(Nanowerk Spotlight) Ensuring the safety of drinking water, food supplies, and environmental samples depends on detecting bacterial contamination before it causes harm. Traditional microbiological tests, such as culturing bacteria on plates or using polymerase chain reaction (PCR) assays, often require specialized equipment and take hours or even days to deliver results. In industries where contamination spreads quickly—such as water treatment, food processing, and healthcare—faster detection methods are essential.
Biosensors have emerged as a promising alternative, capable of identifying bacteria with high sensitivity while reducing processing time. However, many biosensors still rely on external power sources, limiting their portability and real-world applications. Additionally, the enzymes commonly used in biosensing degrade over time, reducing performance.
A new study, reported in Advanced Functional Materials (“Self-Powered Biosensor-Based Multifunctional Platform for Detection and In Situ Elimination of Bacteria”) presents a self-powered biosensor that not only detects Escherichia coli (E. coli) but also eliminates it in situ, combining enzymatic energy generation with DNA-based bacterial recognition and an antimicrobial silver ion release mechanism. This approach overcomes long-standing challenges in biosensing and opens new possibilities for real-time bacterial monitoring in the field.
At the core of this biosensor is an enzymatic biofuel cell, a device that generates electricity using biochemical reactions. Biofuel cells use enzymes to catalyze reactions at electrodes, converting chemical energy into electrical signals. When a target substance is present, the reaction produces electrons that flow through an external circuit, creating a measurable electrical output. The enzyme glucose oxidase (GOx) is widely used in biofuel cells because it efficiently oxidizes glucose, generating both electrons and hydrogen peroxide. However, enzymes tend to lose stability when immobilized on electrode surfaces, reducing their catalytic activity and shortening the lifespan of biosensors.
MOFs are crystalline materials composed of metal ions and organic molecules arranged in a highly porous structure. These frameworks have been explored as protective coatings for enzymes, shielding them from degradation while maintaining catalytic efficiency. However, previous attempts to encapsulate enzymes in MOFs often resulted in reduced activity because the rigid structure restricted substrate access to the enzyme.
The researchers in this study solved this problem by designing a hollow MOF structure, referred to as ZIF-8, which provides enzyme protection while allowing glucose to reach the catalytic site more efficiently. This modification increases enzymatic activity by 5.2 times compared to solid MOF systems. The resulting material, called GOx@hsZIF-8, retains 89% of the enzyme’s natural activity and remains stable under acidic conditions, high temperatures, and exposure to organic solvents. This structural refinement ensures that the enzyme remains functional for extended periods, making the biosensor more reliable for real-world applications.
Schematic illustration of EBFCs-based self-powered biosensor for detection and in situ elimination of E. coli based on hollow MOF nanoreactors combined with CHA amplification. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
Beyond enzyme stabilization, the biosensor incorporates a highly selective bacterial detection system. Traditional biosensors often rely on antibodies to recognize target bacteria, but these biomolecules can be expensive to produce and require strict storage conditions. Instead, the researchers used aptamers—short strands of DNA that fold into specific shapes and bind to bacterial surface proteins with high specificity.
An aptamer designed to recognize E. coli was attached to silver nanoparticles (AgNPs), which serve as both detection and antibacterial agents. To regulate when the enzyme becomes active, the researchers added a silica-based barrier, known as a “gatekeeper,” which blocks glucose access to the enzyme unless E. coli is present.
When E. coli is introduced into a sample, the aptamer binds to the bacterial surface, triggering the release of DNA fragments that unlock the silica gatekeeper. This unblocking step allows glucose to reach the enzyme, initiating the oxidation reaction that produces electrons, generating an electrical signal that confirms the presence of bacteria. As a byproduct of this reaction, hydrogen peroxide is also produced. This compound oxidizes the silver nanoparticles, releasing silver ions (Ag+), which have potent antibacterial properties. Silver ions disrupt bacterial membranes and interfere with essential cellular functions, leading to bacterial cell death. This means the biosensor does not simply detect E. coli—it actively eliminates it, reducing contamination risk in real time.
To enhance detection sensitivity, the researchers incorporated a secondary amplification mechanism known as catalytic hairpin assembly (CHA). This process involves specially designed DNA hairpin structures that, once triggered, undergo a chain reaction that amplifies the detection signal. The released DNA fragments from the aptamer-silver complex initiate CHA, which results in the formation of double-stranded DNA structures on the sensor’s electrode. These DNA structures bind to an electroactive molecule, [Ru(NH3)6]3+, enhancing the electrical readout.
The combination of enzymatic biofuel cell power generation, aptamer-based bacterial recognition, and CHA amplification allows the biosensor to detect E. coli at extremely low concentrations—down to 3 CFU/mL. This level of sensitivity is essential for early contamination detection, particularly in food safety and environmental monitoring.
The researchers conducted extensive testing to evaluate the performance of the biosensor. It was able to distinguish E. coli from other common bacteria such as Staphylococcus aureus and Salmonella, demonstrating high specificity. The sensor’s performance remained stable over multiple uses, and it retained functionality even after being stored for several days.
The team also tested the system using real seawater samples, demonstrating that it could accurately detect and eliminate E. coli in complex environmental conditions. Results showed detection accuracy between 91.06% and 101.9%, confirming that the sensor functions reliably in practical settings.
Additionally, the biosensor was tested for reusability: after five cycles, it still retained over 90% of its activity, demonstrating long-term stability. Within two hours, the bacterial count in contaminated samples dropped by 99.9%, confirming that the biosensor’s antimicrobial mechanism was highly effective.
This research represents a significant step toward multifunctional biosensors that combine detection and intervention. Traditional biosensors provide information but do not actively remove contaminants. The ability to neutralize bacteria in situ reduces the risk of secondary contamination and makes the technology more practical for applications in water safety, food processing, and clinical diagnostics. Additionally, because the biosensor is self-powered, it does not require external electricity, making it suitable for deployment in remote or resource-limited settings.
While the results are promising, the study also raises questions about scalability and long-term usability. Silver ions, while effective at killing bacteria, can accumulate in the environment, potentially harming beneficial microbes. Future research may explore controlled release mechanisms to minimize environmental impact while preserving antimicrobial efficiency. Additionally, while the aptamer-based recognition system is highly specific to E. coli, adapting the biosensor for detecting multiple pathogens would require modifying the DNA sequence of the aptamer, which could introduce complexities in manufacturing.
Despite these challenges, the study provides a compelling example of how integrating nanomaterials, enzymatic biofuel cells, and DNA-based recognition systems can create highly sensitive, self-sufficient biosensors. By combining detection and bacterial elimination, this technology could help improve contamination monitoring in food safety, water quality assessment, and medical diagnostics. The ability to generate power internally while responding selectively to bacterial presence addresses key limitations in biosensing and paves the way for future advancements in portable and real-time microbial detection systems.
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