In this episode, Mike and Bob review a few “old school” technologies that don’t use batteries. They still have a place in our arsenal, though!
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Complete Show Notes
5:05 What are Biological Immunoassay Indicators and How Do They Work?
- Biological immunoassay indicators are simply a series of tests that pick up the presence of a substance
- Their high degree of specificity results from the use of antibodies and purified antigens as reagents
- An antigen is basically anything inside a biological system that shouldn’t be there – not just chemicals, but complex proteins and other organisms
- An antibody is a protein or molecule within a body or a cell
- One part of the immune system creates the antibody and sticks it to a foreign substance – once the antibody is where it shouldn’t be, the immune system starts getting rid of any substance the antibody is attached to
7:40 What is a Handheld Assay Test?
- Immunochromatography is used primarily for biological warfare agents
- We’ve been able to synthetically create antigens that bind to specific proteins on certain organisms – handheld assay tests take advantage of that
- These tests start off with a sample going onto a sample delivery pad – this is the first step in filtering out things within the sample that aren’t necessary
- As the sample sits in the staging area, it’s slowly brought up to the conjugate release pad – this is the part of the detector that contains the antibodies, as well as a dye that allows us to see them visually
- At this point, the sample starts to move up the sample pad across a nitrocellulose membrane – this membrane has areas that are able to capture and hold the antibodies
- These areas are the little lines we see on many of the tests – if a line shows up, we have a winner!
10:10 What are the Capabilities of Handheld Assay Tests?
- Used extensively in lab settings and hospital settings for performing a wide variety of tests
- Much more limited in our world, but used to identify many of the major threats we see
- This test gives both qualitative and quantitative results, which is very helpful for our purposes
12:05 What are the Limiting Factors of Handheld Assay Tests?
- These tests are very protein specific, so you need to perform a separate test for each one of the items you’re looking for
- Time can also be a factor – some tests require at least a few minutes for the magic to happen
- It’s important to wait a minute or two in both directions – if you wait too long, you can get a false positive because the antibodies will start moving around the test strip and bind to the collection point
- A matrix effect can also cause you to see both results at once – occurs when there is a product in your sample that prevents the antibodies from sticking to the target protein
- You can avoid this by doing a 1:10 dilution factor and re-running the test – ideas is to dilute enough to reduce the effect of the non-binding agent
- Be sure to always check your control line – without a control line, you might have something in your sample that’s producing bad results
- You can also get a false positive if the substance you’re testing for is similar to what you’re testing – antibody sees a protein on an organism, but doesn’t know it’s not the organism you’re looking for
- Another false positive is referred to as the hook effect, which is what happens when too much of an antigen is added to the assay test
18:35 What are Chemical Agent Monitors (CAMs) and How Do They Work?
- Comprised of a variety of colorimetric indicators – includes colorimetric detector tubes, indicating papers (pH paper and meters), reagents, and test strips
- All of these tests use a chemical reaction to create a change in something’s (a medium’s) color – this is intentionally vague
- Types of colorimetric indicators:
- pH paper
- Used when we’re testing for acids and bases – color changes accordingly
- Some high-quality papers even indicate the specific number of the acid or base
- Basics are blue, while acids are red
- You’ll see a wide variety of pH papers on the market – some are very simple, while others are more complicated and specific
- There’s always plenty of room for human error when you’re using pH paper – judging colors with the human eye can be problematic, especially since everyone sees color differently
- pH paper strips can also get bleached out before we get a chance to read them
- Also not great when you’re dealing with dyed or dirty products since the strips will just turn brown
- Colorimetric tubes
- Colored cigarette-shaped object with sand, glass screens, cotton, etc.
- Break off the tip, put it into your pump, and pull an air sample based on the directions on the tube
- Air sample goes through a series of reagents that are typically solid
- Tube then shows you the color changes as the concentration intensifies based on the gradients on the glass (or other directions)
- Widely used in industry – pull a specific chemical to make sure you’re not dealing with any other chemicals
- Very chemical-specific, so they help you verify the readings on your meters
- Cross-sensitivities aren’t really an issue with colorimetric tubes, which is very helpful
- This method can be expensive since you have to test each substance individually – this also means you need a lot of them
- M8 paper
- Military version of pH paper for chemical warfare agents
- Dip paper in sample – colorimetric change occurs and you then compare it against three potential agents
- Largely used to detect nerve agents and blister agents
- Lots of cross sensitivities to deal with, which can be problematic
- Chip sets
- Also referred to as CMS kits (i.e. Dräger)
- Puts colorimetric tubes onto 10 or more plastic rectangles – electronic system reads the barcode on the chip and tells you exactly what to do
- Very simple and effective, but it doesn’t always work – it’s important to be careful when loading the chip into the electronic system
- Doesn’t require you to pump the colorimetric tubes, which is a big positive because it saves you time and effort
- Test strips
- Examples include Spilfyter strips, water finding strips, and chemical finding strips
- Work similarly to pH paper – take multiple samples and drop it across 5 or 6 tests
- Provides information on hydrocarbons, pH, oxidizers, nitrates, etc.
- Also includes water-finding paste, hydrocarbon-finding paste, dyes, KI paper, F paper, etc.
- Limiting factors are similar to what we deal with when using pH paper
- pH reagents
- Dip reagent into water, add red and yellow dye to create a graph indicator, overlay colors, and get your pH reading
- These are generally much more specific than a general pH strip and are often used when maintaining pools
- Limiting factors are similar to what we deal with when using pH paper
- M256A1 chemical agent detector kits
- Canadian-made kit used for the detection of blister, blood, and nerve agents
- Kit contains 12 vapor samplers, M8 detector paper, and instruction cards
- Vapor samplers are sealed in individual plastic laminated foil envelopes, used once, and then discarded
- Each vapor sampler holds five test components used in an analysis:
- Glass ampoules
- Hinged heater assembly
- Three test spots
- Hinged protective strip
- Lewisite-detecting tablet with a running tab
- The two glass heater ampoules are used with the heater assembly to detect the blister agents
- There are three labeled test spots on each sampler – each one is a different shape and made from a different material for a specific analysis
- The blister agent test spot is square and made of chromatographic media
- The blood agent test spot is round and made of a glass fiber filter
- The nerve agent spot is star-shaped and made from filter paper
- Expected color changes are printed above each test spot and take around 15-20 minutes to occur
- A protective strip is hinged to the sample over the blood and nerve agent test spots to protect them from accidental contamination
- The Lewisite detector tab is covered by a protective plastic pull-tab that must be removed before use
- False readings may occur under high temperatures and when exposed to petroleum products
- Capable of detecting chemical warfare agents in small amounts
- This test is very difficult to do properly in one shot – takes a lot of practice and training to get it right
- Cross-contamination is also a problem when using M256A1 chemical agent detector kits
- pH paper
- Colorimetric methods are seldom used as part of an integrated system for detecting and identifying chemicals – instead, they’re often used independently or to confirm a preexisting analysis
- Colorimetric tubes and pH paper comprises about 27% of the chemical detection equipment that’s used
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