Highly Efficient Fabrication of Fluorescent "Turn-On" Lateral Flow Strips for Highly Sensitive Detection of Small Molecules Based on Self-Assembly of AuAg Nanoclusters.

Currently, fluorescent "turn-on" lateral flow assay (FONLFA) has shown enhanced "naked eye" detection sensitivity for small molecules, while it is urgent to adopt biocompatible fluorescent nanomaterials and needs new strategies to simplify the preparation process. In this study, a highly effective method was proposed to produce FONLFA strips for the detection of small molecules. The gold-silver nanoclusters (AuAgNCs) were immobilized onto the nitrocellulose membrane of the strips by the self-assembly of poly(sodium 4-styrenesulfonate), antigen, and AuAgNCs. The immobilization process entails a straightforward mixing of the three components, taking merely 1 min, thereby bypassing the necessity for chemical modification of fluorescent nanomaterials. The strategy offers a significantly simplified process, which substantially enhances the efficiency of the strip fabrication. Utilizing this method, a FONLFA was developed for carbendazim with a visual limit of detection (vLOD) reduced by 40-fold compared with the conventional colorimetric lateral flow assay (LFA). Furthermore, the approach demonstrates versatility by enabling the immobilization of AuAgNCs and streptavidin, which facilitates the development of aptamer-based FONLFAs. The designed aptamer-based FONLFA for kanamycin exhibited a 50-fold reduction in the vLOD compared with conventional colorimetric LFAs. Therefore, FONLFA holds promising potential for widespread applications in the analysis of small molecules.

Rapid and ultra-sensitive lateral flow assay for pathogens based on multivalent aptamer and magnetic nanozyme.

Ultra-sensitive LFA methods for pathogen detection commonly depended on tedious and time-consuming nucleic acid amplification. Here, a high affinity multivalent aptamer (multi-Apt) for S. aureus was obtained through exquisite engineering design. The scaffold and conformation of the multi-Apt were found to be key factors in the detection signal of aptsensors. After optimization, the binding affinity of the multi-Apt to S. aureus was improved by more than 8-fold from 135.9 nM to 16.77 nM. By the joint use of the multi-Apt and a multifunctional nanozyme Fe3O4@MOF@PtPd, a fast and ultra-sensitive LFA for S. aureus was developed (termed MA-MN LFA). In this method, a Fe3O4@MOF@PtPd nanozyme was modified with vancomycin and could efficiently capture and separate S. aureus. Moreover, the multi-Apt worked together with the nanozyme to bind with S. aureus to form a ternary complex at the same time, which simply the fabrication of LFA strip. The developed MA-MN LFA could detect S. aureus as low as 2 CFU/mL within 30 min and a wide linear range of 10-1 × 108 CFU/mL was obtained. The detection is easily operated, fast (can be completed within 30 min) and versatile for Gram-positive pathogens, thus has great potential as a powerful tool in pathogen detection.

A colorimetric sensor array based on nanoceria crosslinked and heteroatom-doped graphene oxide nanoribbons for the detection and discrimination of multiple pesticides.

Nanozymes have demonstrated high potential in constructing colorimetric sensor array for pesticides. However, rarely array for pesticides constructed without bio-enzyme were reported. Herein, nanoceria crosslinked graphene oxide nanoribbons (Ce-GONRs) and heteroatom-doped graphene oxide nanoribbons (Ce-BGONRs and Ce-NGONRs) were prepared, demonstrating excellent peroxidase-like activities. A colorimetric sensor array was developed based on directly inhibiting the peroxidase-like activities of the above three nanozymes, which realized the discrimination and quantitative analysis of six pesticides. In the presence of pesticides including carbaryl (Car), fluroxypyr-mepthyl (Flu), thiophanate-methyl (Thio), thiram (Thir), diafenthiuron (Dia) and fomesafen (Fom), the peroxidase-like activities of three nanozymes were inhibited to different degrees, resulting in different fingerprint responses. The six pesticides in the concentration range of 0.1-50 µg/mL and two pesticides mixtures at varied ratios could be detected and discriminated, and minimum detection limit for pesticides was 0.022 µg/mL. In addition, this sensor array has been successfully applied for pesticides discrimination in lake water and apple samples. This work provided a new strategy of constructing simple and sensitive colorimetric sensor array for pesticides based on directly inhibiting the catalytic activities of nanozymes.

Fluorescence "turn-on" sensing for five PDE5 inhibitors in functional food based on bimetallic nanoclusters.

Some phosphodiesterase type-5 (PDE5) inhibitors are active ingredients of prescription drugs that are widely used in the treatment of erectile dysfunction (ED). Recently, a large number of substances with this activity have been developed. Illegal addition of PDE5 inhibitors to foods could lead to cardiovascular diseases and even death, which poses a serious threat to food safety, therefore an on-site rapid screening method is urgently needed. Herein, a host functionalized bimetallic nanoclusters, CD/Au Ag NCs, were synthesized through self-assembly of 6-Aza-2-thiothymine gold nanoclusters (ATT-Au NCs), Arginine silver nanoclusters (Arg-Ag NCs) and carboxymethyl ß-cyclodextrin (ß-CMCD). The introduction of Rhodamine 6G (R6G) could quench the fluorescence of CD/Au Ag NCs based on the inner filter effect (IFE) and fluorescence resonance energy transfer effect (FRET). Importantly, it was discovered that several PDE5 inhibitors exhibited a higher binding affinity to ß-CMCD and could displace R6G binding with CD cavity, which disrupted the fluorescence quenching effects and resulted in the fluorescence recovery of CD/Au Ag NCs. This fluorescence turn-on signal could be utilized for the detection of PDE5 inhibitors. At present, emerging PDE5 inhibitor analogues pose a great challenge to food safety due to their unknown efficacy and safety. The proposed method holds the advantages of high sensitivity, simple probe synthesis, easy operation, and simultaneous detection of multiple PDE5 inhibitors. Meanwhile, the successful application in functional food sample demonstrated its high application potential in multiple PDE5 inhibitors screening.

A simplified fluorescent lateral flow assay for melamine based on aggregation induced emission of gold nanoclusters.

A novel lateral flow assay (LFA) was developed based on the aggregation induced emission (AIE) of gold nanoclusters (AuNCs) for the detection of melamine. We compared the interaction between melamine and AuNCs prepared with 6-Aza-2-thiothymine (ATT) and its four structural analogs as ligands and found that the ATT-AuNCs showed the best AIE induced by melamine. Then the ATT-AuNCs were directly immobilized on the test line of LFA strips as reporters. The sensing platform exhibited a linear response to melamine from 1 to 100 µM (R2 = 0.997) with a detection limit of 217 nM. Moreover, this LFA strip could discriminate 1.0 µM melamine clearly by the naked eyes within 3 min. The recoveries of 91.6-101.5% were attained in milk and baby formula samples. This strip inherited the superior characteristics of low background interference of aggregation-induced fluorescence recognition and LFA technology, thus effectively avoiding the use of antibodies, aptamers, and other biological elements.

[Application of confocal technology based on polycapillary X-ray lens in measuring thickness].

A confocal micro X-ray fluorescence thickness gauge based on a polycapillary focusing X-ray lens, a polycapillary parallel X-ray lens and a laboratory X-ray source was designed in order to analyze nondestructively the thickness of thin film and cladding material. The performances of this confocal thickness gauge were studied. Two Ni films with a thickness of about 25 and 15 microm respectively were measured. The relative errors corresponding to them were 3.5% and 7.1%, respectively. The thickness uniformity of a Ni films with a thickness of about 10 microm was analyzed. This confocal technology for measuring the thickness was both spatially resolved and elemental sensitive, and therefore, it could be used to measure the thickness of the multilayer sample and analyze the thickness uniformity of the sample. This confocal thickness gauge had potential applications in analyzing the thickness of sample.