Ninhydrin as a universal screening tool for body fluids
Tine, Emily Marion
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Ninhydrin is one of the most widely used chemical reagents for the enhancement of latent fingerprint impressions on porous substrates^1-22. Ninhydrin (2,2-dihydroxyindane-1,3-dione) reacts with the amino acids most commonly encountered in the sweat of fingerprints, producing an intense purple color^1. Since ninhydrin reacts with amino groups in organic compounds, the chemical ought to be able to positively react with biological materials collected at crime scenes that contain amino acids associated with the nucleic acids in DNA^1,21. Previous studies have investigated the use of ninhydrin as a screening tool for specific types of biological material^21,22. Driscoll et al. has found that treating buccal swabs with ninhydrin has greatly assisted in locating the buccal cells for subsequent DNA analysis^22. Bayer et al. has shown that ninhydrin can be an effective screening method of swabs containing an unknown content of biological material and can detect cellular material on handled items^21. In addition, ninhydrin has repeatedly been shown to have minimal effect on DNA and downstream PCR processes^16,21,22. Present methods for body fluid identification test for only one body fluid at a time, i.e. identifying three different body fluids would require that three different assays be employed. Pre-screening certain items with ninhydrin could assist crime scene investigators in collecting the most probative samples, rather than randomly selecting from items that may or may not contain any biological material. Ninhydrin is inexpensive, easy to use and has the potential to be an effective screening tool for various types of biological material. Additionally, a tool that encompasses various types of biological materials is beneficial to crime scene investigators by minimizing the resources needed and providing a broader situational use. In this study, the capability of ninhydrin to react with dilute blood, neat semen, neat saliva, vaginal secretions, neat urine and perspiration was determined. In addition, the efficacy of various methods for processing and developing the ninhydrin reaction as well as the effectiveness of ninhydrin as a screening tool on various substrates were explored. Furthermore, the effect of ninhydrin on subsequent presumptive and confirmatory body fluid testing was examined. The results show that ninhydrin can successfully enhance latent blood, semen, saliva, vaginal secretions, urine and perspiration. Different substrates affected the visualization of ninhydrin-processed stains, thus the type of substrate should be considered when using ninhydrin, and methods may need to be adjusted accordingly. Further, ninhydrin processing does not appear to detrimentally affect subsequent presumptive and confirmatory screening for blood, semen and urine. Saliva testing results were inconsistent and must be further studied to determine whether or not ninhydrin negatively affects the outcome of these tests. Not all stains that reacted positively with ninhydrin were body fluids. Whole milk, beer, Red Bull® and Naked Juice protein smoothie all showed a purple color change when processed with ninhydrin. The best ninhydrin solvent overall was determined to be HFE7100 due to its cleaner application and more consistent results than petroleum ether. The use of a steam iron may detrimentally impact secondary screening of body fluids; suspected body fluids should be processed with ninhydrin in a laboratory oven at approximately 70℃ to prevent potential loss of evidence.