Luminol in the Forensic and Medical Fields
Luminol was introduced in 1937 to be used for blood detecting in crime scenes (Quickenden et al., 2001). Since then, it has become widely used as a chemical reagent and in medical studies. The chemiluminescent attribute is what makes luminol so valuable in a variety of practical situations (Encyclopædia Britannica). Luminol is gradually creating an inexpensive alternative and a quick solution to many of our medical queries. In the medical field, it is replacing machines related to respiratory diseases; while in the forensic field, luminol is another significant tool when there is little immediate evidence (Robinson et al., 1999). Even so, there are still alternatives for each of these situations, which leads to concluding whether luminol is practical and more useful than its predecessors.
Luminol is chemiluminscent when oxidized. The energy released from the oxidation of a florescent molecule, luminol in this case, excites electrons to a higher state. This in turn creates the luminescence (Encyclopædia Britannica). It is important to realize that luminol does not stand alone in these reactions. A solution of luminol must require specific alkaline metal conditions (Blum et al., 2006). A study done by Blum and her colleagues uncovered a stronger, longer lasting formula that reflected the ideal solution for luminol blood detecting reagent: “with the alkaline condition…pH11, the [ideal] reactant concentration [is] Luminol : 5 mM, NaOH : 25 mM, H2O2 : 50 mM” (2006). Hydrogen peroxide is seemingly always paired with luminol, as it is the least corrosive of all the solutions to the substance sample being exposed to the reagent (Hochmeister et al., 1999).
Although luminol does not possess any significant corrosive qualities, the solutions mixed with it are severely corrosive (Hochmeister et al., 1999). Hochmeister and his colleagues did a study on the effect of chemicals used in forensic sciences on the human blood immunoassay, and they concluded that “the [immunoassay] is [sensitive to] exposure to certain detergents and household bleaches and prolonged exposure to certain preparations of luminol” (1999). The formula created by Blum et al. proved that over time the luminol devours the hemoglobin in the blood with the fast acting oxidation (2006). With the loss of the reactant hemoglobin, the reaction could not last long, an indication that harm was done to the DNA, which was contained in the hemoglobin (Rose et al., 2001). Frégeau and his colleagues did studies to see how much DNA can be recovered from aged bloody fingerprints and concluded that “some loss of biological material will take place…[when] the bloodprints are very small, the loss of blood cells…may result in insufficient amounts of DNA which…would jeopardize the DNA analysis. Caution is…recommended…to ensure that sufficient biological material is retained…” (2000).
The chemiluminescence observed in forensic sciences with luminol is a product of the oxidation between luminol and hemoglobin (Hochmeister et al., 1999). The actual reaction occurs because of a catalyst, the iron, present in hemoglobin (Rose et al., 2001). Luminol oxidizes in the presence of ions of Fe(II), Fe(III), and Cu(II). According to Quickenden and his colleagues, luminol can also catalyze in the prescense of “[hypochlorite], animal hemoglobin, plant peroxidases… disinfectants or antiseptics containing potassium permanganate or iodine…copper(II) ions from water pipes or wires and Fe(II) and Fe(III) ions from rusting iron” (2001). This can cause problems in both the forensic and medical fields, as this creates a “false-positive result” (Quickenden, 2001). In criminal justice, finding a blood stain where one never existed could send someone to jail on false evidence. In medical examinations, diagnosing a patient wrong because of the false results could lead to the patient taking medicine they never needed.
Rose and his colleagues stated that luminol is “now being used widely as an analytical tool for many laboratory and environmental applications, including immunoassays, [the] monitoring of metabolic pathways, detection of free radicals, analysis of a variety of trace metals, and detection of other inorganic substances” (2001). Yet luminol has a strikingly significant place in medical technology. The chemiluminescent quality of luminol allow it to be used as a “dye” of sorts, and also as an indicator of an unhealthy balance of a certain substance (Encyclopædia Britannica). A solution of luminol and hydrogen peroxide is currently being developed to replace nitric oxide tests for asthma patients. The original machine used NO + O3 to measure amounts of NO2 produced. Patients with asthma generally have a greater amount of NO released than a healthy person (Robinson et al., 1999). The more NO present, the more NO2 released, therefore resulting in a stronger chemiluminescence of NO + O3. This machine is expensive and not practical; the new machine developed using luminol/hydrogen peroxide solution was more efficient. Robinson and her colleagues, after doing many experiments on this new machine, concluded that
The measurement of nitric oxide concentrations in exhaled breath with adequate sensitivity, precision, and response time for clinical measurements has been demonstrated. The instrument has advantages of small size, low power consumption, and simplicity over currently used nitric oxide detectors. Since the detector is portable, inexpensive, and well suited for use in a clinical setting, there is potential for greatly expanding the research on nitric oxide levels in the respiratory system. It is anticipated that nitric oxide measurements can be used as a diagnostic tool and aid in developing better treatments for asthma and other respiratory diseases (1999).
The advances in luminol studies always reveal another problem that arises with the use of luminol, but the usefulness of luminol far outweighs the consequences. Luminol is irreplaceable in the forensics field as a blood detecting reagent (Quickenden et al., 2001). Even though over a long period of time, the DNA may become damaged, the luminol chemiluminescence does not last long enough for the DNA to be fully damaged (Hochmeister et al., 1999). As a medical diagnostic chemical, luminol is simply cheap and much more efficient than what already exists for modern doctors. (Robinson et al., 1999). Since luminol's discovery, it has only risen in convenience and practicality. Is luminol more efficient than other chemilumiscent substances used in forensics and medicine?
Blum, L.J., Esperanca, P., Rocquefelte, S. A new high-performance reagent and procedure for latent bloodstain detection based on luminol chemiluminescence. Can. Soc. Forensic Science Journal (2006);39(3):81-100.
Frégeau C.J., Germain O., Fourney R.M. Fingerprint enhancement revisited and the effects of blood enhancement chemicals on subsequent Profiler Plus™ fluorescent short tandem repeat DNA analysis of fresh and aged bloody fingerprints. Journal of Forensic Science 2000;45(2):354-380.
Hochmeister M.N., Budowle B., Sparkes R., Rudin O., Gehrig C., Thali M., Schmidt L., Cordier
A., Dirnhofer R. Validation studies of an immunochromatographic 1-step test for the forensic identification of human blood. Journal of Forensic Sciences 1999;44(3):597-602.
Luminescence. (2009). InEncyclopædia Britannica. Retrieved November 08, 2009, from Encyclopædia Britannica Online: http://www.britannica.com/EBchecked/topic/351229/luminescence
Robinson, J.K., Bollinger, M.J., Birks J.W. Luminol/H2O2 chemiluminescencedetector for the analysis of nitric oxide in exhaled breath. Analytical Chemistry 1999;71(22):5131-5136.
Rose, A.L., Waite, T.D. Chemiluminescence of luminol in the presence of iron(ii) and oxygen: oxidation mechanism and implications for its analytical use. Analytical Chemistry 2001;73(24):5909-5920
Quickenden, T.I., Cooper, P.D. Increasing the specificity of the forensic luminol test for blood. Luminescence 2001;16:251-253.