Lu-Lu Qu

Silver nanoparticles on cotton swabs for improved surface-enhanced Raman scattering, and its application to the detection of carbaryl

AbstractWe describe the preparation of a cotton swab for use in surface enhanced Raman scattering (SERS) by assembling silver nanoparticles (Ag-NPs) on common cotton. The flexibility of such cotton swabs allows for a close contact with sample surfaces by swabbing. This can considerably improve the sample collection efficiency. These cotton swabs exhibit excellent SERS activity as shown by the detection of rhodamine 6G at 0.81 pM concentration. The reproducibility of the intensity of SERS peaks is within 10xa0%. The applicability is demonstrated by in-situ detection of the fungicide carbaryl on a cucumber with an irregular surface. This combination of superior SERS activity, high reproducibility, accessibility in irregularly-shaped matrices and low-cost production indicates that such swabs offer a large potential in analytical SERS.n Graphical AbstractA cost-effective surface enhanced Raman scattering (SERS) cotton swab is developed by assembling silver nanoparticles on common cotton. The SERS cotton swab can be used for in-situ sensitive detection of pesticide residue.

Novel titanium dioxide-graphene-activated carbon ternary nanocomposites with enhanced photocatalytic performance in rhodamine B and tetracycline hydrochloride degradation

AbstractnA novel ternary nanocomposite consisting of activated carbon (AC) and titanium dioxide (TiO2) decoration in the presence of reduced graphene oxide (TiO2–rGO–AC) was fabricated by a facile hydrothermal synthesis method for use as a high-performance photocatalyst. The as-prepared TiO2–rGO–AC nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and UV–Vis diffuse reflectance spectroscopy. The results demonstrated that the TiO2 and activated carbon were well dispersed on the rGO surface. The photocatalytic performance of the TiO2–rGO–AC nanocomposite was evaluated as a catalyst for the photodegradation of rhodamine B. The degradation rate was 3.4 times higher than that of pure TiO2 under simulated solar light irradiation. The enhancement of photocatalytic performance is attributed to the adsorption of AC which significantly increased the organic molecule concentration near the catalytic surface, allowing the effective transfer and separation of photogenerated electrons. TiO2–rGO–AC photocatalyst is also effective for the degradation of tetracycline in aqueous solution, suggesting wide application of these nanocomposite materials in various fields including air purification and wastewater treatment.

On-demand fabrication of surface-enhanced Raman scattering arrays by pen writing, and their application to the determination of melamine in milk

AbstractAn on-demand, disposable and portable surface-enhanced Raman scattering (SERS) array has been prepared by modifying the surface of cellulose paper and patterning it with silver nanoparticles (AgNPs) via pen-writing technique. The paper is initially modified with hexadecenyl succinic anhydride to generate a hydrophobic top layer that is capable of concentrating melamine (and other hydrophobic analytes) by preventing the mainly aqueous sample from spreading on the paper. The AgNPs are subsequently written onto the hydrophobic paper with a high degree of control to form large-scale SERS sensing arrays. The resulting arrays demonstrate outstanding Raman scattering enhancement as demonstrated for the fluorescent dye Rhodamine 6G which can be detected by SERS with an 80 pM limit of detection (LOD) without interference by fluorescence. The reproducibility in the preparation of spots has a relative standard deviation of <15% (for nxa0=xa0128 spectra). The arrays were applied to the determination of the illicit milk additive melamine. The plot of SERS intensity at Δνxa0=xa0681xa0cm−1 versus the logarithm of melamine concentration is linear in the concentration range from 0.3 to 20xa0mg·L−1, and the LOD is 0.27xa0mg·L−1. In our perception, the disposable arrays presented here integrate the advantages of easy production and reliable reproducibility, and therefore are an ideal choice for use in SERS detection.n Graphical abstractAn on-demand, disposable and portable surface-enhanced Raman scattering (SERS) array has been developed by pen writing. Such a SERS array can be applied for the highly sensitive determination of the illicit milk additive melamine, which holds great promise for field-deployable applications.

Highly reproducible and sensitive silver nanorod array for the rapid detection of Allura Red in candy

Allura Red (AR) is a highly stable synthetic red azo dye, which is widely used in the food industry to dye food and increase its attraction to consumers. However, the excessive consumption of AR can result in adverse health effects to humans. Therefore, a highly reproducible silver nanorod (AgNR) array was developed for surface enhanced Raman scattering (SERS) detection of AR in candy. The relative standard deviation (RSD) of AgNR substrate obtained from the same batch and different batches were 5.7% and 11.0%, respectively, demonstrating the high reproducibility. Using these highly reproducible AgNR arrays as the SERS substrates, AR was detected successfully, and its characteristic peaks were assigned by the density function theory (DFT) calculation. The limit of detection (LOD) of AR was determined to be 0.05u202fmg/L with a wide linear range of 0.8-100u202fmg/L. Furthermore, the AgNR SERS arrays can detect AR directly in different candy samples within 3u202fmin without any complicated pretreatment. These results suggest the AgNR array can be used for rapid and qualitative SERS detection of AR, holding a great promise for expanding SERS application in food safety control field.

Removal of Antibiotics From Water with an All-Carbon 3D Nanofiltration Membrane

Recent industrial developments and increased energy demand have resulted in significantly increased levels of environmental pollutants, which have become a serious global problem. Herein, we propose a novel all-carbon nanofiltration (NF) membrane that consists of multi-walled carbon nanotubes (MWCNTs) interposed between graphene oxide (GO) nanosheets to form a three-dimensional (3D) structure. The as-prepared membrane has abundant two-dimensional (2D) nanochannels that can physically sieve antibiotic molecules through electrostatic interaction. As a result, the prepared membrane, with a thickness of 4.26xa0μm, shows both a high adsorption of 99.23% for tetracycline hydrochloride (TCH) and a high water permeation of 16.12xa0Lxa0m−u20092xa0h−u20091xa0bar−u20091. In addition, the cationic dye methylene blue (MB) was also removed to an extent of 83.88%, indicating broad applications of the prepared membrane.

Highly reproducible solid-phase extraction membrane for removal and surface-enhanced Raman scattering detection of antibiotics

A disposable solid-phase extraction (SPE) membrane was developed for rapid removal and sensitive surface-enhanced Raman scattering (SERS) detection of antibiotics in water samples. The membrane was fabricated on commercially available SPE column by filtration of the activated carbon modified with silver nanoparticles (Ag NPs/AC). The prepared SPE membrane exhibited outstanding preconcentration ability due to the high adsorption properties of AC, and excellent ability to enhance Raman signal resulting from “hot spots” between the embedded Ag NPs, improving the sensitivity of SERS detection. A detection limit (LOD) of 5.0u2009×u200910−11 and 1.6u2009×u200910−10xa0M was achieved for rhodamine 6G and p-aminothiophenol. In addition, the membrane exhibited high reproducibility with spot-to-spot variation in SERS spectral intensity less than 15%. Based on the membrane, the qualitative and quantitative analysis of the antibiotics in aqueous solution was accomplished with the LOD at nM level, demonstrating the feasibility of the disposable SPE membrane for in situ rapid preconcentration and detection.

Thin Layer Chromatography Combined with Surface-Enhanced Raman Spectroscopy for Rapid Sensing Aflatoxins

A fast and facile method was developed for on-site detection of aflatoxins (AFs) in moldy agricultural products using thin layer chromatography combined with surface-enhanced Raman spectroscopy (TLC-SERS). Four different AFs were successfully separated by TLC and then a small portable Raman spectrometer, with gold colloids as the SERS-active substrate, was applied to identify the separated spots. TLC-SERS application to on-site detection of AFs was systematically investigated. Qualitative and quantitative AF detection was found to be easily accomplished and limits of detection were estimated to be 1.5u2009×u200910-6, 1.1u2009×u200910-5, 1.2u2009×u200910-6, and 6.0u2009×u200910-7 M for AFB1, AFB2, AFG1, and AFG2, respectively. The proposed method was also highly selective, enabling successful AF identifications in complex extracts from moldy peanuts. The study showed that TLC-SERS could be effectively used for separation and detection of these four AFs, demonstrating good prospects for on-site qualitative screening of agricultural products.