Compact and portable device for monitoring cutaneous photosensitivity after photodynamic therapy

Photodynamic therapy (PDT) is used in numerous established and emerging clinical applications involving systemic administration of photosensitizers or their precursors. Although PDT offers lower off-target toxicity than most cancer treatments, systemic photosensitization can cause cutaneous phototoxicity. This risk could be mitigated with improved post-treatment monitoring. For example, the FDA-approved photosensitizer Photofrin® requires patients to avoid bright light for at least 30 days. 5-ALA-induced protoporphyrin IX (PpIX) has relatively favorable pharmacokinetics, though patients are required to avoid bright light for 48 hours following systemic administration. Clinical adoption for outpatient applications (e.g., investigational use in oral lesions) could be enhanced by real-time cutaneous monitoring to determine safe light exposure immediately after discharge. We developed the Cutaneous Photosensitivity Detection (CPD) device, engineered as a simple-to-use instrument for measuring cutaneous accumulation of protoporphyrin IX (PpIX) or Photofrin®. The prototype device integrates a 405nm LED excitation source, a 600 nm long-pass optical filter, and a photodiode sensor housed within a custom 3D-printed enclosure. This hardware is complemented by a reflectance-based correction method to normalize fluorescence intensity, compensating for skin tone–dependent attenuation, allowing for comparison of absolute measured values across patient populations with differing skin types. In this work, we demonstrate device validation using standardized PpIX solutions, hydrogel phantoms, ALA-induced 3D cancer cell cultures, and murine models, and compare performance with established fluorescence imaging systems. The CPD device exhibited high sensitivity to clinically relevant PpIX concentrations and showed strong correlation with measurements from a commercial in vivo imaging platform. Its portable design supports bedside and home-health use, enabling evidence-based discharge decisions and remote monitoring of photosensitivity after PDT. Beyond PDT safety assessment, the platform shows potential for broader biomedical applications, including non-invasive monitoring of systemic disorders linked to photosensitivity or abnormal porphyrin metabolism.