Upconversion photoluminescence analysis of fluoroquinolones

The characteristics of the upconversion (UC) photoluminescence (PL) of fluoroquinolones (FQs) are reported here for the first time. Using UC PL, a simple, sensitive, and cost-effective method of determining FQs was developed that eliminated interference arising from biological background fluorescence and did not require UV light to excite the FQ (in contrast to downconversion PL), which is an advantage given that UV is potentially damaging to organisms. Ciprofloxacin (CPFX) and levofloxacin (LVFX), two important FQs, were studied. The effects of acidity, temperature, the solvent used, ionic strength, and stable time on the UC PL from the two FQs were also investigated. The UC PL intensity was found to be proportional to the concentration of CPFX over the range 0.05–100 μmol/L with a correlation coefficient of 0.9992, and proportional to the concentration of LVFX over the range 0.05–100 μmol/L with a correlation coefficient of 0.9991. The limit of detection (LOD) was 6.05 nmol/L for CPFX and 5.64 nmol/L for LVFX. The proposed method was successfully used to determine FQs in human serum and pharmaceutical samples. The recoveries of the two FQs ranged from 96.0% to 103.2% and the RSD was < 2.62%.