Optimisation and validation of cost-effective water-based solutions of acid fuchsin for detecting fingermarks in blood.

Fingermark impressions in blood are commonly encountered at violent crime scenes and represent a critical trace that can link an individual to the scene. A range of techniques are available for detecting and enhancing bloody impressions; however, many chemical methods involve using hazardous solvents or require alternative light sources to visualise fluorescence. This is particularly challenging for bloody impressions on dark substrates. An alternative treatment is the protein dye known as acid fuchsin (commonly known as 'Hungarian Red'), which can be visualised under both white light and fluorescence lighting. However, there is limited research available on this method, especially concerning its use in detecting bloody fingermarks on dark surfaces and its fluorescence qualities. To address these knowledge gaps, this study broadly aimed to evaluate the effectiveness of acid fuchsin for enhancing bloody fingermarks on a range of common substrates, along with comparing the performance of a formulation made from base components against a commercially-available Hungarian Red reagent. Through a multi-phased experimental approach, results supported an all-in-one treatment that contained 2 % SSA, 0.2 % acid fuchsin, and deionised water as the most effective. This formulation performed as well or better than commercial Hungarian Red, amido black and acid yellow in the validation trial. Enhanced impressions could be visualised under white light on light and dark surfaces, whilst 530 nm excitation provided improved detection via both fluorescence and absorption modes depending on substrate background interference. Moreover, the reagent was applied by spraying directly onto substrates placed at near-vertical angles, with no evidence of any fingermarks being affected by running or inadequate fixing. The ability to enhance and visualise bloody impressions on light and dark surfaces, under white light or excitation, using a single, water-based treatment is highly advantageous to operational crime scene examiners and forensic scientists.