Scanning Magneto-Inductive Sensor for Quantitative Assay of Prostate-Specific Antigen

Among analytical tests available for point-of-care diagnostics, the lateral flow immunoassay (LFIA) stands out for its low-cost, speed, portability, and ease of use. By its nature, this paper-based instrument is qualitative, intended to provide a positive/negative reading. LFIA, coupled to a quantitative readout device that did not compromise its advantages, would be a powerful tool for many clinical and biological applications. A promising enabling strategy is the use of superparamagnetic nanoparticles as labels. Their reduction of visual signal compared to gold or latex reporters is compensated by their magnetic induction, which enables absolute quantification with magnetic sensors. In this letter, a magnetic LFIA reader is presented that exploits spontaneous magnetic switching, a characteristic of superparamagnetism, to produce a quantifiable electromagnetic induction in an alternating current carrier. In contrast to other magnetic sensors, this approach does not require the application of external magnetic fields, which greatly reduces its complexity. The capability of the system for bioanalyte quantification has been proved by successfully measuring prostate-specific antigen levels in the interval of clinical interest.