Liquid crystal biosensor with aptamer recognition for highly sensitive and quantitative norfloxacin detection via whispering gallery mode

As the fluoroquinolone antibiotics, norfloxacin has the advantages of antibacterial properties and efficient inhibition of bacterial DNA replication. Because of its strong binding affinity toward DNA helicases, this compound is chemically stable and exhibits limited biodegradation in environmental matrices. Prolonged use or discharge can enrich antibiotic resistance genes among microbial communities and contribute to persistent contamination. Herein, a nematic liquid crystal (LC) microlaser based on an aptamer recognition was reported and explored its application of norfloxacin ultrasensitive detection in soil. The rapid, real-time and quantitative monitoring of norfloxacin was achieved by exploiting whispering gallery mode (WGM) resonances in LC microdroplets functionalized with a specific aptamer as the molecular recognition element. Through resonance simulation and size-dependent experiments, the feasibility of using LC microlaser as a WGM microresonator was demonstrated. The optimal concentration of CTAB and DNA aptamer was 1 μM and 100 nM, respectively, which could realize the configuration transition of LC microdroplets from radial to bipolar. The devised norfloxacin sensor showed high sensitivity with a detection limit of 0.3 ng/mL, which was an order of magnitude lower than that reported for polarized optical microscope (POM) methods. In addition, the successful detection of various concentrations of norfloxacin in soil samples underscored the practical utility in environmental monitoring. The aptamer-based WGM-LC microlaser provides a highly sensitive approach for norfloxacin detection. The laser recognition probe does not require fluorescent or chromogenic labels, which affords significant advantages for rapid, real-time, and quantitative biosensing. This platform is expected to be extensible to ultrasensitive detection of other drugs, proteins, or environmental pollutants, particularly suited for integration into microfluidic devices for on-site environmental monitoring and public health risk assessment.