Researchers have developed a smart new way to detect nitrofen—a toxic herbicide—in water using a fluorescent sensor made from carbon quantum dots (CQDs) and molecularly imprinted polymers (MIPs). This could be a game-changer for environmental monitoring, especially in areas affected by agricultural runoff.
Study: Fluorescent Molecular Imprinted Sensor Based on Carbon Quantum Dot for Nitrofen Detection in Water Sample. Image Credit: tawanroong/Shutterstock.com
Published in the journal Polymers, the study highlights how this sensor offers a fast, sensitive, and selective method for identifying harmful contaminants in water—something that's becoming more urgent as pollution levels continue to rise.
Why Nitrofen Detection Matters
Nitrofen has long been valued for its herbicidal properties, but its persistence in the environment poses risks to both human health and aquatic ecosystems. Detecting it accurately—especially at low concentrations—is crucial for effective water quality monitoring.
Traditional methods often struggle with selectivity and stability in complex environments. That’s where the CQD-MIP combination comes in. CQDs are nanoscale carbon particles known for their excellent fluorescence properties, making them ideal for optical sensing. Meanwhile, MIPs provide tailored recognition sites that mimic natural molecular interactions, enhancing the sensor’s ability to isolate nitrofen even in the presence of similar compounds.
Building the Sensor: A Step-by-Step Overview
The sensor development began with the synthesis of CQDs using a one-pot hydrothermal method. In this process, 2.05 grams of citric acid and 1 gram of urea were dissolved in 15 milliliters of ultrapure water. The solution underwent ultrasonic treatment for five minutes to ensure it was well mixed. It was then sealed in a 20 mL polytetrafluoroethylene reactor and heated in an autoclave at 200 °C for six hours. After cooling to room temperature, the dark green liquid was freeze-dried to yield solid CQDs, which were stored at 4 °C until further use.
To construct the molecularly imprinted polymers (MIPs), the researchers employed a reverse microemulsion technique. A 5 mg/mL solution of the synthesized CQDs was combined with methacrylic acid (MAA) and nitrofen, which served as the template molecule for imprinting. The polymerization process was triggered by adding an initiator and carried out at a controlled temperature. As the MIP formed, it developed recognition sites tailored to nitrofen’s molecular structure—key to enhancing the sensor’s selectivity.
Fluorescence measurements were taken using a Hitachi F-4600 spectrophotometer, with the excitation wavelength set at 335 nm and emission monitored between 370 and 520 nm. By analyzing changes in fluorescence intensity, the researchers were able to observe the interaction between CQDs@MIPs and nitrofen.
To evaluate the sensor’s performance, they tested a range of nitrofen concentrations in ethanol. A standard calibration curve was created to link fluorescence response with nitrofen levels, and the limit of detection (LOD) was determined through statistical analysis. The sensor’s real-world applicability was further confirmed through recovery studies using actual water samples.
Key Findings and Performance
To ensure optimal sensor performance, the researchers focused on fine-tuning the carbonization process of the CQDs. They found that a four-hour carbonization period provided the best results—maintaining stable fluorescence while minimizing photobleaching over time.
The sensor’s ability to detect nitrofen was confirmed through a clear drop in fluorescence intensity when the target molecule was introduced. This quenching effect indicated a strong interaction between the CQDs and nitrofen, confirming the sensor’s responsiveness. Further optimization revealed that an APTES-to-nitrofen ratio of 6:1 produced the most distinct fluorescence signal, highlighting the importance of imprinting conditions in enhancing selectivity.
Structural and morphological analyses supported the quality and consistency of the synthesized CQDs, reinforcing their suitability for environmental applications. To test real-world performance, the researchers conducted recovery experiments using actual water samples. These tests demonstrated the sensor’s effectiveness in practical settings, validating both its sensitivity and reliability.
What This Means for Environmental Monitoring
The study presents a well-rounded solution to a pressing environmental challenge. By combining the high optical sensitivity of CQDs with the molecular recognition capabilities of MIPs, the researchers created a sensor that is not only efficient and stable but also selective enough for real-world applications.
Importantly, this work lays a foundation for broader applications. While the focus here is on nitrofen, the same approach could be extended to detect other environmental pollutants, offering a flexible platform for water quality surveillance.
Journal Reference
Chen Y., Zhou Y., et al. (2025). Fluorescent Molecular Imprinted Sensor Based on Carbon Quantum Dot for Nitrofen Detection in Water Sample. Polymers 17(6):816. DOI: 10.3390/polym17060816, https://www.mdpi.com/2073-4360/17/6/816