Au nanoparticle preconcentration coupled with CE-electrochemiluminescence detection for sensitive analysis of fluoroquinolones in European eel (Anguilla anguilla)

A colorimetric aptasensor fabricated with group-specific split aptamers and complex nanozyme for enrofloxacin and ciprofloxacin determination

Developing simultaneous detection methods for multiple targets is crucial for the field of food analysis. Herein, enrofloxacin (ENR) and ciprofloxacin (CIP) were taken as model targets. For the first time, a strategy to generate group-specific split aptamers was established by revealing and splitting the critical binding domain, and the split aptamers were exploited to design a four-way DNA junction (4WJ) which could regulate the enzymatic activity of chitosan oligosaccharide (COS)-AuNPs nanozyme to develop a colorimetric aptasensor. A pair of split aptamers were obtained for ENR (K_d = 15.00 nM) and CIP (K_d = 4.870 nM). The mechanism of COS binding with double-stranded DNA in the 4WJ was elucidated. Under optimal conditions, the colorimetric aptasensor enabled a wide linear detection range of 1.4-1400 nM and a limit of detection (LOD) of 321.1 pM and 961.0 pM towards ENR and CIP, respectively, which exhibited excellent sensitivity, selectivity, and availability in detecting ENR/CIP in seafood. This study expands the general strategies for generating robust aptamers and nanozyme complex and provides a good reference for developing multi-target detection methods.

A CaCuSi4O10/GCE electrochemical sensor for detection of norfloxacin in pharmaceutical formulations

This study reports on a calcium copper tetrasilicate (CaCuSi₄O₁₀)/glassy carbon electrode (GCE) electrochemical sensor developed for rapid sensing and quantification of an antibacterial drug, norfloxacin, using both cyclic voltammetry and differential pulse voltammetry. The sensor was fabricated by modifying a glassy carbon electrode with the CaCuSi₄O₁₀. Electrochemical impedance spectroscopy was performed and the Nyquist plot showed that the CaCuSi₄O₁₀/GCE had a lower charge transfer resistance of 22.1 Ω cm² compared to the GCE with a charge transfer resistance of 43.5 Ω cm². Differential pulse voltammetry showed that the optimum pH for the electrochemical detection of norfloxacin in potassium phosphate buffer solution (PBS) electrolyte was pH 4.5 and an irreversible oxidative peak was found at 1.067 V. Two linear ranges were established at 0.01 to 0.55 μM and 0.55 μM to 82.1 μM, and the limit of detection was ca. 0.0046 μM. We further demonstrated that the electrochemical oxidation was controlled by both diffusion and adsorption processes. The sensor was investigated in the presence of interferents and was found to be selective toward norfloxacin. The pharmaceutical drug analysis was done to establish method reliability and a significantly low standard deviation of 2.3% was achieved. The results suggest that the sensor can be applied in the detection of norfloxacin.

Simultaneous determination of the four key fluoroquinolones and two antipsychotics in fish and shrimp by LC-MS/MS

In this study, we developed and validated a liquid chromatography triple quadrupole tandem mass spectrometry (LC-MS/MS) method used to simultaneously determine levels of four fluoroquinolones (ofloxacin, norfloxacin, lomefloxacin, and pefloxacin) and two antipsychotics (diazepam and methaqualone) in fish and shrimp. The samples were extracted with a mixture of anhydrous sodium sulfate and acetonitrile, and purified by C₁₈ cartridge solid-phase extraction with an optimized eluent. The MS² method was applied to recognize the molecular structure of these compounds according to a main fragmentation scheme. The key ions of identification and quantification were deduced from chemical structures. Multiple reaction monitoring was used to quantitatively analyse the compounds of interest. Satisfactory linearities were obtained (R² ≥0.99) with the limits of quantitation (LOQs) ranging between 0.03 and 1.96 μg kg^-1. The recoveries were 74-122%, with a relative standard deviation (RSD) below 4.9% for these compounds at the spiking level of three, five, and ten times the LODs, respectively. The LC-MS/MS method allows precise and sensitive determination of residues of six important banned veterinary drugs in fish and shrimp tissue. This methodological approach solved the problem imposed by the need for two or more analysis methods to analyse the compounds of interest described in this study.