Analytical Significance of Encroachment in Multiplexed Bead-Based Flow Cytometric Assays

Method to Determine the Optimal Aptamer-to-Bead Ratio by Using Flow Cytometry

Research on the effective attachment of aptamers to beads, which is essential for using aptamers, has made relatively little progress. Here, we demonstrate a new method based on flow cytometry to determine the optimal aptamer-to-bead ratio for aptamer immobilization. The fluorescence intensity increased with a gradual two-fold increase in the aptamer fluorescence concentration, peaked at an aptamer-to-bead ratio of 2.56 × 10⁵, and tended to decrease at higher ratios. A similar pattern was observed in an additional analysis using fluorescence microscopy. However, measurement of the free aptamer concentration after the aptamer-bead conjugation reaction revealed a large aptamer loss compared to the 1.28 × 10⁵ aptamer-bead ratio. In addition, the binding efficiency of the aptamer/bead to the target was highest at the aptamer-to-bead ratio of 1.28 × 10⁵. Taken together, our data suggest that the proposed method is the best and easiest for determining the optimal aptamer-to-bead ratio.

Magnetic particles encoding a suspension probe for ultra-sensitive and quantitative determination of atrazine

As a highly toxic and widely used herbicide, atrazine poses a serious threat to food safety as well as overall environmental and human health. Due to complex matrix interference and the difficulty of signal enrichment, there is an urgent need for a convenient, fast, and ultrasensitive method that detects trace atrazine without concern for matrix effects. Here, we provide the first account of a sensitive and rapid suspension probe based on magnetic microspheres used to detect atrazine in herbs. The self-made magnetic beads featured -COOH groups and were used as the carrier to construct immunofluorescent probes. These probes then conjugated with the atrazine antigen through an activated ester method, ultimately binding to the antibody. Homogeneous detection was ensured using flow cytometry and the microflow optical channel along with allophycocyanin-conjugated goat-anti-mouse secondary antibody (APC-IgG-SecAb) as the fluorescent signal. The magnetic suspension probe allowed for high target enrichment and the inherent two-dimensional selective detection of flow cytometry effectively avoided any matrix interference. This method had good linearity across 1.69-23.19 ng mL^-1. The IC₅₀ and LOD values were 4.81 ng mL^-1 and 0.95 ng mL^-1, respectively; the sensitivity was increased three-fold relative to ELISA. After complete optimization, 2-N-morpholinoeth-anesulfonic acid was used as the coupling solution and maintained good mono-dispersity, stability, and reactivity for the labelled microspheres during the process. The entire experiment was simple, and effectively used reagents; moreover, both the labor required and detection time were greatly reduced. Critically, the strategy presented here greatly reduced interference from complex matrices, and saved preparation for matrix-matched solutions when different herbs were screened. Overall, this strategy was sensitive, rapid, eco-friendly, and labor-saving; collectively, these attributes make it well-suited for on-site screening of atrazine contamination and will allow for increased food safety.

Comparative flow cytometric analysis of immunofunctionalized nanowire and nanoparticle signatures

Flow cytometry is one of the gold-standard techniques used in clinical medicine for quantitative immunoassaying. The continuous development of its probes, commonly fluorescent nanoparticles, is important. Lately, the introduction of quantitative multiplexed immunoassay has challenged the use of nanoparticles as probes. Functionalized fluorescent silica-based magnetic nanowires are investigated under flow cytometry as a novel probe category. The preparation and full characterization of these multimodal nanowires is reported and compared to those of silica-based magnetic nanoparticles by flow cytometry. Full characterization includes transmission electron microscopy and fluorescence microscopy imaging, flow cytometric assaying, superconducting quantum interference device (SQUID) magnetization, and Mössbauer spectroscopy measurements. This work shows that loaded silica nanowires have intrinsic geometrical advantages when compared to similar spherical particles due to their unique "flow cytometry fingerprint" when utilized as magnetic carriers for immunodetection applications. These advantages account for a 17% yield in detecting the functional binding between THP-1 and ICAM-1, by utilizing a much lower concentration than that required for the nanoparticles.