1. A Usable Framework for Future Biosensors

The BEADS system establishes a complete workflow for transforming receptor-based biosensing into a deployable format.
Future teams can reuse our plasmid constructs (LexA-based Y2H system) as templates for new targets simply by swapping the ligand-binding domain, but what truly makes the project reusable is that it is physically preservable—our yeast cells can be stored and rehydrated outside a laboratory environment.
This enables other teams to move beyond proof-of-concept and into field-ready implementation, an area that has long limited synthetic biology projects.

2. Standard Operating Procedure (SOP) for Yeast Storage and Distribution

We created a comprehensive SOP for the preservation of genetically engineered yeast using freeze-drying (lyophilization).
It is specifically designed to maintain viability, plasmid stability, and biosensor function during storage, transportation, and community use.

Purpose

Step Overview

1. Cultivation

• Grow yeast in YPD or SD medium at 30 °C with shaking until OD₆₀₀ ≈ 1.0–1.5
• Goal: achieve high metabolic activity while preserving plasmid expression.

2. Harvesting

• Centrifuge at 4000 rpm for 10 min; wash twice in sterile PBS or distilled water.
• This step removes residual media that could interfere with drying.

3. Addition of Protective Matrix (SMM)

• Add protective medium containing:
• skim milk powder
• 4.5% maltose
• 18% maltitol
• Function: protein–sugar matrix that cushions cells, stabilizes membranes, and preserves protein structure during drying.
• Optional additives: 5–10% trehalose or glycerol for additional membrane stabilization.

4. Pre-Freezing

• Rapidly freeze samples at −40 °C or in liquid nitrogen to minimize ice-crystal damage.
• Freeze evenly in small aliquots for consistent drying performance.

5. Lyophilization (Freeze-Drying)

• Conduct primary drying under vacuum at −40 °C → −10 °C, then secondary drying up to 20 °C to remove residual moisture.
• Duration: 24–72 h depending on sample size and equipment.

6. Sealing and Packaging

• Seal vials or bags under vacuum or nitrogen.
• Recommended packaging:
• Aluminum foil pouches for field distribution
• Glass vials for lab storage
• Add desiccant sachets to maintain dryness.

7. Storage Conditions

8. Rehydration for Use

• Add ~1 mL sterile water or testing medium.
• Mix gently and incubate at 25–30 °C to recover activity.

3. Why This SOP Matters to Future Teams

This SOP bridges the engineering gap between lab research and field usability. Most synthetic biology projects remain confined to controlled conditions because live cells degrade quickly. Our system makes engineered yeast portable, long-lived, and field-deployable.
Future iGEM teams can immediately:

• Reuse our SMM matrix recipe and drying procedure to preserve their own engineered yeast (biosensors, probiotics, logic circuits).
• Adapt the procedure to different protective agents (trehalose, PVP, sorbitol) using our comparison tables to match their strain and cost constraints.
• Package yeast into sealed tubes or well plates for classroom kits, public demonstrations, or international shipment without relying on cold-chain transport.
• Validate biosensor function post-storage using our recovery and rehydration steps to ensure accuracy after months of dormancy.

This is not a theoretical method—it is a deployable infrastructure-level contribution that allows biological sensors to exist outside the lab bench.

4. Creating a Global Standard for Accessible Bio-Detection

Our freeze-drying procedure, protective medium formulation, and packaging design provide a blueprint for reproducible biosensor distribution. Teams working on water safety, environmental toxicity, or pathogen detection can now focus on detection specificity while adopting our validated storage and preservation framework.
The BEADS SOP transforms how synthetic biology projects can be shared, tested, and experienced. It allows future teams to mail yeast kits to schools, NGOs, or research partners safely, creating an open, collaborative ecosystem where biological tools are as distributable as electronics.

5. Packaging

A major part of our project was developing practical, fieldable packaging formats that make our yeast-based BPA detection system usable outside of a laboratory. The packaging is directly linked to our freeze-drying (lyophilization) SOP, which allows the engineered yeast to remain stable, transportable, and ready for rehydration.
Our goal was to make biological testing accessible to everyday users—parents, students, and community members—without requiring specialized equipment. All our proposed formats use lyophilized yeast pellets with embedded protective agents and nutrients, sealed to prevent contamination and moisture absorption.

1. Outdoor Kit – Cartridge Tube with Dropper

This design is the most immediately achievable version of our system. A transparent 1.5–2 mL cartridge tube contains the freeze-dried yeast pellet and nutrients. Users collect a small amount of water (around 1 mL) using the provided dropper and add it directly into the tube.
After several hours at ambient temperature (around 25–30 °C), the rehydrated yeast begins sensing BPA.

• Result interpretation: blue coloration = BPA detected; clear = no BPA.
• Advantages for future use: simple, inexpensive, and portable.
• Storage: vacuum-sealed in foil or plastic to maintain dryness.
  This version demonstrates how lyophilized biosensors can be distributed for field testing and citizen science projects.

2. Home Kit – Pregnancy Test–Style Stick

This is a conceptual prototype for future development.
A disposable plastic stick holds a sealed reaction chamber preloaded with lyophilized yeast, nutrients, and a colorimetric substrate.
The user adds a few drops of water into the chamber and seals it again. After several hours, if BPA is present, the result window turns blue.
Although this design is not yet validated, it shows how our yeast system could evolve into a simple household BPA test, similar to existing consumer diagnostics.

3. School Lab Kit – Transparent 12-Well ELISA Plate

Designed for education and outreach, this format uses a 12-well transparent plate (3×4 layout) preloaded with lyophilized yeast pellets in each well.
Each well can contain a different reporter strain or control.
Students pipette ~1 mL of water sample into each well, rehydrating the yeast. After overnight incubation, wells expressing lacZ (with X-gal substrate) turn blue.

• Use case: classroom experiments and demonstrations.
• Advantages: reusable layout for comparison between samples, safe for students under standard lab conditions.
  This kit allows schools to use our system to teach environmental awareness and basic synthetic biology concepts.

4. Storage and Protection

All of our packaging designs follow the same storage logic defined in our freeze-drying SOP:

• Protective matrix: 9% skim milk powder, 4.5% maltose, and 18% maltitol.
• Sealing: vacuum-packed or nitrogen-flushed containers to prevent moisture and oxidation.
• Recommended containers:
• Aluminum foil pouches for light and moisture protection
• Glass vials for lab-scale storage
• Vacuum-sealed bags for bulk distribution

These materials ensure long shelf life (6–24 months at room or refrigerated temperature) and preserve yeast viability without refrigeration.

5. Future Application

Our packaging system shows that biological sensors can exist as stable, distributable products.
Future teams can reuse our approach by:

• Embedding their own engineered yeast or bacterial strains in the same lyophilization-protection mixture.
• Adopting the cartridge, stick, or plate formats to suit different audiences.
• Following our sealing and storage steps to maintain viability and safety.

By designing packaging that connects directly to a validated preservation method, we provided the iGEM community with a realistic model for bringing biosensors out of the lab—making them testable, teachable, and usable by anyone.

6. What We Ultimately Bring

Our contribution extends beyond a single BPA detection system. We deliver a standardized storage and logistics framework for living biosensors—something the iGEM community can immediately use to turn proof-of-concept ideas into real, accessible solutions.
By defining exactly how to preserve, ship, and reuse engineered yeast, we make biological sensing practical for classrooms, citizens, and scientists anywhere in the world.