Su Ruifang,Zheng Hongru,Dong Shuyue,Sun Rui,Qiao Shangna,Sun Hongjing,Ma Xinyue,Zhang Tiehua,Sun Chunyan
The development of a novel method for melamine detection that uses a FAM–aptamer–G-quadruplex construct due to the efficient quenching ability of an aptamer-linked G-quadruplex is reported herein. The construct, which is labeled with the fluorescent dye 6-carboxyfluorescein (FAM), consists of two parts: a melamine-binding aptamer and a G-rich sequence that can form a G-quadruplex structure. Because of the specific recognition of melamine by the T-rich aptamer, this aptamer folds into a hairpin structure in the presence of melamine, which draws the G-quadruplex closer to the FAM fluorophore, leading to the quenching of the fluorescence of FAM. Thus, a highly sensitive and selective fluorescence strategy for assaying melamine was established. Under optimal conditions, the fluorescence quenching is proportional to the concentration of melamine within the range 10–90 nM, and the method has a detection limit of 6.32 nM. Further application of the method to plastic cup samples suggested that it permitted recoveries of between 97.15% ± 1.02 and 101.92% ± 2.07. The detected amounts of melamine spiked into the plastic cup samples and the corresponding amounts measured by HPLC were in good accordance, indicating that this fluorescent method is reliable and practical. Owing to its high sensitivity, excellent selectivity, and convenient procedure, this strategy represents a promising alternative method of melamine screening.
Graphical abstract
A simple, quick, effective turn-on fluorescence assay for the determination of fipronil (FIP) was built based on the yellow fluorescence of FAM-aptamer and excellent quenching capability of the oxidized single-walled carbon nanohorns (The oxidized SWCNHs). Oxidized SWCNHs with the great advantage of good dispersibility in solution were generated by link to carboxyl group and were added to a specific FAM-aptamer at an optimal concentration to form an “on–off” oxidized SWCNH/FAM-aptamer fluorescent sensor. The structures of the oxidized SWCNHs were verified, and the comprehensive properties were evaluated by characterization techniques. This paper has exploited oxidized SWCNHs as a quenching agent to detect fipronil for the first time. Under the optimized conditions, the limit of detection (LOD) for fipronil was 3 nM, and the recovery of fipronil varied from 88.6% to 112.7% in different real samples with relative standard deviations (RSDs) not more than 5%. The developed method could be successfully applied for the determination of fipronil in tap water, honey and corn samples.
Two-dimensional platforms generate considerable interests due to diverse application. We report a “turn-on” fluorescent nanoprobe for prostate-specific antigen (PSA) detection. It is based on cobalt oxyhydroxide nanosheets (CoOOH NSs). Fluorescein amidite (abbreviated as FAM)-labeled aptamer probe (abbreviated as FAM-aptamer) has been adsorbed onto the nanosheets. Energy transfer between substrate and optical species has induced the quenching of FAM-aptamer emission. The strong affinity of FAM-aptamer to the target PSA causes the formation of a rigid aptamer structure. The integration between FAM-aptamer and CoOOH NSs has been drastically affected. The release of the aptamer probe from the nanosheet surface has been realized. The green luminescence has been recovered. The dynamic nanosensor exhibits highly sensitive performance toward PSA with a linear detection range from 0.1 to 5 ng/mL. Its detection limit is measured to be 56.1 pg/mL. Therefore, a simple and efficient sensing platform for the detection of prostate cancer can be established.
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