Sticky fingers

Reveal fingerprints with superglue

Difficulty:
Danger:
Duration:
15 minutes
Experiment's video preview

Safety

  • Put on protective eyewear.
  • Conduct the experiment on the plastic tray.
  • Superglue is very hard to wash off. Don't try this method for revealing fingerprints on any surfaces other than the Petri dish provided.
  • Avoid touching the superglue directly with your skin (fingers). It IS superglue and super sticky.
  • The vapors of cyanoacrylate are slightly toxic, avoid direct inhalation.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

The finger print did not appear. What can be wrong?

There are several reasons why the fingerprint could not be revealed.

First, make sure you did not forget to leave a fingerprint on the inside of the Petri dish lid. Perhaps wanting to quickly become a true crime scene investigation expert, you just lost sight of this small but important detail.

Second, make sure that the Petri dish is closed tightly. If the container with cyanoacrylate vapors is not hermetically sealed, the concentration of monomer and water vapors may be insufficient to form a polymer layer on the fingerprint.

Third, we should try to redo the experiment using a larger amount of water and glue. Perhaps the amount of reagents was not enough in the performed experiment.

A little glue got on my hands. What should I do?

A small amount of cyanoacrylate glue on the skin should not hurt you. If you are not allergic to the substance, the worst thing that can happen is a slight irritation. However, it is best to remove the glue from the skin as soon as it dries.

If you have spilled a lot of glue, first remove its excess with paper towels, napkins or pieces of fabric. Let the remaining glue to dry, and then gently remove it. If there was hair on the skin area were the glue dropped, it will be a bit unpleasant. But alas, that is the payback for not handling superglue carefully enough.

Step-by-step instructions

  1. Fill an empty disposable cup with water.

  2. With a Pasteur pipette, transfer a couple drops of water into a Petri dish.

  3. Add a couple drops of superglue into the Petri dish, but do not mix the drops of water with glue!

  4. Take off one protective glove. Take a Petri dish cover and leave a fingerprint on it from the inside.

  5. Place the cover with the fingerprint onto the Petri dish with glue and water. Wait 5 min.

  6. Take off the cover with the fingerprint.

  7. Place the cover onto a black paper or dark fabric background. You will see the fingerprint!
Graphical step-by-step instruction

Expected result

Superglue vapors are absorbed by fats contained in the fingerprints left on the plastic Petri dish. Glue hardens promptly due to the presence of water vapors in the system. Inspect the fingerprint using a piece of dark paper or fabric.

Disposal

When finished, place a piece of paper over the superglue drop. Dispose of with household garbage.

Scientific description

What is superglue?

Superglue is a liquid compound made of cyanoacrylates which create a strong bond almost instantly. The molecules of cyanoacrylate react rapidly in the presence of other substances, most notably with water. Because some trace of water can be found on almost anything, superglue will bond immediately and tightly to almost any object. Methyl, ethyl and butyl cyanoacrylates are the most common commercially available superglue products.

cyan_en

Since cyanoacrylates react almost instantaneously when they come in contact with moisture, a small amount of an additive, usually an acid, is added to slow down the hardening process a little. To help ensure that the resulting glue is a proper consistency, silicon dioxide (SiO2), or silica, is often used as a thickening agent.

Learn more

Cyanoacrylate, or superglue, was originally discovered in 1942 by Dr. Harry Coover. However, at that time, the cyanoacrylate formulation wasn’t suitable for his project, being too sticky, and he abandoned it. The idea lay dormant until nine years later in 1951, when Dr. Coover “rediscovered” his invention. His discovery was a significant scientific achievement. The main advantage of cyanoacrylate glues is their ability to almost instantly bind parts together. Unlike most gluing compounds, the cyanoacrylate glue action is based on polymerization, rather than the gradual evaporation of a solvent. Moreover, cyanoacrylate glue is always ready to use: it is a one-component liquid mixture which doesn't require any pre-mixing of its components prior to application, as two-component epoxy glues do. In addition, the most common cyanoacrylate glue hardening agent – water – is always present in air, and therefore able to promote an instantaneous binding reaction.

How is the fingerprint revealed?

In the presence of moisture from the air, cyanoacrylate reacts with the amino acids found in the fingerprint. The cyanoacrylate molecules begin to link and form chains triggered by the water molecules. They spin around in long strands and form a strong plastic mesh of glue on the surface of the fingerprint; thus revealing a crisp pattern of the unique details of an individual fingerprint.

Learn more

An intriguing question to ask yourself is - why does a white deposit form only on the surface of the fingerprint and not on the entire surface of the item that comes in contact with the superglue vapor? Interestingly, a cyanoacrylate layer does actually form on the entire surface! However, a fingerprint contains a significant amount of amino acids and these act as a polymerization activator. The amino acids promote polymerization and make the fingerprint pattern much more pronounced and consequently much more visible.

What is water needed for?

Water is needed to initiate or start the polymerization process, i.e. the formation of long chains of cyanoacrylate monomers:

detectives_glue_polymerisation_scheme

In this case, water acts as a polymerization activator. Indeed, the reaction between water H2O and cyanoacrylate molecules allow the latter to react with the next cyanoacrylate molecule and so forth, creating a chain reaction.

detectives_glue_acrylate_water_polym

Learn more

Interestingly, cyanoacrylates remain in a stable liquid state unless they come in contact with a polymerization activator. The most common activator is water, however, there are other substances that promote polymerization. Among these are amines and alkalis such as sodium carbonate (Na2CO3, sodium bicarbonate or baking soda NaHCO3) , portland cement, and limestone (CaCO3. This knowledge has very practical applications. For example, filling the gap between two objects that require glueing with baking soda before applying superglue, promotes a fast and strong bond. This is especially effective in a dry atmosphere or at low temperatures.

Follow up

Fingerprints on plastic

Repeat the experiment, but this time leave a fingerprint on a piece of a plastic bag or on a plastic file for filing documents. Such a surface is also suitable to work with superglue!

Try to reveal a fingerprint left on aluminum foil.

For these experiments, use a Petri dish as a chamber for developing prints. Remember: to receive a quality print there should be enough vapors of superglue inside the camber.

Prints on a glass bottle

Who drank all the soda? Make your own investigation! It is easiest to conduct the experiment with a small glass bottle (0,2 l).

To reveal the prints on a small bottle, take a plastic water or lemonade bottle 2 l in volume. Carefully cut off the upper part (about 1/3 height). Don’t cut up to the end, that way it will be easier to close the chamber for revealing prints. Add a little bit of water into the bottle. On the side with no moisture, add a few drops of superglue. Now carefully put the glass bottle on which you want to reveal prints into the 2 l bottle with water and glue. Close the “chamber”. Wait for 5-10 minutes. The prints on the glass bottle are easier to see against black paper or fabric.

Compare the prints with the ones you received earlier (or the ones you got in other experiments). So who drank all the soda?

How fast does glue harden?

Let's investigate the speed of the polymerization of glue in the presence of different hardeners. For this purpose, conduct 3 parallel experiments.

Apply a few drops of glue on a transparent plastic surface (best to use a file for documents). To the first drop, add no other substances. To the second one add a pinch of baking soda, the third – a pinch of citric acid. Trace how quickly the glue hardens. Don’t forget to record the time. It is easy to check whether the glue has hardened – just poke it with an ordinary toothpick.

That's interesting!

Superglue serves detectives

A method for revealing fingerprints with cyanoacrylate vapors was first applied in Japan in 1978. Despite revealing fingerprints on smooth surfaces, this method allows for finding them in places where other methods wouldn't normally work. For example, processing with cyanoacrylate vapors followed by deposition of fluorescent powders allows for revealing killer’ fingerprints on a victim’s body within 12–16 hours after a crime took place. In the video below, you can observe how detectives perform the procedure, combining two methods at once: developing fingerprints by superglue fuming and after that – revealing them with the use of a powder.

Superglue in medical industry

Most cyanoacrylates are toxic. Prolonged exposure may cause nose and throat mucous membranes irritation from inhaling the vapors and sometimes even skin rushes from working with cyanoacrylate glues. Furthermore, cyanoacrylates are toxic not only to people. Many bacteria causing inflammation in human are also sensitive to these compounds. Nevertheless, some cyanoacrylates are just mildly toxic.

detectives_glue_octylcyanoacrylate_en

Ability to polymerize in presence of water and biologically occurring amines (including proteins) makes cyanoacrylates a promising material for gluing living tissues. Octyl-2-cyanoacrylate is used to glue together wound edges and can be handy in a first-aid kit. Besides arresting of bleeding, it also inhibits pathogen bacteria growth. Moreover, cyanoacrylates are used for arresting of bleeding in stomach and gullet. Current research focuses on cyanoacrylate formulations for even connecting layers of nerve tissue! A successful reconnection of a dissected spinal cord has already been demonstrated. Obviously, application of this technique in medicine is just a question of time.