"
## 1 Introduction
The idea is to adopt a soil-plant system as a \"living\" sensor having the following prerogatives: self-generating, eco-friendly, non-toxic, with zero CO2 emission, and biodegradable. It is worth noting that this latter feature is guaranteed considering that the system is part of nature; it is fully biodegradable and can be \"naturally\" absorbed (i.e., at the end of life). Full biodegradability can also be achieved through the adoption of suitable electrodes (i.e., bio-polymers). The main characteristics regard the possibility of using the \"natural\" sensing properties of plants and intrinsic chemo-electrical transductions to obtain an output voltage as a function of the physical quantity of interest. The choice of plant is of particular interest and represents a crucial selection, to consider a living sensor sensitive only to a specific measurand and not to other physical quantities. In this context, the sensing characteristics of plants have been widely studied in the context of plant biology and various studies have been conducted in the field of electrophysiology [23]. In fact, after the first recorded action potential in an inesectivorous plant [24], research in this area has increased dramatically and it is still ongoing, with great actuality and scientific relevance. It is worth noting that, still, many aspects of plant responses are not sufficiently well-elaborated and understood. Plant electrostimulations, response to external physical quantities and stress, intracellular measurements, and depolarizing currents and fluxes (i.e., Cl\({}^{-}\) and Ca\({}^{2+}\)) are fundamental points which involve the electrophysiology of plants, vegetal organisms, and the study of health and applied stress in plants through electrical signals generated by the plant itself [25; 26; 27]. It thus becomes apparent how plants are able to generate electrical responses as a function of external physical quantities. For example, in [28], the authors propose a plant, genus _mytillocatus_, with electrodes implanted inside it in order to demonstrate that, with electrodes, it was possible to harvest the glucose and O2 produced during photosynthesis to generate energy. The authors investigated the current responses upon the illumination/darkness cycles. Both the evolutions of the O\({}_{2}\) electroreduction current and of glucose electro-oxidation current were measured demonstrating the maximum electrical response in the order of 0.5 uA. The choice of the living organism in fact is of primary importance, and, in order to be considered a sensor, the following characteristics are required: the definition of performance, features, robustness, \"natural\" insensitivity, ability to measure only one physical quantity of interest and be insensitive to the others, metrological characteristics and characterization also as a function of influence and interference quantities, hysteresis, nonlinear behavior, etc. [23; 27; 29]. It should also be noted that the aspect of electrical contacts is crucial since a living sensor should be able to work and operate for a long time without damaging the plant with directly implanted contacts [30]. For this reason, an electrical decoupling mechanism represents an essential characteristic to be accounted for, in order to implement a living sensor [31]. Obviously, the choice of the soil-plant system is also crucial for finding plants that require a small amount of water and restrained growth. Obviously, the choice of plant is not trivial and requires a metrological study in order to have a system that not only generates electrical signals but is able to generate a voltage, without the adoption of batteries, with the amplitude corresponding to the measurand.