Super-resolution optical microscopy using a glass microsphere nanoscope

A technique that allows direct optical imaging of nanostructures and determines quantitatively geometric nanofeatures beyond the classical diffraction limit by using high-refractive index glass microspheres is introduced. The glass microsphere is put on the nanostructure that is immersed in oil. When illuminated by conventional oil-immersion microscope objective, a magnified virtual image of the sample is projected by the microsphere and recorded by the same objective. The image reveals the sub-diffraction nanofeatures of the sample due to a highly focused focal spot generated by the microsphere, i.e. a so-called "photonic nanojet". Experimental results on nanostructures demonstrates a resolution of ~ λ/4 - λ/7, where λ is the illumination wavelength, by using a 60 μm glass microsphere and a normal wideband halogen lamp as illumination source

A cell-on-paper system for the study of secretion

A simple and generally applicable system was designed to detect and quantify electroactive molecules released from cells grown on paper

Capacitive flexible force sensor

We have realized a flexible force sensor, composed of four redundant capacitors, the operation of which is based on the measurement of a load-induced capacitance change. We use polyimide both as flexible substrate and as elastic dielectric between two levels of finger-shaped aluminum electrodes. In particular we have developed a technology for realization of polyimide micro-features with gentle slopes to facilitate subsequent metallization processes. Thereby, we could improve step coverage and electrical contacting between the two metallization levels, as well as the mechanical stability of the sensor. The smooth polyimide slopes were obtained by combining lithographic resist-reflow techniques with dry etching procedures. We have electrically characterized the capacitors using an impedance analyzer and obtained a typical force sensitivity of 1-2 fF/N

Low temperature pyrex/silicon wafer bonding via a single intermediate parylene layer

We introduce a new low temperature (280 °C) parylene-C wafer bonding technique, where parylene-C bonds directly a Pyrex wafer to a silicon wafer with either a Si, SiO2 or Si3N4 surface with a bonding strength up to 23 MPa. The technique uses a single layer of parylene-C deposited only on the Pyrex wafer. Moreover, the process is compatible for bonding any type of wafer with small-sized micropatterned features, or containing microfluidic channels and electrodes. This technique can be an alternative for conventional bonding methods like anodic bonding in applications requiring a low-temperature and diverse bonding interfaces

Cathodic pretreatment improves the resistance of boron-doped diamond electrodes to dopamine fouling

The resistance of cathodically and anodically treated boron-doped diamond electrodes to dopamine fouling was investigated. It was found, using cyclic voltammetry and electrochemical impedance spectroscopy, that the cathodic preparation offers an increased resistance to fouling, in addition to an enhanced electrochemical response

Fast detection of single nanoparticles in a microfluidic channel by a microlens array in combination with a conventional optical microscope

We present the use of a microlens array in combination with a conventional optical microscope set-up for the detection of single nanoparticles (NPs) in fluid medium. Optically transparent dielectric microspheres are patterned in a microfabricated well array template and used as microlenses focusing the light originating from a microscope objective into so-called photonic nanojets that expose the medium within the microfluidic channel. When the NPs pass the nanojets, the detection signal is highly enhanced, Au NPs with size down to 50 nm, fluorescent NPs down to 20 nm in size, as well as biomolecule-linked NPs are clearly observed

Study of Spatio-Temporal Immunofluorescence on Bead Patterns in a Microfluidic Channel

We performed a direct immunoassay inside a microfluidic channel on patterned streptavidin-coated beads, which captured fluorescently-labeled biotin target molecules from a continuous flow. We arranged the beads in a dot array at the bottom of the channel and demonstrated their position- and flow rate-dependent fluorescence. As the target analyte gets gradually depleted from the flow when passing downstream the channel, the highest fluorescence intensity was observed on the most upstream positioned dot patterns. We propose a simple analytical convection model to explain this spatio-temporal fluorescence

Lens array by electrostatic patterning of dielectric microspheres in a Parylene-C well template

We present the fabrication of a microlens array which can be integrated into a microfluidic device. In the demonstrated technique, a microwell array is firstly fabricated in a Parylene-C layer by a standard cleanroom process. Afterwards, the optically transparent dielectric microspheres with high refractive index are patterned inside the well template by utilizing an electrostatic technique. The mechanism of microsphere patterning is studied, and the lens effect of the microsphere is experimentally verified in a water-based medium. We also present a detailed two-dimensional numerical optical simulation study on the patterned microspheres using the Finite Element Method (FEM)

A microcalorimetric platform for studying the heat produced by chemical reactions in microliter volumes

We describe the development of a microcalorimetric platform for accurate measurement of the heat power generated by chemical/biochemical reactions in liquid volumes of a few 10 µL, which we used to measure the heat of mixing of 1-propanol in deionized water. The system allows fast overall stabilization to a setpoint temperature with a stability of ± 1 mK. The combination of an open-well sample reservoir with a commercial nanocalorimetric chip (Xensor Integration) makes the platform easy to use and very versatile. The open-well format allows preloading a sample by pipetting, while fluidic interconnections enable injecting subsequently additional reagents