A novel measuring system for the determination of paramagnetic particle labels for use in magneto-immunoassays

Hill, Andrew; Luxton, Richard; Hawkins, Peter; Richardson, Julie

Abstract

Coated micrometer-sized paramagnetic particles (PMPs) are readily available and widely used in immunoassays, mainly for separation and as a solid phase. We have described in a separate paper a model sandwich assay in which ≈ 1 × 105 to 1 × 106 PMPs (2.8 μm diameter) are immobilised on a plastic strip at the end of the assay. In this paper, we describe the design of an instrument that is capable of determining the number of PMPs on the plastic strip. The paper also describes a method of making standard plastic strips with known numbers of PMPs on them. A strip, when placed in a coil of wire in parallel with a capacitor, causes the resonant frequency of the coil to decrease because of the presence of the PMPs. The decrease in frequency relates directly to the number of PMPs on the strip. A circuit based on a voltage-controlled oscillator and a phase-locked loop is used to accurately measure the resonant frequency of the coil. The instrument is capable of detecting at least 1×105 PMPs immobilised on a plastic strip and has a linear response (r=0.99) for up to at least 3.33 × 106 PMPs. In terms of the iron content of the PMPs, the detection limit is ≈ 1.2 μg Fe in the paramagnetic particles and the sensitivity is ≈ 3 Hz per μg of Fe. The instrument is small and compact and together with a suitable magneto-immunoassay will have many applications, including near-patient monitoring. © 2001 Elsevier Science B.V. All rights reserved.

• Presentation Conference Type: Conference Paper (published)
• Publication Date: Nov 7, 2001
• Journal: Biosensors and Bioelectronics
• Print ISSN: 0956-5663
• Publisher: Elsevier
• Peer Reviewed: Not Peer Reviewed
• Volume: 16
• Issue: 9-12
• Pages: 1127-1132
• DOI: https://doi.org/10.1016/S0956-5663%2801%2900241-X
• Keywords: paramagnetic labels, magneto-immunoassays, phase-locked loop, coil design, immobilised paramagnetic particles, near-patient monitoring
• Public URL: https://uwe-repository.worktribe.com/output/1088444
• Publisher URL: http://dx.doi.org/10.1016/S0956-5663(01)00241-X
• Additional Information: Additional Information : The technology described in the paper has been the basis of four international patents. The magnetic detection technology described has been instrumental in the awarding of two CASE studentships to further develop and exploit the technology.