Transforming human hair fibers into carbon dots: Utilization in flexible films, fingerprint detection, counterfeit prevention and Fe3+ detection

Creating environmentally-friendly fluorescent carbon quantum dots (HCQDs) from human hair is a straightforward process with versatile applications. These HCQDs, derived from non-toxic hair, are produced through a one-step microwave (MW) method and have gained increasing attention due to their exceptional properties. Despite the availability of various advanced HCQDs, their full potential remains untapped. Thanks to their remarkable optical characteristics, HCQDs serve as highly sensitive nano-probe agents for the fluorometric measurement of Fe3+ ions. The fluorescence (FL) intensity of the nano-probe exhibits a linear correlation with Fe3+ ion concentration ranging from 0 to 50 μM, boasting a limit of detection (LoD) of approximately 0.13 μM. This sensitivity is achieved through resonance energy/electron transfer-induced FL quenching. Remarkably, carbon dots (CDs) obtained from human hair function as ink-free patterned substrates, making them ideal for printing and the nondestructive collection and detection of latent fingerprints (LFPs). Immersing LFPs in HCQDs@poly(vinyl alcohol) (HCQDs@PVA) solution yields flexible, transparent films with consistent luminescent LFPs and clear ridge features for accurate personal identification. Importantly, this technique allows for the lifting and identification of long-term exposed LFPs from various surfaces without causing any damage. The segregation of HCQDs within the polymer matrix during film formation is the mechanism responsible for LFP collection and visualization. Overall, HCQDs@PVA composites exhibit outstanding performance, suitable for applications in fluorescent patterns, flat panel displays, LFP analysis, and anti-counterfeiting (AC) labeling.