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As an emerging fluorescent nanomaterial, gold nanoclusters are of increasing interest in sensing and imaging because of their stable luminescence properties, large Stokes shift and low toxicity. Here, red-emitting gold nanoclusters stabilized by 6-Deoxy-6-mercapto-β-cyclodextrin (6-SH-CD@Au NCs) were successfully synthesized based on photo-reduction method for the detection of chlortetracycline. Under alkaline conditions, chlortetracycline transforms into iso-chlortetracycline (iso-CTC), which has a distinct blue fluorescence at 415 nm. The fluorescence intensity at 415 nm changed with increasing concentration of chlortetracycline and inner filter effect (IFE) of 6-SH-CD@Au NCs, while the fluorescence of the gold nanocluster at 670 nm decreased due to the IFE of iso-CTC. This fluorescent system detected chlortetracycline with good linearity in the concentration range of 5 nM-1 μM, and the limit of detection is 2.7 nM. The developed fluorescence sensor and test paper assay had been successfully applied for the detection of chlortetracycline in milk samples. The results demonstrated that the ratiometric sensor has advantages of simplicity, high sensitivity and specificity, cost-effectiveness and ease of operation. [Display omitted] • The novel photo-reduction strategy for the synthesis of gold clusters is a simple green process. • The method has good selectivity and sensitivity for chlortetracycline. • The fluorescent sensor was successfully applied to the detection of CTC in milk. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) is a kind of biological hydrolase which plays a key role in the normal growth of the body. Therefore, it is necessary to establish a simple and accurate method for quantitative detection of ALP. In this work, gold nanoclusters with bovine serum albumin as a template (BSA-AuNCs) were rapidly synthesized in 20 s based on microwave-assisted. Subsequently, manganese dioxide (MnO 2) was generated in situ on the surface of the gold nanoclusters which quenched the fluorescence of BSA-AuNCs. The quenching mechanism was explored and found that it was through the combined effect of fluorescence resonance energy transfer and inner filter effect. The quantitative detection of ALP was achieved through a simple enzymatic reaction and a redox reaction. The developed method was simple and convenient, and the detection limit for ALP was 1.5 mU mL−1. In addition, this fluorescence sensor had good selectivity and could accurately detect ALP in human serum, which demonstrated its potential applications in clinical diagnosis. [Display omitted] • Gold nanoclusters with strong red fluorescence were synthesized ultra-rapidly by microwave-assisted method. • Manganese dioxide grew in situ on the surface of BSA-gold nanoclusters. • The developed fluorescent sensor was low cost and the experimental operation was simple. • The fluorescent sensor was successfully applied to the detection of alkaline phosphatase in human serum. [ABSTRACT FROM AUTHOR]