Sustainable latent fingerprint enhancement with ink-free printing and shape memory behavior using Parthenium Hysterophorus-derived carbon dots

Abstract

We developed a method to produce red fluorescent carbon dots from Parthenium hysterophorus leaves (PCDs) through hydrothermal carbonization. These PCDs exhibit consistent photoluminescence, emitting light regardless of excitation, with a 6.01 ns fluorescence lifetime and a 10.2% quantum yield. They possess a fine size of 4.4 nm, excellent hydrophilicity, and stability in a pH range of 4–11. Leveraging their optical properties, these PCDs function as precise nano-probes for detecting Fe3+ ions, demonstrating a linear correlation within 0 to 50 μM concentrations and a low detection limit of approximately 0.14 μM. Emitting light at about 620 nm, these PCDs remain visible even in daylight. When applied to fingerprints on various substrates and dried, they reveal distinct prints under 365 nm UV light, retaining stability for 24 h. This resilience is attributed to preventing fluorescence reduction, achieved through the coffee-ring effect and electrostatic interactions during drying. Employing deep learning with the YoLOv8 algorithm, fluorescence images of these latent fingerprints (LFPs) exceptionally resemble standard controls. These PCDs serve a dual role as fluorescent ink and nanocomposite films within a PVA matrix, demonstrating potential in anti-counterfeiting applications. This study presents a straightforward method for synthesizing PCDs with intense red luminescence, establishing them as a versatile platform for Fe3+ sensing, flexible fluorescent films, latent fingerprints, and anti-counterfeiting pursuits.