Spore and micro-particle capture on an immunosensor surface in an ultrasound standing wave system

Martin, Stacey P., Townsend, Rosemary J., Kuznetsova, Larisa A., Borthwick, Kathryn A.J., Hill, Martyn, McDonnell, Martin B. and Coakley, W. Terence (2005) Spore and micro-particle capture on an immunosensor surface in an ultrasound standing wave system. Biosensors & Bioelectronics, 21 (5), 758-767. (doi:10.1016/j.bios.2005.01.013).

Abstract

The capture of Bacillus subtilis var. niger spores on an antibody-coated surface can be enhanced when that coated surface acts as an acoustic reflector in a quarter wavelength ultrasonic (3 MHz) standing wave resonator (Hawkes, J.J., Long, M.J., Coakley, W.T., McDonnell, M.B., 2004. Ultrasonic deposition of cells on a surface. Biosens. Bioelectron. 19, 1021–1028). Immunocapture in such a resonator has been characterised here for both spores and 1 ?m diameter biotinylated fluorescent microparticles. A mean spatial acoustic pressure amplitude of 460 kPa and a frequency of 2.82 MHz gave high capture efficiencies. It was shown that capture was critically dependent on reflector thickness. The time dependence of particle deposition on a reflector in a batch system was broadly consistent with a calculated time of 35 s to bring 95% of particles to the coated surface. A suspension flow rate of 0.1 ml/min and a reflector thickness of 1.01 mm gave optimal capture in a 2 min assay. The enhancement of particle detection compared with the control (no ultrasound) situation was ×70. The system detects a total of five particles in 15 fields of view in a 2 min assay when the suspending phase concentration was 104 particles/ml. A general expression for the dependence of minimum concentration detectable on; number of fields examined, sample volume flowing through the chamber and assay time shows that, for a practical combination of these variables, the threshold detection concentration can be two orders of magnitude lower.

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Contributors

Author: Martyn Hill

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