Kirill Zinoviev

A novel optical waveguide microcantilever sensor for the detection of nanomechanical forces

This study presents a novel generic multipurpose probe based on an array of 20 waveguide channels with microcantilevers acting as optical waveguides operated in the visible range. The principle of operation is based on the sensitivity of energy transfer between two butt-coupled waveguides to their misalignment with respect to each other. The technique can be considered an alternative to the known methods used for the readout of the nanomechanical response of microcantilevers to the external force exerted on them. The cantilever displacement can be detected with a resolution of 18 fm//spl radic/Hz. The limit is generally defined by the shot noise of a conventional photodetector used for the readout of the output signal. Real-time parallel monitoring of several channels can be realized. In contrast to devices based on the atomic force microscope detection principle, no preliminary alignment or adjustment, except for light coupling, is required. The detection of the cantilever deflection at subnanometer range was demonstrated experimentally.

Integrated Bimodal Waveguide Interferometric Biosensor for Label-Free Analysis

The performance of an interferometric device based on integrated Bimodal Waveguides (BiMW) for sensing is demonstrated. The sensors are fabricated using standard silicon technology and can achieve a detection limit of 2.5·10- 7 RIU for homogeneous sensing, rendering in a very high sensitive device. The applicability of the bimodal waveguide interferometer as label-free biosensor has been demonstrated by the real-time monitoring of the biomolecular interaction of BSA and antiBSA. Due to their simplicity, the interferometric devices could be further integrated in complete lab-on-a-chip platforms for point-of-care diagnostics showing them as a powerful instrument for biochemical analysis.

Carbon-nanotube sensitized nematic elastomer composites for IR-visible photo-actuation

Liquid crystal elastomers (LCEs) are of considerable interest for their potential as actuators, due to the ability of aligned monodomain LCEs to reversibly change their bulk dimensions in response to a phase change. Many LCEs reported in the literature will contract in one dimension in response to a temperature change or irradiation with ultraviolet light. For practical applications, photo-actuation is a more useful technology than thermal actuation due to the achievable speed and localization of the response. The use of UV light sources to ‘switch’ the materials is impractical, however, due to considerations of both safety and cost. Sensitization of LCEs to light of higher wavelengths may be achieved by mixing a small concentration of carbon nanotubes (CNTs) into the polymer matrix; CNTs will absorb light over a large range of wavelengths, and convert it into local heat, thus triggering the required phase changes in the LCE. In this article we demonstrate that a low concentration of multi-walled CNTs does not affect the thermal response of the polymers but does significantly enhance their response to infra-red (IR) and visible light.

Localised Actuation in Composites Containing Carbon Nanotubes and Liquid Crystalline Elastomers

A liquid crystalline elastomer-carbon nanotube (LCE-CNT) composite displays a reversible shape change property in response to light. The development of some systems such as tactile devices requires localised actuation of this material. A method is reported that combines mechanical stretching and thermal crosslinking of an LCE-CNT for creating sufficiently well-aligned liquid crystal units to produce localised actuation. The method demonstrates that it is feasible to optically drive a LCE-CNT film within a localised area, since only the walls of the stretched parts of the film contain aligned LC domains.

Silicon Photonic Biosensors for Lab-on-a-Chip Applications

In the last two decades, we have witnessed a remarkable progress in the development of biosensor devices and their application in areas such as environmental monitoring, biotechnology, medical diagnostics, drug screening, food safety, and security, among others. The technology of optical biosensors has reached a high degree of maturity and several commercial products are on the market. But problems of stability, sensitivity, and size have prevented the general use of optical biosensors for real field applications. Integrated photonic biosensors based on silicon technology could solve such drawbacks, offering early diagnostic tools with better sensitivity, specificity, and reliability, which could improve the effectiveness of in-vivo and in-vitro diagnostics. Our last developments in silicon photonic biosensors will be showed, mainly related to the development of portable and highly sensitive integrated photonic sensing platforms.

Silicon chips detect intracellular pressure changes in living cells

The ability to measure pressure changes inside different components of a living cell is important, because it offers an alternative way to study fundamental processes that involve cell deformation. Most current techniques such as pipette aspiration, optical interferometry or external pressure probes use either indirect measurement methods or approaches that can damage the cell membrane. Here we show that a silicon chip small enough to be internalized into a living cell can be used to detect pressure changes inside the cell. The chip, which consists of two membranes separated by a vacuum gap to form a Fabry-Pérot resonator, detects pressure changes that can be quantified from the intensity of the reflected light. Using this chip, we show that extracellular hydrostatic pressure is transmitted into HeLa cells and that these cells can endure hypo-osmotic stress without significantly increasing their intracellular hydrostatic pressure.

Bending kinetics of a photo-actuating nematic elastomer cantilever

Liquid crystal elastomers (LCE) containing embedded carbon nanotubes (CNTs) contract when exposed to light, due to LC disordering induced by the ability of CNTs to absorb light and convert it into thermal energy. A cantilever made of LCE-CNTs exposed to light demonstrates dynamic bending due to inhomogeneous strain distribution caused by exponential heat generation across the cantilever width. Analysis of bending dynamics helps to extract parameters that are important for designing actuators based on these materials. In this work, we have carried out direct measurements of temperature evolution inside the cantilever and related its kinetics to the applied irradiation power.

Liquid-crystalline elastomer micropillar array for haptic actuation

A new liquid-crystalline elastomer-based micropillar array with pushing properties is obtained by the two-step crosslinking process, where the micropillars are oriented by uniaxial compression before the final curing. This orientation process allows the formation of a two-dimensional prolate polydomain conformation of the polymer backbone and the mesogens, and opens huge opportunities for the use of liquid-crystalline elastomers in microsystems and haptic applications.

Dimension dependence of the thermomechanical noise of microcantilevers

Thermomechanical noise determines the lowest detection limits of microcantilever-based devices for measuring forces and surface stress variations. In this work, arrays of 334-nm-thick single-crystalline silicon microcantilevers with dissimilar lengths and widths from 50to500μm and 20to200μm, respectively, have been fabricated to calculate the minimal detectable force and surface stress on the basis of the measurement of the spring constant, resonance frequency, and quality factor. The calculated minimal detectable force and surface stress are of the orders of 10−15NHz−1∕2 and 10−7Nm−1Hz−1∕2, respectively, and both follow a nonintuitive dependence on the dimensions. The minimal detectable force decreases as the cantilevers are shorter and narrower, whereas the minimal detectable surface stress decreases by making the cantilevers shorter and wider. Theoretical expressions of the minimal detectable force and surface stress are provided as a function of the material properties, cantilever dimensions, and qual...

T-shaped microcantilever sensor with reduced deflection offset

The authors have designed and fabricated arrays of microcantilevers with a geometry that shows reduced initial angular offset and angle deviation between the cantilevers of the array. This feature allows to detect the displacement of the cantilevers using the optical beam deflection technique and a single split photodetector. The structure is analytically and numerically simulated to demonstrate its feasibility. In addition, experimental measurements of the angle offset corroborate the offset and the angle deviation reduction. Finally, they illustrate the potential of these micromechanical structures as sensors by measuring a monolayer of single stranded DNA.