No abstract

A label free method based on spectral correlation interferometry has been developed for highly sensitive detection of pyrethroids by competitive immunoassay on the surface of sensor chips made of widely available microscopy glass cover slips. It is shown that the method allows independent optimization of each step of the sensor surface modification. This fact may be used to increase the efficiency of development of protocols for a wide spectrum of immunoassays that employ glass surface as a solid phase. Detection of 3 phenoxybenzoic acid, which is one of the most stable metabolites of a large number of pyrethroids, on the surface of the optimized sensor chips has been demonstrated on the level of 15 pg/ml. That is 50 times better than the sensitivity of the enzyme linked immunosorbent assay (ELISA).

A 3-channel biosensor based on spectral correlation interferometry (SCI) has been adapted for direct optical detection of antigens by measuring changes in thickness of a biolayer on functionalized glass slips employed as affordable single-use sensor chips. The instrument is insensitive to the bulk refractive index of a solution under test and provides signals in metrological units (pm or nm). Using real-time monitoring with the SCI, protocols for fabrication of sensor chips with different functional (epoxylated, carboxylated, and biotinylated) surfaces for antibody immobilization have been developed and optimized to minimize chip-to-chip variations and achieve better limit of detection (LOD), shorter assay time, and longer shelf life. The optimized coupling surfaces have been compared for detection of human serum albumin (HSA) used as a model agent of medical significance. The dynamic ranges for measuring the HSA concentration were 0.07-20, 0.12-30, and 0.25-10 μg/ml, and the assay durations were less than 20, 15, and 30 min for the epoxylated, carboxylated, and biotinylated chips, respectively. The advantages of each type of sensor chip have been shown, namely, the carboxylated chips feature the shortest assay time, the epoxylated ones demonstrate the best LOD, and the biotinylated chips exhibit the longest shelf life in an unprotected environment. The developed protocols of antibody immobilization can be used in different biosensors and assay techniques including those based on fluorescent, magnetic or plasmonic labels, etc. The SCI is well compatible with various partially transparent layers used in biosensing and with microarrays for multi-analyte detection.