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A reliable and robust colorimetric assay for highly selective detection of intact S. aureus employing nanoceria as chromatic agents. [Display omitted] • Glucose oxidase was employed to in situ produce H 2 O 2 in immunoassay. • Stable nanoceria was used as quantitative chromogenic indicators. • Capture antibody-bacteria-aptamer configuration was adopted in this assay. • The immunoassay has demonstrated functionality for S. aureus detection in real samples. Rapid and reliable detection of foodborne pathogens is a key requirement for food safety. Traditional rapid ELISA methods assessed by the ability of horseradish peroxidase to oxidize a chromogenic substrate such as 3, 3′, 5, 5′-tetramethylbenzidine in the presence of H 2 O 2 may result in the high rate of negative responses because of the instability of H 2 O 2 and product. Here, we report the use of redox active nanoceria as colorimetric indicator in immunoassay taking Staphylococcus aureus as a model. The nanoceria is fully water-soluble and can be stored as least 90 days in the refrigerator while maintaining the same performance. Moreover, it does not require external H 2 O 2 , as glucose oxidase used in the immunoassay can catalyze the oxidation of glucose to produce H 2 O 2 in situ , which is more robust in signal readout. Taken together, these results demonstrate that nanoceria are potentially suitable as colorimetric substrate in the development of novel enzyme immunoassays. [ABSTRACT FROM AUTHOR]

Combining the unique optical properties of metal nanoparticles and the specific recognition of aptamer, aptamer-nanoparticle conjugates have been extensively used in a wide range of applications, particularly multifunctional nanoparticles for cell detection and molecular imaging. Conventional conjugates prepared by chemisorption of monothiol-modified oligonucleotides onto nanoparticle surfaces suffer from a lack of stability when exposed to a variety of small molecules. If silver is used in place of gold, then this lack of stability is even more pronounced. In this study, we reported here the effective and facile strategy of preparing stable silver nanoparticle-aptamer conjugates by in situ generation of strong metal affinity capping ligands, dithiocarbamates modified anti-prion protein aptamer. The conjugates produced are stable and can withstand NaCl concentration at 0.25 mol/L. Meanwhile, they could be applied in the cellular prion protein imaging successfully. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) spectra, which can provide large information about trace amount of chemical and biological species have been widely performed as a well-established tool in complex biological system. In this work, coomassie brilliant blue (R-250) with high affinity to proteins and high Raman activity was employed as a Raman reporter to probe prion protein (PrP) through a dual-aptamer mechanism, and thus an original strategy for PrP determination was proposed, which showed great potential to turn on the SERS response through specific recognition of anti-prion aptamers towards the target protein. Aptamers (Apt1 and Apt 2) recognizing distinct epitopes of PrP with high affinity were first conjugated to Ag@Si NPs, and Ag@Si-PrP/R-250-Ag@Si conjugates were obtained in the presence of PrP/R-250, inducing dramatically enhanced Raman signal. SERS responses enhanced with increasing amount of PrP and a linear equation of I SERS =6729.7+3091.2 c PrP was obtained in the range of 3.0–12.0×10 −9 M with the determination coefficient of 0.988. The proposed strategy is simple, rapid, and high specificity to probe protein–aptamer recognition in the solution. [ABSTRACT FROM AUTHOR]

A new type of highly selective aptamer-labeled fluorescent silica nanoparticles [Apt-tris(2,2′-bipyridyl)ruthenium(II)@SiO NPs] were prepared through the reverse microemulsion method by using prolonged fluorescence lifetime ruthenium complexes of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)) as the source of the fluorescence for cellular prion protein imaging. Investigations showed that the newly prepared Ru(bpy)@SiO NPs possessed superior advantages of strong fluorescence, low toxicity, and easy surface modification for bioconjugation. Cell imaging experiments indicated that Apt-Ru(bpy)@SiO NPs had great tendency to human bone marrow neuroblastoma cells (SK-N-SH cells), since they can express large amount of prion protein on the surface of the cell, while in HeLa cells this phenomenon disappeared for the reason that HeLa cells cannot express prion proteins. [ABSTRACT FROM AUTHOR]

Highlights: [•] We report a solution-based MEF sensing platform. [•] Metallic surface-dye distance is controlled by changing the thickness of silica shell. [•] Dual-aptamer was involved to recognize distinct binding epitopes of the same target. [•] Ag@Si NPs was used as an excellent probe for darkfield light scattering imaging. [ABSTRACT FROM AUTHOR]