Abstract
In recent years, the chemical modification of optical fibers (OFs) has facilitated the manufacture of sensors because OFs can identify several analytes present in aqueous solutions or gas phases. Nevertheless, it is imperative better to understand the chemical interactions in this molecular system to generate low-cost and efficient sensors. This work presents a theoretical and experimental study of organic polymeric functionalized OF structures and proposes a cost-effective alternative to monitor breathing and humidity. The device is based on silicon optical fibers functionalized with (3-Aminopropyl) triethoxysilane (APTES) and alginate. The theoretical analysis is carried out to validate the activation of the silicon dioxide fiber surface; moreover, the APTES–alginate layer is discussed. The computational simulation suggests that water can be absorbed by alginate, specifically by the calcium atom linked to the carboxylic acid group of the alginate. The analysis also demonstrates a higher electrostatic interaction between the water and the OF–APTES–alginate system; this interaction alters the optical fiber activated surface’s refractive index, resulting in transmission power variation. The humidity analysis shows a sensitivity of 3.1288 mV/RH, a time response close to 25 s, and a recovery time around 8 s. These results were achieved in the range of 50 to 95% RH. Moreover, the recovery and response time allow the human breath to be studied. The proposed mechanism or device is competitive with prior works, and the components involved made this sensor a cost-effective alternative for medical applications.
Highlights
To active the silicon dioxide of the optical fibers (OFs), which is depicted in the transversal view in Figure 1A, it was soaked in HCl [5 M] for 30 min, which promotes the generation of hydroxyl groups on the OF surface, as Zhang and co-workers explain [5]
Biosensors 2021, 11, 324 binding system is depicted in Figure 2A; the APTES
The study reveals that water molecules can be easi by the calcium located thecalcium end of the structure
Summary
Human breathing monitoring is nowadays more relevant due to the COVID-19 pandemic. This parameter is related to humidity detection. One alternative is humidity optical fiber sensors, which require the functionalization of optical fibers (OFs). The selective layer can be designed to promote sensors applied to several science fields and highlight biological and biochemical applications [2,3]. In this regard, the state-of-the-art method uses functionalized OF (f-OF) with small molecules, such as organic acids [4], representing some biomolecules such as DNA [5]
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