# A Portable Optical Sensor for Microplastic Detection: Development and Calibration
## 3 Results and Discussion
### Beta Test of Absorption in Real Life Environment  
In the experimental phase, four distinct lasers--red, green, bright green (yellow), and blue--were utilized, as detailed in the experimental section. The samples were irradiated, and absorbance values were obtained using the BPW34 sensor following the previously established calibration procedure. This setup ensured consistency and allowed for a reliable comparison across different laser configurations. The first sample set consisted of microplastics placed on the right side of a microscope slide, with a thickness not exceeding 0.8 mm (Figure 20). On the left side of the slide, a 2 \(\times\) 2 cm section of the outer layer of a golden apple hypanthium was positioned to serve as the organic reference material. The tests were conducted seven times in an uncontrolled environment to evaluate the variability of the measurements and assess the equipment's portability for use in various locations. The samples were radiated and then saved in a CVS file and were ready for analysis for each wavelength. This is shown in Figures 21 and 22. Figure 20: The figure shows the experimental setup displaying the placement of microplastics (right) and organic material (golden apple hypanthium, left) on a microscope slide. This arrangement highlights the comparison between synthetic and organic samples for analytical purposes. Normalized signals for each laser wavelength (470 nm, 525 nm, 570 nm, and 636 nm) were obtained for both microplastics and organic samples. These signals are shown in Figure 23 for microplastics and in Figure 24 for organic materials. As expected, organic materials consistently exhibited higher light transmittance and lower absorbance compared to microplastics, aligning with theoretical predictions. This behavior is crucial for the rapid and reliable identification of microplastics within mixed samples. Figure 21: The figure shows the graphical user interface for controlling and monitoring a system in ‘LED Mode’, featuring a graph that displays the voltage value of the wavelength 636 applied to microplastics. Figure 22: The figure shows the sensor applying different wavelengths to detect microplastics over deposited microplastics, currently using the 636 nm wavelength. Additionally, as the wavelength shifted toward the red and infrared regions of the spectrum, microplastics exhibited lower absorbance, as illustrated in Figure 25. This trend suggests that microplastics are more easily distinguishable at these wavelengths, providing a practical advantage for detection systems designed to operate within this spectral range. We calculated the average absorbance for each test to facilitate material classification, yielding unique optical fingerprints for microplastics and organic samples (Figures 26 and 27). These fingerprints provide a foundation for implementing advanced classification methods, such as fuzzy logic or neural networks. The calculated voltage values represent the material's signature and can be directly employed to train classification models. Figure 23: The figure shows the normalized intensity profiles for microplastics at four laser wavelengths: blue (470 nm), green (525 nm), bright green (570 nm), and red (636 nm). The figure highlights the stability and distinct signatures of the microplastics across the wavelengths. Figure 24: The figure shows the normalized intensity profiles for organic materials at four laser wavelengths: blue (470 nm), green (525 nm), bright green (570 nm), and red (636 nm). Organic samples exhibit higher transmittance and distinct spectral behavior compared to microplastics. The experimental results underscore the potential for integrating intelligent systems into the prototype. Future work aims to develop robust classification algorithms capable of distinguishing materials in real-time by leveraging optical fingerprints. These advance  
Figure 27: The figure shows the average absorbance values for organic materials at laser wavelengths of blue (470 nm), green (525 nm), bright green (570 nm), and red (636 nm).