The sensor combines rice straw-derived biochar with conductive polymers to form a molecularly imprinted sensing platform with a detection limit of 0.03 nanograms per millimeter. The researchers suggest this rapid, low-cost sensor could complement conventional laboratory testing.
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Food Supply Contamination Challenges
Electrochemical sensors are widely used in food safety and quality control because they can convert chemical interactions into measurable electrical signals. Conventional sensors often rely on biological recognition elements such as antibodies or enzymes, but these materials have limited stability, short service lives, and high production costs.
Molecularly imprinted polymers (MIPs) provide a durable biomimetic alternative by creating synthetic binding sites that match the shape, size, and functional groups of specific target molecules. When combined with conductive carbon materials, MIPs benefit from increased surface area and faster electron transfer, thereby improving sensing performance.
Biochar, a carbon-rich material produced from agricultural biomass, is an inexpensive and sustainable support. After carboxyl modification, its reactive surface promotes strong polymer attachment, thereby enhancing sensor sensitivity and signal transfer.
Fabrication of Polymer and Biochar Sensor
To fabricate the sensor, researchers synthesized mesoporous biochar from rice straw through nitrogen-assisted high-temperature pyrolysis. The raw biochar was then modified with citric acid to enrich its surface with carboxyl groups. This created a reactive surface that was deposited onto fluorine-doped tin oxide glass to form the conductive electrode.
Target-specific recognition was achieved by chemically attaching the template molecule, ceftiofur sodium, to the functionalized biochar before electropolymerizing 3,4-ethylenedioxythiophene around it to form a conductive polymer network. After polymerization, the template molecules were chemically removed, leaving molecularly imprinted cavities that matched the shape and functional groups of ceftiofur sodium.
Enhanced Sensor Characteristics and Performance
Structural characterization confirmed that the resulting sensor possessed a stable mesoporous architecture with a large active surface area and a strongly negative surface charge. This promotes efficient electron transfer and sensitive electrochemical detection.
Electrochemical characterization showed that the conductive polymer enhanced electron transfer and increased the electroactive surface area compared with unmodified biochar. When ceftiofur sodium rebound to the molecularly imprinted cavities, charge transfer was inhibited, producing an electrical response proportional to the antibiotic concentration.
Control experiments using non-imprinted electrodes confirmed that this response resulted from specific molecular recognition rather than nonspecific surface adsorption.
Analytical Sensitivity and Real-World Application
The sensor demonstrated high analytical sensitivity over a broad range of antibiotic concentrations while maintaining excellent selectivity. Structurally related beta-lactam antibiotics, including penicillin, ampicillin, amoxicillin, and cefepime, as well as common milk constituents such as casein, vitamins, and minerals, produced negligible interference.
When tested on real raw milk samples, the sensor demonstrated high accuracy and reproducibility, yielding target recovery rates between 97%
and 106.5%. When several unpasteurized commercial and local vendor milk samples were tested, the results closely aligned with liquid chromatography-mass spectrometry measurements.
Storage testing also demonstrated that the electrode preserved approximately 90% of its initial sensing performance even after more than a month of cold storage.
Implications for Dairy Quality Assurance
This sensing platform has strong potential for food safety testing and for monitoring the dairy supply chain. Converting agricultural waste into a high-performance electrode eliminates the need for noble-metal nanomaterials and could lower manufacturing costs.
Beyond detecting ceftiofur sodium, the polymer sensing platform could be tailored to identify different veterinary antibiotics. Its versatility supports the development of low-cost, portable sensors for future on-site food quality monitoring and agricultural safety.
Future Directions in Portable Food Safety Testing
This study demonstrates that biochar-supported molecularly imprinted sensors can use sustainable agricultural waste to achieve highly sensitive electrochemical detection. The ability to detect ceftiofur sodium at sub-nanogram levels in complex milk samples highlights the potential of synthetic polymer sensors as a rapid, low-cost alternative to conventional laboratory testing.
Future work should focus on integrating this sensing platform into portable microfluidic devices and test strips for on-site food safety monitoring. With further development, these advancements could enable routine screening throughout the dairy supply chain, helping identify contaminated products before they reach consumers.
Journal Reference
Kumari, S., et al. (2026). Molecularly imprinted electrochemical sensor based on poly(3,4-ethylenedioxythiophene)/carboxylated biochar for ceftiofur estimation in milk. Scientific Reports. DOI: 10.1038/s41598-026-60595-7, https://www.nature.com/articles/s41598-026-60595-7.
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