EXPRESS: A Low-Cost 3D-Printed Ocular Microspectrophotometer for Teaching Visible Spectroscopy.

Visible microspectrophotometry enables the non-destructive acquisition of spectral information from microscopic regions and constitutes a valuable tool for the experimental teaching of spectroscopy, microscopy, and optical instrumentation. This work presents the design, fabrication, and evaluation of a low-cost ocular microspectrophotometer (OMP), developed using 3D printing and designed for integration with conventional optical microscopes.The device incorporates a diffraction grating, optical apertures, and a CMOS sensor to acquire continuous spectra over the 433-827 nm wavelength range from microscopic regions approximately 40 µm in diameter. In addition, a Python-based algorithm was developed to convert spectral images into transmittance vectors and calibrate the pixel-to-wavelength relationship. The system achieved a spectral resolution of approximately 0.84 nm/pixel and was validated using reference optical filters.Its educational potential was demonstrated through the spectral characterization of the RGB subpixels of a smartphone LCD screen and the analysis of the transmittance of a plant leaf. These activities provide an effective means of introducing concepts such as additive color synthesis, spatial resolution, light-matter interaction, and digital image processing. The OMP constitutes an accessible and reproducible platform that integrates additive manufacturing, digital image processing, and hands-on experimentation for teaching spectroscopy, microscopy, and the design of scientific instrumentation.