Quantitative imaging of dielectric permittivity and tunability with a near-field scanning microwave microscope

We describe the use of a near-field scanning microwave microscope to image the permittivity and tunability of bulk and thin film dielectric samples on a length scale of about 1 micron. The microscope is sensitive to the linear permittivity, as well as to nonlinear dielectric terms, which can be measured as a function of an applied electric field. We introduce a versatile finite element model for the system, which allows quantitative results to be obtained. We demonstrate use of the microscope at 7.2 GHz with a 370 nm thick barium strontium titanate thin film on a lanthanum aluminate substrate. This technique is nondestructive and has broadband (0.1-50 GHz) capability. The sensitivity of the microscope to changes in relative permittivity is 2 at permittivity = 500, while the nonlinear dielectric tunability sensitivity is 10^-3 cm/kV.Comment: 12 pages, 10 figures, to be published in Rev. Sci. Instrum., July, 200

Optical control of photon tunneling through an array of nanometer scale cylindrical channels

We report first observation of photon tunneling gated by light at a different wavelength in an artificially created array of nanometer scale cylindrical channels in a thick gold film. Polarization properties of gated light provide strong proof of the enhanced nonlinear optical mixing in nanometric channels involved in the process. This suggests the possibility of building a new class of "gated" photon tunneling devices for massive parallel all-optical signal and image processing.Comment: 4 pages, 4 figure

Micro-fabrication of Carbon Structures by Pattern Miniaturization in Resorcinol-Formaldehyde Gel

A simple and novel method to fabricate and miniaturize surface and sub-surface micro-structures and micro-patterns in glassy carbon is proposed and demonstrated. An aqueous resorcinol-formaldehyde (RF) sol is employed for micro-molding of the master-pattern to be replicated, followed by controlled drying and pyrolysis of the gel to reproduce an isotropically shrunk replica in carbon. The miniaturized version of the master-pattern thus replicated in carbon is about one order of magnitude smaller than original master by repeating three times the above cycle of molding and drying. The micro-fabrication method proposed will greatly enhance the toolbox for a facile fabrication of a variety of Carbon-MEMS and C-microfluidic devices.Comment: 16 pages, 5 figure

Биотест-системы на основе полимерных микросфер

In work the modern condition of a problem on synthesis of polymeric microspheres and reception on their basis the test-systems for various kinds of diseases is considered.В работе рассмотрено современное состояние проблемы по синтезу полимерных микросфер и получение на их основе тест-систем на различные виды заболеваний

Высокочувствительные тест-системы на основе конъюгатов «полимерная микросфера – биолиганд» для экспресс-диагностики протеинопатий

The main approaches to the creation of highly sensitive test systems based on polymeric microspheres with immobilized bioligands intended for rapid diagnostics of proteinopathy were considered. The effect of these test systems is based on the latex agglutination reaction between the antigens grafted to the surface of polymeric microspheres and antibodies contained in a biological sample. The issues related to obtaining and optimal properties of polymeric microspheres, which must contain functional groups reactive toward bioligands at their surface were analyzed. Problems associated with immobilization of bioligands on the surface of the polymeric microspheres and the possibility to improve the composition and preparation of test systems were considered. Special attention is given to obtaining test systems for the diagnosis of thyroid disease by means one of its antigens – thyroglobulin.Рассмотрены основные подходы к созданию высокочувствительных тест-систем на основе полимерных микросфер с иммобилизованными биолигандами, предназначаемых для экспресс-диагностики протеинопатий. Действие этих тест-систем основано на реакции латексной агглютинации между антигенами, химически привитыми к поверхности полимерной микросферы, и антителами к ним, содержащимися в биологическом образце. Проанализированы вопросы, связанные с получением и оптимальными свойствами полимерных микросфер, которые должны содержать на своей поверхности реакционноспособные по отношению к биолиганду функциональные группы. Рассмотрены проблемы, связанные с иммобилизацией биолигандов на поверхности этих полимерных микросфер, а также возможностями сохранения их нативной формы за счет использования спейсеров. На примере получения тест-систем для диагностики заболеваний щитовидной железы рассмотрены проблемы, возникающие при их конструировании

Mesenchymal Stem Cell Responses to Bone-Mimetic Electrospun Matrices Composed of Polycaprolactone, Collagen I and Nanoparticulate Hydroxyapatite

The performance of biomaterials designed for bone repair depends, in part, on the ability of the material to support the adhesion and survival of mesenchymal stem cells (MSCs). In this study, a nanofibrous bone-mimicking scaffold was electrospun from a mixture of polycaprolactone (PCL), collagen I, and hydroxyapatite (HA) nanoparticles with a dry weight ratio of 50/30/20 respectively (PCL/col/HA). The cytocompatibility of this tri-component scaffold was compared with three other scaffold formulations: 100% PCL (PCL), 100% collagen I (col), and a bi-component scaffold containing 80% PCL/20% HA (PCL/HA). Scanning electron microscopy, fluorescent live cell imaging, and MTS assays showed that MSCs adhered to the PCL, PCL/HA and PCL/col/HA scaffolds, however more rapid cell spreading and significantly greater cell proliferation was observed for MSCs on the tri-component bone-mimetic scaffolds. In contrast, the col scaffolds did not support cell spreading or survival, possibly due to the low tensile modulus of this material. PCL/col/HA scaffolds adsorbed a substantially greater quantity of the adhesive proteins, fibronectin and vitronectin, than PCL or PCL/HA following in vitro exposure to serum, or placement into rat tibiae, which may have contributed to the favorable cell responses to the tri-component substrates. In addition, cells seeded onto PCL/col/HA scaffolds showed markedly increased levels of phosphorylated FAK, a marker of integrin activation and a signaling molecule known to be important for directing cell survival and osteoblastic differentiation. Collectively these results suggest that electrospun bone-mimetic matrices serve as promising degradable substrates for bone regenerative applications