Chunxiu Liu

An ascorbic acid amperometric sensor using over-oxidized polypyrrole and palladium nanoparticles composites

We constructed a highly responsive ascorbic acid (AA) sensor utilizing over-oxidized polypyrrole (OPPy) and Palladium nanoparticles (PdNPs) composites (OPPy-PdNPs). In the presence of PdNPs, polypyrrole (PPy) was coated on a gold (Au) electrode through cyclic voltammetry (CV) and over-oxidized at a fixed potential in NaOH solution. The PdNPs were characterized using ultraviolet-visible (UV-vis) spectrum and transmission electron microscopy (TEM). The surface of OPPy-PdNPs on the Au electrode was investigated using field-emission scanning electron microscopy (FE-SEM). Results revealed that the OPPy-PdNPs-modified Au electrode (OPPy-PdNPs/Au) has the capacity to catalyze the oxidation of AA by lowering its oxidation potential to 0 V. The OPPy-PdNPs/Au electrode exhibited 2 different linear concentration ranges. In the low concentration range (1-520 μM), OPPy-PdNPs/Au exhibited a direct linear relation with current responses and had high sensitivity (570 μA mM(-1)cm(-2)) and a high correlation coefficient (0.995). In contrast, in the higher concentration range (120-1600 μM), the relationship between current responses and concentration of AA can be represented by a two-parameter sigmoidal equation. In addition, the sensor exhibited a short response time (less than 2s) and a very low limit of detection of 1 μM. The electrochemical AA sensor constructed in this study was simple, inexpensive, reproducible, sensitive, and resistant to interference. Thus, the proposed sensor has great potential for detecting AA in complex biosystems and can be applied in various fields, particularly neuroscience.

A novel dual mode microelectrode array for neuroelectrical and neurochemical recording in vitro

The communication between neurons is inherently electrical and chemical in nature. In situ, simultaneous acquisition for the dual mode signals is important for neuroscience research. In this paper, the concept of dual mode neural microelectrode array (MEA) sensor was proposed, and a low cost thin film MEA chip for in vitro test was fabricated using standard lithography technology. The sensor incorporates arrayed microelectrodes, a counter electrode and a reference electrode on one glass slide, which is suitable for electrophysiological and electrochemical recording in vitro. Electrophysiological recordings were carried out on acute hippocampus slice. Local field potentials and three different spike firing patterns with the amplitude ranging from ± 20 μV to ± 60 μV were acquired by the arrayed microelectrodes. Electrochemical current response of the microelectrodes to calibrated dopamine solution was tested. A good linear relationship between the current and dopamine concentration was observed, with the detection sensitivity of 4671 μA mM(-1)cm(-2) and a correlation coefficient of 0.986. The sensor is novel for its capability of detecting in vitro dual mode neural signals on one single chip.

Candidate Milky Way satellites in the Galactic halo

Aims. Sloan Digital Sky Survey (SDSS) DR5 photometric data with 120 ◦ <α <270 ◦ ,2 5 ◦ <δ< 70 ◦ were searched for new Milky Way companions or substructures in the Galactic halo. Methods. Five candidates are identified as overdense faint stellar sources that have color-magnitude diagrams similar to those of known globular clusters, or dwarf spheroidal galaxies. The distance to each candidate is estimated by fitting suitable stellar isochrones to the color-magnitude diagrams. Geometric properties and absolute magnitudes are roughly measured and used to determine whether the candidates are likely dwarf spheroidal galaxies, stellar clusters, or tidal debris. Results. SDSSJ1000+5730 and SDSSJ1329+2841 are probably faint dwarf galaxy candidates while SDSSJ0814+5105, SDSSJ0821+5608, and SDSSJ1058+2843 are very likely extremely faint globular clusters. Conclusions. Follow-up study is needed to confirm these candidates.

Kernel regression for determining photometric redshifts from Sloan broad‐band photometry

We present a new approach, namely kernel regression, to determine photometric redshifts for 399 929 galaxies in the Fifth Data Release of the Sloan Digital Sky Survey (SDSS). Kernel regression is a weighted average of spectral redshifts of the neighbours for a query point, and higher weights are associated with points that are closer to the query point. One important design decision when using kernel regression is the choice of bandwidth. We apply 10-fold cross-validation to choose the optimal bandwidth, which is obtained as the cross-validation error approaches its minimum. The results show that the optimal bandwidth is different for different input patterns: the lowest rms error of photometric redshift estimation arrives at 0.019 using colour+eClass as the inputs, the lowest rms errors comes to 0.020 using ugriz+eClass as the inputs. Where eClass is a galaxy spectral type, and 0.021 using colour+ r as the inputs. Thus, in addition to parameters such as magnitude and colour, eClass is a valid parameter with which to predict photometric redshifts. Moreover, the results suggest that the accuracy of estimating photometric redshifts is improved when the sample is divided into early-type and late-type galaxies; in particular, for early-type galaxies, the rms scatter is 0.016 with colour+eClass as the inputs. In addition, kernel regression achieves high accuracy when predicting the photometric eClass (σ rms = 0.034) using colour+ r as the input pattern. For kernel regression, the accuracy of the photometric redshifts does not always increase with the number of parameters considered, but is satisfactory only when appropriate parameters are chosen. Kernel regression is a comprehensible and accurate regression method. Experiments reveal the superiority of kernel regression over other empirical training approaches.

Development of Amperometric Lactate Biosensor Modified with Pt-black Nanoparticles for Rapid Assay

For point-of-care determination, a disposable biosensor for the analysis of L-lactate in athletes serum samples was developed and optimized. The planar electrochemical biosensor was fabricated with gold thin-film two-electrode system and was modified with platinum-black nanoparticles and ferricyanide mediator. Platinum-black nanoparticles were deposited on the electrodes to improve the sensitivity and stability. Lactate oxidase (LOD, E.C.1.1.3.2) was immobilized on working electrodes with ferricyanide as mediator to improve the electron transfer ability by lowering the work potential to +0.2 V. The optimizations of the deposition of platinum-black nanoparticles, concentration of LOD, and concentration of ferricyanide in this article have resulted in the development of a lactate electrode with a wide linear range of 1–20 mM lactate, a high sensitivity of 1.43 µA mM−1, a fast detection time of 50 s, and a coefficient variation (CV) of 0.0549. The activity of biosensor held above 90% after one year storage at room temperature. The biosensor was successfully applied to the determination of L-lactate in serum samples without dilution. This disposable biosensor combined with portable meter is promising for rapid determination of point-of-care lactate.

Development and Application of 16-Channel Two-Mode Recording System for Neurochemical and Neuroelectrical Signals

Abstract A 16-channel two-mode recording system used for detection of neurochemical and neuroeletrical signals was developed. The instrument system consists of hardware and software components whose current and voltage resolutions are 10 pA and 0.6 μV, respectively. The software adopted multithreading, multicache, and other techniques to achieve real-time detection, spike separation, IIR filter, chronoamperometry, cyclic voltammetry, etc. The performance of the system was demonstrated in electrophysiological experiment and dopamine concentration measurement. The signal-to-noise ratio ( S/N ) recorded from VTA of SD rat was 9.7. The current response increased linearly with the concentration of dopamine in the range of 0.1–378 μM with a correlation coefficient of 0.9958. The results indicated that the recording system had high resolution and was suitable for electrophysiological and the electrochemical signal detection.

Application of Planar Microelectrode Array Modified by Nano-structure Titanium Nitride on Dual Mode Neural Information Recording

Abstract The nano-structure TiN was modified on the laboratory self-made planar microelectrode array pMEA by magnetron sputtering method. The performance of modified pMEA was investigated. The research on neuroelectrical and neurochemical recording was studied in vitro. The impedance of the modified pMEA was decreased almost one order of magnitude, and the background noise level was reduced to ±6 μV. In the same testing environment, the signal-to-noise ratio (SNR) of modified electrodes was 1.7 times of bare electrodes. The SNR of neuroelectrical recording on the brain slice of SD rats reached 10:1, and the weak signal such as ±12 μV was separated easily. For neuroelectrical recordings, the detection limit of dopamine (DA) solution reached 50 nM with the 2:1 SNR. In the concentration range of 0.05–100 μM, the linearly dependent coefficient of the DA oxidation currents was 0.998. The modification of nano-structure TiN on pMEA reduced pMEA impedance and background noise level, meanwhile the SNR was increased. The weak signals of neuroelectrical and neurochemical recording were successfully recorded.

Elastic and related transport cross sections for singly charged ion?atom scattering involving H, Be and C atoms and their ions

The elastic scattering of protons on Be and C atoms and of Be+ and C+ ions on hydrogen atoms is investigated using the multichannel quantal molecular orbital close-coupling method. The elastic, momentum transfer and viscosity cross sections, relevant to particle transport modelling, are calculated in the energy range 10−4 eV–10 keV. The corresponding charge transfer and target or projectile excitation cross sections are also calculated for comparison. The influence of channel couplings on the elastic processes is analysed. The molecular structure information required for the cross-section calculations was obtained by employing the multireference single- and double-excitation configuration interaction method.

A novel method to directionally stabilize enzymes together with redox mediators by electrodeposition

This paper depicts a novel method to directionally stabilize enzymes together with redox mediators by electrodeposition. Chitosan was used as a stabilizing matrix. By electrochemical removal of local H(+), chitosan close to working electrode became locally insoluble, and enzymes and redox mediators in chitosan were stabilized. The microelectrode on home-made microelectrode array (MEA) served as the working electrode. Three model enzymes--horseradish peroxidase (HRP), glucose oxidase (GOD), and glutamate oxidase (GlOD)--were used to fabricate different biosensors, and the redox mediator model was a poly(vinylpyridine) complex of Os(bpy)2Cl and a diepoxide (PVP-Os). Biosensors fabricated by the method exhibited very high performance. For HRP biosensor fabricated by this method, the sensitivity was 5.274 nA μM(-1) mm(-2), with linear detection range (LDR) of 2-220 μM and limit of detection (LOD) of 1 μM (S/N=3); for GOD biosensor, the sensitivity was 2.65 nA μM(-1) mm(-2), with LDR of 4-500 μM and LOD of 2 μM (S/N=3); for GlOD biosensor, the sensitivity was 0.33 nA μM(-1)mm(-2), with LDR of 4-500 μM and LOD of 2 μM (S/N=3). Since this method is very simple and especially suitable for directionally introducing enzymes and redox mediators onto microelectrode without contaminating other sites in the same microenvironment, it could be used for fabricating in vivo or in vitro 2nd generation biosensors in μm-scale, especially in neuroscience.

Detection of Bacillus Anthracis Using Fluorescence Immunoassay with Quantum Dots Labels

Abstract A method for detecting Bacillus anthracis ( B. anthracis ) was developed using indirect immunofluorescence technique with quantum dots (QDs) as fluorescent probes. B. anthracis could be selectively labeled with QDs, which was demonstrated by fluorescence microscope and F4500 spectrofluorometer. A laboratory-made system including biosensor and device was used as detection apparatus. A linear relationship of the fluorescence intensity and log total count of B. anthracis was obtained with correlation coefficient of 0.9554 from 1 × 10 2 CFU mL −1 to 1 × 10 6 CFU mL −1 and a low relative standard deviation (RSD) of 2.19%. By comparing the fluorescence intensity of B. anthracis and other bacillus, this method showed good specificity. Because of simple operation and less detection time (1 h) than traditional methods and quantitative detection, this method has potential prospect in monitoring B. anthracis and other biowarfare agents.