(Nanowerk Spotlight) Inside a wound, a complex chemical battle unfolds. As healing progresses, the wound environment shifts between acidic and basic states, each change signaling different stages of recovery or infection. These pH fluctuations create a major challenge for medical sensors – they can mask or amplify other chemical signals, making it difficult to detect dangerous infections before they become severe.
The stakes are particularly high for detecting Pseudomonas aeruginosa, an opportunistic bacterium that thrives in wounds. This pathogen secretes pyocyanin, a toxic compound that damages surrounding tissue and helps the infection spread. Early detection of pyocyanin could allow faster intervention, but current sensors struggle to provide reliable readings as the wound’s chemistry changes.
Traditional approaches to wound monitoring have focused on measuring single markers – either tracking pH changes or detecting specific bacterial signals. But these isolated measurements tell an incomplete story. A sensor might detect elevated pyocyanin levels, suggesting infection, when the reading is actually distorted by the wound’s changing acidity. Conversely, dangerous bacterial growth might go unnoticed if pH changes mask the infection markers.
Medical researchers have long recognized this challenge but creating sensors that can reliably operate in the dynamic environment of a healing wound has proved difficult. The ideal solution would need to continuously monitor multiple chemical signals while accounting for how they influence each other. It would also need to be flexible, biocompatible, and affordable enough for widespread use.
Recent advances in materials science, particularly in carbon-based electronics and conducting polymers, have opened new possibilities for creating such integrated sensing systems. These materials can be engineered at the nanoscale to create highly sensitive detectors while remaining flexible enough for use in bandages.
A research team at Prince of Songkla University in Thailand, led by Professor Itthipon Jeerapan, has developed a novel smart bandage system that addresses this challenge through an integrated dual-sensor approach. Their wearable technology, reported in Nano-Micro Letters (“A Fully‑Printed Wearable Bandage‑Based Electrochemical Sensor with pH Correction for Wound Infection Monitoring”), combines detection of pyocyanin, a chemical signal produced by Pseudomonas aeruginosa bacterial infections, with continuous monitoring of pH levels that could otherwise interfere with accurate readings. This represents a significant advance in wound monitoring capability.
The conceptual presentation of the bandage-based sensing array for determining pyocyanin and pH in wound with a pH-correction system for infection monitoring. a Schematic illustration of the bandage-based sensor to directly monitor the wound status and photographs showing the sensors (Scale bar: 2 cm). b (1) The electrochemical sensing of pyocyanin on the porous CNT/graphene electrode. (2) Square wave voltammograms (SWVs) for detection of pyocyanin with (1–4) 0, 5, 50, and 100 μM pyocyanin on the porous CNT/graphene electrode. c (1) The electrochemical sensing of hydronium ions on the PANI/CNT composite electrode. (2) Potential-time response of the potentiometric pH sensor to various pH solutions. d Comparison of predicted pyocyanin concentrations using the traditional regression method (blue) and our proposed method (pink) for pyocyanin concentration analysis at different pH values. (Image: Reprinted from DOI:10.1007/s40820-024-01561-8, CC-BY) (click on image to enlarge)
“Our system uses a carefully engineered combination of materials to achieve its capabilities,” Jeerapan tells Nanowerk. “At its core are two specialized electrodes printed directly onto standard medical bandages: one uses a porous mixture of carbon nanotubes and graphene to detect pyocyanin, while the second combines conducting polymers with carbon nanotubes to monitor pH levels. The porous structure of the pyocyanin sensor enhances its sensitivity by increasing the surface area available for detection.”
The researchers demonstrated that traditional single-calibration wound sensors produce substantial errors when pH levels fluctuate – up to 30% under basic conditions or 11.6% in acidic environments. Their dual-sensor system addresses this through continuous pH monitoring and automated correction of infection measurements using sophisticated algorithms that analyze both square wave voltammetry and potentiometry data.
The technology showed particular promise in testing with bacterial cultures. When exposed to different concentrations of P. aeruginosa bacteria, the system could track both bacterial growth and pyocyanin production in real-time. The sensors maintained accuracy across the full pH range typically found in wounds (pH 6.5-8.5).
Critical to the system’s success is its novel material engineering. The team developed a screen-printable conductive ink combining graphene, carbon nanotubes, and calcium carbonate to create a porous sensing surface. After printing, the calcium carbonate is dissolved away, leaving a highly sensitive electrode with increased surface area. This porous structure demonstrated superior electron transfer capabilities and enhanced interaction with target molecules compared to traditional flat sensors.
The system processes measurements using partial least squares regression analysis, which enables real-time correction of pyocyanin measurements based on current pH conditions. This mathematical approach allows the system to maintain accuracy even as wound conditions change over time.
Mechanical testing showed the bandage maintains its sensing capabilities even under repeated bending and flexing, crucial for real-world use. The materials demonstrated biocompatibility in testing with L-929 mouse fibroblast cells, showing high cell survival rates that confirm their suitability for wound contact.
The research establishes new possibilities for creating more sophisticated and reliable medical monitoring devices. “Our use of readily available materials and standard screen-printing techniques suggests potential for scaling up production while keeping costs manageable,” Jeerapan points out. “Furthermore, our approach to integrating multiple sensors with intelligent data processing could serve as a model for developing other types of smart bandages and wearable medical monitors.”
Several technical challenges remain before this technology can see widespread clinical use. These include ensuring long-term stability under real-world conditions and developing standardized protocols for data collection and analysis. However, the research demonstrates how combining multiple sensing technologies with intelligent data processing can overcome limitations that have historically hampered medical monitoring devices.
The development points toward a future where wound dressings actively participate in the healing process by providing continuous, accurate monitoring of infection status and wound conditions. As healthcare continues to move toward more personalized and home-based care models, such integrated sensing approaches may become increasingly important for providing accurate, continuous health monitoring outside of traditional clinical settings.
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