Detection of biomarkers at low concentrations is essential for early diagnosis of numerous diseases. In many sensitive assays, the target molecules are tagged using fluorescently labeled probes and captured using magnetic beads. Current devices rely on quantifying the target molecules by detecting the fluorescent signal from individual beads. Here, we propose a compact fluorescence-based magnetically aggregated biosensors (MAB) system. Using the device to detect human Interleukin-8, we demonstrated a 0.1 ng/L limit of detection and a 4-log dynamic range, performance which is on par with the most sensitive devices, but is achieved without their bulk and cost.
One of the most common capture surfaces is a magnetic bead. However, magnetic beads exhibit strong autofluorescence, which often overlaps with the emission of the reporter fluorescent dyes and limits the analytical sensitivity of the assay. Here, we photobleached several widely used magnetic beads and reduced their autofluorescence to 1% of the initial value. The photobleached beads were stable over time and their surface functionality was retained. In a high sensitivity LX-200™ system using photobleached magnetic beads, human interleukin-8 was detected with a 3-fold improvement in analytical sensitivity and signal to noise ratio over results achievable with non-bleached beads.