Chemometric-assisted visible diffuse reflectance spectroscopy for accurate microscale discrimination of handwritten blue pen inks

Accurate, non-destructive, and cost-effective analytical methods are highly desirable in forensic ink examination. This study evaluates the discrimination capability of microscale visible diffuse reflectance spectroscopy combined with chemometric analysis. A simple optical setup operating in a narrow visible range was used to obtain 10 µm spot-size reflectance measurements from handwritten samples, yielding excellent repeatability (RSD < ± 2%). Reflectance spectra from nine blue pen inks were classified using Linear Discriminant Analysis, achieving 94.17% cross-validated accuracy and 97.5% accuracy in blind testing. The results show that this new approach enables reliable ink discrimination across diverse handwritings even when the spectral profiles are highly similar, and it supports forensic document analysis without causing any damage to the evidence.