An alternative to discarded plastic: A report of polymer optical fiber made from recycled materials for the development of biosensors

It is still a challenge to reduce the amount of plastic discarded in the environment. In this scenario, a low-cost method of producing polymer optical fibers (POFs) (mainly compared to powder extruders or pulling towers) from discarded plastics that have transparency is presented in this work using the extrusion method. As a result, this study reports an alternative to the disposal of transparent plastics: the manufacturing of POFs that can be used for different applications, including the fabrication of sensors. Temperature, curvature angle, refractive index and pH sensors were made with the recycled POFs. As part of the optical characterization of the fabricated POF, we used the cutback method to measure the attenuation and a spectrophotometer to determine the relationship between the transmittance and wavelength for Polymethyl Methacrylate (PMMA) and Polyethylene Terephthalate (PET) materials. The mechanical characterization was conducted with a strain-stress test. For temperature sensing, the temperature ranged from room temperature (T approximate to 25 degrees C) to T approximate to 50 degrees C using a furnace. In this test, PMMA POF had a linear behavior. The linear regression fits the experimental data for PMMA POF (R-2 = 0.97), while PET POF had little variation in optical power at temperatures lower than T = 45 degrees C, exhibiting nonlinearity in this case (determination coefficient lower than 0.9, R-2 = 0.815). In angle sensing, both POFs showed linear behavior: PMMA (R-2 = 0.973) and PET (R-2 = 0.914). Similarly, both fibers were able of measuring refractive index with a linear behavior: PMMA (R-2 = 0.968) and PET (R-2 = 0.944). Then, the PMMA and PET POFs were doped with Rhodamine B dye to obtain a pH sensor. The proposed approach resulted in pH sensors with sensitivities of 517.85 a.u./pH and 277.14 a.u./pH for the PMMA and PET, respectively. Thus, the results of this work show the feasibility of using recycled plastics on the biosensors production, where the plastics discarded to the environment can be recycled as sensors for environmental sensing.