Direct identification of forensic body fluids by MALDI-MS
The rapid identification of human body fluids is meaningful for forensic casework. Yet, current methods suffer from several limitations like poor sensitivity, time consuming and big sample consumption. Herein, we developed a mass spectrometry method to distinguish human body fluids (blood, semen, urine, sweat, saliva) based on small molecular region with no pretreatment, microliter sample consumption and high throughput. A highly sensitive and high salt-tolerance matrix N-(1-naphthyl) ethylenediamine dihydrochloride (NEDC) was used to efficiently detect metabolites in complex humoral environment. Some characteristic small metabolic molecules such as heme, hemin, creatinine, phosphate acid, uric acid, citric acid and lactic acid were identified and served as potential biomarkers to differentiate different body fluid types. Further principle component analysis (PCA) was performed to cluster the body fluid samples and three principal components allowed 75% clustering of all body fluid types. Blind testing revealed nine out of ten unknown body fluid samples could be correctly classified to their corresponding group. This novel method can efficiently differentiate five body fluids with minimal interferences due to the storage time (less than 12 months) and carrier materials (cotton, fabric and tissue). The whole process from sampling to collection of mass spectra of body fluids can be finished in less than 10 minutes. We believe this developed strategy has significant implications for rapid and effective human body fluid screening in forensic casework.