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To obtain sensitive analytical detection methods, many unique materials have been developed and made them promising candidates for biosensing. In this study, a type of core-shell gold nanorods, GNR@Au 2 S/AuAgS/CuS, possessing peroxidase-like activity was prepared in a simple, facile manner. A colorimetric strategy for detection of blood glucose, insulin and differentiating type 1 and type 2 diabetes was developed based on the unique GNR@Au 2 S/AuAgS/CuS. The sensitive colorimetric approach for detection of glucose in the dynamic range of 2.5–200 μM was first established based on the catalytic performance of GNR@Au 2 S/AuAgS/CuS. Meanwhile, the catalytic activity of the peroxidase-like GNR@Au 2 S/AuAgS/CuS can be regulated by introducing the high affinity and specific reaction between DNA aptamer and insulin on the surface of GNR@Au 2 S/AuAgS/CuS, which allows the colorimetric assay to be extended to the detection of insulin, and a quantitative analysis of insulin based on the specific recognition can be implemented at the range from 0.014 to 1.08 μU/mL. Furthermore, colorimetric approach coupling peroxidase-like performance and specific recognition on the surface of GNR@Au 2 S/AuAgS/CuS nanoparticles was developed to measure glucose/insulin ratio and directly differentiate type 1 and type 2 diabetes mellitus. Practical human serum samples were tested and only the glucose/insulin ratio greater than 2.2 (μU/mL) may lead to the appearance of color change. The coupling of this different bioassay on the same nanoparticles reflects the versatility and integration characteristics of the colorimetric assay and is highly promising for improving diabetes management. Image 1 • Core-shell gold nanorods, GNR@Au 2 S/AuAgS/CuS, possessing peroxidase-like activity were prepared with facile method. • A colorimetric assay for detection of blood glucose and insulin was developed based on GNR@Au 2 S/AuAgS/CuS nanoparticles. • Strategy coupling peroxidase-like performance and specific recognition was developed to measure glucose/insulin ratio. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • UV-induced peroxidase-like activity of gold nanoclusters (AuNCs) was prepared with simple method. • A colorimetric assay was developed by integrating the AuNC-chitosan composite membrane with varying colored GNPs serving as output signal. • The extendable colorimetric strategy was used to differentiate pathogenic bacteria and detect SE-B with high sensitivity. Abstract In this study, gold nanoclusters (AuNCs) in the presence of chitosan were prepared assisted by UV irradiation, which exhibit peroxidase-like property tested with H 2 O 2 /3,3,5,5-tetramethylbenzidine (TMB). The chitosan-AuNCs composite membrane also behaves peroxidase-like property and was characterized by TEM, AFM and SEM, which reveal the formed membrane was homogeneous and the AuNCs are predominantly spherical and well-dispersed without agglomeration in the membrane. A colorimetric assay was established by integrating immunoreactions occurred on the enzyme mimicking AuNC-chitosan composite membrane with varying colored GNPs serving as output signal. Three kinds of bacteria were chosen to serve as model bacteria to evaluate the selectivity of this sensor and Staphylococcus aureus (S. aureus), can be easily differentiated from Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis). Such a colorimetric sensing is an extendable strategy due to the recognition element of probe may be replaceable on the catalytic AuNC-chitosan composite membrane. Staphylococcal enterotoxin B (SE-B) as low as 1.0 × 10−12 g/mL may be sensitively detected by naked-eye readout. As a practical application, the developed colorimetric strategy was used for rapid onsite screening strategy for S. aureus and detecting SE-B in food samples. This colorimetric strategy provides promising platform for rapid onsite screening pathogenic bacteria and detection of enterotoxin in food safety and environmental monitoring. [ABSTRACT FROM AUTHOR]