A sample-to-answer framework for on-site body fluid identification based on microbial signature

On-site body fluid identification can rapidly provide decisive evidence for crime scene reconstruction and suspect apprehension. However, current laboratory-based methods are unsuited to field-based scenarios. Protein-based biochemical strategies fail to amplify trace biomolecules and protein is susceptible to denaturation, while nucleic acid-based approach relying on RNA profiling or DNA methylation inevitably requires purification, endonuclease digestion or bisulfite conversion that conflict with speediness and convenience. Therefore, a rapid, portable, and user-friendly strategy is urgently needed for on-site body fluid identification.

In this study, a systematic sample-to-answer framework for on-site body fluid identification is established based on microbial signature. A tailor-made lysis buffer is formulated to lyse Streptococcus salivarius and Lactobacillus crispatus, characteristic of saliva and vaginal secretion respectively, releasing nucleic acids for direct amplification without further purification. Due to the excellent efficiency under straightforward condition, loop-mediated isothermal amplification is employed for characteristic DNA recognition. Besides, a lateral flow device is assembled, enabling result interpretation by naked eye. To suppress carryover contamination under rudimentary field conditions, uracil-DNA glycosylase-based anti-aerosol strategy is further integrated. The sole apparatus required is only a heater for isothermal incubation during amplification. Hence, a handheld device of cigarette-case size is designed and fabricated to fit this framework and on-site deployment. The reagents for amplification are mixed and lyophilized beforehand to simplify the procedure more and avoid cold-chain transport.

A systematic sample-to-answer framework for on-site body fluid identification is established, enabling accurate identification of body fluid left on various carriers involving sexual assault and confinement. The entire workflow can be completed within 1 h, substantially reducing the operational complexity and equipment requirement of conventional laboratory-based assays. This framework demonstrates its feasibility as a rapid and practical tool for on-site body fluid identification and highlight its potential for field deployment in forensic investigations.