Hai-Feng Ji

Detection of pH variation using modified microcantilever sensors

A micromechanical technique for measuring solution pH using modified silicon (SiO2) and silicon nitride (Si3N4) microcantilevers is described. As the modified surface of the cantilever accumulates charge proportional to the pH of the surrounding liquid, the cantilever undergoes bending due to the differential surface stress. Results are presented for chemically modified (4-aminobutyltriethoxysilane, 11mercaptoundecanoic acid) and metal-modified (Au/Al) surfaces over a pH range 2‐12. Aminosilane-modified SiO2/Au cantilevers performed robustly over pH range 2‐8 (49 nm deflection/pH unit), while Si3N4/Au cantilevers performed well at pH 2‐6 and 8‐12 (30 nm deflection/pH unit). The influences of other ions on cantilever bending were found to be negligible below 10 ˇ2 M concentration.

Moore's law in homeland defense: an integrated sensor platform based on silicon microcantilevers

An urgent need exists for the development of inexpensive, highly selective, and extremely sensitive sensors to help combat terrorism. If such sensors can be made miniature, they could be deployed in virtually any situation. Terrorists have a wide variety of potential agents and delivery means to choose from for chemical, biological, radiological, or explosive attacks. Detecting terrorist weapons has become a complex and expensive endeavor, because a multitude of sensor platforms is currently needed to detect the various types of threats. The ability to mass produce and cost effectively deploy a single type of sensor that can detect a wide range of threats is essential in winning the war on terrorism. Silicon-based microelectromechanical sensors (MEMS) represent an ideal sensor platform for combating terrorism because these miniature sensors are inexpensive and can be deployed almost anywhere. Recently, the high sensitivity of MEMS-based microcantilever sensors has been demonstrated in the detection of a variety of threats. Therefore, the critical requirements for a single, miniature sensor platform have been met and the realization of an integrated, widely deployable MEMS sensor could be near.

In situ detection of calcium ions with chemically modified microcantilevers

We report a novel technique of micromechanical detection of trace amounts of calcium ions by using microcantilevers modified with ion-selective self-assembled monolayers (SAMs). The SAM-modified microcantilevers undergo bending due to selective adsorption of calcium ions. Experiments conducted under flow conditions show that the modified cantilevers respond sensitively to calcium ions (Ca(2+)); a Ca(2+) concentration of 10(-9) M can be detected with this technique. Other cations, such as Na(+) and K(+), do not have any effect on the deflection of these cantilevers. We demonstrate two different kinds of SAMs having selectivity for calcium ions.

Solvent effect on the self-assembled structure of an amphiphilic perylene diimide derivative.

An amphiphilic electron-deficient (n-type) perylene diimide has been synthesized and characterized. The diimide contains a hydrophobic long chain on one end and a hydrophilic ethoxy chain on the other. The self-assembly of this molecule in polar and nonpolar solvents has been demonstrated by concentration- and temperature-dependent absorption and fluorescence spectroscopies. Analysis of the spectral change for the aggregates shows typical J-aggregates for structures precipitated from polar solvents and H-aggregates for structures precipitated from nonpolar solvents. SEM and TEM micrographs and a suggested packing scheme, compatible with the formation of nanostrips in nonpolar solvents and nanofibers in polar solvents, are presented.

Growth of 2D black phosphorus film from chemical vapor deposition

Phosphorene, a novel 2D material isolated from bulk black phosphorus (BP), is an intrinsic p-type material with a variable bandgap for a variety of applications. However, these applications are limited by the inability to isolate large films of phosphorene. Here we present an in situ chemical vapor deposition type approach that demonstrates progress towards growth of large area 2D BP with average areas >3 μm2 and thicknesses representing samples around four layers and thicker samples with average areas >100 μm2. Transmission electron microscopy and Raman spectroscopy have confirmed successful growth of 2D BP from red phosphorus.

A novel self-assembled monolayer (SAM) coated microcantilever for low level caesium detection

We report a new sensor concept based on an ion-selective SAM modified microcantilever which can detect caesium ion concentrations in situ in the range 10−11–10−7 M and shows potential for use in developing a new family of real time in situ metal ion sensors with high sensitivity/selectivity and low cost, for chemical and biological applications.

A pH Sensor Based on a Microcantilever Coated with Intelligent Hydrogel

Abstract Hydrogels that contain different amounts of amino groups were used to modify microcantilevers for the pH measurements. These microcantilevers deflected upon exposure to various pH solutions due to the swelling and shrinking of the hydrogels. The microcantilever deflection, as a function of pH, is nearly linear in a wide pH range. A significant 1000 nm/pH bending response was observed from a Gel‐4 coated microcantilever, which could be used for precise pH measurements. Such hydrogel coated microcantilevers could potentially be used to prepare microcantilever chemical and biological sensors when molecular recognition agents are immobilized into the polymer.

Temperature- and Pressure-Sensitive Paint Measurements in Short-Duration Hypersonic Flow

Surface temperatures and pressures were measured on an elliptic cone lifting body in a hypersonic e owe eld using thin-e lm (» 5πm) temperature- and pressure-sensitive paints (TSPs and PSPs ). The tests were conducted in the 48-inch hypersonic shock tunnel (48-inch HST) at Calspan‐University of Buffalo Research Center and were part of a more comprehensive experimental study examining the three-dimensional characteristics of laminar, transitional, and turbulent e ow over the model. Measurement opportunity in the 48-inch HST was limited by the short duration of steady freestream conditions of the driven gas; image acquisition times were » 3 ms. Images of the coatings applied to the broad side of the symmetric elliptic cone were calibrated with in situ static pressure and surface-e lm temperature measurements. The TSP results illustrate the higher heat transfer rates and change in boundary-layer transition over the model surface caused by the nose geometry, and the PSP results show a mild pressure gradient over the interrogated surface region. Submillisecond TSP acquisition using a high-speed imager demonstrated the feasibility of measuring the surface temperature rise.

Self-Assembly of Perylenediimide and Naphthalenediimide Nanostructures on Glass Substrates through Deposition from the Gas Phase

Micrometer-long nanobelt and nanowires from deposition of perylenediimide (PTCDI) and naphthalenediimide (NPDI) in glass substrates from the gas phase were demonstrated. The electron diffraction pattern of PTCDI shows that the PTCDI molecules are oriented with their long axis perpendicular to the belt and the pi-pi stacking direction parallel to the belt. No crystal structure of the NPDI nanowires was observed. This is a new strategy to assemble organic molecules to nanostructures, typically for those having very low solubility in solvents. The approach would completely eliminate the effect of side chains.

Rapid visual detection of phytase gene in genetically modified maize using loop-mediated isothermal amplification method

Transgenic maize plant expressing high phytase activity has been reported and approved by Chinese government in 2009. Here, we report a highly specific loop-mediated isothermal amplification (LAMP) method to detect the phytase gene in the GMO maize. The LAMP reaction takes less than 20min and the amplification is visible without gel electrophoresis. The detection sensitivity of the LAMP method is about 30 copies of phytase genomic DNA, which is 33.3 times greater than the conventional PCR method with gel electrophoresis. The quantitative detection results showed that the LAMP method has a good linear correlation between the DNA copy number and the associated Tt values over a large dynamic range of template concentration from 6×10(1) to 6×10(7) copies, with a quantification limit of 60 copies. Therefore, the LAMP method is visual, faster, and more sensitive, and does not need special equipment compared to traditional PCR technique, which is very useful for field tests and fast screening of GMO feeds.