Highly Stable, Nondestructive, and Simple Visualization of Latent Blood Fingerprints Based on Covalent Bonding Between the Fluorescent Conjugated Polymer and Proteins in Blood

Abstract

Latent blood fingerprints (LBFPs) can provide critical information of foul play and help identify the suspects at violent crime scenes. The current methods for LBFP visualization are still not satisfactory because of the low sensitivity or complicated protocol. This study demonstrates a simple and effective LBFP visualization strategy by integrating a new amphiphilic fluorescent amino-functionalized conjugated polymer with the cotton-pad developing protocol. LBFPs on various substrates are visualized by simply covering them with the polymer solution-soaked cotton pads. The images display clear fingerprint patterns, ridge details, and sweat pores, even on very challenging substrates such as painted wood and multicolored can. The gray value analysis confirms semiquantitatively the enhancement of the contrast between ridges and furrows. Even LBFPs with various contaminations or aged for more than 600 days are effectively developed and visualized. The developed fingerprint images show superior stability over long storage time and against solvent washing. Moreover, the polymer causes no degradation of DNAs in the blood, suggesting the possibility of further DNA profiling and identification after development. The mechanistic investigation suggests that the formation of positive or inverted images can be attributed to the synergistic effects from the affinity between polymer and blood, and the affinity betwen polymer and substrate, as well as the slight quenching of polymer fluorescence by blood. Furthermore, the covalent bonding between the protonated primary amino group and proteins in blood endows the stability of the developed fingerprints. The result rationalizes the molecular design of the fluorescent polymer and sheds new light on the future strategies to effective LBFP visualization in practical applications.

A Universal Developing Strategy for Fingermark Detection and Enhancement Based on Disodium Iminodiacetate-Functionalized Conjugated Polymer

“…Such fluorescence enhancement can be attributed to the increase in absorbance to a small degree, but the main reason should be sweat-induced polymer aggregation, which leads to AIEE behavior. Interestingly, when having blood on the polymer film, the absorption spectrum displayed extremely strong absorbance, coming from blood, which overshaded the absorption of the polymer; and the emission of polymer was significantly quenched; such observation can be explained by the inner filter effect and has been discussed in our previous study focus on blood fingermark development . Even with such a quenching effect, the blood fingermark can still be visualized by the polymer solution since there is some interaction between them, and the adhered polymer can still emit relatively weak fluorescence to give the patterns.…”

“…Interestingly, when having blood on the polymer film, the absorption spectrum displayed extremely strong absorbance, coming from blood, which overshaded the absorption of the polymer; and the emission of polymer was significantly quenched; such observation can be explained by the inner filter effect and has been discussed in our previous study focus on blood fingermark development. 22 Even with such a quenching effect, the blood fingermark can still be visualized by the polymer solution since there is some interaction between them, and the adhered polymer can still emit relatively weak fluorescence to give the patterns. In summary, the spectral study of the polymer in solid upon different fingermark components further confirmed the AIEE behavior of the polymer induced by sweat during fingermark development.…”

“…Researchers are working hard to apply different types of fluorescent materials for the development and enhancement of fingermarks, providing a variety of options for forensic investigation. ,− Fluorescent conjugated polymers (CPs) have the advantages of low toxicity, photostability, high quantum yield, and tunable structure that are essential for fingermark development. − Our group has successfully developed a series of conjugated polymer-based materials to effectively develop or enhance blood or sebaceous fingermarks. − Recently, we advanced an “adaptive development strategy”, and with this concept, we successfully visualized blood or sebaceous fingermarks with the same fluorescent reagent and the same developing protocol. , There are two critical points for this “adaptive strategy”. The first is introducing multiple groups (or chemical structures), some of which can interact with sebaceous components, while others can interact with blood components.…”

Colloidal Polymer Nanoparticles as Smart Inks for Authentication and Indication of Latent Fingerprints and Scratch

“…This is a fine powder that is applied to a surface with a brush, and it adheres to the oils and sweat left by the suspect’s fingers. The powder will highlight the ridges and valleys of the fingerprint, making it visible to the naked eye or under a magnifying glass. , In this study, the powder of PMD that has the highest fluorescence emission was used for identification of latent fingerprints. As shown in Figure , the hidden fingerprint on a glass surface was dusted by the fine powder of PMD, and the pictures were taken by smartphone after shaking the glasses several times.…”

Multifunctional Eu(iii)-modified HOFs: roxarsone and aristolochic acid carcinogen monitoring and latent fingerprint identification based on artificial intelligence

“…[6][7][8] Owing to their poor optical contrast with the substrates, LFPs are invisible to the naked eye and require visualization. 9,10 At crime scenes, LFPs are the most arduous to investigate among the three common types of fingerprints including visible fingerprints, indented fingerprints, and LFPs. [11][12][13] Therefore, two major studies on LFPs are crucial.…”