Mobility and height detection of particle labels in an optical evanescent wave biosensor with single-label resolution

Abstract

Van Ijzendoorn, et al.. Mobility and height detection of particle labels in an optical evanescent wave biosensor with singlelabel resolution. Journal of Physics D: Applied Physics, IOP Publishing, 2010, 43 (15) AbstractParticle labels are used in biosensors to detect the presence and concentration of analyte molecules. In this paper we demonstrate an optical technique to measure the mobility and height of bound particle labels on a biosensor surface with single-label resolution. The technique is based on the detection of the particle-induced light scattering in an optical evanescent field. We show that the thermal particle motion in the evanescent optical field leads to intensity fluctuations that can accurately be detected. The technique is demonstrated using 290 bp (99 nm) DNA as an analyte, and using polystyrene particles and magnetic particles with diameters between 500 nm and 1000 nm as labels. The particle intensity histograms show that quantitative height measurements are obtained for particles with uniform optical properties, and the intensity versus position plots reflect the analyte-antibody orientation and the analyte flexibility. The novel optical detection technique will lead to biosensors with very high sensitivity and specificity.

Bond characterization by detection and manipulation of particle mobility in an optical evanescent field biosensor

“…[16] The DNA strands are tagged with Texas Red on one end and biotin on the other end; [16] the particles have a streptavidin coating and the cartridge surface is coated with polyclonal antibodies against Texas red. [11] After coating the cartridge, the surface is blocked in a PBS buffer containing 1% (w/v) BSA, 10% (w/v) sucrose and 0.1% (w/v) sodium azide and stored at 4°C. Before use, the cartridge is washed with 100 mM borate buffer (pH 8.5) containing 0.05% (v/v) Tween 20.…”

“…non-spherical, rough surface and inhomogeneous content) can show an increase in scattering intensity fluctuations, thus leading to an overestimation of the height displacement. [11] MagSense particles are observed in Transmission Electron Microscopy images to be smooth and spherical, but some particles may still have minor defects or an inhomogeneous content, leading to a small increase in measured height, which becomes noticeable for short tether lengths. We examined the occurrence of heights smaller than the tether length for both particle types by studying the intensity-position plots, and found many differences in mobility between different cases.…”

“…[6,7] In this paper we integrate the magnetic tweezer and tethered particle motion techniques in a biosensor system, and we measure the particle mobility in three dimensions with nanometre resolution by using an optical evanescent field. [8][9][10][11] We will show that the combination of these three techniques enables the characterization of the bond between a particle and a biosensor surface. As a model analyte we use double stranded DNA with lengths between 105 bp and 590 bp (36 nm to 201 nm), in order to get bond lengths on the order of the evanescent field depth.…”

Electrostatic height modulation of bound particle labels by buffer exchange in an evanescent wave biosensor

“…We have previously shown that measuring the thermally induced intensity fluctuations of single, optically uniform particles leads to accurate measurements of the height distribution of the particles. 22 The histogram of the measured scattered intensity ͑30 s measurement at 60 Hz, exposure time of 1 ms͒ of the images of a single MagSense particle bound to 290 bp DNA is shown in Fig. 3͑a͒.…”

“…We repeated this measurement for four particles, each bound to DNA of a different length. For each particle, we calculated the maximum height displacement ⌬h = d p ln͑I max / I min ͒, where d p is the penetration depth of the evanescent field ͑95 nm in our setup 22 ͒, and I max and I min are the maximum and minimum intensity values for which the measured probability decreases below 8%, equivalent to a thermal energy larger than 2.5 k B T. In Fig. 3͑b͒ the maximum height displacement of the four particles is plotted as a function of the buffer molarity.…”