Evaporative Drying in a Desiccator Jar (for Cellular Reagents)
Lyophilisation-free method for drying bacterial cell aliquots into room-temperature-stable reagent format, using a sealed desiccator jar with calcium sulfate pellets and a static 37°C incubator. The core innovation making cold-chain-free enzyme distribution feasible at community-lab scale (per Bhadra et al. 2021 PLoS ONE, CC-BY 4.0). Written for a novice audience.
Version History
Version 0.1.1 Viewing Latest
Effective: 2026-04-20All `procedure N` references converted to Markdown hyperlinks pointing at https://librebiotech.org/?action=show&id=N — enables in-app click-through to referenced sibling procedures. Text content otherwise preserved.
Version 0.1.0
Effective: 2026-04-20Initial release. Atomic technique supporting procedure 59 (OpenTaq Cellular Reagent Production). Drawing on Bhadra et al. 2021 PLoS ONE (CC-BY 4.0, full attribution preserved via references and EXTERNAL_URL). Procedural content written fresh for novice audience; parameters and timing drawn from the paper's specification.
Procedure Details
- PC1 / CL1 containment required when drying GMO cells. The heat-inactivation step (separate technique) is what makes the dried product safe to distribute outside the containment facility; pre-heat-inactivation cells are still viable GMO.
- Hot incubator. 37°C is mild but burns are possible from prolonged contact with internal surfaces.
- Sharp tool warning. Using an 18-gauge needle to punch holes in PCR cap lids: steady hand, always push away from yourself, use a firm surface.
- Hot glue / sealing materials. Allow cool before handling; avoid skin contact with molten glue.
- Desiccant dust. Calcium sulfate pellets can crumble; avoid inhaling dust. Work in a ventilated area.
- Cross-contamination. Do not mix this jar with food, other unrelated cultures, or heavily-handled benchwork. This is a clean drying operation; treat accordingly.
What you need ready:
- Desiccator jar (~118 mL sealed plastic or glass jar with lid). New or thoroughly cleaned + 70% ethanol wiped + dried.
- Fresh or regenerated calcium sulfate pellets (Drierite 8 mesh or similar). Regenerate by baking at 200°C for 2 h, cool in sealed container before use. If pellets appear pink/purple, they're saturated — regenerate.
- Upstream cell suspension (for LibreBiotech procedure 59: concentrated BL21(DE3)/pATetO-Taq in 1X PBS at OD600 6.0–7.0). Prepared fresh; do not store on ice more than 30 min before aliquotting.
- 0.2 mL 8-tube PCR strip (standard, with individual caps — not flat cap lids).
- 18-gauge needle (larger-bore needles work too but give more hole area and risk faster contamination entry). Single-use preferred; sterile if possible.
- P10 pipette + filter tips for 3 µL aliquots.
- Benchtop incubator at 37°C static — dedicated to this operation if possible (contamination risk from shared incubators).
- Hot glue gun + glue sticks OR clear adhesive tape, for sealing post-drying.
- Labels and marker with batch lot number, date, contents.
- A sealed storage container (another desiccator or airtight box) with fresh desiccant, for post-drying storage.
Mental model: you're removing water from the cell aliquot while the enzyme inside stays active. The desiccant absorbs the water vapour; the cap hole provides a controlled egress. Too little airflow (no hole) and it won't dry; too much airflow (wide open tube) and it dries unevenly and risks contamination.
- Setup (15 min): load desiccant, label strips, prepare needle.
- Aliquotting (15–30 min per batch): 3 µL per well × 8 wells × 2–3 strips.
- Hole-punching (5 min): one hole per tube cap.
- Drying (24–48 h, hands-off): static 37°C incubator.
- Sealing + labelling (10 min): hot glue or tape; label.
- Heat inactivation (10 min): 60°C, separate procedure.
- Total active time: ~45–75 min spread across 2–3 days.
-
Micropipette
Liquid handling
Specs: P10 with filter tips
For 3 µL aliquot dispensing -
Biosafety cabinet
Safety
Specs: Class II Type A2 or equivalent
For aliquotting; PC1 required -
Desiccator jar
Storage
Specs: ~118 mL sealed plastic or glass
Reusable; clean between batches -
Benchtop incubator
Thermal regulation
Specs: 37°C static, ≥5 L chamber
Dedicated if possible to avoid contamination -
Heat block
Thermal regulation
Specs: 60°C capable for heat inactivation
For post-drying heat inactivation step
-
Drierite 8 mesh
(W. A. Hammond Drierite) Desiccant
Qty: 60 mL per jar
Calcium sulfate pellets; regenerate at 200°C × 2h before reuse -
0.2 mL 8-tube PCR strip
PCR tube strip
Qty: 2-3 strips per jar
Individual caps required (not flat lid strips); fresh per batch
Protocol Parameters Captured per-assay on each run; exported as ISA-Tab Parameter Value columns
| Name | Type | Required | Default | Unit | Description |
|---|---|---|---|---|---|
desiccant_amount_mL |
number | — |
60
|
milliliter (UO:0000098) | Volume of calcium sulfate desiccant per jar. 60 mL (half of ~118 mL jar) is standard. Too little desiccant = incomplete drying; too much = no room for tube strips. |
incubation_temp_c |
number | — |
37
|
degree Celsius (UO:0000027) | Static incubator temperature during drying. 37°C is the paper's specification. Higher (42°C) accelerates drying but risks enzyme denaturation in particularly fragile constructs. |
drying_time_hours |
number | — |
24
|
hour (UO:0000032) | Initial drying duration. Check at 24 h; extend if wet; typical completion is 24–48 h depending on ambient humidity. |
cap_hole_gauge |
number | — |
18
|
— | Needle gauge used to punch cap holes. 18-gauge standard. Smaller gauges (e.g. 21) slow drying; larger (e.g. 14) risk contamination. |
aliquot_volume_ul |
number | — |
3
|
microliter (UO:0000101) | Volume of concentrated cell suspension per PCR tube well. 3 µL is the paper's specification for Taq. Smaller aliquots (1–2 µL) dry faster but yield fewer reactions; larger (5 µL) may not dry completely. |
Procedure Steps (Version 0.1.1)
Prepare the desiccator jar. Clean with 70% ethanol, allow to dry. Fill half the jar volume (~60 mL) with fresh or freshly-regenerated calcium sulfate pellets. Do not overfill — the tube strips need airspace above.
Retrieve your upstream concentrated cell suspension (from procedure 59 or equivalent). The suspension should be at OD600 6.0–7.0, in cold 1X PBS, prepared within the past 30 minutes.
Vortex the suspension briefly (2–3 seconds) to ensure even distribution of cells. Cells rapidly sediment in dense suspensions; measure OD600 after mixing if it's been more than 5 minutes.
In the biosafety cabinet, aliquot 3 µL of the suspension into each well of a 0.2 mL 8-tube PCR strip. Work through the strip systematically: well 1 → well 8. Use a P10 with a filter tip, changing tips only if you contact the tube wall (not between wells).
Repeat for a second and (optionally) third PCR tube strip — each 50 mL upstream culture typically yields 2–3 strips (16–24 aliquots total).
Cap each tube firmly. Make sure caps are FULLY seated — partial closure risks the cap popping off during drying.
Using an 18-gauge needle, punch a single small hole in the top of each cap. Work on a firm, non-slip surface, and punch AWAY from your other hand. One hole per cap is sufficient; more holes speed drying but increase contamination risk.
Place the tube strips into the prepared desiccator jar. Position them horizontally across the jar, above the desiccant layer — the cap holes should be oriented upward to let moisture escape.
Close the desiccator jar lid firmly. The sealed environment forces water vapour into the desiccant.
Transfer the jar to a 37°C static benchtop incubator. Do NOT use a shaking incubator — agitation disturbs the drying and risks tube-strip displacement.
Incubate for 24 hours. After 24 h, open the jar briefly and inspect a sample well. If fully dry, proceed to step 12. If residual moisture is visible, return to incubator for another 24 h.
When fully dry, remove the jar from the incubator. Allow to cool to room temperature for 10 min before opening (reduces condensation from the temperature drop).
Seal each tube cap hole. Option A: use a hot glue gun to apply a small drop of hot glue over each hole, allowing ~2 min to cool per strip. Option B: apply a small square of clear adhesive tape across the tops of the caps. Hot glue is more robust; tape is faster.
Label each strip with a cryo-safe marker: batch lot number (format: OT-YYYYMMDD-NN), date dried, contents (e.g. 'OpenTaq cellular reagent'), and storage conditions.
Heat-inactivate the sealed strips using the LibreBiotech heat-inactivation technique procedure: 60°C × 10 min in a dry heat block. This step inactivates any residual viable GMO cells while preserving Taq enzyme activity (Taq survives to >95°C).
Perform activity QC on one randomly-chosen tube per batch: rehydrate in standard PCR master mix with positive-control template, run amplification, verify band at expected size. Discard entire batch if QC fails.
Transfer QC-passed strips to a storage container — another sealed desiccator jar with fresh desiccant, or an airtight box lined with fresh Drierite pellets. Store in a dark cabinet at room temperature (20–25°C).
Record the batch in LibreBiotech: Process record with procedure_version, Sample records per strip with lot-number annotations, Assay record with activity QC result and gel image, storage location annotation on each Sample.
Expected outcome. Sealed PCR tube strips containing dried bacterial residue at the bottom of each tube (small brown-ish ring or film). The tube should visibly appear empty of liquid; all moisture evaporated into the desiccant. Typical yield: 2–3 strips (16–24 single-use aliquots) per 50 mL upstream culture.
Visual QC. Each well should be completely dry — no residual droplets, no sheen of moisture on the tube walls. Wells that aren't fully dry go back into the jar for another 24 h; partial drying leaves moisture that encourages microbial regrowth on rehydration.
Storage. In a sealed container with fresh desiccant, at room temperature (20–25°C), in a dark cabinet. Shelf life at room temperature is ≥2.5 months per the reference paper; refrigerated storage extends this to months more.
Rehydration for use. Add PCR master mix directly to the dried well; the enzyme rehydrates into the reaction volume. No pre-rehydration buffer needed. The dried cells lyse during the first PCR denaturation step (~95°C), releasing Taq.
Activity QC (mandatory, per batch). Rehydrate one tube with a standard PCR master mix and positive-control template. Run a standard amplification. Confirm a clear band at the expected size; confirm no band in the no-template control. Discard the entire batch if activity QC fails.
Troubleshooting.
| Symptom | Likely cause | Fix |
|---|---|---|
| Wells still wet after 48 h | Desiccant saturated, high ambient humidity | Regenerate or replace desiccant (bake 200°C × 2 h); try a smaller jar / more desiccant ratio |
| Active reagent in some wells, not others | Cap hole seal failed on individual wells; uneven aliquot mixing | Recheck hot-glue / tape seals; re-vortex upstream suspension before aliquotting; track which wells fail to identify the aliquot-order issue |
| Visible mould on dried pellet | Contamination during aliquotting or drying | Discard batch; remake with fresh materials; verify incubator is clean |
| All wells have weak amplification | Upstream induction failed; cells dried without enzyme expressed | Retest upstream culture by SDS-PAGE if possible; verify aTC stock is fresh; remake from fresh transformant |
| Strong PCR in NTC | Cross-contamination during aliquotting or sealing | Dedicated pipettes + filter tips; check glove hygiene; remake batch |
References
- Bhadra S, Nguyen V, Torres J-A, Kar S, Fadanka S, Gandini C, Akligoh H, Paik I, Maranhao AC, Molloy J, Ellington AD (2021). Producing molecular biology reagents without purification. PLoS ONE 16(6):e0252507. DOI Link paper
- LibreBiotech procedure 59 — OpenTaq Cellular Reagent Production (parent use case for this technique). Link protocol