Chelex DNA Extraction for Citizen Submitters (Kitchen Edition)
Kitchen-grade adaptation of lab-standard Chelex-100 DNA extraction (Walsh, Metzger & Higuchi 1991). Designed for citizen contributors performing BSL-1 extractions at home with sous-vide / kettle-bath / stove thermal paths, gravity settling (no centrifuge), and plastic disposable transfer pipettes. Yields PCR-ready DNA template from small tissue samples (~20 mg) for citizen-science mislabelling studies and similar audience-contribution pipelines. Derived from procedure 71 (lab-grade Chelex) with kitchen-safe equipment substitutions. Not a clinical or regulatory-grade assay.
Procedure Details
- BSL-1 only. Only work with food you would eat. Not for human or clinical samples.
- Hot water caution. Boiling water baths + screw-cap tubes under pressure can eject material on opening. Use tube racks or heat-resistant tongs; never place face over a just-opened hot tube.
- Proteinase K (if used): inhalation of powdered forms can trigger allergic sensitisation. Liquid form with gloves is adequate.
- Chelex-100 is inert and non-toxic; do not ingest.
- Standard kitchen hygiene. Wash hands + surfaces before and after. Treat like making a risky cake.
Sample specification. ~20 mg tissue (rice-grain size, ~3 mm cube) per sample. Raw or sashimi-grade preferred. Cut into 3–5 smaller fragments for better lysis surface area.
Chelex working suspension preparation (one-off, lasts ~500 extractions). 950 mL distilled water + 0.4 g table salt + 50 g Chelex-100 resin in a clean jar. Shake/stir. Label "5% Chelex suspension" with date. Stored at room temperature. Suspension settles fast — shake vigorously for 10 seconds before each use.
Tube labelling. Each sample gets a labelled 1.5 mL or 2 mL screw-cap microcentrifuge tube. Write the sample ID on both the cap and the side in permanent marker.
Thermal equipment. Any of: (a) sous-vide immersion circulator — easiest; (b) slow cooker on "keep warm" + thermometer — verify 55–62 °C; (c) pot of water on stove + thermometer — manual temperature management. All three work.
- Active work: ~30 minutes per session.
- Total elapsed: ~1 hour (includes two incubations).
- When to extract: same day as sample collection ideally. Day-after fine if refrigerated. Do not leave raw fish on the counter.
- Chelex extract stable at −20 °C for weeks; ship ambient-post (DNA-in-water stable at room temperature for 7–14 days).
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Plastic transfer pipette (disposable)
Liquid handling
Specs: 3 mL Pasteur-style, graduated preferred
Fresh pipette per transfer operation. Precision within ±50 µL is acceptable for Chelex extraction. -
Digital thermometer (probe)
Measurement
Specs: Food-grade penetrating, ±1 °C
Optional if sous-vide is used. Required for slow-cooker and stove thermal paths. -
Freezer (−20 °C)
Storage
Specs: Domestic kitchen freezer
For extract storage. -
Kitchen kettle
Thermal regulation
Specs: Electric or stovetop, vigorous boil
For 95–100 °C bath. Alternative: pot on stove. -
Sous-vide immersion circulator
Thermal regulation
Specs: Temperature-controlled 55–60 °C
Primary thermal path for 56 °C incubation. Alternatives: slow cooker on 'keep warm' + thermometer, OR stove + thermometer + pot.
-
NaCl
Chemical
Qty: 0.4 g
For one-off Chelex suspension preparation. Iodised or non-iodised fine. -
Microcentrifuge tube
Consumable
Qty: 2 each
1.5 mL or 2 mL screw-cap. Must be heat-rated — snap-cap or medicine tubes may crack in boiling water. Fresh tube per sample. -
Proteinase K
Enzyme
Qty: 5 µL
20 mg/mL liquid form (NEB P8107S or equivalent). Optional; extend incubation to 60 min without. -
Chelating resin
Reagent
Qty: 200 µL
5% w/v Chelex-100 suspension (Bio-Rad 142-1253 or generic equivalent) in distilled water with trace NaCl. Shake vigorously before pipetting — resin settles fast. -
Nuclease-free water
Reagent
Qty: 950 mL
For one-off Chelex suspension preparation (makes ~500 extractions). Supermarket distilled water fine.
Procedure Steps (Version 0.1.0)
Label a 1.5 mL or 2 mL screw-cap microcentrifuge tube for each sample on both the cap and side with a permanent marker.
Transfer ~20 mg tissue (rice-grain size, ~3 mm cube) to the labelled tube, cutting into 3–5 smaller fragments with clean scissors or a knife. Rinse and wipe tools between samples to avoid cross-contamination.
Shake the 5% Chelex-100 suspension jar vigorously for 10 seconds (resin settles fast). Immediately dispense ~200 µL of the shaken suspension into the tube using a disposable plastic transfer pipette.
If Proteinase K is available: add 5 µL (~1 drop from a small transfer pipette). If unavailable, proceed without — extend the next step to 60 minutes.
Close the tube tightly. Tap gently to mix. Do not shake vigorously.
Incubate at 56 °C for 30 minutes (or 60 minutes without Proteinase K). Sous-vide: place tubes in a sealed ziplock bag, drop into the bath. Slow cooker: rest tubes in a floater, verify 55–62 °C with thermometer. Stove: pot of water at 56 °C (verified with thermometer), remove from heat, drop tubes in with tongs or a metal strainer.
Transfer tubes to a vigorously boiling water bath (kettle, stove pot, or equivalent) for 10 minutes. Keep tubes upright; water must not enter the tube. Use tongs or a strainer.
Remove tubes carefully with tongs. Transfer to a countertop. Let stand upright undisturbed for at least 10 minutes so the Chelex resin settles to the bottom and the DNA-containing liquid forms a clear top layer.
Using a clean disposable transfer pipette, carefully draw up ~100 µL of the clear top layer, avoiding contact with the settled Chelex pellet at the bottom. Transfer to a new fresh labelled tube.
Cap the new tube tightly. Label with the original sample ID plus an 'ext' suffix (e.g. sample-001-ext). Store at −20 °C in a domestic freezer until shipping or downstream use.
Expected outcome. ~100 µL clear liquid transferred to a fresh labelled tube, stored at −20 °C. This is the DNA template, ready to ship to the bench (for citizen-science pipelines) or proceed directly to PCR.
Storage. Extracted template: −20 °C, up to several weeks. Ambient-post shipping viable for 7–14 days without cold chain.
Troubleshooting.
| Symptom | Likely cause | Fix |
|---|---|---|
| Chelex resin in top layer | Pipetted too deep; insufficient settling | Let settle another 10 min; try again with fresh pipette |
| Tissue didn't dissolve at 95 °C | Normal — DNA still released into solution | Proceed; tissue fragments in bottom are fine |
| No Proteinase K available | Extended incubation needed | Use 60 min at 56 °C instead of 30 min |
| Tube cracked in boiling water | Wrong tube type | Use proper screw-cap microcentrifuge tubes; discard sample + redo |