Label-free DNA detection with a nanogap embedded complementary metal oxide semiconductor

A nanogap embedded complementary metal oxide semiconductor (NeCMOS) is demonstrated as a proof-of-concept for label-free detection of DNA sequence. When a partially carved nanogap between a gate and a silicon channel is filled with charged biomolecules, the gate dielectric constant and charges are changed. When the gate oxide thickness reduces, the threshold voltage is significantly affected by a change of the charges, whereas it is scarcely influenced by a change of the dielectric constant. In the case of DNA, those two factors act on the threshold voltage oppositely in an n-channel NeCMOS but collaboratively in a p-channel NeCMOS because of the negative charges of DNA. Hence, a p-channel NeCMOS with a thin gate oxide is more attractive for DNA detection because it enhances the shift of threshold voltage; that is, it improves the sensitivity of DNA detection. In addition, the shift of threshold voltage according to the nanogap length is also investigated and the longer nanogap shows more shift of the threshold voltage.     

Poly(dimethylsiloxane)-based protein preconcentration using a nanogap generated by junction gap breakdown

Simple and efficient sample concentration tools are the key to the application of proteomics in a biological system. In this paper, we developed a method to realize a nanofluidic preconcentrator on a poly(dimethylsiloxane) (PDMS)-based microfluidic channel. The originality of our preconcentration device is the simple nanogap formation using the junction gap breakdown phenomenon between two PDMS microchannels, without using any photolithography and etching techniques. From the dc current measurement, we confirm that the nanogap formed between two microchannel junctions with approximately 80 nm depth. Using this device, we achieve the concentration volume of beta-phycoerythrin protein as high as 70 pL, which is 120-fold larger than that from our previous reports, with a concentration factor as high as 10(4) within 1 h. Also we show the availability of protein preconcentration under several different buffers (phosphate, acetate) at several different pH values (pH 5 to pH 9).     

A nonvolatile plasmonic switch employing photochromic molecules

We demonstrate a surface plasmon-polariton (SPP) waveguide all-optical switch that combines the unique physical properties of small molecules and metallic (plasmonic) nanostructures. The switch consists of a pair of gratings defined in an aluminum film coated with a 65 nm thick layer of photochromic (PC) molecules. The first grating couples a signal beam consisting of free space photons to SPPs that interact effectively with the PC molecules. These molecules can reversibly be switched between transparent and absorbing states using a free space optical pump. In the transparent (signal "on") state, the SPPs freely propagate through the molecular layer, and in the absorbing (signal "off") state, the SPPs are strongly attenuated. The second grating serves to decouple the SPPs back into a free space optical beam, enabling measurement of the modulated signal with a far-field detector. In a preliminary study, the switching behavior of the PC molecules themselves was confirmed and quantified by surface plasmon resonance spectroscopy. The excellent (16%) overlap of the SPP mode profile with the thin layer of switching molecules enabled efficient switching with power densities of approximately 6.0 mW/cm2 in 1.5 microm x 8 microm devices, resulting in plasmonic switching powers of 0.72 nW per device. Calculations further showed that modulation depths in access of 20 dB can easily be attained in optimized designs. The quantitative experimental and theoretical analysis of the nonvolatile switching behavior in this letter guides the design of future nanoscale optically or electrically pumped optical switches.     

Molecular sensing with the tunnel junction of an Au nanogap in solution

The tunnel junction of a gold nanogap was fabricated electrochemically for a molecular sensing device in solution. The tunnel junction was sensitive enough to detect the variation of a potential barrier within the nanogap, such as the chemical adsorption of molecules. By monitoring the variation of the tunneling current, which represents the change of a potential barrier due to molecular adsorption, the molecules could be detected.     

Dual-chemiresistor GC detector employing monolayer-protected metal nanocluster interfaces

The synthesis and testing of two gold-thiolate monolayer-protected (nano)clusters as interfacial layers on a dual-chemiresistor vapor sensor array are described. Responses (changes in dc resistance) to each of 11 organic solvent vapors are rapid, reversible, and linear with concentration at low vapor concentrations, becoming sublinear at higher concentrations. Limits of detection (LODs) range from 0.1 to 24 parts per million and vary inversely with solvent vapor pressure. When configured as a GC detector and used to analyze 0.5-L preconcentrated samples of the 11-vapor mixture, the array provides LODs of < or = 700 parts per trillion for most vapors, comparing favorably with those from an integrated array of polymer-coated surface acoustic wave sensors configured and tested similarly. This first report on the use of such an array as a GC detector shows that the combination of response patterns and GC retention times improves capabilities for vapor recognition compared to the sensor array alone or to single-detector GC systems. Spray-coated nanocluster thin films can be deposited reproducibly and exhibit response stability in air that ranges from fair to excellent for up to several months. Scaling the active device area down by a factor of 16 has no significant effect on sensitivity. Implications of these results for portable vapor sensing systems are discussed.     

Quantum model of space-charge-limited field emission in a nanogap

This paper presents a modified Thomas-Fermi-approximated quantum model for space-charge-limited field emission in a nanogap with metal electrodes, where the image-charge potential (including anode screening), direct tunnelling, space-charge effects and exchange-correlation effects of the tunnelling current are treated in a one-dimensional quantum model. It is found that the traditional Fowler-Nordheim (FN) law (even with the classical model of anode screening) is no longer valid in a nanogap of less than 10?nm. The smooth transition of our proposed model to the traditional FN law extended to large gap spacing is demonstrated. Application of the model to estimate the emission area of an experimental I-V curve in a nanogap is discussed.     

In-service monitoring of the current switch metal condition

Results of studying the in-service switch metal damage based on hardness scatter results are presented. Characteristics to estimate the damage level of the metal are proposed.     

A simple heat switch for use at millikelvin temperatures

A simple technique is described for fabricating a high conductivity silver-aluminium joint for use in the construction of an aluminium superconducting heat switch which can be operated in the millikelvin temperature range.     

Suspended and localized single nanostructure growth across a nanogap by an electric field

Direct growth of a suspended single nanostructure (SSN) at a specific location is presented. The SSN is grown across a metallic nanoscale gap by migration in air at room temperature. The nanogap is fabricated by industrial standard optical lithography and anisotropic wet chemical silicon etching. A DC current bias, 1 nA, is applied across the metallic gap to induce nanoscale migration of Zn or ZnO. The history of the voltage drop across the gap as a function of time clearly indicates the moment when migration begins. The shape of SSNs grown across the nanogap by the migration is asymmetric at each electrode due to the asymmetric electric field distribution within the nanogap. An SSN can be used as the platform for two-terminal active or passive nanoscale electronics in optoelectronics, radio frequency (RF) resonators, and chemical/biological sensors.     

简单蚀刻法制备具有可控高度的金属纳米线阵列

采用多孔阳极氧化铝(AAO)作为模板,运用电化学沉积法在模板的微孔中组装金属Ni纳米线,然后用磷铬酸蚀刻表层AAO模板,暴露出规整有序、具有可控长度的Ni纳米线阵列.分别用SEM、TEM与SAED对Ni纳米线阵列进行了表征.研究了蚀刻时间与AAO模板质量的减少及暴露出来的Ni纳米线阵列长度之间的关系.结果表明,磷铬酸是较NaOH溶液更为温和有效的AAO模板蚀刻剂,通过控制模板溶解时间,可以实现对裸露于AAO模板外纳米线长度的精细有效控制.该蚀刻方法普遍适用于以AAO为模板所制得的准一维纳米阵列结构.     

Transverse conductance of DNA nucleotides in a graphene nanogap from first principles

The fabrication of nanopores in atomically thin graphene has recently been achieved, and translocation of DNA has been demonstrated. Taken together with an earlier proposal to use graphene nanogaps for the purpose of DNA sequencing, this approach can resolve the technical problem of achieving single-base resolution in electronic nucleobase detection. We have theoretically evaluated the performance of a graphene nanogap setup for the purpose of whole-genome sequencing, by employing density functional theory and the nonequilibrium Green's function method to investigate the transverse conductance properties of nucleotides inside the gap. In particular, we determined the electrical tunneling current variation at finite bias due to changes in the nucleotides orientation and lateral position. Although the resulting tunneling current is found to fluctuate over several orders of magnitude, a distinction between the four DNA bases appears possible, thus ranking the approach promising for rapid whole-genome sequencing applications.     

Molecular crystal lithography: a facile and low-cost approach to fabricate nanogap electrodes

A novel cost-efficient and facile technique, molecular crystal lithography, to fabricate nanogap electrodes efficiently is reported. The gap width of the electrodes can be tuned from ～9 nm to several micrometers. Organic field-effect transistors based on the nanogap electrodes all exhibit a high performance, indicating the effectiveness and practicability of molecular crystal lithography for mass production of nanogap electrodes.     

Robust design employing a genetic algorithm

The minimization of variability in a key design feature or performance measure, in the presence of variability in the realized values of design parameters, is discussed and an analytic solution for quadratic performance measures is provided. Solutions are based on the determination of optimum nominal (or design point) values for the design parameters, subject to constraints in the form of a given nominal performance at the design point and limits on the nominal values of the design parameters, which preserve the design concept. The more general, numerical, problem solution is addressed and a previously described deterministic procedure which generated multiple local optima is improved by the replacement of a simplex search method with a sophisticated genetic algorithm which, with suitable parameter values and choice of Lagrange multiplier, converges only to the required global minimum within the specified design parameter limits. Further improvements are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

Holographic switch with a ferroelectric liquid-crystal spatial light modulator for a large-scale switch

A holographic switch with a ferroelectric liquid-crystal spatial light modulator is proposed for large switching systems such as those used in subscriber networks. Preliminary experiments have achieved a one-input, 48-output switch. The relationship between the power of the control-light source and the number of outputs is calculated; the results agree well with the experiment. The calculation suggests that 10384-output switching can be obtained with a 25-mW control-light source. It should therefore be possible to control a large-scale switch with low-power control-light sources.     

Size-controlled simple fabrication of free-standing, ultralong metal nanobelt array

Free-standing, ultralong (up to several millimeters) nanobelts of gold, silver, and copper were fabricated by a template approach. Firstly, a metal nanofin array was prepared on a substrate via metal nanocoating of the template surface and selective removal of the metal top layer and template. Electroless plating and sputtering were employed for the metal nanocoating. In this approach, the minimum width and thickness of the Au nanobelt were 95 and 30 nm, respectively. Systematic control of the nanobelt width (from 95 to 350 nm) was successfully achieved by adjusting the template height. Free-standing nanobelts of several millimeters in length were fabricated and maintained their unique structure and alignment, even on a mesh grid.     

Switching transient analysis of a metal/ferroelectric/semiconductor switch diode with high speed response to infrared light

A thin PbTiO(3)-n-p(+) silicon switch diode has been developed, in which the switching voltage (the turned-on voltage) changes in proportion to the infrared light power. The diode has a rapid response time of 0.65 mus compared with other conventional infrared sensors. It is attributed to the rapid switching device structure and the smaller pyroelectric layer thickness, 50 nm. In this paper, we have analyzed the rapid switching transient response by using heat conduction and switching theory successfully. The experimental results are in agreement with the theoretical analysis.