Chapter 11: Serology Techniques: Past, Current, and Future

The chapter examines primary binding assays, including enzyme-linked immunosorbent assays that offer high sensitivity for detecting specific antigens and immunochromatographic lateral flow tests that enable rapid field-based screening of biological evidence. Secondary binding methods such as immunodiffusion and immunoelectrophoresis provide precipitation-based confirmation, while agglutination assays utilize visible antigen-antibody reactions for presumptive testing. A significant portion of the chapter addresses advanced molecular strategies for precise bodily fluid identification. DNA methylation profiling leverages epigenetic markers, particularly the analysis of 5-methylcytosine patterns that vary across tissue types to determine fluid origin. RNA-based methodologies employ messenger RNA and microRNA biomarkers with tissue-specific expression patterns, such as KLK3 for seminal fluid or MMP7 and MMP11 for menstrual secretions, allowing definitive fluid classification. Proteomic analysis utilizes tandem mass spectrometry to sequence peptide fragments and cross-reference them against protein databases, identifying diagnostic biomarker proteins unique to particular bodily fluids. The chapter also explores microbial DNA analysis as an emerging identification tool, recognizing that the human microbiota exhibits fluid-specific bacterial compositions, with organisms such as Streptococcus species predominating in oral secretions and Lactobacillus species in vaginal fluids. Together, these techniques represent a continuum from classical immunological approaches to contemporary molecular methods, each contributing distinct evidentiary value and analytical power to forensic investigations.