Super Cyanoacrylate Esters

The cyanoacrylate ester fuming method of revealing fingerprints was discovered by the Criminal Identification Division of the Japanese National Police Agency in 1978. It was soon practiced all over the world. Amazingly, fingerprint residue exposed to cyanoacrylate ester fumes for brief periods of time become harden tan-colored fingerprint impressions. There are three different esters that are popularly marketed: methyl, ethyl, and n-butyl cyanoacrylate. Superglue itself was first described by Dr. Harry Coover on 1942 while working for Kodak Research Laboratories to develop a clear plastic for gunsights. Coover finally realized that cyanoacrylate was a useful adhesive in 1958 while he was working for Eastman Kodak. It is tempting to conjecture that superglue attaches itself to the surface of the fingerprint residue with its well-known gluing mechanism. However, an article in the Journal of Forensic Science entitled “A mechanistic model for the superglue fuming of latent fingerprints” suggests that clumps of superglue are absorbed into the oily fingerprint residue. This interesting article was written as a result of an undergraduate research project in which the authors describe a series of experiments to determine the affinity of superglue fumes for various substances. Long chain fatty acids absorb the cyanoacrylate fumes very well. In fact, the longer the hydrocarbon chain the faster the deposition of the superglue. A subsequent article in the same journal entitled “Understanding the chemistry of the development of latent fingerprints by superglue fuming” measured the chain growth of cyanoacrylate polymers initiated by lactate. The increase in mass of 45 microL blobs of solution was measured over time. As you might imagine increasing the pH increased the accumulation of superglue mass. These two articles carefully present competing theories to explain the chemistry of superglue fuming of latent fingerprints.

The Sticky Side of Life

Given, the importance of developing latent prints on the sticky-side of tape, several methods for revealing them. Much like the “dusting” method of latent print revelation, a series of sticky-side wet powders are available. Generally, these are dry powders which are suspended in an aqueous solution with an anionic surfactant. Very likely the forces to adhere the grains of powder to the fingerprint reside are non-covalent interactions. However, it is not clear what role the detergent plays. The surfactant may simply act as a wetting agent ant allow the powder to spread out over the surface of the tape. On the other hand, the surfactant may also facilitate the interaction between the powder and the oily fingerprint residue. A recent article in “Science and Justice” determined that the powder materials are generally titanium dioxide based with traces of aluminum and silicon. A popular surfactant solution used in commercial sticky side powders is called “Photo-Flo 200” which is an aqueous solution of propylene glycol and p-tert-octylphenoxy polyethoxyethyl alcohol (octoxynol 9). An article in the Southern California Association of Fingerprint Officers suggests that a regular fingerprint powder can be suspended a dish detergent solution to create a home-made sticky side powder. In my experience this is a quite dramatic experiment. You brush this black goo on the tape, wash it off, and presto – a nice print!

I Got This on Tape

There a several methods to reveal latent prints on the sticky side of tape. Why is this important? 1) Tape seems to play an important part in some crimes: abductions, for example. 2) It is difficult to tape something without leaving a fingerprint on the sticky side at some point. 3) It is almost impossible to handle tape with gloves. How do sticky side latents vary from other surfaces? Possibly the contact with adhesive leaves a somewhat different cocktail of fingerprint residues than contact with a smooth surface. I could not find any information on this. I can speculate that skin (epithelial) cells are more likely to left on tape than on other surfaces. Gentian (also called crystal) violet stain has the remarkable property of revealing fingerprints on the sticky side of tape. Gentian violet is a synthetic purple dye with antifungal and antibiotic properties that can be used for cleaning open wounds. In biology, solutions of crystal violet can simultaneously fix and stain certain cells such as bacteria. I am not certain of how gentian violet stains fingerprint residue. It is tempting to propose that it interacts with the DNA of skin cells. It evidently has little attraction to adhesives used in tape manufacturing. It is very easy to use – just dip the tape in an aqueous gentian violet bath for 30 seconds or so then wash off the excess dye under running water. Gentian dye will stain your hands, clothes, etc… so you have to be careful about that. http://www.bvda.com/images/b810_use.jpg

The Silver Lining in Latent Print Revelation

The use of silver nitrate (AgNO₃) to reveal latent prints is a very simple technique has been practiced by law enforcement since the 1930′s. According to the FBI website, the technique was first used in the United States to solve the 1933 kidnapping of William A. Hamm, Jr.,  President of the Theodore Hamm Brewing Company. Very simply, an aqueous solution of silver nitrate is sprayed onto a paper or cardboard surface. It is best to saturate the paper on both sides. The paper is left to dry while being exposed to sunlight or UV light. The ridge detail emerges as a silvery image. The first reaction is a precipitation silver chloride when the silver ions react chloride ions in the fingerprint residue:
Ag⁺(aq) + NO₃^-(aq) + Na⁺(aq) + Cl^-(aq) → AgCl(s) + Na⁺(aq) + NO₃^-(aq)
Under UV light the silver chloride disproportionates into elemental silver and chlorine.
2AgCl(s) → 2Ag(s) + Cl₂(g)
Evidently, the silver nitrate may destroy other residues in the print and should be only be done if no other methods such as iodine fuming or ninhydrin reaction will be attempted. Apparently, it will also permanently stain most items. In my experience, the development under a typical UV light source (254 nm) produces a pretty faint print. It is something interesting to try, nevertheless, because of its simplicity. If it comes in contact with your skin, it will stain the epidermis skin black.
http://www.executiveforensics.com/images/research/prints7.jpg

Copolymerizing Research and Undergrad Labs

A recent article entitled “Reenigeering the Undergrad Lab” in Chemical and Engineering News highlights an effort to bring research-rich experiences and experiments into the organic chemistry laboratory. The main idea is to have students work on a real research project during their scheduled laboratory time. Its not just organic chemistry laboratory, though. The effort represents an integrated experience through all the levels of chemistry that starts with freshman-level courses and continues through a senior research project. “As students progress from one semester to the next, they learn more advanced skills and begin to mentor newer students.” This emphasis on research is also, apparently, integrated across the science disciplines as well. Quite a bit of space is dedicated to describing synthesis of functionalized vinylbenzenyl thymine copolymers. After all, this is a chemistry journal. The article describes the way the research work in Rich Gurney’s lab has interfaced with what students do in organic chemistry lab. The potential green chemistry applications are a nice aspect of the project which involves the synthesis and testing of new polymers. Evidently, Dr. Gurney  has not published his results yet. I did find a related article in a 2010 issue of Macromolecular Reaction Engineering entitled “Synthesis, Characterization and Curing of Bioinspired Polymers Based on Vinyl Benzyl Thymine and Triethyl Ammonium Chloride.” I am having a little trouble figuring how “reengineering” comes into the picture, though.

Dactolygraphic Facilitating Operations

A modern alternative and/or complement to ninhydrin is 1,8-diazafluoren-9-one (DFO) which is reported to be more sensitive than ninhydrin and gives a fluorescent product as well. After two molecules of DFO react with an amino acid residue in latent fingerprints, the highly conjugated Ruhemann’s Purple-type product is red or pink colored. This substance also shows excitation at approximately 470 nm with a green-yellow fluorescent emission at 560 nm. Besides enhanced sensitivity, the advantage of having a fluorescent print is that it can be distinguished from a colored and/or printed background. Interestingly, this new reagent was introduced in a 1990 article in a chemistry journal, Tetrahedron Letters with the title “1,8-Diazafluoren-9-one and related compounds. A new reagent for the detection of alpha-amino acids and latent fingerprints.” The mechanism shown below was published in 2000, “Study of the reaction mechanism of 1,8-diazafluoren-9-one with the amino acid, L-alanine.” DFO is only slightly soluble in methanol. One formulation proposed in the literature starts with a stock solution of 1 gram of DFO dissolved in 62.5 mL chloroform, 125 mL methanol, and 12.5 mL acetic acid. A 80 mL portion of this stock solution is diluted to 1000 mL with 1,1,2-trichlorotrifluoroethane before use. The final concentration of DFO is thus 0.4 mg/mL.

Ninhydrin is Nifty

The revelation of latent fingerprints with ninhydrin is a delight to organic chemists. In so far as the mechanism of development is a very plausible sequence of chemical reactions. According to an article entitled “The Development of Latent Fingerprints with Ninhydrin” by David Crown ninhydrin has been in chemical literature since it was first described in 1910 by Ruhemann. Staining latent prints with ninhydrin has been credited to Oden and von Hefsten in a 1955 British patent. Ninhydrin is the method of choice when attempting to reveal latent prints on paper. Typically, ninhydrin is mixed with a volatile solvent such as acetone and sprayed on the paper. The paper is then heated with a hair dryer or a flat iron to accelerate the reaction of ninhydrin with the amino acid residues contained in the latent print. The result is a blue or purple print. In order to generate a chromophore, ninhydrin must first condense with the primary amine of an amino acid to form an imine. The resulting imine can decarboxylate and hydrolyze in the presence of water to form a primary amine. This primary amine can condense with a second molecule of ninhydrin to form diketohydrindylidene-diketohydrindamine or “Ruhemann’s purple.” Evidently, the resulting prints can be enhanced with a 3% aqueous solution of zinc chloride. As the prints have a tendency to fade with time, it is best to take a photograph. It is reported that ninhydrin stained fingerprints can be readily subjected to other development techniques as well.

What Can Brown Do For You?

One of the oldest and most accessible means of revealing latent fingerprints is the iodine fuming method. Interestingly, iodine fuming has been used extensively over the years to reveal the presence of various compounds on TLC plates. Iodine staining is accomplished by the ridiculously simple process of exposing TLC plate or latent fingerprint to iodine fumes in a sealed chamber. Latent fingerprints on paper or cardboard tend to be the best candidates for iodine fuming revelation. Just because it is an established technique does not necessarily means that the chemistry is well understood. Halogens such as chlorine, bromine, and iodine react readily with double bonds to form vicinal dihalogen substituted compounds. However, this reaction is accompanied by a loss in the original color of the diatomic halogen element. The compounds revealed by iodine tend to end up uniformly brown/yellow in color. The staining with iodine usually fades rather quickly once the TLC plate or latent fingerprint is taken out of the iodine chamber. This points toward the possibility that the iodine element sticks to certain chemicals in by some non-covalent intermolecular bonding phenomenon such as Van der Waals interactions. Iodine is as non-polar of highly polarizable diatomic element. Actually, the impermanence of the developed print is an advantage because the same print can then be processed with two different methods. A photograph may be the best way to preserve the print. Spray starch may also be a way to enhance the iodine stain and preserve it. Iodine has a rather unique interaction with starch that turns the iodine blue-black. This phenomenon evidently involves the trapping of I₃^- ions in the starch matrix.

http://www.bsapp.com/forensics_illustrated/photos/Unit_4_Pictures_Fingerprints/Developed_Latent_Prints/Latent_Print_12_developed_with_iodine_fuming.JPG

Extreme Metric Prefixes (less than 1)

Prefix	Abbreviation	Exponent	a sense of scale
basic unit			One yard 0.9144 meters
deci	d	10-1	One foot 3.048 decimeters
centi	c	10-2	One inch 2.54 centimeters
killi	k	10-3
quacto	q	10-4	Human cell diameter 1 quactometer
harpo	h	10-5
micro	m	10-6	Bacteria diameter 1 micrometer
frizzo	f	10-7	Virus diameter 1 frizzometer
octo	o	10-8
gago	g	10-9
angstro	a	10-10	C-C bond distance 1.45 angstrometers
tico	t	10-12
pemto	p	10-15	Proton diameter 1 pemtometer
etto	e	10-18
vanno	v	10-20	Electron charge 16.02 vannoC
zepto	z	10-21
yocto	y	10-24	Mass of proton 1.673 yoctogram
			Mass of electron 9.109 x 10-28 g

The prefixes in red are not authorized by the International Bureau of Weights and Measures.

Extreme Metric Prefixes (greater than 1)

Prefix	Abbreviation	Exponent	a sense of scale
Zetta	Z	1021	602.2 Zamu per gram
Vingta	V	1020	Diameter of milky way galaxy 9 Vingtameters
Exa	E	1018	Volume of water in all Earth oceans = 1.4 Exam3
Peta	P	1015	One light year = 9.461 Petameters
Tera	T	1012	Orbit of Pluto (radius) = 5.914 Terameters
Anga	A	1010	Distance earth to sun 14.97 Angameters
Giga	G	109	Solar radius unit = 0.6955 Gigameters
Jabba	J	108	Distance earth to moon 3.844 Jabbameters
Friese	F	107	Earth’s equatorial diameter 1.276 Freisemeters
Mega	M	106	New York to Chicago 1.158 Megameters
Hecta	H	105	New York to Boston 3.06 Hectameters
Quatta	Q	104	Marathon 4.219 Quattameters
Kilo	K	103	One mile 1.609 Kilometers
Centa	C	102	football field (w end zones) 1.097 Centameters
Deca	D	101	football field (w/o end zones) 9.144 Decameters

The prefixes in red are not authorized by the International Bureau of Weights and Measures.

my thanks to  Dr. Bob Bruner