<p>The present work describes the development of a novel photoelectrochemical platform based on bismuth titanate and bismuth oxyiodide (BiOI) for low potential determination of 3-(3,4-dihydroxyphenyl)-L-alanine (DHLA). Herein, Bi₄Ti₃O₁₂ (BIT) and Bi₁₂TiO₂₀ (BTO) were combined with BiOI in order to find the more photoelectroactive material for DHLA. The morphological, spectroscopic, structural, and electrochemical characteristics of the materials were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical impedance, UV–visible diffuse reflectance, and amperometry. The BIT sample presented plate-like particles, and it was consistent with the presence of orthorhombic Bi₄Ti₃O₁₂, while the BTO presented irregular noddle-like particles, and it was consistent with cubic Bi₁₂TiO₂₀. The photoelectrochemical measurements showed that the samples based on Bi₁₂TiO₂₀ presented higher photoactivity than those based on Bi₄Ti₃O₁₂. After evaluating the most photoelectroactive bismuth titanate, a fluorine-doped tin oxide glass slide (FTO) was modified with the Bi₁₂TiO₂₀-based bismuth titanate and bismuth oxyiodide composite (BiOI/BTO/FTO) and applied for the detection of the 3,4-dihydroxy-L-phenylalanine molecule. Under optimized conditions, the BiOI/BTO/FTO photoelectrochemical platform presented a linear response range from 12.7 to 316.9 µmol L⁻¹. The BiOI/BTO/FTO platform was successfully applied to a drug sample with recovery values ranging from 98.14 to 103.88%.</p>