Multi-fluorescent cationic carbon dots for solid-state fingerprinting

Carbon nanomaterials have been widely explored in bioimaging and biosensing, but their application in forensic science and technology is rare. In this report, we show one-pot synthesis of cationic Carbon Dots (cCDs) and their application in fingerprinting analysis. The cCDs show narrow size distribution (< 10 nm), decent quantum yield (c.a. 46%), and a band gap of 2.75 eV. The cCDs exhibit cationic charge and show excitation-dependent multi-fluorescence characteristics. The cCDs show no production of reactive oxygen species and thus are safe to use. Interestingly, they also possess bright liquid as well as solid-state fluorescence. We demonstrate that a well-resolved patterned fingerprint can be obtained within a short time (2-3 min) from different physical surfaces and can be studied using a simple cell phone camera enabling accurate visualization up to third-degree detailing of the fingerprint. Owing to multi-fluorescence characteristics of cCDs, a detailed investigation of the fluorescent patterns was carried out by a three-dimensional multiphoton confocal microscopy. In comparison to traditional methods, the cCDs fluorescence-based fingerprinting shows improvements towards rapid image capture and analysis. Thus, the cCDs form a promising material for rapid fingerprint detection in forensic sciences.