Introduction
Why a UV Spectrometer?
High-Performance-Liquid-Chromatography (HPLC) is expensive. It's like. Really. Really. Expensive. The need for a reliable and cheap (at least in comparison) PET degradation assay has led to many innovations, including titrimetry, fluorimetry, chromatography, and spectrometry. However, they are all limited by their discrete measurement, often limited to once every 15-30 minutes. By continuously monitoring the degradation progress, we are also able to much more effectively visualize and analyse the different properties of our variants, such as mHET inhibition. Our hardware aims to bridge the gap between expensive systems and the need for affordable, continuous data collection by developing a low-cost UV spectrometer.
What is an UV-Vis Spectrometer
The hardware is placed on a hot plate set to the degradation temperature. Since the quartz cuvettes are immersed in a water bath, the system requires time to reach thermal equilibrium. A quartz collimator lens is used to parallelize the light emitted from the UV LED as it passes through the quartz cuvette. Because of their benzene ring, many of the byproducts from PET depolymerization absorb UV light in the 240–260 nanometer range. Our sensor specifically measures the light intensity at 254 nm. By monitoring changes in light intensity at this wavelength, we can estimate the concentration of these byproducts.
Design Iterations
Throughout development, we went through multiple iterations to refine our UV spectrometer design. Below are entries for each iteration:
Iteration 1: Initial proof-of-concept using off-the-shelf UV LEDs and sensors. This stage focused on testing whether TPA absorbance at 250 nm could be reliably detected.
Iteration 2: Improved optical alignment with collimator lenses. We also standardized cuvette positioning to reduce measurement variability.
Iteration 3: Added heating cartridge and temperature sensors to maintain samples at ~60°C, mimicking enzymatic activity conditions.
Iteration 4: Integrated servo-based shaking system to allow mixing during measurements, preventing concentration gradients.
Iteration 5: Electronics and software refinements for stable sensor readings, noise reduction, and better data logging.
Iteration 6: Final iteration with multiple cuvettes (8 total) for parallel testing of enzyme variants, leading to our completed spectrometer prototype.
Materials
Components and Functions
Our design of UV-Vis Spectrometer includes multiple components, including:
| Component | Price | Function |
|---|---|---|
| Arduino Uno | $25 | The arudino is the brains of the operations. It handles all the controls and data logging. |
| UV LED (254 nm) | $58 | The LED is used as the UV source. We chose 254 nm because its around the peak UV absorbance of TPA, MHET, and BHET |
| Photodiode Sensor | $XX | We chose this specidic photodiode because its sensitivity also peaks around 254nm. |
| Quartz Cuvettes | $XXXXXXX | This is likely the most expensive and crucial part of the hardware. Quartz is necessary because glass and many other materials also absorb UV light. |
| Stepper Motor | $XXXX | Not something we should have skimped on in the first place. While high torque nema stepper motors may seem like overkill (and it is), in the case of this hardware, which will be run for atleast 48 hours overkill is underkill. |
| Motor Driver | $XXXX | Because stepper motors can't be directly controlled by arduinos, the motor controller acts as an interface between them. |
| Power Supply | $XXXX | A power supply is needed to power the motor becuase it draws more voltage then the arduino can provide. |
| Wires | $XX | Well... Wires |
Models and Prices
Full list of the materials and their price to build the UV-Vis Spectrometer:
Results
Section 7
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References
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