Shixuan He

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.

Direct growth of graphene nanowalls on the crystalline silicon for solar cells

We developed a simple approach to fabricate graphene/Si heterojunction solar cells via direct growth of graphene nanowalls on Si substrate. This 3D graphene structure was outstanding electrode network and could form fine interface with Si substrate. Moreover, direct growth method not only simplified manufacturing process, but also avoided damages and contaminants from graphene transfer process. The short-circuit current (Jsc) increased greatly and could reach 31u2009mA/cm2. After HNO3 doping, the energy conversion efficiency was increased up to 5.1%. Furthermore, we investigated the influence of growth time on the cell performance.

Identification and analysis of Triphenyltin chloride with surface enhanced Raman scattering spectroscopy

Triphenyltin (TPhT) is a kind of organotin compounds which have been used ubiquitously as herbicide, pesticide, and fungicide in agriculture. The present study provides the possibility to detect and monitor TPhT with normal Raman spectroscopy and surface enhanced Raman scattering (SERS) spectroscopy. Firstly, the complete vibrational Raman spectra characterization of TPhT along with the IR spectroscopy were reported for the first time. Then a wide range of pH values were carried out to choose the optimal pH value in TPhT detection by using Raman spectroscopy. Afterwards, Raman spectra of various TPhT solutions were collected and analyzed. The results indicate that the optimal pH value for TPhT detection by Raman spectroscopy is 5.5, and with silver nanoparticles (Ag NPs) as SERS substrate is an effective technique for trace TPhT detection with an enhancement by 5 orders of magnitude and the detection limit can be as low as 0.6xa0ng/L within less than 30xa0s. Finally, in this study, the residual of TPhT on apple peel was investigated by casting different concentrations of TPhT on apple peel under the current optimized condition. The result demonstrates that TPhT could be detected based on its SESR spectra at 6.25xa0ng/cm(2) in standard solutions.

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.

Objective-type dark-field imaging spectroscopy applied to monitor the orientation of nonspherical gold nanoparticles

Abstract. An objective-type dark-field imaging spectroscope is used for imaging the orientation of single nonspherical nanoparticles. This simple and effective technique is able to simultaneously provide the spectral and spatial information of single nanoparticles. The orientation information of the nanoparticles is determined by investigating their polarization dependent longitudinal and transverse plasmon resonant wavelengths. The determination of the nanoparticles’ orientation could be used as a complementary tool to fluorescent labeling in biological applications.

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.

In situ fabrication of graphene nanowalls as active surface-enhanced Raman scattering substrate

Graphene-wall (G-wall) nanostructure was directly grown on the surface of copper foil by plasma enhanced chemical vapor deposition (PECVD) method, and then was employed as active G-wall surface-enhanced Raman scattering (GW-SERS) substrate. To investigate the SERS activity of this G-wall substrate, rhodamine 6G was used as a target molecule. And better Raman enhancement ability was observed, compared with the graphene film on the copper foil. Meanwhile, this novel G-wall based GW-SERS substrate not only maintained the high SERS activity, but also could be easily obtained in large scale. Moreover, the substrate could avoid the use of noble metals, self-assembled steps, complicated photolithograph treatments, as well as the graphene transferring processes. And the GW-SERS substrate could provide the high SERS activity and eliminate fluorescence background noise. Hence, this GW-SERS substrate could be potentially applied for detecting trace amount of analytes in future analytical detection fields.