Multiplex body fluid identification using surface plasmon resonance imaging with principal component analysis

Body fluid identification is a key component in forensic casework, providing important information for the reconstruction of criminal events. Body fluid identification in combination with DNA analysis allows the linking of individuals to criminal acts and can therefore be of great importance in determining the outcome of criminal court cases. However, none of the current body fluid identification methods meet all forensic requirements, such as a high sensitivity, a high specificity and the ability to analyse multiple body fluids in a single run. In this pilot-study, we explore, for the first time, surface plasmon resonance imaging (SPRi) with antibody-based detection to serve as a novel multiplex body fluid identification assay for blood, semen, saliva, urine and sweat using minimal sample preparation. A training set consisting of ten donors per body fluid was analysed to determine whether body fluid specific response signals could be obtained. Principal component analysis (PCA) was performed as a statistical tool to cluster the body fluid samples by response signal pattern reduction and to uncover the sources of variation between the body fluids. Four principal components allowed complete clustering of all body fluid types. Blind testing of body fluid samples revealed that five out of eight unknown samples could correctly be clustered to their corresponding group, three out of eight samples were identified as inconclusive. Although optimization of the current SPRi method is required for use in the forensic field, this pilot-study demonstrates the feasibility of SPRi to differentiate five forensically relevant body fluids.