Omar Khalid
Plastic is a common material that we interact with daily. Due to its smooth and non-porous nature, it is particularly good at collecting fingerprints. The duration that fingerprints stay on plastic depends on the type of plastic and environmental factors. For instance, fingerprints on rigid plastic can last for up to five years if undisturbed, while flexible plastic surfaces may retain fingerprints for a few weeks to a few months. Additionally, storage temperature plays a role in the preservation of fingerprints on plastic, with refrigeration and freezing showing slower deterioration compared to room temperature storage. The Crazy Glue method, which uses cyanoacrylate, is an effective technique for developing fingerprints on plastic surfaces.
| Characteristics | Values |
|---|---|
| Plastic surfaces that collect fingerprints | Plastic bags, smooth and non-porous plastic, glass, aluminium foil, polished metals, polished woods, china, smooth painted surfaces, hard plastic surfaces |
| Techniques to develop fingerprints on plastic | Cyanoacrylate fuming, aluminium powder |
| Factors affecting fingerprint deterioration | Storage temperature, handling and packaging |
| Duration of fingerprint preservation on plastic | Rigid plastic: up to 5 years if undisturbed; Flexible plastic: a few weeks to a few months |
| DNA extraction from fingerprints on plastic | Full DNA profile can be obtained even after 40 days |
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What You'll Learn
Plastic surfaces that collect fingerprints
Plastic is a common surface that can collect fingerprints. Fingerprints on plastic can be categorised as either patent (visible) or latent (invisible) prints. Latent fingerprints on plastic can be developed for up to 5 years if they remain undisturbed. On rigid plastic, fingerprints can last for 5 years or more, while on flexible plastic surfaces, they can be developed for a few weeks to a few months.
Plastic surfaces that are smooth and non-porous are more likely to collect fingerprint evidence. This is because latent fingerprints are formed when the body's natural oils and sweat on the skin are deposited onto another surface. Smooth and non-porous surfaces, such as plastic, provide a suitable environment for the retention of these fingerprints.
One common method for collecting latent fingerprints on plastic is by dusting the surface with fingerprint powder. If any prints appear, they are photographed and then lifted from the surface using clear adhesive tape. The tape is then placed on a latent lift card to preserve the print. However, this method may contaminate the evidence, so investigators may also use an alternate light source or apply cyanoacrylate (super glue) before using powders.
Another factor to consider is the thickness of the plastic surface. Thin-layered plastic can make it more difficult to lift fingerprints, as the process of lifting the print may remove some of the plastic material as well. Despite this challenge, DNA can still be extracted from fingerprints on plastic, even after 40 days, according to a study by Lana Ostojic et al.
In summary, plastic surfaces, especially those that are smooth and non-porous, can effectively collect fingerprints. Latent fingerprints on plastic can be developed and analysed using various techniques, providing valuable information for forensic investigations.
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The duration of fingerprints on plastic
Plastic is a common substrate for fingerprints, with more than 90% of the evidence exhibits processed by the Drug Enforcement Administration's South Central Laboratory in Texas being plastic. Plastic bags, in particular, are very good at collecting fingerprints. Plastic can be categorised in terms of porosity, and the porosity of the substrate affects the duration of fingerprints. Usually, plastic is non-porous or rarely semi-porous. Porous substrates are usually not found with plastic.
Latent fingerprints on plastic surfaces can be developed for up to 5 years. On rigid plastic, the fingerprints can last for 5 years or more if they remain undisturbed. In contrast, fingerprints on flexible plastic surfaces can be developed for up to a few weeks to a few months. The development technique used also affects the duration of fingerprints. For example, Cyanoacrylate fuming is effective on textured and smooth plastic surfaces. Additionally, proper handling, packaging, and storage temperature are critical factors in preserving fingerprint evidence. Findings from a study on the development of fingerprint impressions on plastic bags over time and under different storage temperatures indicated the importance of storing specimens in a freezer if an extended time period will elapse before processing.
Thin layered plastic makes it difficult to lift fingerprints. However, DNA can be extracted from fingerprints on plastic. A study by Lana Ostojic et al. found that a full DNA profile could be obtained even after 40 days from fingerprints.
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Techniques to develop fingerprints on plastic
Fingerprints on plastic are typically "patent fingerprints", which are visible to the naked eye and do not require any powder or chemicals for their development. However, "latent fingerprints" are not visible and require chemical development to be made visible.
One of the most common methods for collecting latent fingerprints is by dusting a smooth or nonporous surface with fingerprint powder. If any prints appear, they are photographed and then lifted from the surface with clear adhesive tape. The tape is then placed on a latent lift card to preserve the print. However, fingerprint powders can contaminate the evidence and ruin the opportunity to perform other techniques. Therefore, investigators may examine the area with an alternate light source or apply cyanoacrylate (super glue) fumes before using powders.
Another method for developing latent fingerprints on plastic is by using chemical developers. For example, ninhydrin causes prints to turn purple, which makes them easily photographed. DFO (1,2-diazafluoren-9-one) is another chemical used to locate latent fingerprints; it causes fingerprints to glow when illuminated by blue-green light. Ruthenium Tetroxide (RuO4) is another fuming method employed for the development of latent fingerprints on a variety of surfaces, including plastic.
In addition, there are some less common methods for developing latent fingerprints on plastic. One method is to use a liquid casting compound such as AccuTrans®, which can be used to lift powdered latent prints from rough, textured, or curved surfaces. Another method is to use a vacuum metal deposition technique using gold and zinc, which has shown promise for investigators.
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DNA extraction from fingerprints on plastic
Fingerprints can remain on plastic surfaces for varying lengths of time, depending on the type of plastic. On rigid plastic, fingerprints can last for up to 5 years if undisturbed, while on flexible plastic surfaces, they can be developed for a few weeks to a few months. The porosity of the plastic substrate also plays a role in fingerprint development, with non-porous or semi-porous surfaces more likely to retain fingerprints.
Extracting DNA from fingerprints on plastic is possible, and it can aid in identifying individuals and has forensic applications. A study by Lana Ostojic et al. found that a full DNA profile could be obtained from fingerprints on plastic even after 40 days. The sensitivity of DNA detection methods is crucial, as touch samples typically contain limited DNA quantities, which can further diminish during collection and analysis.
To enhance the detection of fingerprints on plastic and facilitate DNA extraction, various techniques can be employed. One approach is to use sequential treatments to improve the contrast between the fingerprint residues and the underlying substrate. For example, laser enhancement in combination with sequential treatments like CA fuming and RUVIS (reflected ultraviolet imaging system) has proven effective in visualizing latent fingerprints on black polyethylene plastic.
The choice of fingerprint visualization method can impact the success of DNA profiling. While DNA profile development is not guaranteed due to variable DNA quantities in latent fingerprints, appropriate visualization techniques can maximize both fingerprint detection and the generation of usable DNA profiles. For instance, the use of laser enhancement and sequential treatments has resulted in DNA profiles with higher peak heights and a greater number of alleles.
In summary, DNA extraction from fingerprints on plastic surfaces is a valuable technique in forensic science. The longevity of fingerprints on plastic and the ability to extract DNA provide important clues for identification and investigation. Further research and improvements in DNA recovery methods will enhance the reliability and applicability of this approach in forensic settings.
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Storage conditions for fingerprints on plastic
Plastic prints occur when a finger presses against a soft material, such as wax, soap, or putty, leaving a three-dimensional impression. Latent prints, which are invisible to the naked eye, are left by the natural oils and sweat on the skin's surface and require special techniques to develop and visualize.
The length of time a fingerprint remains on plastic depends on several factors:
- Type of plastic: Some polymers hold prints better. Rigid plastics can retain fingerprints for up to five years if undisturbed, while flexible plastic surfaces can retain them for a few weeks to a few months.
- Weather and storage conditions: Heat, humidity, and sunlight can cause prints to fade. Prints last longer when stored in cool, dark places.
- Handling: Prints deteriorate faster with more handling.
- Cleaning: Washing or wiping plastic can destroy existing prints.
Forensic teams use various methods to capture and preserve fingerprints on plastic, including:
- Powder dusting: A fine powder is gently brushed over the surface, sticking to the oils and revealing the print.
- Chemical development: Chemicals such as cyanoacrylate, ninhydrin, or DFO can be used to develop a visible print.
- Casting: A casting compound is poured over the print to create a 3D replica of the fingerprint.
- VMD (vacuum metal deposition): A thin layer of metal, such as zinc or gold, is deposited onto the plastic to visualize the ridge detail.
When storing fingerprints, it is essential to use archival-quality materials such as acid-free papers, UV-protective sleeves, and moisture-resistant containers to protect against environmental factors and ensure the longevity of the fingerprint evidence.
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Frequently asked questions
Fingerprints on rigid plastic can last for up to 5 years if they remain undisturbed. On flexible plastic, they can be developed for a few weeks to a few months.
Plastic is usually non-porous or rarely semi-porous, whereas porous materials like cloth or wood are less likely to retain fingerprints. Plastic bags, smooth painted surfaces, and hard plastic surfaces are good at collecting fingerprints.
The "Crazy Glue" method, also known as Cyanoacrylate fuming, is often used to develop fingerprints on plastic. This involves heating the chemical cyanoacrylate, which then adheres to the fingerprints. Fluorescent dye is added, and under ultraviolet or laser light, the fingerprint glows.
