Strawberries are a type of fruit that spoils easily, becoming highly susceptible to deterioration during storage, transportation, and sale due to fluctuations in temperature, humidity, or microbial contamination. Such spoilage not only causes economic losses, but also threatens consumer health and market confidence. Our project aims to address the challenge of detecting strawberry spoilage in a timely manner, achieving the goal of “early detection, early warning, and early intervention.”

In the biological component, we engineered bacterial strains that produce a colorimetric response to volatile organic compounds (VOCs) generated during spoilage. In the hardware component, our task was to convert this biological reaction into a visual, operable, and reproducible detection system.

This integration enables engineered bacteria to function beyond the laboratory, extending their use to real-world environments such as warehouses, vendor stalls, and transportation conditions. By channeling the gases released from strawberry piles into bacterial reaction chambers through an airflow system, users can visually assess the degree of spoilage based on color changes and take preventive actions in advance.

Our hardware system has undergone three generations of iteration, evolving from the initial laboratory prototype to a portable transportation version, gradually achieving an integration of visualization, semi-quantitative analysis, automation, and safety. This transformation allows biological design to truly move beyond the laboratory bench, becoming a practical device that can help preserve agricultural products in real-world settings, while also opening up new possibilities for the application of synthetic biology in food quality monitoring.

At the beginning of the hardware design, we conducted multiple rounds of Human Practices (HP) research. Our interviews and surveys covered strawberry consumers, vendors, wholesalers, cold-chain logistics workers, as well as scientific researchers and biosafety experts. The needs and feedback from these diverse stakeholders directly shaped our design direction.

• Consumers emphasized that freshness and safety are their primary concerns when purchasing strawberries. Many mentioned that if there were a “simple and intuitive way” to visualize strawberry quality before purchase, it would greatly increase their trust. Therefore, we established the goal of “early detection + visualization”, allowing spoilage to be detected before any visible signs appear through color-based signals.
• Vendors and wholesalers focused on the need for fast, intuitive detection that does not add extra workload. Since most of them lack professional training and cannot operate complex laboratory instruments, we defined the goal of “user-friendly, one-step operation”, ensuring the device can be easily used in market stalls and storage environments.
• Researchers and biosafety experts pointed out that any device involving engineered bacteria must have a clearly defined biosafety boundary. Based on this, we set the goal of “fully enclosed system + contact-free deactivation”, ensuring that from structural design to operational procedure, users never directly handle bacterial liquid.
• Transportation and cold-chain workers stressed that spoilage occurs most frequently during transport, where the environment is complex, power supply unstable, and vibration inevitable. Therefore, we established the goal of “mobility, shock resistance, independent power supply, and temperature compensation.”

In summary, our hardware system was designed around six core objectives:

1、Early Detection — Provide pre-warning before spoilage becomes visible.

2、User-Friendliness — Simple, intuitive, and one-button operation.

3、Multi-Scenario Adaptability — Applicable in storage, market stalls, and transportation.

4、Biosafety — Fully enclosed operation with automatic sterilization.

5、Low Cost & Reproducibility — Transparent BOM and open-source design.

6、Data Stability — Maintain consistent detection under temperature fluctuations.

These goals were not conceived in isolation, but were refined through continuous communication, validation, and feedback, ultimately guiding the three generations of hardware iterations that followed.

Need

At the early stage of hardware design, we needed to construct a basic system capable of simulating the gas flow and sampling path in a strawberry storage environment, in order to verify the device structure, airflow connections, and operational feasibility. The goal of this stage was to provide a prototype foundation for future miniaturized and automated designs, rather than performing actual spoilage detection.

Notion

Our concept was to establish a laboratory-based device for testing gas collection and circulation. It could simulate the release of volatile organic compounds (VOCs) or other gases from a pile of strawberries and, through connections between tubing, air pumps, and containers, test whether the airflow could pass smoothly through the system and maintain a controlled flow rate under sealed conditions.

Narrative (Design and Implementation)

The first-generation system consisted of two main components: a standard laboratory filtering flask and a desktop air pump.

The assembly procedure was as follows:

• A plastic tube was inserted into a strawberry pile or a simulated sample to collect gases;
• The other end of the tube was connected to the inlet port of the filtering flask, through which gases were drawn into the flask by the air pump;
• Inside the flask, a testing liquid or simulated culture medium was preloaded to observe the transfer and mixing of gases within the liquid;
• The outlet port on the opposite side of the flask was connected to the pump’s exhaust port, forming a closed airflow circuit.

Through this setup, we successfully verified several key engineering parameters, including the airflow path design within the flask, seal integrity, flow rate control, and the impact of tubing length on air pressure, providing essential baseline data for further optimization.

For the first-generation laboratory prototype, we recorded detailed videos throughout the assembly and verification process to help future teams better reproduce and understand our project.

Nuances (Limitations and Problems)

This generation mainly served to test airflow and structural design, but it still had significant shortcomings:

• Bulky size and reliance on laboratory equipment, making it unsuitable for field deployment;
• Overpowered air pump, which rapidly evacuated gas from small sample areas, preventing a stable flow field;
• Non-standardized components with poor compatibility, requiring manual adjustments that reduced operational efficiency;
• Lack of modularized safety design, still depending on manual judgment and disassembly.

Next Step (Improvement Direction)

Through this first-generation system, we confirmed the basic feasibility of the airflow design, while identifying limitations in size, portability, and operational complexity inherent to laboratory equipment. In the next stage, we planned to replace glassware with modular plastic structures, integrate an adjustable flow air pump and standardized interfaces, making the system lighter, safer, and more user-friendly, while laying the groundwork for future portability and multi-point detection capabilities.

Notion (Concept Overview)

After completing the first-generation hardware prototype, we identified several limitations in practical application. We aimed to further optimize the design so that the device would become more robust, intuitive, and effective in strawberry storage and retail scenarios. Due to our limited hardware engineering experience, we decided to seek professional advice from hardware manufacturers.

The core idea of the second generation was to transform the “engineering concept platform” of the first generation into a compact, semi-quantitative, and user-friendly integrated device for non-professional users. We designed a four-stage series of reaction units at the detection end, integrated with a built-in micro air pump and a time control panel, completing a closed-loop system with inlet/outlet anti-misconnection ports and a contact-free safety bottle on the shell.

This configuration allows the device to be easily deployed in warehouses and market stalls, providing semi-quantitative color gradient readings from strong to weak, while ensuring that the user never needs to touch any liquid or internal components, significantly reducing both operational difficulty and risk.

Narrative (Design and Implementation)

1) Structural Overview

The entire device adopts a portable box-style shell. The top panel includes five threaded tube slots arranged from left to right: the first four are detection tubes (1–4), and the last one serves as the safety bottle.

Each tube cap is equipped with a dual-channel interface: the short inlet port connects to a thin inner tube reaching the liquid phase at the bottom, while the long outlet port remains in the upper gas phase.

At the lower right corner of the panel is the time control window, beneath which are four physical buttons (Time +, Time −, Reset, Start).

Two main ports are located at the upper left: red for sampling inlet and blue for outlet, both connected to the internal manifold for quick connection.

Inside the case, a micro air pump with shock absorbers is installed. Short silicone tubes and a manifold link the pump to the four-tube module. The power supply and control board are mounted on anti-vibration brackets, with all cables fixed using clips to prevent loosening during transport.

2) Function Modules and Configuration (Summary Table)

Module	Function / Key Features
Shell & Panel	Portable box design; five threaded tube slots; red/blue main ports; time window + four physical buttons
Four-Tube Series	Creates concentration/exposure gradient; dual-channel geometry (short inlet to liquid, long outlet to gas)
Micro Air Pump	Provides stable airflow; built-in damping; short connection to manifold minimizes pressure loss
Manifold & Tubes	Internal routing: “Sampling → 1 → 2 → 3 → 4 → outlet/safety bottle”; external hoses differentiated by diameter
Control Board	Sets ventilation duration; countdown display; audible alarm on completion
Safety Bottle	Final closed disposal container; compatible with waste liquid bottle for dual protection
Injection Port	Compatible with 5 mL syringe; enables closed injection/discharge under sealed conditions

3) Airflow & Interface Design (Anti-Misconnection / Anti-Backflow)

To ensure that non-professional users cannot connect components incorrectly, we adopted a non-symmetrical port diameter system: the inlet side (sampling → device) uses a thick tube, while the outlet side (device → exhaust/safety bottle) uses a thin tube, supported by color coding (red = inlet, blue = outlet).

The four internal detection tubes are connected in shortest-path series, reducing flow resistance and dead volume.

A multi-hole sampling probe is inserted into the strawberry pile for distributed sampling, minimizing local fluctuation.

Each detection tube’s short inlet extends into the liquid phase, ensuring full gas-liquid contact, while the long outlet is located in the gas phase to minimize droplet carryover.

The airflow can either be directly exhausted or switched into a closed safety loop (see “SOP”), achieving full containment.

4) Control and Time Compensation (Environmental Consistency)

The second-generation design applies a “time-as-compensation” strategy: when ambient temperature deviates from standard conditions, the total ventilation time can be extended or shortened to maintain data comparability.

The control panel displays remaining time via countdown, with an audible alarm upon completion.

The control board supports power-off memory, allowing the device to resume with default settings.

A long-press reset function restores factory timing parameters to prevent accumulated drift during repeated use.

A Temperature–Time reference table is included in the Wiki to guide users in selecting appropriate settings under different seasonal or warehouse conditions.

To improve the precision of our time-control module under variable environmental conditions, we developed a mathematical model that simulates how temperature affects bacterial growth rate, promoter activation, and violacein synthesis.

This model, established through curve fitting and differential equation analysis, quantitatively predicts the detection time required under different temperatures — for instance, approximately 6 hours at 30 °C and 9 hours at 25 °C to achieve the same response observed at 37 °C.

5) Closed Safety Disposal (Contact-Free)

After testing, the user does not need to open any tube or touch any liquid.

By simply switching two external hoses, the user connects the outlet path to the safety bottle, then activates the recirculation mode. The liquid is gradually pushed from tube 4 → 3 → 2 → 1 into the disposal medium inside the safety bottle (optionally followed by a waste liquid bottle).

The entire process is fully sealed and unidirectional, preventing backflow, splashing, or direct contact.

6) Manufacturing & Assembly Notes (Reproducibility)

The case and front panel can be made from a standard portable box with a custom panel. Tube holders can be 3D-printed or embedded to ensure vertical alignment and sealing.The manifold should use integrated rigid connectors to minimize junction points.Tubes are pre-cut and numbered to ensure consistency.Injection ports adopt universal taper joints for compatibility with 5 mL syringes.Internal components are modularized — the pump–manifold–tube frame forms one module, and the control board–display–button system forms another.Maintenance involves module replacement rather than individual part repair, reducing downtime.

For the second-generation portable detection system, due to its structural complexity, we have prepared a highly detailed instructional video. If any part of the design seems unclear, we strongly recommend watching this video for a deeper understanding of the system’s structure and operation.

SOP (Operating Procedure)

Before field operation, the user completes pre-assembly indoors:

Inject the prescribed volume of reaction liquid into the four detection tubes via syringe ports; add disposal medium to the safety bottle and seal tightly.

Ensure the red inlet and blue outlet ports on the panel are in default positions.

At the site, insert the multi-hole probe into the center of the strawberry pile (where airflow is minimal), ensuring holes are surrounded by fruit.

Connect the thick sampling tube to the red inlet port firmly.

Power on the device and set the ventilation duration on the control panel based on ambient temperature (longer at lower temperatures).

Press Start, and the system begins countdown operation.

Air is drawn sequentially through tubes 1–4, ensuring consistent gas-liquid contact and forming a visible color gradient.

When the countdown ends, a buzzer signals completion; users may record or photograph results.

Then, switch to contact-free disposal: reconnect the blue outlet to the safety bottle, align the other tube per instructions, and restart the pump in recirculation mode.

The liquid will be pushed from tube 4 → 3 → 2 → 1 into the safety bottle until levels drop to marked lines.

Finally, power off the system, remove the sampling probe, seal the red inlet port, and store the safety bottle per protocol.

Throughout the process, the operator only handles external hoses and buttons, never opening or contacting the internal medium.

Due to the complexity of the operating procedure (SOP), we have prepared a complete step-by-step demonstration video. We encourage you to watch the video to gain a clearer understanding of our device’s working principle and operational process.

Nuances (Limitations and Problems)

Our early research indicated that the transportation phase is the most critical stage for strawberry spoilage.

To ensure our device could adapt to this context, we interviewed logistics personnel to understand their practical needs.

The feedback revealed that the current product was still not convenient enough — transport workers preferred lightweight portable devices rather than systems dependent on laboratory-like conditions.

This insight made us realize that the design must go beyond laboratory prototypes to address real transportation challenges.

Thus, portability and miniaturization became key directions for further iteration, ensuring the device could function effectively during actual transit conditions.

Next Step (Improvement Direction)

In response to these findings, we defined three major upgrade paths for the third-generation system:

• Replace fixed AC power with a mobile power source;
• Introduce an insulated box + heating pad + temperature probe system for automatic temperature control, reducing the need for manual compensation;

Incorporate in-situ UV sterilization to reduce reliance on liquid disposal media and enhance biosafety in mobile use.

Additionally, the internal manifold and tubing will be fixed on a customized support frame, further improving shock resistance and structural stability.

Need

We realized that applying the device in transportation environments required it to be more portable, stable, and resistant to environmental fluctuations during transit. This understanding led us to explore further optimization of the second-generation design to ensure better adaptability and practicality in real-world scenarios.

We brought our prototype to the School of Biomedical Engineering at Shanghai Jiao Tong University and consulted with experts in related fields. Under their guidance, we completed the final product design and integrated several additional functional modules based on actual application needs.This step ensured both the scientific robustness of our system and its real-world alignment, making the device more feasible for future industrial applications.

Therefore, the core objective of the third-generation system was to enable the detection device to operate independently, stably, and safely under mobile, low-temperature, and vibrating conditions.

Notion (Concept Overview)

The third-generation system maintained the overall “four-stage series + safety bottle closed-loop” framework but integrated the entire structure into an insulated unit.

It introduced mobile power supply, automatic temperature control, and a UV sterilization module, forming a self-powered, self-regulating, and self-protecting portable detection platform.

The conceptual focus of this generation can be summarized as the “Three Selfs”:

• Self-powered — Freed from fixed power supply limitations.
• Self-regulating — Built-in temperature feedback loop.
• Self-safety — UV sterilization replaces chemical deactivation.

Narrative (Design and Implementation)

1) Overall Structure and Shell Design

The core detection unit from the second-generation system was encapsulated inside a dedicated thermal insulation box.

The outer shell, made of high-density EVA foam composite plastic, provides excellent shock absorption and insulation.

The inner surface is lined with reflective aluminum film to reduce heat loss.

The detection module is fixed at the bottom of the box, with four detection tubes and a safety bottle arranged in a central groove.

Soft anti-vibration pads are embedded on both side walls to prevent movement during transport.

Three external access holes were added at the rear of the box:

• Power interface (connects to mobile power bank)
• Gas pathway interface (for sampling tubes)
• Temperature sensor port (connects to external temperature display)

2) Mobile Power Supply System

A high-capacity mobile power bank serves as the main energy source, supplying 5V DC to the air pump and control board through a DC converter, allowing continuous operation for 5–6 hours.

The power bank is removable and rechargeable, ensuring easy replacement.

To prevent poor contact due to vibration, anti-loosening connectors were used at the power interface, maintaining stable airflow and chip operation.

3) Temperature Control and Feedback System

To counter reduced detection efficiency caused by low ambient temperatures, we integrated a closed-loop thermal regulation system consisting of a heating pad, temperature probe, and automatic thermostat module.

The heating pad is placed beneath the detection module, while the probe measures air temperature at the box center.

When the temperature drops below 36°C, heating starts automatically; when it exceeds 37°C, power is cut off — maintaining conditions near standard laboratory levels.

An external LED temperature display allows real-time monitoring, and during transport, the system automatically adjusts within a ±2°C range.

Simulated tests confirmed that even in 5°C ambient conditions, the interior could maintain 37°C ±2°C for over four hours, ensuring stable detection performance during transport.

4) UV Sterilization Module

The third-generation system replaced the previous alcohol-based sterilization with a built-in UVC LED sterilization lamp (275 nm).

The lamp, fixed inside the upper-right corner of the insulation box, operates via a dedicated power switch.

After testing, the user simply turns off the pump and activates the UV module, which irradiates the detection chamber for 15 minutes, sterilizing both surfaces and liquids.

Advantages of this design:

• No need for flammable liquids
• No chemical residues, minimizing contamination
• Fully enclosed, contact-free sterilization process
• Can be activated during or after transport

5) Anti-Vibration and Sealing Design

To address the high risk of vibration during transportation, we implemented several design measures:

• Integrated modular mounting: the pump, manifold, and detection unit are fixed as a single structure.
• Flexible hose bends provide shock absorption.
• Foam padding protects all glass/plastic tube slots.
• Double-lock latches on the outer shell prevent accidental opening during bumps.

Operating Procedure (Transport Scenario SOP)

Before departure, the operator pre-fills liquids and installs the safety bottle under laboratory conditions, then secures the detection module inside the insulation box.

During transport, the multi-hole sampling probe is inserted into the center of the strawberry container (airflow region) and connected to the red sampling port, ensuring a tight seal.

Once the mobile power bank is turned on, the temperature control loop activates automatically.

The user sets the desired detection duration and starts the air pump via the control panel.

During operation, air flows sequentially through the four detection tubes, while the control chip handles automatic timing.

After arrival or test completion, the pump is turned off, and the UV sterilization program is activated.

The device performs sterilization and disposal while fully sealed.

As with the previous versions, we have also produced a detailed introduction video for the third-generation system, and we sincerely invite you to watch it to better understand its design and operation.

Thermal Retention Test of the Third-Generation System

To evaluate the insulation performance of our third-generation device, we placed the entire system inside a household refrigerator and monitored its internal temperature over four hours. For safety and accuracy, the initial set temperature was adjusted to 40 °C, considering the relatively large internal space and the potential temperature difference between the heating pad sensor and the actual air inside the box. When first placed in the refrigerator, the measured temperature was 39.3 °C, and after four hours, it stabilized at 37.2 °C. This result demonstrates that the system maintains heat effectively even under low external temperatures.

To ensure accurate measurement, two independent temperature probes were used: one to control the heating pad’s operation, and another inserted into the center of the insulated chamber to record the actual internal temperature.

In the accompanying figure, the left image shows the setup at the beginning of the test, while the right image shows the temperature of 37.2 °C after four hours.

Effect and Significance

The third-generation system marks a major transition from static point detection to dynamic monitoring, achieving mobility, thermal stability, and biosafety simultaneously in transport applications.

It can operate autonomously in vehicle environments, unaffected by temperature changes, power instability, or vibration, realizing true on-site applicability.

Replacing liquid sterilization with the UV module significantly improves safety and environmental friendliness.

The system achieves four major technological breakthroughs — independent operation, automatic temperature regulation, UV sterilization, and anti-vibration protection — laying a solid foundation for future automation and intelligent upgrades.

Need (Requirements and Vision)

Finally, we consulted 3D modeling experts regarding our product. We hope that the next generation of hardware can achieve automated operation, digital readout, and network-based monitoring, so that quality assessment of strawberries and other perishable foods becomes as common and reliable as using a thermometer. To achieve this, we need to integrate all functional components, and the experts provided us with valuable 3D modeling guidance, setting a clear direction for our future design.

We envision that the next generation of hardware will operate autonomously, perform digital data acquisition, and support online monitoring, making the detection and evaluation of strawberry freshness as widespread and dependable as temperature measurement.

Notion (Concept and Direction)

The core concept of the fourth-generation system is to transform the detection device into an intelligent terminal. It will no longer be a single physical detector, but a comprehensive monitoring node capable of sensing, recording, transmitting, and analyzing data. The envisioned fourth-generation hardware will feature several key upgrade directions:

Auto-switching Flow System

By integrating micro solenoid valves between the four reaction tubes, the system can automatically switch airflow channels according to preset timing, enabling periodic and multi-point detection. This means users will no longer need to manually switch tubing. The device will automatically collect samples and complete phased detection over extended periods, realizing the possibility of continuous monitoring.

Optical Reading Module

Traditional visual observation will be replaced by an optical sensing system. Each detection tube will be equipped with an LED light source and a photosensitive sensor beneath it, continuously detecting color changes in the liquid and converting them into digital signals. Through the microcontroller’s data processing unit, the system will automatically generate color variation curves and upload the results to terminal devices, achieving true quantitative detection.

Mobile App & Cloud Connection

We plan to use Bluetooth or Wi-Fi modules to synchronize detection data with a mobile app or cloud server. Users can view historical records, real-time trends, and receive automated spoilage risk levels and predicted times based on system analysis. In vehicle-based transportation, data can be combined with GPS tracking to show the real-time freshness status of each shipment, forming an intelligent cold-chain monitoring map.

Modular and Scalable Design

Future devices will adopt modular assembly, allowing the air pump, control unit, detection module, and sterilization module to be replaced independently. This will not only simplify maintenance but also enable functional expansion for various applications — such as detecting different fruits, swapping bacterial reaction chambers, or enabling multi-point simultaneous sampling.

Enhanced Biosafety Encapsulation

We plan to introduce Hydrogel Encapsulation or Microchamber Containment technologies, immobilizing the biological components within hydrogels or multilayer membranes. This design will prevent any liquid movement or leakage risks, achieving a “dry reaction” combined with single-use modular safety, ensuring a higher level of biosafety and reliability.

Future Vision and Impact

This generation of the system is no longer just about hardware optimization, but about a cross-level integration from engineering to information technology. By enabling detection results to be displayed in real time on mobile devices and analyzed automatically through cloud algorithms, our device evolves from a single-point experimental tool into an intelligent node within the food supply chain. It can collaborate with cold-chain temperature control systems for dual monitoring of temperature and spoilage signals, or connect with market management platforms to provide real-time data support.

Ultimately, we envision applications far beyond strawberries — extending to blueberries, cherries, flowers, seafood, and other freshness-sensitive products. This represents a critical step from “usable” to “sustainably usable”, combining biosensing with digital technology to create a new paradigm for food safety and supply chain management. Through automation and data integration, our hardware is no longer just a detector, but an intelligent quality-monitoring terminal. It reflects not only our team’s commitment to continuous innovation in engineering and system design, but also the potential of synthetic biology to address real-world challenges — bringing science closer to daily life, supporting industries, and safeguarding safety.

Through four generations of iteration, our hardware system has gradually evolved from a laboratory prototype to real-world applications, and further toward mobility and intelligence. The first generation verified the basic feasibility of the airflow structure; the second generation realized practical detection in storage and vendor scenarios; the third generation made the device truly adaptable to transportation environments; and the fourth generation (Future Work) envisions advancement toward automation, digitalization, and intelligent operation.

This entire process reflects our engineering philosophy of “Feasible → Usable → Easy-to-use → Intelligent.” Each generation’s improvement directly responded to Human Practices feedback, driving the system toward being low-cost, portable, safe, and data-driven.

Comparison of Four Generations

Dimension / Generation	Generation 1 (Lab Prototype)	Generation 2 (Storage/Vendor Version)	Generation 3 (Transport Version)	Generation 4 (Future Work)
Core Objective	Verification of airflow feasibility	Miniaturization & user-friendliness	Mobility & temperature stability	Automation & intelligence
Application Scenario	Laboratory testing	Storage and market stalls	Vehicle transportation	Multi-scenario coverage
Power Supply	Desktop power source	Fixed power	Mobile power bank	Low-power self-sustaining
Temperature Adaptation	None	Time compensation	Insulation box + thermostat	Intelligent temperature algorithm
Safety Measures	Manual operation, no disposal	Safety bottle (liquid disposal)	UV sterilization + anti-vibration	Dry reaction / hydrogel encapsulation
Mobility	Very low (bulky)	Medium (portable box)	High (transport adaptable)	Full (miniaturized, wearable)
User-Friendliness	Lab personnel only	Simple (buttons + syringe)	One-click + auto temperature control	Fully automatic + App display
Detection Method	Single-point colorimetric test	Semi-quantitative gradient (4-tube series)	Semi-quantitative + stable operation	Optical quantitative sensing + cloud analysis
Cost Level	High (lab apparatus dependent)	Reduced (modular plastic components)	Medium (added thermal & UV modules)	Controllable (modular mass production)
Future Value	Concept proof	Prototype for practical testing	True field application

Throughout the hardware design process, we have consistently adhered to the principle of “low cost, high reproducibility, and broad accessibility.”

When selecting materials and structural components, the team prioritized universal and easily replaceable parts, ensuring that the entire device can be reproduced in standard teaching laboratories or maker spaces with minimal difficulty.

To achieve this goal, all key functions were divided into independently purchasable modules — including the air pump, control board, power supply, tubing, outer shell, and safety module, all of which can be sourced through common commercial channels.

All design blueprints, 3D modeling files, wiring diagrams, and operation manuals will be released in an open-source format, allowing teams worldwide to replicate and improve the device under the same standardized framework.

In terms of cost control, we repeatedly tested various combinations of materials and suppliers to achieve the lowest possible unit cost while maintaining functionality and reliability.

The third-generation system (Transport Version) can already be produced at a total cost of around ¥200 RMB (≈ $28 USD) per unit, and mass production could further reduce it to ¥150 RMB (≈ $21 USD).

For the fourth-generation system (Future Work) — which adds sensing and automation modules for digital operation — the total cost is expected to remain under ¥250 RMB (≈ $35 USD).

Overall, through modularization, standardization, and open-source sharing, our system achieves a balance between low cost and high reproducibility, transforming the hardware from a laboratory-only device into a truly scalable, educational, and manufacturable engineering product.

Material Cost & Reproducibility Table (Dual Currency)

Module / Component	Function Description	Unit Price (RMB ¥)	Unit Price (USD $)	Notes
Micro Air Pump	Provides stable airflow	¥25	$3.5	Common portable USB-powered pump
Control Chip Module (with buttons & display)	Time control & logic	¥20	$2.8	Arduino or timer IC applicable
Threaded Test Tubes + Fittings (x5)	Detection chambers & safety bottle	¥15	$2.1	Reusable plastic tubes
Tubing System (hose + manifold + connectors)	Airflow routing	¥10	$1.4	Cuttable silicone tubing
Power Module (Mobile Power Bank)	Portable power supply	¥30	$4.2	Standard 20,000mAh power bank
Insulation Box & Lining Materials	Temperature & vibration control	¥25	$3.5	Adapted from food insulation box
UV LED Sterilization Module	Safety sterilization unit	¥15	$2.1	UVC 275nm module
Outer Shell & Mounting Frame	Structural support & housing	¥20	$2.8	3D-printed or plastic-molded parts
Injection Interface & Accessories	Sealed injection & maintenance	¥5	$0.7	Standard 5mL syringe + tapered adapter
Total Cost (Per Unit)	—	≈ ¥165–¥195	≈ $23–$27	—

If open-source files are used to 3D-print housings and mounts, or if bulk component purchases are made, the unit cost can be further reduced by approximately 20%.

Manual Introduction

Our team, Squirrel-SouthEast, has created one of the most detailed open-source hardware manuals in iGEM, a 61-page document with more than 45,000 words. This manual is not only a record of our own project, but also a comprehensive guide for future iGEM teams who wish to reproduce, adapt, or extend our strawberry spoilage detection system.

By sharing every step — from sourcing materials and assembling modules to operating, maintaining, and troubleshooting — we aim to make our work reproducible, educational, and expandable. We hope this manual will serve as both a technical foundation and an inspiration for future teams to continue innovating in hardware design and agricultural monitoring, carrying forward the iGEM spirit of openness and collaboration.

Overview

Safety has been a central consideration throughout the design and operation of the Strawberry Spoilage Detection System.

Our device was developed under Biosafety Level 1 (BSL-1) conditions, ensuring that all operations are safe for users, the environment, and the public.

Although the current system does not involve live engineered bacteria during demonstration or testing, the hardware structure is designed to fully comply with iGEM’s biosafety standards and to prevent any possible release of biological materials.

Hardware-based Safety Measures

Safety Aspect	Design Feature	Function / Preventive Purpose
Closed-loop airflow	Sealed tubing and screw-cap chambers	Prevents any gas or aerosol leakage
Safety Screen Chamber	Final stage liquid chamber	Neutralizes or traps residual volatile compounds
UV Sterilization Module	275 nm UV LED	Enables contact-free disinfection after each operation
Non-reversible tubing design	Different inlet/outlet diameters	Prevents misconnection and accidental backflow
Low-voltage power system	Operates entirely on 5V DC	Eliminates electrical hazard and overheating risk
Temperature control module	Automatic feedback loop	Avoids overheat or damage to biological reagents

Operational Biosafety Practices

Even though most testing is performed using simulated indicator liquids instead of live cells, the operational protocol maintains full BSL-1 compliance:

• All experiments are conducted in a controlled environment with trained personnel.
• Disinfection is performed through UV exposure and ethanol wipe-downs after every cycle.
• Waste liquids are neutralized before disposal; no genetically modified material is released.
• During transport or demonstration, the device remains sealed and self-contained.

Risk Assessment Summary

Potential Risk	Risk Level	Preventive Measure
Leakage of test liquid	Low	Double sealing + vertical chamber design
Tube backflow	Low	Direction-specific connectors
Electrical overheating	Low	Temperature limit < 40°C
UV exposure	Moderate	UV safety switch + indicator LED
Improper disposal	Low	Mandatory UV disinfection + ethanol neutralization

Safety Philosophy

Our design philosophy emphasizes engineering safety through prevention — ensuring that biological risks are eliminated not by reaction but by structure.

The entire system reflects the iGEM principle that biosafety should be inherent in design, not added afterward.

Safety is not a step in our process — it is part of our design.

The Strawberry Spoilage Detection System by Team Squirrel-SouthEast represents a bridge between synthetic biology and practical agricultural monitoring. Through three generations of design and refinement, we developed a low-cost, modular, and user-friendly biosensing device that transforms complex biological detection into a portable, safe, and accessible tool for real-world use.

Looking forward, we aim to enhance automation and intelligence by integrating optical sensors, wireless connectivity, and mobile applications, building a smart freshness monitoring network with cloud-based data analysis. Ultimately, our project showcases how engineering design in iGEM can turn biological concepts into impactful, real-world tools that promote food safety, sustainability, and education.

Through design, iteration, and open sharing, we believe small devices can create large impacts.

The Strawberry Spoilage Detection System was made possible through the guidance, support, and collaboration of many individuals. We extend our heartfelt thanks to Dr. Liu Jinrong, whose mentorship and engineering insight shaped every stage of development. We also thank the 2023 iGEM Team XHD-Wuhan-China, whose open-source design provided the foundation for our second-generation system.

Our gratitude further goes to the biology and engineering teachers who offered valuable feedback on biosafety, airflow, temperature control, and sterilization design. This project embodies the collaborative spirit of the iGEM community, where knowledge and innovation are shared across teams and generations to transform ideas into practical, impactful tools.

With deep appreciation, Team Squirrel-SouthEast dedicates this work to all who guided, supported, and inspired us along the way.