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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]

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]

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]