Surface-enhanced Raman scattering (SERS) is a promising analysis technique for detecting various analytes in complex samples due to its unique vibrational fingerprints and high signal enhancement. However, impurity interference and substrate unreliability are direct suppression factors for practical application. Herein, we synthesize polydopamine@gold (PDA@Au) nanowaxberry, where Au nanoparticles are deposited on the surface of PDA sphere with high density and uniformity. Seed-mediated synthesis is used for fabrication of nanowaxberry. Au seeds are deposited on the surface of PDA sphere, then I ion coordinating ligand is employed to form stable AuI complex with AuCl, which decreases reduction potential of AuCl and avails formation of shell structure. Such nanowaxberry has high density of voids and gaps in three-dimensional space, which could absorb analytes and benefit practical SERS detection. Using malachite green as a model analyte, nanowaxberry realizes highly sensitive detection with low limit of detection (1 pM) and good reproducibility (relative standard deviation of about 10%). Meanwhile, the nanowaxberry is employed for practical detection of thiram, benzidine, and 2,4-dinitrotoluene in the environmental water, juice, apple peel, and soil. The high performance makes nanowaxberry to be potentially used for pesticides detection, pollutants monitoring, and forbidden explosives sensing in complex samples.
Surface-enhanced Raman scattering (SERS) has proven to be an effective technique for identifying and providing fingerprint structural information on various analytes in low concentration. However, this analytical technique has been plagued by the ubiquitous presence of organic contaminants on roughened SERS substrate surfaces, which not only often result in poorer detection sensitivity but also significantly affect the reproducibility and accuracy of SERS analysis. Herein, we developed a clean, stable, and recyclable three-dimensional (3D) chestnutlike Ag/WO (0 < x < 0.28) SERS substrate by simple hydrothermal reaction and subsequent green in situ decoration of silver nanoparticles. None of the organic additives were used in synthesis, which ensures the substrate surfaces are completely clean and free of interferences from impurities. The innovative design combines the SERS enhancement effect and self-cleaning property, making it a multifunctional and reusable SERS platform for highly sensitive SERS detection. Using malachite green as a model target, the as-prepared SERS substrates exhibited good reproducibility (relative standard deviation of 7.5%) and pushed the detection limit down to 0.29 pM. The enhancement factor was found to be as high as 1.4 × 10 based on the analysis of 4-aminothiophenol. The excellent regeneration performance indicated that the 3D biomimetic SERS substrates can be reused many times. In addition, the fabricated substrate was successfully employed for detecting thiram in water with a detection limit of 0.32 nM, and a good linear relationship was obtained between the logarithmic intensities and the logarithmic concentrations of thiram ranging from 1 nM to 1 μM. More importantly, the resultant SERS-active colloid can be used for accurate and reliable determination of thiram in real fruit peels. These results predict that the proposed SERS system have great potential toward rapid, reliable, and on-site analysis, especially for food safety and environmental supervision.
In this paper, the soluble salt-assisted route has been extended to the low-cost and scalable preparation of ZnO nanostructures via the simple oxidation of Zn-Na2SO4 mixture followed by washing with water. The as-prepared ZnO nanopowders are of nanoscaled size, hexagonal phase, and pure, without being stained by Na2SO4. Their optical band gap is 3.22 eV, exhibiting a red-shift of 0.15 eV in comparison with pure ZnO bulk, and their optical absorbance is strong in the region of 200-400 nm, suggesting their full utilization of most of the UV light in sunlight. The product shows evident photocatalytic activity in degradation of RhB under solar light irradiation, and then its solar light degradation efficiency is close to that under UV irradiation, indicating that there is a possibility of practical application. More importantly, the obtained ZnO nanoparticles, because of the quick precipitation by themselves in solution with no stirring, could be easily recycled without any accessorial means such as high-speed centrifuge. The low-cost and scalable preparation, high photocatalytic activity, and convenient recycling of this ZnO nanomaterial gives it potential in purifying waste water. Hence the interesting results in this study indicate the wide range of the soluble salt-assisted route for the industrial preparation of many other advanced nanomaterials.
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