Dependence of transport rate on area of lithography and pretreatment of tip in dip-pen nanolithography.

This study examines the lithographic capacity of tips in dip-pen nanolithography (DPN). The dependence of the transport rate (R) decay on the area of lithography (A(lith)), the dependence of A(lith) on the lithographic time (t), and the effect of piranha cleaning on the lithographic capacity are considered herein. The dependencies in the line-drawing lithography process are studied using 16-mercaptohexadecanoic acid (MHA) ink. On the basis of the linear decay dependence discovered in the R-A(lith) dependence, piranha treatment can increase the lithographic capacity by up to 35.5-fold, an improvement that may originate from a change in the tip's surface chemistry. Moreover, a theoretical model is derived to describe the A(lith)-t dependence accurately and to predict the tips' lifetime. Furthermore, an experiment involving DPN-based nanostructure fabrication demonstrates the importance of monitoring the tips' transport rate and lifetime. In addition to shedding light on the physical and chemical principles behind DPN, this study provides a comprehensive model for a quantitative analysis of the tips' behavior.

Diagnostic devices for isothermal nucleic acid amplification.

Since the development of the polymerase chain reaction (PCR) technique, genomic information has been retrievable from lesser amounts of DNA than previously possible. PCR-based amplifications require high-precision instruments to perform temperature cycling reactions; further, they are cumbersome for routine clinical use. However, the use of isothermal approaches can eliminate many complications associated with thermocycling. The application of diagnostic devices for isothermal DNA amplification has recently been studied extensively. In this paper, we describe the basic concepts of several isothermal amplification approaches and review recent progress in diagnostic device development.

Preparation of protein nanoarray on silicon surface by atomic force microscopy nanofabrication.

Atomic force microscopy (AFM) with bias control is employed to fabricate oxidized nanopatterns on a silicon surface with a feature size as low as 50 nm. Nanopatterns made by a Pt/Ir coating probes have larger feature size than these made by the probe without, but the patterning speed is fast, 0.1 s per dot. 20 nm gold nanoparticles are immobilized on oxide nanopatterns to elucidate the dimensions of the nanoparticles on an oxide nanopattern. These patterning conditions are utilized to prepare a nanoarray for the immobilization of biotins to interact with free streptavidins. The resultant height of the biotin labeled on oxidized nanopattern is 0.93 +/- 0.1 nm and the combined height of biotin-streptavidin is 5.14 +/- 0.45 nm, as determined using the imaging functions of AFM. Based on the experimental results, a nano biochip of silicon dioxide can be utilized to monitor molecular interactions on the nanometer scale under static conditions and without the labeling of fluorescence dyes.

Nanopatterning on silicon wafers using AFM-based lithography--for solar cells.

In this report, the nanopatterning method based on atomic force microscopy (AFM) with electrical bias to form the oxide patterns on silicon wafer is described. Under constant bias, 30 V, the linear pattern size is proportional to the rising humidity in the working environment. According to our experimental results, the sizes of the most circular nanopatterns are in the range from 50 nm to 70 nm depending on the applied bias and interaction time. In the results of evaluating the generation of oxidative production, the diameters and the number of oxide two dimensional nanopattern array, defaulted to 25 dots in 1 microm2, appeared in the AFM images have increasing tendency with the larger bias and the longer dwell time. Moreover, the imaging features of nanopatterns caused by bias 30 V have better performance than those by 10 V, and the dwell time only takes 0.015 s per dot.

Tensile bond strength of Er, Cr: YSGG laser-irradiated human dentin to composite inlays with two resin cements.

The purpose of this study was to investigate the tensile bond strength of composite inlays to human dentin with two different cavity preparation tools (bur versus Er, Cr: YSGG laser) and with two different bonding procedures (total-etch: Variolink II versus self-etch: Maxcem). The specimens were divided into four groups: bur-cut/Variolink II, bur-cut/Maxcem, laser-ablated/Variolink II, and laser-ablated/Maxcem. The following characteristics were then investigated: morphological change, dentin-resin cement interface, surface roughness, and tensile bond strength. Results demonstrated that the tensile bond strengths of the four groups were 19.11 +/- 5.88 MPa, 8.54 +/- 2.38 MPa, 13.72 +/- 3.43 MPa, and 12.11 +/- 3.71 MPa, respectively. We concluded that Variolink II provided higher tensile bond strength to composite inlays than Maxcem. On the other hand, the bond strength of Variolink II with dentin cavity prepared by Er, Cr: YSGG laser was statistically lower than that prepared by bur.

Tip-enhanced fluorescence with radially polarized illumination for monitoring loop-mediated isothermal amplification on hepatitis C virus cDNA.

A tip nanobiosensor for monitoring DNA replication was presented. The effects of excitation power and polarization on tip-enhanced fluorescence (TEF) were assessed with the tip immersed in fluorescein isothiocyanate solution first. The photon count rose on average fivefold with radially polarized illumination at 50 mW. We then used polymerase-functionalized tips for monitoring loop-mediated isothermal amplification on Hepatitis C virus cDNA. The amplicon-SYBR® Green I complex was detected and compared to real-time loop-mediated isothermal amplification. The signals of the reaction using 4 and 0.004 ng∕µl templates were detected 10 and 30 min earlier, respectively. The results showed the potential of TEF in developing a nanobiosensor for real-time DNA amplification.

Metallic tip enhanced fluorescence for DNA replication monitoring.

We have successfully performed localized loop-mediated isothermal reactions of hepatitis B virus (HBV) and hepatitis C virus (HCV) on the apex (50~100 nm) of metallic tips coated with Bst polymerases. The SYBR green molecules binding to the new formed HBV DNA inside the optical near fields were excited by two-photon fluorescence microscopy, and directly imaged in far field. Another reporter primer is used for HCV replication detection. Preliminary results are presented in this manuscript.

Nanodots array rapidly fabricated by Dip-Pen nanolithography with temperature and humidity control.

This study demonstrates the advantage of Dip-Pen Nanolithography (DPN) as a research and design tool for metal nano-structure fabrications. We design two different gold nano-structures, which are fabricated by DPN etching method with temperature and humidity control. The plasmon resonance frequencies of both structures are measured with dark field scattering spectroscopy. Our results show that with temperature and humidity control, DPN is highly potential in developing photonic circuit, solar cell and biomedical devices due to the rapid fabrication and cost effectiveness.

Detection of tip-enhanced fluorescence from loop-mediated isothermal amplification of hepatitis B virus by two-photon microscopy.

Tip-enhanced fluorescence of localized DNA replication by loop-mediated isothermal amplification (LAMP) is a potential way to observe real-time biological reaction confined in nanometer scale. We successfully coated Bst polymerase on the apex (~100 nm) of an atomic force microscope (AFM) tip and performed localized LAMP reaction of hepatitis B virus (HBV). By using this tip-based reaction, the replicated HBV DNA can be directly imaged to be 400~500 nm spots by using two-photon excitation fluorescence microscopy.

Electrical properties of single and multiple poly(3,4-ethylenedioxythiophene) nanowires for sensing nitric oxide gas.

The electrical properties of conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), nanowires were studied to develop nitric oxide (NO) gas sensors with low working temperatures. A nanowire with a diameter of 300 nm was fabricated using dip-pen nanolithography (DPN) across a 55 microm gap between a pair of electrodes. The electrical properties of single or multiple PEDOT nanowires were examined by plotting the current-voltage (I-V) curves in the range -3 V to +3 V at temperatures between 298 K and 393 K. The conductance of parallel wires was normalized with respect to the dimensions of the fabricated nanowires. The single nanowire exhibited nonlinear conductance associated with hysteresis but multiple wires did not. The currents increased with the temperature and the I-V characteristics were consistent with the power law G(T)alphaT(alpha) with alpha approximately 5.14 and 5.43. The responses to NO were highly linear and reproducible, indicating that sensing using PEDOT nanowires was reliable with a minimal concentration of NO of 10 ppm.

Surface plasmon resonance biochip based on ZnO thin film for nitric oxide sensing.

In this study, the design of a novel optical sensor that comprises surface plasmon resonance sensing chip and zinc oxide nano-film was proposed for the detection of nitric oxide gas. The electrical and optical properties of zinc oxide film vary in the presence of nitric oxide. This effect was utilized to prepare biochemical sensors with transduction based on surface plasmon resonance. Due to the refractive index of the transparent zinc oxide film that was deposited on the gold film, however, changes will be observed in the surface plasmon resonance spectra. For this reason, the thickness of zinc oxide film will be investigated and determined in this study. The interaction of nitric oxide with a 20 nm zinc oxide layer on gold leads to the shift of the resonance angle. The analysis on the reflectance intensity of light demonstrates that such effect is caused by the variation of conductivity and permittivity of zinc oxide film. Finally, a shift in surface plasmon resonance angle was measured in 25 ppm nitric oxide at 180 C and a calibration curve of nitride oxide concentration versus response intensity was successfully obtained in the range of 250 to 1000 ppm nitric oxide at lower temperature of 150 C. Moreover, these effects are quasi-reversible.

Nano fabrication of conducting polymers for NO gas by Dip pen nanolithography.

We present a novel fabrication method by using dip pen nanolithography with Poly (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) for nitric oxide (NO) gas sensor in this report. PEDOT is a kind of conducting polymer which will change its conductance upon NO adsorption. Herein, we have used PEDOT with traditional thick film and DPN nanowires across electrodes. By using traditional thick film device, the lowest detection limit for NO is 3.87 ppm. The preliminary results of DPN nanowires can have aspect ratio (L/W) for up to 220 times and thus have large sensing surface area for higher sensitivity.