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Malathion is a toxic organophosphorus pesticide. When ingested by humans, it affects the nervous system and endangers health. Herein, a new type of aptamer-based sensor was developed for its determination. The results demonstrate that this sensor has high sensitivity and good selectivity and was successfully used for the determination of malathion in apples. The detection mechanism is as follows. The aptamer is adsorbed on the surface of gold nanoparticles (AuNPs) to prevent the aggregation of AuNPs in a high salt solution. After adding malathion, the aptamer specifically binds to malathion and is removed from the surface of the AuNPs. The quantity of aptamer adsorbed on the surface of AuNPs had a negative relationship with the malathion concentration. The unmodified AuNPs aggregated to different degrees in NaCl solution. In the Fehling reaction, various degrees of aggregated AuNPs catalyze the reduction to different size Cu2O and exhibit different resonance scattering intensities. An excellent linear response between the resonance scattering spectra intensity and malathion concentration was obtained. The limit of detection of the developed method was 5.24 ng/L (15.86 pM). The recovery and repeatability for the apple samples were satisfactory. [ABSTRACT FROM AUTHOR]

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]

• A novel fluorescence switching aptasensor for ultrasensitive detection of Kana was developed. • Aptamer as fluorescence switching was simple to fabricate. • The constructed aptasensor showed high selectivity and accuracy. • The limit of detection, accuracy and recovery rate of the developed fluorescence aptasensor were satisfied. We developed a fluorescent switching based on bovine serum albumin stabilized gold nanoclusters (BSA-AuNCs) and kanamycin (Kana) aptamer to detect Kana. Red fluorescence of BSA-AuNCs was turn off when Kana aptamer was assembled on the surface of BSA-AuNCs. However, after adding Kana, the specific aptamer detached from the surface of the BSA-AuNCs and formed the complex of aptamer-kanamycin, then the red fluorescence of BSA-AuNCs was turn on. The fluorescence intensity of BSA-AuNCs can be mediated by the amount of Kana aptamer. A good linear response for Kana was obtained in the concentration range 0.04 nM to 7.0 nM. The assay was used to detect Kana in milk matrix, and the accuracy and recovery of the method were satisfied. It is worth noting that the aptamer mediated BSA-AuNCs fluorescent switching was simple and easy to fabricate, which can provide a novel assay for the detection of small molecules. [ABSTRACT FROM AUTHOR]

• The building materials of sensor were low cost and the experimental operation was simple. • The developed colorimetric sensor showed high sensitivity, selectivity and stability for GEN detection. • The detection limit, detection accuracy and recovery rate were satisfied. The residue of gentamicin (GEN) in food is a serious threat to human health. Therefore, it is urgent to develop a simple and highly sensitive method for effectively detecting GEN in food. In this study we proposed a lysine-functionalized gold nanoparticles (AuNPs) colorimetric sensor to detect GEN simply and quickly. The detection mechanism as follows: The interaction between lysine and AuNPs causes lysine to adsorb on the surface of AuNPs. After the addition of GEN, the strong hydrogen bond between GEN and lysine promotes the aggregation of AuNPs. The color of AuNPs changed from wine red to blue, which produced obvious color change. UV–vis spectrometer was used to detect it. The results showed that the colorimetric sensor had high selectivity and sensitivity for the detection of GEN, and the linear range and limit of detection were 5–60 nM and 1.22 nM, respectively. In addition, this method has been successfully applied to the quantitative detection of GEN in milk, and the accuracy and recovery were satisfied. [ABSTRACT FROM AUTHOR]