Junhong Lü

Coexistence of reentrant-spin-glass and ferromagnetic martensitic phases in the Mn2Ni1.6Sn0.4 Heusler alloy

A giant exchange bias field of up to 1170 Oe was observed in the Mn2Ni1.6Sn0.4 Heusler alloy. A reentrant spin glass phase and a ferromagnetic martensitic phase coexist below the blocking temperature as confirmed by dc magnetization and ac susceptibility measurements. Exchange bias in Mn2Ni1.6Sn0.4 is thought to originate from the interface exchange interaction between the reentrant spin glass phase and the ferromagnetic martensitic phase. X-ray diffraction and selected area electron diffraction results demonstrate that excess Mn atoms occupy Ni and Sn sites randomly. In this way, Mn-Mn clusters are formed and constitute the reentrant-spin-glass phase.

Capturing and depositing one nanoobject at a time: Single particle dip-pen nanolithography

A convenient technique for transferring nanoparticles in a one-particle-at-a-time fashion is presented. This technique, termed as single particle dip-pen nanolithography, employs an atomic force microscope (AFM) tip to “grab” individual gold nanoparticles on surfaces. The nanoparticles attached to the AFM tips can be then controllably released and redeposited site specifically on surfaces. Patterns composed of single gold particles have been fabricated.

Single-base resolution and long-coverage sequencing based on single-molecule nanomanipulation

We show new approaches towards a novel single-molecule sequencing strategy which consists of high-resolution positioning isolation of overlapping DNA fragments with atomic force microscopy (AFM), subsequent single-molecule PCR amplification and conventional Sanger sequencing. In this study, a DNA labelling technique was used to guarantee the accuracy in positioning the target DNA. Single-molecule multiplex PCR was carried out to test the contamination. The results showed that the two overlapping DNA fragments isolated by AFM could be successfully sequenced with high quality and perfect contiguity, indicating that single-base resolution and long-coverage sequencing have been achieved simultaneously.

Martensitic transformation and magnetic domains in Mn50Ni40Sn10 studied by in-situ transmission electron microscopy

The structural features, martensitic transformation, and magnetic domains in the Mn50Ni40Sn10 Heusler alloy are investigated by in-situ transmission electron microscopy and Lorentz microscopy. A rich variety of microstructural phenomena arising from structural and magnetic transitions are demonstrated at low temperatures. The “5M” or “6M” superstructure modulations and needle-shaped martensites have been clearly observed in the martensitic phase. Structural evolutions of magnetic domains are revealed under in-situ applied magnetic fields using Lorentz microscopy. The structural domains and reversibility of the phase transitions are analyzed based on our experimental observations and discussed in comparison with results of low-temperature magnetization.

DISPERSION AND FIXATION OF ADENO-ASSOCIATED VIRUS WITH GLUTARALDEHYDE FOR AFM STUDIES

Sample preparation is an important procedure for atomic force microscope (AFM) studies. However, flexible virus particles have a tendency to aggregate together and are easily compressed during sample preparation or by AFM tip that subsequently hamper studying of virus by AFM. Herein, low concentration chemical reagent of glutaraldehyde (2%, v/v) is pre-mixed in virus suspension that facilitates the dispersion and observation of recombinant serotype 2 adeno-associated virus particles deposited on mica surface with little deformation.

Multi-metal element analysis for the identification of foodborne pathogenic bacteria

Mineral element contents, combined with multivariate analysis, were used for the identification and classification of foodborne pathogens from a common genus (Rhodococcus equi, Staphylococcus spp., Listeria spp., Salmonella spp., Shigella spp., Escherichia coli, Enterobacter sakazakii, Yersinia enterocolitica and Vibrio spp.). 45 macro- and trace mineral elements of 30 foodborne pathogens were determined by a semiquantitative inductively coupled plasma mass spectrometry (SQ-ICP-MS) technique. The elemental analysis identified 10 significant elements (28Si, 43Ca, 57Fe, 47Ti, 52Cr, 55Mn, 66Zn, 88Sr, 137Ba and 208Pb) by ANOVA in different types of pathogens. Principal component analysis (PCA) reduced the 10 variables to 6 principal components which could explain 98.40% of the total variance. The classification models constructed by the Fisher linear discriminant analysis (Fisher LDA) and back-propagation artificial neural network (BP-ANN) achieved correctly classified rates of 86.9% and 91.3%, respectively. The results indicated that the combination of multi-metal element composition determination and multivariate analysis can be used as fingerprint to quickly identify and classify foodborne pathogens.