Fluoroquinolone antibiotic residues are environmental contaminants. Since these chemicals are not easily biodegradable, developing a rapid and cost-effective method for their detection is a growing concern in the forensic industry. In a study published in Analytical Chemistry, researchers have designed a microfluidic photoelectrochemical (PEC) aptasensor using photoactive AgBr/CuBi2O4 (ACO) composites for rapid and ultrasensitive detection of environmental contaminants.
Fluoroquinolone antibiotics, such as ofloxacin (OFL) and ciprofloxacin (CIP), contaminate the environment by suppressing the activity and growth of microorganisms.
This study explores a novel approach for detecting ofloxacin and ciprofloxacin by controlling the luminol release in self-powered microfluidic photoelectrochemical aptasensors.
How do Fluoroquinolone Antibiotics Become Environmental Contaminants?
Fluoroquinolone antibiotics (FAs) treat bacterial infections in humans and animals. They are effective against a wide spectrum of gram-negative and gram-positive pathogenic bacteria.
However, the residues of these antibiotics have emerged as possible contaminants. The presence of antibiotics in surface water and animals can harm human health through the food chain. Fluoroquinolone antibiotics, including ofloxacin, ciprofloxacin, norfloxacin, enrofloxacin, and lomefloxacin, coexist in the environment, making their detection more challenging.
Limitations of Traditional Detection Techniques
Enzyme-linked immunosorbent assays, immunoassays, high-performance liquid chromatography, and capillary electrophoresis have been used to detect fluoroquinolone antibiotics.
However, various drawbacks such as time-consuming, extensive pretreatment and high equipment cost restrict the applicability of these techniques. Consequently, developing a simple, robust, cost-effective analysis technique is necessary.
Advantages of Using PEC Sensors
A photoelectrochemical sensor is an innovative and rapidly evolving analytical tool based on the photoelectrochemical process and biological or chemical probe recognition.
It outperforms standard optical and electrochemical sensors due to the complete isolation of the optical sources and electrochemical signals.
Self-powered photoelectrochemical sensors convert optical signals to electrical signals without external power. These sensors have a simple structure compared with redundant three-electrode systems. The sensors display a broad dynamic range and remarkable sensitivity in pesticide residue detection, biological assays, and food analysis.
Even though the PEC sensor's performance has reached an acceptable level, multi-target quantitative analysis remains a hurdle. Developing a portable and compact PEC sensor for ultrasensitive examination is one of the most important demands in the forensic industry.
Using Microfluidic Photoelectrochemical Aptasensor to Detect Contaminants
An analytical framework that integrates a PEC sensor with a microfluidic device for ultrasensitive detection of ciprofloxacin and ofloxacin has been explored.
A self-powered microfluidic PEC aptasensor was designed by employing direct Z-scheme ZnIn2S4/CdS as the photoanode and AgBr/CuBiO4 as the photocathode to achieve multi-target quantitative detection of ofloxacin and ciprofloxacin.
Luminol molecules were implanted in the porous structure of silicon dioxide nanospheres (PSiO2) by electrostatic adsorption between PSiO2 and aptamer (OFL) to increase the cathodic photocurrent signal.
Instead of using a platinum counter electrode to supply electrons, CdS nanorod arrays (CZIS) coated with ZnIn2S4 were used as the photoanode.
A signal-off CIP detection was measured via an aptamer(CIP) and target-specific recognition in the photoanode. A scanning electron microscope (SEM) helped analyze the microstructures and morphologies of AgBr/CuBi2O4 composites.
X-ray photoelectron spectroscopy (XPS) experiments were conducted with a 2000 XPS system with a charge neutralizer and a monochromatic Al K source. Energy dispersive spectrometer (EDS) data and electron microscope pictures were analyzed using an emission scanning electron microscope (ESEM).
Important Findings of the Study
The self-powered PEC aptasensor created by merging a direct Z-scheme ZnIn2S4/CdS photoanode with AgBr/CuBi2O4 photocathode into a microfluidic device successfully detected ciprofloxacin and ofloxacin.
The matching band structure of AgBr and CuBi2O4 greatly aided charge transfer and separation. ZnIn2S4/CdS composites with stable photocurrent signals supplied an abundance of electron carriers to the PEC system.
The pristine CuBi2O4 sample had homogeneous nanocuboids on its surfaces with a mean diameter of 34 m. In ACO composites, the development of direct Z-scheme heterojunctions significantly facilitated electron/hole pair separation.
The luminol released via specific recognition between the OFL and aptamer(OFL) reacted with •O2−, and emitted chemiluminescence, leading to a signal-on state. The steric hindrance effect in the photoanode caused by the combination of CIP and aptamer(CIP) created successful signal-off CIP detection.
The microfluidic PEC aptasensor displayed high stability, repeatability, and selectivity for OFL and CIP detection based on the signal "on-off-on" mechanism. High linearity for OFL and CIP was established, with detection limits of 0.022 and 0.06 pg/mL, respectively.
The microfluidic PEC sensing technology demonstrated the ability for multi-target quantitative analysis of two different types of fluoroquinolone antibiotics in real milk and water samples.
The proposed analytical method has the potential to be a strong contender for the analysis of ultrasensitive fluoroquinolone antibiotics in various environmental samples.
Wu, T., Du, Y., Dai, L., Li, J., Song, X., Feng, J., Xueying Wang, Qin W., & Huangxian, J. (2022) A Direct Z-Scheme AgBr/CuBi2O4 Photocathode for Ultrasensitive Detection of Ciprofloxacin and Ofloxacin by Controlling the Release of Luminol in Self-Powered Microfluidic Photoelectrochemical Aptasensors. ACS Publications. https://pubs.acs.org/doi/10.1021/acs.analchem.2c00889