Trying to find traces of latent blood at a possible crime scene is always very challenging, especially when the supposed crime scene has been thoroughly cleansed several times. There are several options available to the Crime Scene Forensic. BlueStar, Luminol, and Florescence are only some of the more particle techniques for use on larger scenes. Although I will be focusing on the Fluorescein Method of Latent Blood Detection; the other techniques may be just as viable.

Fluorescein can be obtained in various forms. Depending upon the formulations that are being followed, mixing a batch can be complex. However, there are prepackaged kits that can be obtained from various vendors that make it as simple as "just adding water"! Two such kits are sold under the registered trademark HemaScein, and another vendor under the trademark Flora-Scene. Since HemaScein, Flora-Scene, and Fluorescein are the same basic formulations, this paper will refer only the chemical name Fluorescein.

Fluorescein is a presumptive blood test for latent bloodstain detection. It has been used in forensic applications to reveal trace amounts of blood. Traces of latent blood can be detected even after repeated cleansing of the crime scene. Fluorescein is highly sensitive to the hemassociated molecules (enzymes and iron) in the red blood cells, (1:105,000 depending upon the dilution rate of the working solution) [1-2]. Traces of these hemassociated molecules will embed themselves on the substright, even after multiple cleanings. Fluorescein can also be used to discover and enhance shoe tracks leading from a bloody crime scene thus allowing investigators to follow the suspect's trail [3]. Fluorescein can be used to locate traces of latent blood on clothing, even after it has been laundered several times (best preformed at the lab). It can also be used on vehicles (inside and out) [4]. Some studies have been conducted on the development of bloody latent finger/palm prints [5]. There are two basic forms of Fluorescein that are typically used in forensics.

Fluorescein can be either aqueous or alcohol-based. Both formulations will work. However, alcohol-based solutions are more difficult to make, and can be very volatile, and extreme caution must be taken when used. An open flame or static electricity can ignite the alcohol fumes possibly causing an explosion.

Both Fluorescein and Luminol are on the suspected list of carcinogens yet; Fluorescein has a Food and Drug Administration (FDA) approval for medical usage [6]. Since the 1960's Fluorescein has been used to diagnose blood flow status in the retinas by injecting it directly into the vessels of the eyes, and as a topical used in diagnosis of corneal abrasions, ulcers, infections & dry eye [7-8]. Other medical applications of Fluorescein include injecting it into the blood system to study the blood flow to tumors, grafts, etc. (also known as Fluorescein mapping) along with other medical diagnostic procedures [9] [10-11]. Nevertheless, caution should always be employed when using either aqueous or alcohol protocols. The other chemicals used in the aqueous-based Fluorescein formula are zinc and sodium hydroxide, both of which can be commonly found in most households. Again, proper handling and disposal of all reagents should be employed at all times.

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