Ratiometric fluorescence sensing of hazardous ciprofloxacin based on aggregation induced emission enhancement of thiolate-protected gold nanoclusters induced by La3+ ion

[Display omitted] •A ratiometric fluorescent probe was designed for detecting ciprofloxacin (CIPRO).•The mechanism was based on La3+-enhanced fluorescence of GSH@AuNCs.•The probe displayed outstanding detection stability due to ratiometric response.•The probe also possessed the features of fast response and excellent sensitivity.•The probe was successfully applied to the determination of CIP in human urine and milk samples. In this research work, ultrasensitive and reliable ratiometric sensor was designed for assay of ciprofloxacin (CIPRO). The platform consists of thiolate-protected gold nanoclusters (GSH@AuNCs) with high fluorescence quantum yield and long-term stability. In the existence of lanthanum (La3+) ion, the GSH@AuNCs emission was sharply raised owing to the formation of La3+/GSH@AuNCs system accompanied with aggregation-induced emission enhancement (AIEE). Addition of CIPRO, a good La3+ ion coordinator, decreased the fluorescence emission of La3+/GSH@AuNCs system at 610 nm significantly as a result of disaggregation caused by the removal of La3+ ion from GSH@AuNCs surface. Furthermore, the blue emission of La3+-CIPRO coordination complex appears at 440 nm. Under optimized conditions, the fluorescence ratios (F440/F610) were linearly increased with increasing the CIPRO amount within the range of 0.003–200 µM with a limit of detection equal to 0.2 nM (S/N = 3). The as-fabricated La3+/GSH@AuNCs system possesses outstanding reliability and sensitivity for the detection of CIPRO. The system was effectively used to assay CIPRO in human urine and milk specimens with recoveries % of 97.6–102.3 % and 96.7–105.7 % for urine and milk samples, respectively and RSD % did not exceed 2.5 %, suggesting the accuracy of the method.