**Figure 1.**

*(a) The smartphone spectrometer with the inset (top-left) of a plastic fiber assembled into the built-in flash. (b) The spectral images from different-sized plastic fibers are shown.*

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**Figure 2.**

*MB solutions with a spectral view from 0.1 to 10 ppm.*

*From Sophisticated Analysis to Colorimetric Determination: Smartphone Spectrometers…*

Styrene polymer using a 3D printer (Zortrax M200) with a 150-g polymer. Two pieces of plastic fiber cables were used in the design. The first 1.5-mm-diameter fiber carried the light from the smartphone flash to the cuvette while the second fiber cable with a diameter of 0.25 mm transmitted the light from cuvette to the camera which passed through the assay. The diameter of the second cable was critical as the light for spectral data was carried with this cable. Therefore, the effect of diameter on spectral data was analyzed using 0.25-, 0.5-, and 1.0-mm cables as given in **Figure 1b**, and 0.25-mm diameter was found to be adequate based on this experiment. A custom cradle was specially designed to align plastic optical fibers with smartphone optical components. As the cradle was solid, the solution could be placed into the cuvette slot. In order to simplify the spectrometer system design, no collector lens or mirrored components were placed in the light path. Besides cost, the most important factor in choosing plastic optical fibers instead of glass-based fiber optics was the ability to use plastic optical fibers without special tools for

To test the performance of the system, methylene blue (MB) solutions were prepared with different amounts and their respective spectral views are given in **Figure 2**. At the top row, the concentration of the solution varies from 0 ppm (most left), which

*DOI: http://dx.doi.org/10.5772/intechopen.82227*

stripping and cutting.
