Fingerprint examination involves physical as well as chemical examinations. Apprehending a criminal based on the characteristics of minutiae is practised since a long time.
However, a recent study on estimating the approximate time since deposition of fingerprints using colorimetric assays would help in determining the time it takes for a fingerprint sample to degrade and also, the particular amino acid that plays a role in visibility of aging fingerprints.
Direct correlation between Time since deposition and temperature helps investigators to calculate and match the age of fingerprints with the recorded temperature.
The findings say that ninhydrin, Bradford and Sakaguchi assays could make the differentiation up to 84 days at a constant temperature of 21 °C. The ninhydrin assay was used for detecting amino acid content. This assay was found to be capable of differentiating fresh male and aged female fingerprints for the period of the experiment.
Still, it failed to demonstrate a clear and specific decreasing trend over that time. This indicated that it may not be possible to monitor the TSD with ninhydrin assay as ninhydrin interacts with free amino acids.
Bradford assay was used for the detection of six amino acids from fingerprint content. With Bradford assay, the results were comparatively better than ninhydrin and it obtained a decrease in trend.
Sakagushi assay was used to detect the presence of arginine from fingerprint content. A strong intensity of response to minor fluctuations was observed for the first 7 days, followed by a clear decreasing trend.
The Bradford and Sakaguchi assays displayed a decreasing trend and provided differentiation between male and female fingerprints; they were not sensitive enough to establish a specific TSD but an approximate time was potentially possible.
Hence, the fingerprint TSD was possible to be determined using a single amino acid, which slowly decomposes over time. This suggests a possibility that the consistency in response is because of multiple amino acids that contribute to the overall response.
The ultimate goal of this advancement is to transition the chemical assays to investigative methodologies by applying these techniques directly to the fingerprint at crime scenes and thereby generating a colorimetric image.
After applying assays for imaging fingerprints, the colorimetric response on the fingerprint image would then be photographed by an application on a smart device that further allows for the quantification of the colour output.
REFERENCE: Brunelle, E., Eldridge, M., &Halámek, J. (2021). Determination of Time since Deposition of Fingerprints via Colorimetric Assays. ACS omega, 6(19), 12898-12903.