A presumptive test is a chemical test performed at the scene of a crime that can indicate the presence of a body fluid and is used as a first screening of suspected evidence.

They provide a rapid initial assessment that allows for quick indications of present evidence. Additionally, they are more cost-effective than confirmatory tests, making them practical for sites requiring multiple screenings.

The presumptive test involves hydrogen peroxide (H2O2) and the hazardous chemical leucomalachite green (LMG). Due to its hazardous nature, the storage and usage of LMG require extra precaution. However, the current test design puts our CSI in unwanted exposure to the chemical.

ChemSafe is a dispenser that offers the CSI a one-handed solution, improving the usability of presumptive tests. It encapsulates all fumes of LMG in a closed system during storage and dispensing with precision to minimize exposure to LMG.

ChemSafe

A dispenser that offers the CSI a one-handed solution that improves the usability of presumptive tests, encapsulating all fumes of leucomalachite green (LMG) in a closed system during storage and dispensing with precision to minimize exposure to LMG

Introduction:

As a crime scene investigator (CSI), it is common practice to perform "presumptive tests". A presumptive test is a chemical test performed at the scene of a crime that can indicate the presence of a body fluid and is used as a first screening of suspected evidence. If the test is positive, it is sent to the National Forensic Center (NFC), which can provide an accurate result.

Though presumptive tests are never accurate enough to conclude the presence of body fluid on their own, they have many benefits. They provide a rapid initial assessment that allows for quick indications of present evidence, they are more cost-effective than confirmatory tests which makes them practical for sites requiring multiple screenings, and the test is designed to be portable, enabling it to be used in the field.

Working together with the Swedish CSI, it was identified that there were some drawbacks with the presumptive tests as they are designed today. The two chemicals used for the detection of blood are leucomalachite green (LMG) and hydrogen peroxide (H2O2). LMG is hazardous and has the chemical qualities of germ cell mutagenicity, carcinogenicity, reproductive toxicity, and specific organ toxicity for the thyroid, liver, and urinary bladder. Therefore, the storage and usage of LMG should be handled with precaution.

Current pain points:

The chemicals are prepared at the CSI lab and kept in two small plastic containers with lids that are opened at the crime scene whenever a presumptive test is needed.

Opening the lid of the container with LMG exposes the CSI to the hazardous chemical, and both chemicals deteriorate whenever the lids are open.

Both of the containers also expand when the chemicals are exposed to heat, causing the chemicals to occasionally leak into the DNA bag. When this occurs, the hazardous LMG reeks from the bag during storage.

The test is cumbersome because it requires a designated workspace for preparing the chemicals. In some scenarios, a table is positioned near the scene where the test is conducted. However, CSIs often encounter challenging work environments such as rugged terrain or confined spaces, where equipment must be carried. In some situations, the chemicals are instead prepared on a sheet of paper on the ground.

Solution:

ChemSafe is a dispenser that offers the CSI a one-handed solution for presumptive tests, encapsulating all fumes of the LMG in a closed system during storage and dispensing with precision to minimize exposure to LMG. The chemicals are kept in refillable membrane-sealed pressure vessels, prolonging the expiry date of the two chemicals. These pressure vessels are connected to a check valve syringe that is designed to eject one small drop, 14µl, of the pressurized chemicals when the buttons are pressed, resulting in minimal exposure to LGM.

When stored in its durable case, the dispenser's two needles penetrate an additional membrane, sealing off the syringe system and ensuring safe storage.

When the pressure vessels are refilled at the police station, a sticker is added. This sticker includes the date when the chemicals were tested and approved, as well as the expiry date. Additionally, the sticker contains a QR code that connects the device to the responsible CSI. It covers the split line as a means of ensuring quality.

The compact design makes it easy for CSIs to safely store it in their DNA bags, significantly reducing exposure to LMG. Additionally, it offers versatility for various work environments and helps preserve the quality of the chemicals.