Here we report a novel type of bivalent aptasensor based on silver-enhanced fluorescence polarization (FP) for detection of lactoferrin (Lac) in milk powder with high sensitivity and specificity. The novel two split aptamers were obtained from the aptamer reported in our previous SELEX (systematic evolution of ligands by exponential enrichment) selection, and their minimal structural units were optimized on the basis of their affinity and specificity. Also, dual binding sites of split aptamers were verified. The bivalent aptamers were modified to be linked with signal-molecule fluorescein isothiocyanate (FITC) and enhancer silver decahedral nanoparticles (AgNPs). The split aptamers could bind to different sites of Lac and assemble into a split-aptamers-target complex, narrowing the distance between AgNPs and FITC dye. As a result, AgNPs could produce a mass-augmented and metal-enhanced fluorescence (MEF) effect. In general, ternary amplification based on AgNPs, split aptamers, and the MEF effect all contributed to the significant increase of FP values. It was proved that the sensitivity of this assay was about 3 orders of magnitude over traditional aptamer-based homogeneous assays with a detection limit of 1.25 pM. Furthermore, this design was examined by actual milk powder with rapid and high-throughout detection.

In this work, we demonstrate, for the first time, the development of a disposable MoS-arrayed matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) chip combined with an immunoaffinity enrichment method for high-throughput, rapid, and simultaneous quantitation of multiple sulfonamides (SAs). The disposable MALDI MS chip was designed and fabricated by MoS array formation on a commercial indium tin oxide (ITO) glass slide. A series of SAs were analyzed, and clear deprotonated signals were obtained in negative-ion mode. Compared with MoS-arrayed commercial steel plate, the prepared MALDI MS chip exhibited comparable LDI efficiency, providing a good alternative and disposable substrate for MALDI MS analysis. Furthermore, internal standard (IS) was previously deposited onto the MoS array to simplify the experimental process for MALDI MS quantitation. 96 sample spots could be analyzed within 10 min in one single chip to perform quantitative analysis, recovery studies, and real foodstuff detection. Upon targeted extraction and enrichment by antibody conjugated magnetic beads, five SAs were quantitatively determined by the IS-first method with the linear range of 0.5-10 ng/mL ( R > 0.990). Good recoveries and repeatability were obtained for spiked pork, egg, and milk samples. SAs in several real foodstuffs were successfully identified and quantified. The developed method may provide a promising tool for the routine analysis of antibiotic residues in real samples.

No abstract

No abstract

No abstract