This method could address the limitations of conventional chemical synthesis, such as low yields and hazardous chemical waste. The resulting sensor demonstrated strong fluorescence, with antibody attachment enhancing light emission. When CA 125 was added to the antibody-modified sensor, its fluorescence intensity decreased in a concentration-dependent manner, demonstrating a potential optical method for accurate detection of the cancer biomarker.
While gold (Au) and silver (Ag) have traditionally been used in optical sensors due to their excellent optical properties, copper (Cu) has gained attention as a lower-cost alternative. Its abundance, low cost, and multiple oxidation states make it well-suited for developing sensitive biosensors.
Conventional methods for producing copper-based optical materials often require multiple processing and purification steps, resulting in low yields and chemical waste. Low-temperature plasma offers a cleaner alternative by generating reactive ions, radicals, and excited molecules without the high bulk temperatures associated with conventional thermal plasma processing.
This enables rapid material synthesis without high temperatures or large amounts of hazardous chemical reagents.
Synthesis and Characterization of Copper-Pyrrole Material
The researchers developed a radio-frequency low-temperature plasma method to synthesize the copper-pyrrole optical material. After cleaning the reaction chamber with plasma, they prepared a precursor by dissolving copper chloride in liquid pyrrole.
The mixture was exposed to radio-frequency plasma for 10 minutes under sub-Torr pressure, followed by a 10-minute hydrogen reduction step. This process produced several milligrams of optical material per milliliter of precursor. The resulting material was extracted using water and methanol to identify the most effective sensing fraction.
Spectroscopic analyses, including X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR), confirmed the composition and structure of the methanol extract. XPS showed that the material contained approximately 2% copper and 14% nitrogen (N), supporting that the copper was in the +2 oxidation state within the pyrrole matrix.
FTIR further verified strong coordination between copper ions and nitrogen atoms, though the material’s exact chemical structure was not determined.
To prepare the biosensor, the methanol-extracted material was incubated with antibodies against CA 125 for 12 hours. Spectroscopic and zeta-potential measurements supported successful antibody attachment, producing a functionalized material that was subsequently tested using prepared antigen solutions.
Photophysical Properties and Sensor Performance
The copper-pyrrole material demonstrated strong ultraviolet absorption due to charge transfer between the pyrrole ligands and copper ions. It showed excellent stability, retaining its optical performance after two weeks of storage at 4 °C and maintaining consistent fluorescence across a wide pH range (up to pH 10).
Attaching antibodies against CA 125 altered the sensor's properties. The surface charge shifted from positive to strongly negative, confirming successful antibody attachment. This increased fluorescence intensity and shifted the emission toward longer wavelengths. The researchers suggest this could be due to assembly-induced emission, where restricted molecular motion reduces energy loss.
When exposed to increasing concentrations of CA 125, the sensor produced a proportional decrease in fluorescence intensity, along with the appearance of a distinct shoulder peak in the emission spectrum. This predictable response enabled accurate detection of CA 125 at concentrations of 35 U/mL and above, the clinical threshold commonly used to indicate possible ovarian cancer.
Preliminary selectivity tests further indicated that the sensor responded selectively to CA 125 without interference from other common biomolecules or amino acids.
Implications for Clinical Diagnostics
This copper-based sensor has potential for supporting early point-of-care screening for ovarian cancer. Because ovarian cancer is often diagnosed at an advanced stage due to the subtlety of its early symptoms, the rapid detection of CA 125 from small samples could allow earlier diagnosis, routine screening, treatment monitoring, and detection of disease recurrence.
However, further development is needed to investigate whether the material could support point-of-care monitoring, with clinical studies required to determine its diagnostic sensitivity, specificity, and reliability. Furthermore, further work is needed to determine the samples required for clinical testing.
Beyond laboratory testing, the plasma-synthesized sensing material is also well-suited for portable diagnostic devices and microfluidic chips due to its excellent physical stability. In addition, the low-temperature plasma process is fast, scalable, and environmentally friendly, making it suitable for producing a wide range of metal-organic biosensors for detecting cardiac biomarkers, metabolic markers, and environmental contaminants.
Future Directions
This study demonstrates that low-temperature plasma processing is a rapid, scalable, and environmentally friendly method for producing optical biosensors. By replacing expensive noble metals with abundant copper and simplifying the manufacturing process, researchers have provided a practical approach that could be used to develop affordable medical sensing technologies.
Future work should extend this plasma synthesis method to other transition metals and organic precursors while using computational modeling to optimize material design. Clinical evaluation with human serum samples will be an essential next step toward validating the sensor for real-world diagnostic applications.
Journal Reference
Jones, K. M., et al. (2026). Plasma-Corona Enabled Synthesis of Photonic Copper Sensor for the Detection of Ovarian Cancer Marker. Nanomaterials. 16(14). https://www.mdpi.com/2079-4991/16/14/894.
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