Abstract
Inspired by the design from the Damrauer group1, we further modified the 3D-printed UV-Vis spectrometer to improve signal-to-noise as well as data reproducibility. Using readily available components and open-source software, we built a functioning device capable of monitoring light absorption at various wavelengths using several phone models. The experimental data collected for several samples highlight the spectrometer’s potential for educational applications as a cost-effective alternative to commercial instrumentation.
Introduction
The technique of measuring the absorbance of light at various wavelengths for a given sample is known as UV-vis spectroscopy2. The method is useful for determining a substance’s color properties, determining which wavelengths are absorbed and transmitted, and providing information about chemical structure.
In spectroscopy, the amount of light that a substance absorbs at a certain wavelength is measured by its absorbance. The well-known Beer-Lambert Law states that absorbance is directly proportional to both the substance’s concentration and the length of the light path through the sample. Because of the versatility and simplicity of the technique, UV-vis is a commonplace technique in research labs.
However, traditional spectrometers can be expensive and require regular maintenance to keep the instrument running smoothly. To circumvent these issues, in the present work we utilized 3D printing technology along with a previously published model to produce a practical, affordable alternative. After thoroughly analyzing the previously modified model from Herrera and Unwalla et al., we proposed additional modifications that included altering the spectrometer base as well as designing a new cellphone stand that could be adapted for use with multiple cellphone types. Overall, our goals are to improve the ease and reproducibility of the data collection process and to enhance the signal-to-noise of the 3D printed spectrometer.
Experimental details
Materials & Design: Stl files from a previous (Herrera and Unwalla et al) spectrometer model were used. The spectrometer was printed on a LulzBot Workhorse+ printer with MET285-probe head, using black PLA 3D printer filament. The modular components were assembled with glue dots or tape (materials acquired from Amazon).
Procedures: To ensure every phone model is compatible with the spectrometer, a triangular phone holder was designed. The phone stand makes an angle of ~20° relative to the tabletop, and it has a curved lip at the bottom of the stand to ensure the phone stays in place. We also designed and printed a small slider block (29 mm x 41 mm x 11.5 mm; l x w x h) that can be attached to the phone stand using a rubber band. The slider was designed since phone models come in different sizes and may require adjustment for use with the spectrometer. The phone base with an adjustable slider is then placed immediately in front of the spectrometer. The new setup is then ready to collect data images that will be downloaded and analyzed using the free online Image J program. An additional modification to the light bulb and coin battery unit was also implemented in the current design. To prevent the heavy battery from slipping out of the housing, potentially creating issues with data reproducibility and signal-to-noise, we designed a battery holder. The coin slot battery holder was designed to match the height of the light bulb housing, and it contains a thin unfilled channel to stabilize the coin battery.
To minimize noise and unwanted light, data collection is best performed with overhead lights dimmed. The fully assembled 3D printed spectrometer includes (1) the sample holder and cuvette containing the sample of interest, (2) the LED light bulb fitted into the 3D printed housing, (3) the appropriate slit insert. .
To quantitatively use the 3D printed spectrometer, the first step is to capture an image of the light profile from a compact fluorescent light bulb. This image will serve to calibrate the x-axis of the spectrum. After collecting the CFL spectrum, the 3D printed spectrometer setup should not be disturbed. The experimental data collection order is as follows: (1) blank (water or appropriate solvent or buffer), (2) experimental samples. Data images are collected using the camera feature on any cellphone. Once the images are captured, these data are then loaded into and analyzed using Image J. Image files are stacked (overlay) and rotated clockwise by 90°. The image area to be analyzed is then highlighted using the rectangle tool. Plot profiles are then generated and the x-axis is converted from pixels to wavelength using the CFL spectrum and well-defined wavelength values including 435.8, 487.7, 546.1, and 611.66. The blank spectrum intensity at each wavelength is then utilized to convert the gray value into absorbance.
Figure 1. Example of red color dye on 3D Printed spectrometer procedures. (A) Spectrometer setup with cuvette. (B) Sample picture taken with a phone and uploaded into ImageJ. (C) Same image as in panel B, but after rotation by 90° to the right in ImageJ. (D) Spectrum generated in Excel.
Results and discussion
In an effort to improve signal-to-noise, ease of use, and data reproducibility, we made several adjustments to the 3D printed UV-vis spectrometer models from Damrourer et al and Herrera et al. Modifications include (i) designing a phone holder base, (ii) assembling a rubber slider with a block are outlined below, and (iii) constructing a coin battery slot block to stabilize the light bulb and battery.
(i) Phone base- The initial design of the phone holder of the spectrometer from last year was limited by its compatibility with only one specific iPhone model, which restricted its usability. By redesigning the phone base to be wider and triangular, the spectrometer can now accommodate all iPhone models, it reduces the gap between the spectrometer window and the phone camera, and it enhances the spectrometer’s versatility.
Figure 2. 3D printed UV-vis spectrometer footprint before (left) and after (right) addition of the adjustable phone base.
(ii). Rubber slider- Incorporating a rubber band adjustable, sliding retention bar makes it possible to modify the height of the phone base, which guarantees that the camera and optical components are optimally aligned, regardless of the size or model of the phone.
(iii) Coin Slot Holder- To improve the stability of the spectrometer, a coin slot holder with a 22mm hollow path was designed and printed to secure the light bulb and coin battery. This new component ensures that the bulb remains firmly in place during operation, and prevents unintentional displacement of the bulb that could disrupt measurements or cause shifting in the setup after collection of the CFL spectrum.
Figure 3. Coin Slot Holder Design.
To evaluate the quality of data collected on the 3D printed spectrometer, we performed a comparison of data collected on the same samples using a commercial UV-vis spectrometer (Shimadzu UV-2600 UV-Vis Spectrophotometer). The images in Figures 4A, 5A, and 6A were taken on the 3D spectrometer and analyzed on image J. Spectra collected for the same samples using the commercial spectrometer are shown in Figures 4B, 5B, and 6B. From this comparison, we conclude that although the graphs are not exactly the same, the main spectral features are observed at similar wavelengths. (Further details and lab instructions for the example data shown in Figures 4-6 are explained in the “Application of 3D-Printed UV-Vis Spectrometer” research paper).
Figure 4. Experimental data collected for the pH lab, vinegar sample. Data collected using (A) the 3D printed UV-vis spectrometer, and (B) the commercial instrument show similar peaks around 475 nm.
Figure 5. Experimental data collected for the ecology lab, grass sample. Data collected using (A) the 3D printed UV-vis spectrometer, and (B) the commercial instrument show similar peaks around 665 nm, which is consistent with the maximum absorbance wavelength expected for chlorophyll a5.
Figure 6. Experimental data collected for the cosmetic lab, orange eyeshadow sample. Data collected using (A) the 3D printed UV-vis spectrometer, and (B) the commercial instrument show similar peaks centered around 540 nm.
Conclusion
This research reveals that additional modifications to previously published 3D-printed UV-Vis spectrometers improved the ease of use and quality of data that can be collected on samples we encounter in everyday life. Our 3D printed spectrometers yielded similar spectra to those obtained on the commercial instrument. However, attaining high resolution data and achieving adequate sensitivity can be challenging with the 3D printed designs, in part because their performance may be limited by their capacity to control stray light. The new 3D printed spectrometer design offers improved ease of use and reproducibility compared to the previous model, making it a useful tool in high school teaching laboratories. Results from this project make an advanced scientific instrument more accessible by providing a practical answer to budgetary constraints, and improving scientific instruction while stimulating students’ curiosity.
Acknowledgements
We would like to express our sincere gratitude to American Chemical Society Project SEED (J.Z.) and the University of Miami Young Scholars Program (I.D.) for the opportunity to participate in the research described here. J.Z. is grateful to the American Chemical Society Project SEED for their generous funding This project is supported by the National Science Foundation CAREER award under award number 2144239 (to K.M.). We would also like to thank the graduate students in the lab for their assistance. Finally, we gratefully acknowledge the effort and unwavering support from our mentor Dr. Meier.
References
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