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 (CuSO₄) and potassium permanganate (KMnO₄), 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 CuSO₄ and R ² = 0.97 for KMnO₄). 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.