Development of a magnetic immunosorbent for on-chip preconcentration of amyloid β isoforms: Representatives of Alzheimer's disease biomarkers

Determination of amyloid beta (A beta) isoforms and in particular the proportion of the A beta 1-42 isoform in cerebrospinal fluid (CSF) of patients suspected of Alzheimer's disease might help in early diagnosis and treatment of that illness. Due to the low concentration of A beta peptides in biological fluids, a preconcentration step prior to the detection step is often necessary. This study utilized on-chip immunoprecipitation, known as micro-immunoprecipitation (mu IP). The technique uses an immunosorbent (IS) consisting of magnetic beads coated with specific anti-A beta antibodies organized into an affinity microcolumn by a magnetic field. Our goal was to thoroughly describe the critical steps in developing the IS, such as selecting the proper beads and anti-A beta antibodies, as well as optimizing the immobilization technique and mu IP protocol. The latter includes selecting optimal elution conditions. Furthermore, we demonstrate the efficiency of anti-A beta IS for mu IP and specific capture of 5 A beta peptides under optimized conditions using various subsequent analytical methods, including matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), capillary electrophoresis, microchip electrophoresis, and immunoblotting. Synthetic A beta peptides samples prepared in buffer and spiked in human CSF were analyzed. Finally, on-chip immunoprecipitation of A beta peptides in human CSF sample was performed. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4722588]