Jianhua Tong

A millimeter-sized nanomanipulator with sub-nanometer positioning resolution and large force output

Nanomanipulation in space-limited environments (e.g., inside SEM, and particularly in TEM) requires small-sized nano manipulators that are capable of producing sub-nanometer positioning resolutions and large output forces. This paper reports on a millimeter-sized MEMS (microelectromechanical systems) based nano manipulator with a positioning resolution of 0.15 nm and a motion range of plusmn2.55 mum. An amplification mechanism is employed to convert input displacements, generated by conventional electrostatic comb-drive microactuator, to achieve a high positioning resolution on the output side. The device has a high load driving capability, driving a load as high as 98 muN without sacrificing positioning performance. Testing results demonstrate that the mechanism has a high linearity (plusmn2.4%). A capacitive displacement sensor is integrated for detecting input displacements that are converted into output displacements via a minification ratio, allowing closed-loop controlled nanomanipulation. The MEMS-based nano-manipulators are applicable to the characterization/manipulation of nano-materials and construction of nano devices.

Precision patterning of PDMS membranes and applications

This paper presents a method for precision patterning of polydimethylsiloxane (PDMS) membranes based on parylene C lift-off. The process permits the construction of PDMS membranes either with a highly flat, uniform top surface or with a controlled curvature. Effects of varying processing parameters on the geometrical characteristics of the PDMS membranes are described. The paper also demonstrates the application of the PDMS precision patterning method to the construction of PDMS microlens arrays, which require curved top surfaces, and a 3-axis electrostatic positioning stage that uses PDMS membranes with flat surfaces as a bonding material as well as a precisely defined spacer. (Some figures in this article are in colour only in the electronic version)

Determination of trace mercury in water based on N-octylpyridinium ionic liquids preconcentration and stripping voltammetry

A novel method for determination of trace mercury in water is developed. The method is performed by extracting mercury firstly with ionic liquids (ILs) and then detecting the concentration of mercury in organic media with anodic stripping voltammetry. Liquid-liquid extraction of mercury(II) ions by four ionic liquids with N-octylpyridinium cations ([OPy](+)) was studied. N-octylpyridinium tetrafluoroborate and N-octylpyridinium trifluoromethylsulfonate were found to be efficient and selective extractant for mercury. Temperature controlled dispersive liquid phase microextraction (TC-DLPME) technique was utilized to improve the performance of preconcentration. After extraction, precipitated IL was diluted by acetonitrile buffer and mercury was detected by differential pulse stripping voltammetry (DPSV) with gold disc electrode. Mercury was enriched by 17 times while interfering ions were reduced by two orders of magnitude in the organic media under optimum condition. Sensitivity and selectivity for electrochemical determination of mercury were improved by using the proposed method. Tap, pond and waste water samples were analyzed with recoveries ranging from 81% to 107% and detection limit of 0.05 μg/L.

A micro potentiometric immunosensor for hemoglobin-A1c level detection based on mixed SAMs wrapped nano-spheres array

A micro potentiometric immunosensor based on mixed SAMs wrapped nano-spheres array for the detection of hemoglobin-A1c level is presented in this paper. Nano-spheres array is prepared by wrapping nano-gold particle with mixed SAMs on the surface of micro immunosensor. Mixed SAMs make the nano-gold particles distribute uniformly without aggregation and render the signal less susceptible to noise. Based on this nano-spheres array, antibody is covalently immobilized on the immunosensor surface. The micro immunosensor, consisting of ISFET integrated chip and MEMS electrodes array is applied to measure hemoglobin-A1c level by detecting the concentration of hemoglobin-A1c and hemoglobin simultaneously. The responses of the immunosensor are linear over the concentration range of 166.7-570 ng/ml hemoglobin and 50-170.5 ng/ml HbA1c. Whole blood sample obtained from hospital was also examined using this immunosensor. The low relative deviation shows that this micro immunosensor may provide an alternative tool for the determination of HbA1c level.

Millimeter-sized nanomanipulator with sub-nanometer positioning resolution and large force output

Nanomanipulation in space-limited environments (e.g., inside SEM, and particularly in TEM) requires small-sized nano manipulators that are capable of producing sub-nanometer positioning resolutions and large output forces. This paper reports on a millimeter-sized MEMS (microelectromechanical systems) based nano manipulator with a positioning resolution of 0.15 nm and a motion range of plusmn2.55 mum. An amplification mechanism is employed to convert input displacements, generated by conventional electrostatic comb-drive microactuator, to achieve a high positioning resolution on the output side. The device has a high load driving capability, driving a load as high as 98 muN without sacrificing positioning performance. Testing results demonstrate that the mechanism has a high linearity (plusmn2.4%). A capacitive displacement sensor is integrated for detecting input displacements that are converted into output displacements via a minification ratio, allowing closed-loop controlled nanomanipulation. The MEMS-based nano-manipulators are applicable to the characterization/manipulation of nano-materials and construction of nano devices.

Highly-sensitive electrochemical sensing platforms for food colourants based on the property-tuning of porous carbon

It is very challenging to develop highly-sensitive analytical platforms for toxic synthetic colourants that widely added in food samples. Herein, a series of porous carbon (PC) was prepared using CaCO3 nanoparticles (nano-CaCO3) as the hard template and starch as the carbon precursor. Characterizations of scanning electron microscopy and transmission electron microscopy indicated that the morphology and porous structure were controlled by the weight ratio of starch and nano-CaCO3. The electrochemical behaviours of four kinds of widely-used food colourants, Sunset yellow, Tartrazine, Ponceau 4R and Allura red, were studied. On the surface of PC samples, the oxidation signals of colourants enhanced obviously, and more importantly, the signal enhancement abilities of PC were also dependent on the starch/nano-CaCO3 weight ratio. The greatly-increased electron transfer ability and accumulation efficiency were the main reason for the enhanced signals of colourants, as confirmed by electrochemical impedance spectroscopy and chronocoulometry. The prepared PC-2 sample by 1:1 starch/nano-CaCO3 weight ratio was more active for the oxidation of food colourtants, and increased the signals by 89.4-fold, 79.3-fold, 47.3-fold and 50.7-fold for Sunset yellow, Tartrazine, Ponceau 4R and Allura red. As a result, a highly-sensitive electrochemical sensing platform was developed, and the detection limits were 1.4, 3.5, 2.1 and 1.7 μg L(-1) for Sunset yellow, Tartrazine, Ponceau 4R and Allura red. The practical application of this new sensing platform was demonstrated using drink samples, and the detected results consisted with the values that obtained by high-performance liquid chromatography.

Electrochemical enhancement of acetylene black film as sensitive sensing platform for toxic tetrabromobisphenol A

Developing sensitive and simple analytical methods for tetrabromobisphenol A (TBBPA) is very important because TBBPA exists widely in the environment and its biological toxicity is high. Herein, three kinds of acetylene black (AB) films with different morphology and electrochemical reactivity were prepared, and then used to construct different electrochemical sensors for TBBPA. On the surface of AB films, the direct oxidation signals of TBBPA increase greatly, and moreover, the prepared AB films exhibit different enhancement ability toward TBBPA oxidation. The influences of pH value, amount of AB particles and accumulation time were studied on the oxidation signals of TBBPA. As a result, a sensitive electrochemical sensor based on the remarkable enhancement effects of AB film was developed for the rapid detection of TBBPA. The linear range was from 10 to 350 μg L−1, and the detection limit was 6.08 μg L−1 (cal. 11 nM). This new sensing system was used for the analysis of TBBPA in water samples, and good recoveries in the range of 99.3–104.5% were obtained.

FET immunosensor for hemoglobin A1c using a gold nanofilm grown by a seed-mediated technique and covered with mixed self-assembled monolayers

AbstractA micro FET-based immunosensor was developed for the determination of hemoglobin-A1c (HbA1c). The HbA1c/hemoglobin ratio is an important index in diabetes control. The sensor was fabricated by Complementary Metal-Oxide-Semiconductor Transistor (CMOS) and Micro Electronic Mechanical System (MEMS) techniques. The antibodies were immobilized via mixed self-assembled monolayers (SAMs) on a gold nanofilm. The nanofilm was deposited on a gold electrode by seed-mediated growth and gave a uniform and well distributed coverage. Nonspecific sites and interferences by noise were eliminated by covering the AuNPs with mixed SAMs. Compared to the immunosensor fabricated via the mixed SAMs method without gold nanofilm, the immunosensor displays a more than 2-fold sensitivity. The immunosensor is capable of detecting HbA1c and hemoglobin in hemolyzed and diluted whole blood, and results showed good agreement with the established clinical method. FigureBased on CMOS and MEMS techniques, a micro FET-based immunosensor was developed for the hemoglobin-A1c level determination. The antibodies were immobilized based on the mixed self-assembled monolayers and seed-mediated growth method. The immunosensor can detect HbA1c and hemoglobin simultaneously and has good potential for clinical application.

The Graphene/l-Cysteine/Gold-Modified Electrode for the Differential Pulse Stripping Voltammetry Detection of Trace Levels of Cadmium

Cadmium(II) is a common water pollutant with high toxicity. It is of significant importance for detecting aqueous contaminants accurately, as these contaminants are harmful to human health and environment. This paper describes the fabrication, characterization, and application of an environment-friendly graphene (Gr)/l-cysteine/gold electrode to detect trace levels of cadmium (Cd) by differential pulse stripping voltammetry (DPSV). The influence of hydrogen overflow was decreased and the current response was enhanced because the modified graphene extended the potential range of the electrode. The Gr/l-cysteine/gold electrode showed high electrochemical conductivity, producing a marked increase in anodic peak currents (vs. the glass carbon electrode (GCE) and boron-doped diamond (BDD) electrode). The calculated detection limits are 1.15, 0.30, and 1.42 µg/L, and the sensitivities go up to 0.18, 21.69, and 152.0 nA·mm−2·µg−1·L for, respectively, the BDD electrode, the GCE, and the Gr/l-cysteine/gold electrode. It was shown that the Gr/l-cysteine/gold-modified electrode is an effective means for obtaining highly selective and sensitive electrodes to detect trace levels of cadmium.

A microfluidic sensor chip with renewable in-situ copper modified microelectrode for continuous monitoring of nitrate

Miniaturized on-chip electrochemical sensors fabricated by MEMS techniques have been demonstrated to have sufficient sensitivity for environmental sample analysis. However, due to the surface cumulative passivation effects, the decreasing sensitivity towards analytical targets has restricted the low-cost and long term applications of these devices. In this paper, a microfluidic electrochemical sensor with a renewable copper modified micro working-electrode for nitrate measurements is demonstrated. A microchannel and a micro three-electrode-system chip were fabricated to implement sensitive, reproducible and continuous nitrate measurements under an optimal potential protocol. Based on this microfluidic chip, the continuous renewal of the microelectrode surface allowed each measurement to be performed at a fresh and active copper surface, which guaranteed that sensitive and reproducible nitrate determination was achieved for a long period of time. The response of the microsensor towards nitrate was linear over the range from 40 to 3500 µmolL−1 with a detection limit of 10 µmolL−1 (S/N=3). The difference of 30 times measurements was determined as 4.8% at the best conditions, which shows good repeatability of the microsensor.