Introduction

In molecular biology laboratories, nucleic acid contamination is a common and serious issue during nucleic acid-related experiments. It can lead to failed experiments, incorrect PCR amplification, amplification failure, false-positive results, or inaccurate sequencing data.

A molecular laboratory in Suzhou experienced nucleic acid contamination. Nucleic acid fragments were detected in the air, on workbenches, and especially near HEPA filter outlets.

Vantsteri provided a nucleic acid decontamination service using its self-developed Vaporized Hydrogen Peroxide (VHP) disinfection equipment, combined with specialized HVAC disinfection devices.

The laboratory covered approximately 300 square meters and included three HVAC systems. The total decontamination time was five hours.

After treatment, 120 environmental nucleic acid samples were collected from the laboratory. None of the samples tested positive for nucleic acid contamination.

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Background: Why Nucleic Acid Contamination Matters

PCR and other nucleic acid detection technologies are highly sensitive. This sensitivity is one of their greatest strengths, but it also makes molecular laboratories vulnerable to contamination.

Even a very small amount of nucleic acid aerosol or residual PCR product can cause:

• False-positive results
• Incorrect amplification
• Failed PCR reactions
• Cross-contamination between samples
• Unreliable sequencing results
• Loss of confidence in laboratory data

Because nucleic acid fragments are not the same as live microorganisms, ordinary disinfection methods that kill bacteria or viruses may not effectively degrade nucleic acids.

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Case Overview

During the site inspection and environmental assessment, Vantsteri engineers found that nucleic acid contamination in PCR molecular laboratories is commonly associated with three major factors:

1. Laboratory design defects
2. Improper operation and management
3. Incorrect decontamination methods or unsuitable disinfectants

Each factor can contribute to persistent nucleic acid contamination and repeated false-positive results.

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1. Laboratory Design Defects

Some molecular laboratories are not designed and built according to standard PCR laboratory principles.

In certain cases, existing sterile laboratories are converted into molecular laboratories by only modifying functional room layouts. However, the HVAC system may remain unchanged.

This creates a major risk because a sterile environment is not automatically suitable for PCR testing. Molecular laboratories must consider:

• Airflow direction
• Pressure differential distribution
• Functional zoning
• Personnel and material flow
• Whether return air is used
• Separation between pre-amplification and post-amplification areas

If these factors are not properly controlled, nucleic acid aerosols may spread from contaminated areas into clean areas, increasing the risk of false-positive results.

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PCR Laboratory Design Principles

1. Functional Zoning

A PCR laboratory should generally be divided into four independent work areas, moving from pre-amplification to post-amplification:

• Reagent preparation area
• Sample preparation area
• Amplification area
• Product analysis area

Instruments, equipment, consumables, and materials in each area should be dedicated to that area only. The zones should be completely independent from one another.

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2. Airflow Direction

Airflow should move from the pre-amplification area toward the post-amplification area.

Reverse airflow must be avoided, because it may carry amplified products or nucleic acid aerosols back into cleaner upstream areas.

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3. Physical Separation

Different nucleic acid testing areas should be separated into independent rooms with clear identification signs.

There should be no direct passage between functional areas. If two zones are closely connected, a pass box should be installed for material transfer.

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2. Improper Operation and Management

Nucleic acid testing technology is extremely sensitive. If laboratory personnel do not strictly follow operational requirements, nucleic acid contamination can occur easily.

Once contamination occurs, it may lead to false-positive results and reduce the accuracy of testing.

Common sources of nucleic acid contamination include:

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Positive Control Contamination

Positive controls are one of the most common sources of contamination.

When recombinant plasmids are used as positive controls, the risk of contamination can be higher. Constructed pseudoviruses or recombinant viruses used as positive controls may also generate aerosol contamination during nucleic acid extraction.

Contamination may occur when reagents come into contact with:

• Contaminated containers
• Pipettes
• Pipette tips
• Solutions
• Nucleic acid aerosols
• Work surfaces
• Operator gloves or sleeves

Once reagents are contaminated, false-positive results may continue to occur even if sample handling appears normal.

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PCR Product Contamination

PCR product contamination is especially common in laboratories using older PCR workflows.

After repeated amplification, PCR products can reach copy numbers far above the detection limit of PCR assays. One aerosol particle may contain approximately 10⁴ to 10⁶ copies of nucleic acid.

As a result, even extremely small amounts of contamination may be enough to cause false-positive test results.

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3. Decontamination Methods and Disinfectant Selection

Some biosafety cabinet models use recirculating airflow, which can contribute to nucleic acid aerosol formation and distribution.

Once nucleic acid contamination enters the internal airflow or return air system of the cabinet, it can be difficult to remove. Future samples may then become contaminated during normal operation.

Many common disinfection methods can kill microorganisms but are not effective at degrading nucleic acids.

Examples include:

• Ultraviolet light
• Alcohol
• Iodine-based disinfectants
• Glutaraldehyde disinfectants
• Quaternary ammonium compounds

These methods may have antimicrobial effects, but their ability to degrade nucleic acids is limited or inconsistent.

Hypochlorite disinfectants can degrade nucleic acids to some extent, but they are highly corrosive. They are not suitable for many precision instruments or metal components. Corrosion may also affect pipette shafts and reduce the airtight fit of pipette tips.

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Biosafety Cabinet Contamination Risk

Many exposed operations in molecular laboratories are performed inside biosafety cabinets.

For example, a Class II Type A2 biosafety cabinet typically has a minimum inflow velocity of 0.5 m/s at the front opening. Around 70% of the air is recirculated back into the work area through HEPA filtration, while approximately 30% is exhausted through the filter system.

If nucleic acid spills or leaks occur inside the cabinet, part of the contamination may enter the cabinet’s return air system. This can contaminate the next batch of samples.

Therefore, selecting the correct decontamination method is critical.

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VHP-Based Nucleic Acid Decontamination Solution

Vantsteri has studied the effectiveness of common disinfection methods for microbial control and nucleic acid degradation.

The results showed that chlorine-containing disinfectants and high-level hydrogen peroxide disinfection methods can effectively damage nucleic acids, while ultraviolet light alone cannot reliably destroy nucleic acid contamination.

For this laboratory, Vantsteri engineers used:

• Self-developed VHP disinfection equipment
• Specialized HVAC disinfection devices
• Full-room nucleic acid decontamination
• Air duct and filtration outlet treatment
• Environmental sampling verification after treatment

The combined treatment was designed to address both surface contamination and airborne contamination within the laboratory environment and HVAC system.

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Results

The laboratory decontamination was completed in five hours.

After treatment, 120 environmental samples were collected for nucleic acid testing from areas including:

• Air sampling points
• Workbenches
• Operating areas
• HEPA filter outlets
• HVAC-related locations

All 120 samples tested negative for nucleic acid contamination.

The result demonstrated that the combined VHP and HVAC disinfection approach successfully removed detectable nucleic acid contamination from the laboratory environment.

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Key Takeaways

PCR laboratory nucleic acid contamination is not the same as ordinary microbial contamination.

Effective control requires:

• Proper PCR laboratory zoning
• Correct airflow direction from pre-amplification to post-amplification areas
• Complete separation of functional rooms
• Dedicated equipment and consumables for each area
• Strict operational management
• Prevention of positive control contamination
• Control of PCR product aerosols
• Appropriate treatment of biosafety cabinets and HVAC systems
• Use of validated nucleic acid degradation methods

Traditional disinfectants may not be enough. For persistent nucleic acid contamination, professional decontamination methods such as VHP-based treatment and HVAC system disinfection may be required.

Conclusion

Nucleic acid contamination in PCR molecular laboratories can cause false-positive results, failed experiments, and unreliable testing data.

In this Suzhou laboratory case, nucleic acid fragments were detected in the air, workbenches, and HEPA filter outlets. Vantsteri engineers used a combined VHP and HVAC decontamination strategy to treat the 300-square-meter laboratory and its three HVAC systems.

After five hours of treatment, all 120 environmental samples tested negative, confirming the effectiveness of the nucleic acid decontamination process.

This case highlights the importance of proper laboratory design, strict operational management, and scientifically selected decontamination methods for PCR laboratory contamination control.