Sensitive detection of florfenicol residues in food matrices using a label-free liquid crystal aptasensor with UV-functionalized 4-cyano-4'-biphenylcarboxylic acid.

A label-free liquid-crystal aptasensor is reported that transduces florfenicol (FFC)–aptamer binding into optical responses. Nematic 4′-pentyl-4-biphenylcarbonitrile was UV-oxidized to 4-cyano-4′-biphenylcarboxylic acid, whose carboxyl groups enabled coupling of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride/N-hydroxysuccinimide to an amino-terminated complementary oligonucleotide dispersed in the liquid-crystal phase. In FFC-free samples, the aptamer tail hybridized with the immobilized receptor, disrupting homeotropic anchoring and yielding a bright planar texture, whereas FFC binding suppressed hybridization, preserving a dark texture. The percentage brightness values derived from polarized optical microscope images decreased linearly with FFC level within 0.2–80 ng mL⁻¹, with a limit of detection of 0.12 ng mL⁻¹. The sensor also showed good discrimination against co-residual veterinary drugs and metabolites relevant to food matrices. Sensor applicability to real matrices was quantified using QuEChERS extracts of milk and eggs diluted 10× with phosphate-buffered saline and spiked with FFC; the sensor achieved recovery levels within the validation limits and equivalent results to those of high-performance liquid chromatography. The proposed aptasensor stabilizes within ~ 20 min, requires no labels or complex instrumentation, and can be readily adapted to other small-molecule residues by swapping the aptamer.