Robotic Raman-OCT for Non-Destructive Visualization of Concealed Latent Fingerprints and Trace-Residue Profiling

Latent fingerprints concealed beneath opaque barriers or containing chemical residues require a dual-capability approach: non-destructive visualization of ridge structures and precise identification of trace substances. Here, a robotic-assisted Raman-optical coherence tomography (R²-OCT) system is introduced that seamlessly integrates structural and molecular imaging into a unified, non-destructive workflow. A spectral-domain OCT probe (10 µm lateral, 6 µm axial resolution) and a 785 nm fiber-coupled Raman probe are rigidly mounted on a six-axis robotic arm, reliably localizing residue particles down to ≈100 µm for Raman targeting. An initial OCT scan reconstructs a 3D volume and generates curvature-corrected en-face images that clearly reveal concealed ridge patterns and precisely localize micrometer-scale residues. Guided by these coordinates, the robotic arm autonomously repositions and auto-focuses the Raman probe, acquiring spectra in ≈1 s per site. Proof-of-concept studies on latent prints doped with sodium carbonate, calcium carbonate and potassium sorbate confirm accurate residue localization; mixed-residue tests further discriminate potassium nitrate, potassium chlorate and sulfur. Complete characterization of six discrete particles is achieved in ≈20 s, over an order of magnitude faster than conventional raster-based Raman mapping. R²-OCT offers a rapid, non-destructive tool for simultaneous fingerprint visualization and chemical profiling, advancing forensic, biomedical, and material applications.