Wanyi Xie

Multivariate qualitative analysis of banned additives in food safety using surface enhanced Raman scattering spectroscopy

A novel strategy which combines iteratively cubic spline fitting baseline correction method with discriminant partial least squares qualitative analysis is employed to analyze the surface enhanced Raman scattering (SERS) spectroscopy of banned food additives, such as Sudan I dye and Rhodamine B in food, Malachite green residues in aquaculture fish. Multivariate qualitative analysis methods, using the combination of spectra preprocessing iteratively cubic spline fitting (ICSF) baseline correction with principal component analysis (PCA) and discriminant partial least squares (DPLS) classification respectively, are applied to investigate the effectiveness of SERS spectroscopy for predicting the class assignments of unknown banned food additives. PCA cannot be used to predict the class assignments of unknown samples. However, the DPLS classification can discriminate the class assignment of unknown banned additives using the information of differences in relative intensities. The results demonstrate that SERS spectroscopy combined with ICSF baseline correction method and exploratory analysis methodology DPLS classification can be potentially used for distinguishing the banned food additives in field of food safety.

Surface enhanced Raman scattering substrate with metallic nanogap array fabricated by etching the assembled polystyrene spheres array

A sensitive surface enhanced Raman scattering (SERS) substrate with metallic nanogap array (MNGA) is fabricated by etching of an assembled polystyrene (PS) spheres array, followed by the coating of a metal film. The substrate is reproducible in fabrication and sensitive due to the nanogap coupling resonance (NGCR) enhancement. The NGCR is analyzed with the finite difference time domain (FDTD) method, and the relationship between the gap parameter and the field enhancement is obtained. Experimental measurements of R6G on demonstrate that the enhancement factor (EF) of the MNGA SERS substrate is increased by more than two fold compared with the control sample.

High-efficiency dispersion and sorting of single-walled carbon nanotubes via non-covalent interactions

Single-walled carbon nanotubes (SWCNTs) have attracted great attention on account of their superior and tunable electrical properties for promising applications in low-cost and high-performance nano-electronics and thin-film devices. However, SWCNTs are usually produced as a mixture of m-/s-nanotubes with small diameters and long aspect ratios and tend to form bundles or entangled ropes owing to their high van der Waals attraction and π–π interactions among their inter-tubes. Therefore, the dispersion and sorting of SWCNTs with both a high yield and desirable electronic structures has been a great challenge but a long-term motivation to achieve greater practical utility of SWCNTs. This review provides a comprehensive summary of the strategies for the surface modification and dispersion of SWCNTs, and surveys progress on the up-to-date development of SWCNTs enrichment via mainly non-covalent interactions with molecular species. The effect of the molecular architecture on the selective dispersion and sorting of SWCNTs by surfactants, bio-macromolecules, and conjugated polymers is discussed with respect to the structure–property relationship and interaction mechanism.

Ultrafast synthesis of Au(I)-dodecanethiolate nanotubes for advanced Hg2+ sensor electrodes

In this work, an ultrafast and facile method is developed to synthesize Au(I)-dodecanethiolate nanotubes (Au(I)NTs) with the assistance of glycyl-glycyl-glycine (G-G-G). Transmission electron microscopy (TEM) images reveal that the as-prepared Au(I)NTs can be obtained in a 2-h reaction instead of a previous 24-h reaction and are uniform with a hollow structure and smooth surface by virtue of the G-G-G peptide tubular template. According to structural analysis, a possible preparative mechanism is proposed that the G-G-G peptide could help to curl into tube-like morphology in alkaline situation spontaneously to accelerate the formation of Au(I)NTs. Meanwhile, PVDF-stabilized Au(I)NT-modified glassy carbon electrodes present their promising potential for Hg2+ detection.

A novel electrochemical sensor based on nafion-stabilized Au(I)–alkanethiolate nanotubes modified glassy carbon electrode for the detection of Hg2+

A novel method for Hg2+ detection with nafion-stabilized Au(I)–alkanethiolate nanotubes modified glassy carbon electrode has been developed on the basis of the high-affinity metallophilic interaction between Hg(II) and Au(I). Under optimum conditions, this method exhibits two good linear correlations in the concentration range of 1–100 nM and 100–1000 nM respectively, while the detection limit is 0.5 nM.

Fabrication of a trans-scale bimetallic synergistic enhanced Raman scattering substrate with high surface-enhanced Raman scattering activity

A novel enhanced Raman scattering substrate was fabricated using a vacuum-deposited Ag island film on Au film inverted pyramid pits (period is 2 μm). This trans-scale bimetallic synergistic enhanced Raman scattering (TBSERS) substrate was optimized for the detection of bisphenol A, and the detection limit can be as low as 0.5 ppm by this method.

Preliminary identification of unicellular algal genus by using combined confocal resonance Raman spectroscopy with PCA and DPLS analysis

The analysis of algae and dominant alga plays important roles in ecological and environmental fields since it can be used to forecast water bloom and control its potential deleterious effects. Herein, we combine in vivo confocal resonance Raman spectroscopy with multivariate analysis methods to preliminary identify the three algal genera in water blooms at unicellular scale. Statistical analysis of characteristic Raman peaks demonstrates that certain shifts and different normalized intensities, resulting from composition of different carotenoids, exist in Raman spectra of three algal cells. Principal component analysis (PCA) scores and corresponding loading weights show some differences from Raman spectral characteristics which are caused by vibrations of carotenoids in unicellular algae. Then, discriminant partial least squares (DPLS) classification method is used to verify the effectiveness of algal identification with confocal resonance Raman spectroscopy. Our results show that confocal resonance Raman spectroscopy combined with PCA and DPLS could handle the preliminary identification of dominant alga for forecasting and controlling of water blooms.

Fabrication of 3D nanovolcano-shaped nanopores with helium ion microscopy

Both helium and gallium ion beams were employed to fabricate nanopores. Herein, three-dimensional nano-volcano-shaped nanopores (3D-NVNs) were directly formed using helium ion beam with no precursors required, while the gallium ion beam produced V-shaped nanopores. Hundreds of 3D-NVNs were fabricated with a mean diameter of 229 ± 7 nm, where the He ion beam milling rate for the 3D-NVNs was 3.6 ± 0.2 μm3/μC. The height of the 3D-NVNs was greater than their depth when the dose range was 0–10 nC/μm2, while the height remained constant for doses above 10 nC/μm2. Trajectory simulations of the ion bombardment into the gold film clarified that ion implantation could primarily account for the volcano-shaped nanopore formation.Both helium and gallium ion beams were employed to fabricate nanopores. Herein, three-dimensional nano-volcano-shaped nanopores (3D-NVNs) were directly formed using helium ion beam with no precursors required, while the gallium ion beam produced V-shaped nanopores. Hundreds of 3D-NVNs were fabricated with a mean diameter of 229 ± 7 nm, where the He ion beam milling rate for the 3D-NVNs was 3.6 ± 0.2 μm3/μC. The height of the 3D-NVNs was greater than their depth when the dose range was 0–10 nC/μm2, while the height remained constant for doses above 10 nC/μm2. Trajectory simulations of the ion bombardment into the gold film clarified that ion implantation could primarily account for the volcano-shaped nanopore formation.

Assessment of physiological responses and growth phases of different microalgae under environmental changes by Raman spectroscopy with chemometrics

The assessment for cell physiology and growth phases of microalgae plays important roles in ecological and environmental fields since it can be used to forecast water eutrophication level worldwidely. Herein, growth phases and environmental conditions of microalgae were assessed by combining resonance Raman mapping spectroscopy with multivariate analysis methods. And, primary Raman characteristic peaks of microalgae were mined with two-dimensional synchronous spectra. Thereafter, algal growth phases and environmental conditions of microalgae were preliminary classified with different tendencies of characteristic Raman peaks by unsupervised principal component analysis (PCA) and support vector machine (SVM) methods. Our results demonstrated that resonance Raman mapping spectroscopy with PCA and SVM classification models can be used to assess algal growth phases and preliminary predict environmental conditions with characteristic Raman spectra of microalgae in water bodies.

Label-free sensitive detection of Microcystin-LR via aptamer-conjugated gold nanoparticles based on solid-state nanopores

A versatile and highly sensitive strategy for nanopore detection of microcystin-LR (MC-LR) is proposed herein based on the aptamer and host-guest interactions by employing a gold nanoparticle (AuNP) probe. The aptamer of MC-LR and its complementary DNA (cDNA) are respectively immobilized on AuNPs with distinct sizes (5 nm AuNPs for the aptamer and 20 nm for the cDNA), and the constructed polymeric AuNP network via the hybridization of the aptamer and cDNA was disintegrated upon the addition of MC-LR. The specific interactions between the aptamer and MC-LR disrupt and release the cDNA-AuNPs that were then removed by centrifugation, leaving the MC-LR-aptamer-AuNP species in the supernatant for subsequent nanopore determination. By monitoring the current blockade of released MC-LR-aptamer-AuNPs using a specific tailored nanopore (10 and 20 nm in diameter, generated by current dielectric breakdown), we could deduce the presence of MC-LR, as the bulky NP network could not pass through a nanopore with a relatively smaller size. We realized the detection of MC-LR with a concentration as low as 0.1 nM; additionally, we have proved the specificity of the interaction between the aptamer and MC-LR by replacing MC-LR with other congener toxins (MC-RR and MC-YR), chlorophyll (a component abundantly coexists in water), and the mixture of the four.