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[Display omitted] • A biosensor for detecting β-carotene in seaweeds was developed to meet the urgent need. • A composite post-SELEX strategy to generate high-affinity aptamer was proposed. • The optimal aptamer showed 177.5-fold higher affinity than the parent aptamer. • A fluorescent aptasensor based on the conformation-switch of aptamer was developed. β-Carotene is an important bioactive component showing great activities and receiving great attention in recent years. The traditional methods for the accurate detection of β-carotene in food are time-consuming. There is an urgent need to establish rapid quantification methods for β-Carotene. Herein, a label-free fluorescent aptasensor which was based on the conformation-switch of the aptamer probe was developed to detect β-carotene in seaweeds. Firstly, a post-SELEX strategy based on extraction and terminal-fixation was established to evolve the anti-β-carotene aptamer to achieve high affinity. An aptamer probe (β-2-TF) with a 177.5-fold affinity increment was obtained and then applied to develop a probe conformation-switch-based fluorescent aptasensor with the assistance of SYBR Green I (SGI). Under the optimal conditions, the aptasensor exhibited good accuracy and selectivity, with a linear detection range of 62.5–4000 nM and a limit of detection (LOD) as low as 39.64 nM. The developed strategies can act as robust references for the analytical method development in the food field. [ABSTRACT FROM AUTHOR]

Developing simultaneous detection methods for multiple targets is crucial for the field of food analysis. Herein, enrofloxacin (ENR) and ciprofloxacin (CIP) were taken as model targets. For the first time, a strategy to generate group-specific split aptamers was established by revealing and splitting the critical binding domain, and the split aptamers were exploited to design a four-way DNA junction (4WJ) which could regulate the enzymatic activity of chitosan oligosaccharide (COS)-AuNPs nanozyme to develop a colorimetric aptasensor. A pair of split aptamers were obtained for ENR (K d = 15.00 nM) and CIP (K d = 4.870 nM). The mechanism of COS binding with double-stranded DNA in the 4WJ was elucidated. Under optimal conditions, the colorimetric aptasensor enabled a wide linear detection range of 1.4–1400 nM and a limit of detection (LOD) of 321.1 pM and 961.0 pM towards ENR and CIP, respectively, which exhibited excellent sensitivity, selectivity, and availability in detecting ENR/CIP in seafood. This study expands the general strategies for generating robust aptamers and nanozyme complex and provides a good reference for developing multi-target detection methods. [Display omitted] • Enrofloxacin (ENR) and ciprofloxacin (CIP) were taken as the model group targets. • A strategy of generating high-affinity group-specific split aptamers was proposed. • A complex nanozyme with high activity was fabricated with 4WJ, COS, and AuNPs. • A colorimetric aptasensor was developed with the split aptamers and the nanozyme. • The aptasensor achieved simultaneous and sensitive detection of ENR/CIP in seafood. [ABSTRACT FROM AUTHOR]

[Display omitted] • A label-free fluorescent aptasensor was developed for diarrhetic shellfish poisons. • Group-specific split aptamers and silver nanocluster beacon were combined. • The aptasensor can screen simultaneously-three targets in food-related samples. • LOD of 2.282, 19.38, and 13.61 nmolL-1 for the three targets were obtained. • This study can be referred for other food-related small molecules. Poisoning events concerning diarrhetic shellfish poisons (DSPs) are increasing continually. It is extremely necessary to develop simple analysis methods for screening simultaneously different types of DSPs from food-related samples. Okadaic acid (OA) and its analogues, i.e., dinophysistoxin-1 (DTX-1) and dinophysistoxin-2 (DTX-2), are the prevalent DSPs. Herein, a facile and label-free fluorescent aptasensor targeting the three DSPs was constructed with a pair of group-specific split aptamers and silver nanocluster beacon. In presence of the targets, the DNA templates attached at the ends of the split aptamers would be dragged close to trigger enhanced fluorescence signals from silver nanoclusters. The aptasensor offered high sensitivity and good selectivity, with limit of detection of 2.282 nmolL-1, 19.38 nmolL-1, and 13.61 nmolL-1 for OA, DTX-1, and DTX-2, respectively. Moreover, the applicability of aptasensor was well verified with shellfish and seawater samples. This study provides good reference for further exploration on analysis methods for food-related molecules. [ABSTRACT FROM AUTHOR]

[Display omitted] • A class of diarrhetic shellfish poisons were taken as models of small molecule targets. • A pair of group-specific split aptamers were generated for this class of small molecules. • A non-competitive aptasensor was developed with the split aptamers and HCR-AuNPs nanozyme. • The aptasensor achieved highly sensitive and simultaneous detection of the group targets. • The study can be referred to develop strategies for other small molecules in food matrix. Constructing robust group-specific probes and non-competitive analysis methods for small molecules in the fields of food analysis is of great significance. In this study, three diarrhetic shellfish poisons (DSPs) with high safety risks to humans were taken as models of group targets, and a non-competitive and turn-on format colorimetric aptasensor was constructed for simultaneous and highly sensitive detection of the class of DSPs. A pair of anti-DSP split aptamers were generated with group-specific binding affinity to the three targets. The split aptamers were then fabricated with a hybridization chain reaction (HCR)-enhanced AuNPs nanozyme. The aptasensor realized linear detection range of 187.5–3000 pM, high sensitivity with a limit of detection (LOD) as low as 65.36 pM, good selectivity, as well as good accuracy when analyzing the DSPs in shellfish samples. This study provides good reference for developing robust probes and facile biosensors to detect multiple small molecules in food matrix. [ABSTRACT FROM AUTHOR]

Highly efficient detection of group targets is of great significance. Okadaic acid (OA), dinophysistoxin-1 (DTX-1), and dinophysistoxin-2 (DTX-2) are the main diarrhetic shellfish poisons (DSPs) and have similar structures. As essential auxiliary tools, facile methods for simultaneous screening of these three DSPs are urgently needed. In this study, we report an aptamer-based platform which integrates pretreatment and quantitation for preliminary and simultaneous screening of the three DPSs. With computational study-assisted post-selection strategies, a truncated aptamer and a pair of split aptamers were generated with group-specific and high affinity towards the DSPs. The truncated aptamer was adopted to prepare an aptamer affinity column (AAC) for enrichment and purification of DSPs in real samples. The split aptamers were combined with G-quadruplex-hemin nanozyme to fabricate a label-free colorimetric aptasensor for quantitation. The prepared AAC showed good enrichment capacity. The developed colorimetric aptasensor provided high sensitivity, with limit of detection of 0.7011 nM, 14.27 nM, and 5.374 nM towards OA, DTX-1, and DTX-2, respectively, as well as high selectivity and accuracy. UPLC-MS was then only needed to analyze the suspicious positive samples, and highly efficient detection was achieved. This robust platform could be referred for preliminary screening of other group analytes. [Display omitted] • An integrated aptamer-based platform was developed for group targets, i.e., three DSPs. • Two types of group-specific aptamers were generated with proposed post-selection strategy. • The truncated aptamer was adopted to develop affinity column for sample pretreatment. • The split aptamers were used to develop an aptasensor for preliminary screening of the DSPs. • The integrated platform contributed greatly to the highly efficient detection of group targets. [ABSTRACT FROM AUTHOR]

Okadaic acid (OA), dinophysistoxin-1 (DTX-1), and dinophysistoxin-2 (DTX-2) are the main diarrheic shellfish poisons (DSPs). Detection methods to achieve simultaneous detection of the three toxins are urgently needed. In this paper, a terminal fixation design proposed in our previous study was further explored to engineer an aptamer with group-specific recognition ability from an original aptamer binding to one target. Both molecular docking assay and biolayer interferometry assay were applied to reveal the binding mechanisms between three DSPs and the engineered aptamer. Then, a label-free colorimetric aptasensor by fabricating the aptamer with AuNPs@Fe2+ nanozyme was constructed, which provided a wide linear detection range (0.4688–7.5 nM), a very low limit of detection (LOD, 86.28 pM), and good recoveries (96.02–104.9%) when analyzing DSPs in seawater and scallop samples, indicating the engineered aptamer and the developed aptasensor had great potential in recognizing and detecting multiple DSPs in real world. [Display omitted] • A group-specific terminal-fixed aptamer was engineered for three DSPs. • The engineered aptamer showed high affinity at nM level towards the three DSPs. • The aptamer was fabricated with AuNPs@Fe2+ to develop a colorimetric aptasensor. • The aptasensor achieved simultaneous detection of the DSPs with high sensitivity. • The study can be referred to develop multiple-functional aptamers/aptasensors. [ABSTRACT FROM AUTHOR]

• A terminal-fixed anti-saxitoxin aptamer was engineered by terminal hybridization. • The engineered aptamer showed 145-fold higher affinity than the original aptamer. • The engineered aptamer was applied to develop a label-free colorimetric aptasensor. • The aptasensor provided high sensitivity towards saxitoxin determination. • The study can be referred to develop aptamers/aptasensors for other small molecules. Aptamers show great potentials to be applied for the analysis of small molecules, while the applications of aptamers are now suffering from their weak affinity. Herein, saxitoxin (STX) was chosen as a model target of small molecules. A terminal-fixed anti-STX aptamer (TF-M-30f) was firstly engineered by terminal hybridization. Biolayer interferometry assay showed the terminal-fixed aptamer exhibited a 145-fold higher affinity than the original aptamer. Then, the terminal-fixed aptamer was hybridized with a complementary DNA (cDNA) and fabricated with AuNPs nanozyme to develop a label-free colorimetric aptasensor. In the presence of STX, the aptamer was competitively bound, and the cDNA was released to trigger the enhancement of the peroxidase-like activity of the AuNPs. Computational assays were performed to assist in the rational designs. With the optimal conditions, the developed aptasensor provided a limit of detection as low as 142.3 pM, a linear detection range of 0.1457−37.30 nM, high selectivity, and good recoveries of 98.21–114.1% when analyzing STX in seawater and scallop samples, indicating the high applicability of the engineered aptamer and the developed aptasensor. These innovations can be referred to further develop robust aptamers and aptasensors for small molecules. [ABSTRACT FROM AUTHOR]