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Okadaic acid (OA) is a major marine toxin that can cause diarrheic shellfish poisoning (DSP). Because of food safety concerns, simple and reliable field assays are in high demand. Herein, a highly sensitive fluorescent assay for OA in seafood was reported. For this purpose, a duplexed aptamer (DA) based on a conformational change upon binding OA was designed and immobilized on the surface of streptavidin-conjugated magnetic beads (SMBs). With the addition of OA, the DAs melted, and ss-aptamers were released into the solution. After magnetic separation, a terminal deoxynucleotidyl transferase (TdT)-mediated isothermal amplification system was formed via a free ss-aptamer acting as a template. This product with a poly(thymine) tail was directly added to a fluorescent copper nanoparticle (CuNP) formation system, and the ultralong consecutive T-rich sequence provided deposition sites for copper. Finally, the OA concentration was determined by recording fluorescence spectra and calculating the intensity change. This duplexed aptamer-isothermal amplification-based nucleic acid CuNP (DAIA-CuNP) sensor can achieve ultrahigh-sensitivity detection of OA compared to LC-MS and electrochemical methods. This DAIA-CuNP sensor can detect OA with a limit of detection (LOD) of 1.1 ng/L and a good linear range from 1.0 ng/L to 50.0 μg/L in shellfish extract. Additionally, this method is expected to be compatible with a handheld fluorescence reader and can meet field detection needs. • A simple, sensitive, and novel DAIA-CuNPs sensor was firstly proposed for specifically detecting OA in seafood. • A specific duplexed aptamer based on conformational change for OA was designed. • Single stranded T-rich nucleic acid CuNPs signal output system based on the TdT amplification to improve detection sensitivity. • DAIA-CuNPs sensor had a low LOD and wide linear range for OA. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, denatured bovine serum albumin (dBSA) has been developed as a useful scaffold for appending multiple oligonucleotides (ODNs), and the resulted novel dBSA-ODNs covalent hybrid can be self-assembled to the surface of CdTe quantum dots (QDs) via complexation with unoccupied coordination metal sites on QDs'' surface. The formed QDs/dBSA-ODNs bioconjugate could keep a long-term stability in aqueous solution while maintaining its fluorescence quantum yield and spectral properties. Furthermore, the QDs/dBSA-ODNs also can be readily hybridized with an anti-rHuEPO-α aptamers linked AuNPs (Apt-AuNPs) to form a fluorescent resonance energy transfer-based nano-biosensing system for highly sensitive and selective detection of rHuEPO-α protein lowered to 53.6pM in a rapid, simple manner. [Copyright &y& Elsevier]

[Display omitted] • A sensitive and novel mDAIA-NFF sensor was first proposed for OA detection. • A mismatched duplexed aptamer based on conformational change for OA was designed. • A label-free RCA coupled with ThT can further enhance the detection sensitivity. • This sensor detected OA with a LOD of 3.1 ng/L and showed a good linear range. • The method is compatible with handheld fluorimeters for further great promise. We developed a highly sensitive fluorescent assay to detect okadaic acid (OA), a prevalent aquatic toxin posing serious health risks. Our approach uses a mismatched duplexed aptamer (DA) immobilized on streptavidin-conjugated magnetic beads (SMBs) to create a DA@SMB complex. In the presence of OA, the cDNA unwinds, hybridizes with a G-rich segment pre-encoding circular template (CT), and undergoes rolling circle amplification (RCA) to produce G-quadruplexes, which are detected using the fluorescent dye thioflavine T (ThT). The method has a LOD of 3.1 × 10-3 ng/mL, a linear range of 0.1 ∼ 1.0 × 103 ng/mL, and was successfully applied to shellfish samples with spiked recoveries of 85.9% ∼ 102.2% and RSD less than 13%. Furthermore, instrumental analysis confirmed the accuracy and reliability of this rapid detection method. Overall, this work represents a significant advancement in the field of rapid aquatic toxin detection and has important implications for public health and safety. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel IFN-γ aptamers were identified by highly efficient and convenient CE-SELEX within only three rounds. • A cost-effective and practical truncated aptamer was obtained with the aid of molecular simulations. • The developed fiber-optic evanescent wave aptasensor provides a novel methodology for detecting IFN-γ. Interferon-gamma (IFN-γ) is a critical indicator of the immune response to many infections and diseases. Identifying excellent IFN-γ recognition molecules is of great significance for the early diagnosis and treatment of diseases. Herein, anti-IFN-γ aptamers were selected based on capillary electrophoresis-systematic evolution of ligands by exponential enrichment (CE-SELEX) and their affinities were characterized by the biolayer interferometry (BLI) assay. A rational molecular docking strategy was utilized to predict precisely the binding behavior between aptamer and IFN-γ and remove redundant bases of original sequence. Therefore, aptamer IFNG-8 with the highest affinity can be efficiently identified within only three rounds and the truncated aptamer IFNG-8 T with comparable affinity is eventually obtained. With IFNG-8 T as the detection probe, a fiber-optic evanescent wave aptasensor is constructed for the detection of IFN-γ, which shows a wide linear range from 0.1 to 10000 pM and a low limit of detection (LOD) of 0.0718 pM. The developed aptasensor exhibits high selectivity and can be utilized for IFN-γ detection in human serum samples with good recoveries. In summary, the truncated aptamer can serve as a novel optional transducing element and the developed aptasensor provides an innovative methodology for detection of IFN-γ in trace amount. [ABSTRACT FROM AUTHOR]