Atomic Force Microscopy of DNA on Mica and Chemically Modified Mica

Atomic force microscopy (AFM) was used to image circular DNA adsorbed on freshly cleaved mica and mica chemically modified with Mg(II), Co(II), La(III), and Zr(IV). Images obtained on unmodified mica show coiling of DNA due to forces involved during the drying process. The coiling or super twisting appeared to be right handed and the extent of super twisting could be controlled by the drying conditions. Images of DNA observed on chemically modified surfaces show isolated open circular DNA that is free from super twisting, presumably due to strong binding of DNA on chemically modified surfaces

Piezoresistive microcantilever optimization for uncooled infrared detection technology

Uncooled infrared sensors are significant in a number of scientific and technological applications. A new approach to uncooled infrared detectors has been developed using piezoresistive microcantilevers coated with thermal energy absorbing materials. Infrared radiation absorbed by the microcantilever detector can be sensitively detected as changes in electrical resistance as function of microcantilever bending. The dynamic range of these devices is extremely large due to measurable resistance change obtained with only nanometer level cantilever displacement. Optimization of geometrical properties for selected commercially available cantilevers is presented. We also present results obtained from a modeling analysis of the thermal properties of several different microcantilever detector architectures

Optical and infrared detection using microcantilevers

The feasibility of micromechanical optical and infrared (IR) detection using microcantilevers is demonstrated. Microcantilevers provide a simple means for developing single- and multi-element sensors for visible and infrared radiation that are smaller, more sensitive and lower in cost than quantum or thermal detectors. Microcantilevers coated with a heat absorbing layer undergo bending due to the differential stress originating from the bimetallic effect. Bending is proportional to the amount of heat absorbed and can be detected using optical or electrical methods such as resistance changes in piezoresistive cantilevers. The microcantilever sensors exhibit two distinct thermal responses: a fast one ({theta}{sub 1}{sup thermal} < ms) and a slower one ({tau}{sub 2}{sup thermal} {approximately} 10 ms). A noise equivalent temperature difference, NEDT = 90 mK was measured. When uncoated microcantilevers were irradiated by a low-power diode laser ({lambda} = 786 nm) the noise equivalent power, NEP, was found to be 3.5nW/{radical}Hz which corresponds to a specific detectivity, D*, of 3.6 {times} 10{sup 7} cm {center_dot} {radical}Hz/W at a modulation frequency of 20 Hz

Smooth Muscle Cell Phenotype Modulation and Contraction on Native and Cross-Linked Polyelectrolyte Multilayers

Smooth muscle cells convert between a motile, proliferative “synthetic ” phenotype and a sessile, “contractile ” phenotype. The ability to manipulate the phenotype of aortic smooth muscle cells with thin biocompatible polyelectrolyte multilayers (PEMUs) with common surface chemical characteristics but varying stiffness was investigated. The stiffness of (PAH/ PAA) PEMUs was varied by heating to form covalent amide bond cross-links between the layers. Atomic force microscopy (AFM) showed that cross-linked PEMUs were thinner than those that were not cross-linked. AFM nanoindentation demonstrated that the Young’s modulus ranged from 6 MPa for hydrated native PEMUs to more than 8 GPa for maximally cross-linked PEMUs. Rat aortic A7r5 smooth muscle cells cultured on native PEMUs exhibited morphology and motility of synthetic cells and expression of the synthetic phenotype markers vimentin, tropomyosin 4, and nonmuscle myosin heavy chain IIB (nmMHCIIB). In comparison, cells cultured on maximally cross-linked PEMUs exhibited the phenotype markers calponin, smooth muscle myosin heavy chain (smMHC), myocardin, transgelin, and smooth muscle R-actin (smActin) that are characteristic of the smooth muscle “contractile ” phenotype. Consistent with those cells being “contractile”, A7r5 cells grown on cross-linked PEMUs produced contractile force when stimulated with a Ca2+ ionophore

Caracterização morfológica de nanocristais de celulose por microscopia de força atômica

RESUMO O isolamento de nanocristais de celulose (CNCs) de fibras vegetais é uma alternativa promissora para sua aplicação como reforço em matrizes poliméricas. A caracterização dos CNCs é fundamental para a confiabilidade da técnica, além de determinar as aplicações possíveis a partir de cada tipo de fibra. A partir da técnica de microscopia de força atômica, um estudo da morfologia e distribuição dos CNCs de semente de manga, vagem de algaroba, pseudocaule da bananeira e fibra do mesocarpo de dendê foi realizado neste trabalho. Os CNCs foram obtidos via reação hidrolítica com ácido sulfúrico em concentrações que variaram de acordo com a fonte da fibra. Os resultados obtidos revelaram dimensões variando de 300 a 500 nm em comprimento e 4 a 16 nm em diâmetro. A apresentação morfológica em forma de agulha demonstrou que o isolamento das fibras de celulose em CNCs foi efetiva. A razão de aspecto associada à formação cilíndrica em agulha dos CNCs isolados evidenciou o alto potencial das fontes de dendê e de vagem de algaroba para o reforço de bionanocompósitos

Nanoscale Science, Engineering and Technology Research Directions

This report describes important future research directions in nanoscale science, engineering and technology. It was prepared in connection with an anticipated national research initiative on nanotechnology for the twenty-first century. The research directions described are not expected to be inclusive but illustrate the wide range of research opportunities and challenges that could be undertaken through the national laboratories and their major national scientific user facilities with the support of universities and industry

Microsensors to monitor missile storage and maintenance needs

Accurate assessments of reliability and condition based maintenance can only be implemented where a good understanding of ammunition stockpile condition exists. Use of miniaturized intelligent sensors provides an inexpensive means of nondestructively gaining insight into stockpile condition while keeping costs low. In the past, evaluation of ammunition lifetimes has utilized humidity, temperature, pressure, shock, and corrosion. New technologies provide the possibility of obtaining these environmental parameters, as well as a number of other indicators of propellant degradation, including NOx by utilizing a microsensor with capability for remote wireless monitoring. Micro-electro-mechanical systems (MEMS) like microcantilevers promise to revolutionize the field of sensor design. In the automobile industry, micromachined acceleration sensors are now used for triggering airbags and pressure sensors adjust the air-fuel intake ratio in the engine. By applying coatings to the sensor`s surface the behavior of the microdevice can be measurably altered to respond to chemical species as demonstrated by ORNL using microcantilevers to detect mercury vapor and humidity. Ultimately, single-chip detectors with electronics and telemetry could be developed with conceivably hundreds of individual microsensors on each chip to simultaneously monitor identify, and quantify many important chemical species for ammunition as well as measure environmental parameters

Microcantilever sensors

Novel sensors based on bending and resonance frequency changes of (coated silicon) microcantilevers are discussed. Adsorption-induced resonance frequency changes of microcantilevers can be due to a combination of mass loading and change of spring constant resulting from adsorption of chemicals on the surface. Cantilevers also undergo static bending due to adsorption-induced differential surface stress if the adsorption is confined to one surface. Hence cantilever deflection as well as resonance frequency change can be used as the basis for development of novel chemcal sensors