ABSTRACT
Magneto-resistive sensors capable of detecting superparamagnetic micro-/nano-sized beads are promising alternatives to standard diagnostic assays based on absorbance or fluorescence and streptavidin-functionalized beads are widely used as an integral part of these sensors. Here we have developed an immunomicroarray for systematic studies of the binding properties of 10 different micro-/nano-sized streptavidin-functionalized beads to a biotin substrate immobilized on SiO(2) with or without surface modification. SiO(2) surface cleaning, immobilized substrate concentration and surface blocking conditions were optimized. Polyethylene glycol-based surfaces with different end groups on the anchor molecule, 2,4,6-trichloro-1,3,5-triazine (TsT), were synthesized and compared with the standard (3-aminopropyl)triethoxysilane (APTS)/glutaraldehyde chemistry. APTS/glutaraldehyde, directly linked TsT and bare H(2)O(2)-activated SiO(2) performed better than polyethylene glycol-modified surfaces. Two beads, Masterbeads and M-280 beads, were found to give superior results compared with other bead types. Antibody/antigen interactions, illustrated by C-reactive protein, were best performed with Masterbeads. The results provide important information concerning the surface binding properties of streptavidin-functionalized beads and the immunomicroarray can be used when optimizing the performance of bead-based biosensors.
Subject(s)
Immunoassay/methods , Magnetics , Microarray Analysis/methods , Microspheres , Biosensing Techniques , Biotin/chemistry , Biotin/metabolism , C-Reactive Protein/metabolism , Materials Testing , Molecular Structure , Polyethylene Glycols/chemistry , Serum Albumin, Bovine/metabolism , Silicon Dioxide/chemistry , Streptavidin/chemistry , Streptavidin/metabolism , Surface PropertiesABSTRACT
Scanning conductance microscopy investigations were carried out in air on human chromosomes fixed on pre-fabricated SiO2 surfaces with a backgate. The point of the investigation was to estimate the dielectric constant of fixed human chromosomes in order to use it for microfluidic device optimization. The phase shift caused by the electrostatic forces, together with geometrical measurements of the atomic force microscopy (AFM) cantilever and the chromosomes were used to estimate a value for the dielectric constant of different human chromosomes.
