Coordination effect enhanced visualization of latent fingerprint with Eu (TTA)₃phen-SiO₂ microspheres

Latent fingerprint (LFP) powders are crucial in the detection of LFPs in forensic science. However, it is often plagued by poor image resolution and low contrast. Herein, enhanced LFP fluorescence (FL) visualizations are achieved by doping Eu(III) coordination compound Eu(TTA)₃phen directly into SiO₂ microspheres instead of Eu(III) ions. Using the synthesized Eu(TTA)₃phen-SiO₂ microspheres, the fine characteristic structure of LFP can be seen and recognized under 365 nm irradiation, up to Level 3. However, the Eu³⁺-SiO₂ microspheres were difficult to recognize the Level 2,3 fingerprint structure. The difference between the ridge and furrow gray values of Eu(TTA)₃phen-SiO₂ microspheres is 2.1 times that of Eu³⁺-SiO₂ microspheres. The coordination effect increased the asymmetry around Eu(III) ions, resulting in the ultrasensitive ⁵D₀→⁷F₂ transition, thus increasing the FL intensity, and the uniform doping of the Eu(III) coordination compound into SiO₂ also reduced the surface FL quenching due to shielding from oxygen. Under this dual effect, the LFP performance of Eu(TTA)₃phen-SiO₂ microspheres has been significantly improved. We believe that this novel and easy LFP visualization method is a promising routine in specific target detection including criminal investigation, customhouse check-in, and drug control.