Novel assay format permitting the prolonged use of regeneration-based sensor chip technology.

A polyclonal antibody raised against morphine-3-glucuronide (M3G, the main metabolite of heroin and morphine) was used in the development of a novel assay format using a surface plasmon resonance (SPR)-based biosensor. Previously developed assays have generated calibration curves based on differences in the quantity of response units binding to the surface of a chip coated with the analyte. The novel assay described here was based on the development of a standard curve using the slope of a series of consecutive binding interactions. Using this format, regeneration between each assay cycle was no longer required. This increased the useable life span of the chip surface and, as a result, decreased the cost associated with the assay. Thus, at least 15 binding interactions could be carried out before the saturation of antibody on the surface of the chip caused the response to deviate significantly from linearity. After 15 nonregenerated binding interactions, the slope still remained within 1.5% of the slope after a single binding event. Analysis time, and the sample volumes required were also markedly decreased while sensitivity was enhanced. The inhibition assay developed had a detection range of 270 to 17,500 pg ml(-1).

Production of a recombinant anti-morphine-3-glucuronide single-chain variable fragment (scFv) antibody for the development of a "real-time" biosensor-based immunoassay.

A recombinant single-chain variable fragment (scFv) antibody to morphine-3-glucuronide (M3G) was produced using genetic material obtained from the spleen cells of mice immunised with a morphine-3-glucuronide-bovine serum albumin (M3G-BSA) conjugate. Immunoglobulin light (V(L)) and heavy (V(H)) chain genes were amplified and cloned into pAK vectors for generation of recombinant antibody fragments in Escherichia coli. A competition ELISA assay was developed in PBS to characterise the ability of the antibody fragments to recognise free drug and the detection limits were found to be as low as 3 ng ml(-1). Surface plasmon resonance-based inhibition immunoassays were developed. The recombinant antibody was pre-incubated with various concentrations of free drug followed by injection over a morphine-3-glucuronide-thyroglobulin (M3G-THY) immobilised surface. The response of antibody binding to the surface of the chip was inversely proportional to the amount of free drug in solution. Regeneration conditions for antibody binding to the surface were optimised resulting in a binding-regeneration capacity of at least 30 cycles. The inhibition assay for M3G was tested with assay ranges between 3 and 195 ng ml(-1) and 3 and 97 ng ml(-1) in PBS and urine, respectively.

Immunoassay for the determination of morphine-3-glucuronide using a surface plasmon resonance-based biosensor.

Polyclonal antibodies were produced for the development of competitive ELISA's and surface plasmon resonance (SPR)-based BIAcore inhibition assays for the detection of morphine-3-glucuronide (M3G, the main metabolite of heroin and morphine). A conjugate consisting of M3G and ovalbumin was produced and used for the generation of antibodies, for the coating of immunoplates and for immobilisation onto BIAcore chips. Competition ELISA's were developed in PBS and urine to characterise the antibodies ability to recognise free M3G. SPR-based inhibition immunoassays on BIAcore were developed. The regeneration of the surface of a chip immobilised with conjugate following antibody binding, essential for the development of inhibition assays was investigated. Regeneration of the conjugate-coated surface was optimised for both polyclonal antibodies resulting in binding-regeneration capacities of approximately 60 cycles for one antibody and 50 cycles for the second antibody. The inhibition assays developed in urine had ranges of detection of 762-24,400 (antibody 1) and 976-62,500 pg ml(-1) (antibody 2). The inter-day coefficients of variation for the assays ranged from 1.48 to 11.24%.