A Portable, Low‐Cost Spectrophotometer for Absorbance and Selected‐Wavelength Fluorescence Measurements

We present a portable, low‐cost, modular spectrophotometric platform designed for wavelength‐selective optical measurements using interchangeable visible LEDs, an AS7343 multichannel spectral sensor, and Arduino‐based data acquisition. The system was developed to provide a compact alternative for optical absorbance and fluorescence measurements while maintaining performance comparable to conventional laboratory instrumentation. The device was evaluated using aqueous solutions of copper (II) sulfate (CuSO ₄ ) and potassium permanganate (KMnO ₄ ), and results were benchmarked against a standard UV–Vis spectrophotometer. The system demonstrated concentration‐dependent absorbance responses consistent with the Beer–Lambert law, with strong calibration linearity ( R ²  = 0.99 for CuSO ₄ and R ²  = 0.97 for KMnO ₄ ). In addition, the platform was adapted for fluorescence measurements of Rhodamine B via a simple reconfiguration to a 90° excitation–emission geometry. The fluorescence response showed linear behavior over the 0–4‐μM range, yielding an R ² value of 0.97. The results indicate that the proposed system provides reliable optical measurements for both absorbance and fluorescence modalities, offering a flexible and cost‐effective alternative for analytical spectrophotometry applications in resource‐limited laboratory settings.