This paper describes a simple method for the microfabrication of mechanically compliant, magnetically-responsive microstructures. These microstructures were fabricated in one step by using a ferromagnetic photoresist, which, in turn, was prepared by suspending nickel nanospheres in a negative photosensitive epoxy (SU8). The nominal diameter of the nickel nanospheres was 80–150 nm, that is, much smaller than the wavelength of the UV light (365 and 405 nm) used to expose the photoresist. Diffraction and scattering of light from the nanospheres allowed for full exposure of the photoresist, even after the incorporation of nanospheres at levels at which it became opaque. The ferromagnetic photoresist was cross-linked after exposure and development, and yielded a stable, compliant, ferromagnetic pattern. The paper characterizes the effect of the weight density of the nickel nanospheres on the transmittance of films made by this technique at wavelengths from 330 nm to 610 nm. It also describes a number of microstructures made with the photoresist: examples include lines, posts and meshes. As a demonstration, the procedure was applied to the microfabrication of a set of magnetically-actuated micromirrors. These micromirrors achieved large deflections: deflection at the tip of a 12 mm long, 250 µm wide and 70 µm thick cantilever of the ferromagnetic photoresist exceeded 1.4 mm, when actuated by a NbFeB permanent magnet with field strength ∼120 mT. The cantilever maintained its mechanical properties after cycling ∼106 times.

This work describes a technology for performing and monitoring simultaneously several reactions confined in strings of microdroplets having identical volumes but different composition, and travelling with the same speed in parallel channels of a microfluidic device. This technology, called parallel microdroplets technology (PmicroD), uses an inverted optical microscope and a charge-coupled device (CCD) camera to collect images and analyze them so as to report on the reactions occurring in these microdroplets. A concentration gradient of one reactant is created in the microfluidic device. In each channel, a different concentration of this reactant is mixed with a fixed amount of a second reactant. Using planar flow-focusing methodology, these mixtures are confined in microdroplets of pL size which travel in oil as continuous medium, avoiding laminar dispersion. By analyzing the images of parallel strings of microdroplets, the time courses of several reactions with different reagent compositions are investigated simultaneously. In order to design the microfluidic device that consists in a complex network of channels having well-defined geometries and restricted positions, the theoretical concept of equivalent channels (i.e. channels having identical hydraulic resistance) is exploited and developed. As a demonstration of the PmicroD technology, an enzyme activity assay was carried out and the steady-state kinetic constants were determined.

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This work describes a simple optical method for obtaining, in a single still-capture image, the continuous absorbance spectra of samples at multiple locations of microsystems. This technique uses an unmodified bright-field microscope, an array of microlenses, and a diffraction grating to disperse the light transmitted by samples of 10-to 500-m dimensions. By analyzing in a single image the first-order diffracted light, it is possible to collect the full and continuous absorbance spectra of samples at multiple locations (to a spatial resolution of Ϸ8 m) in microwells and microchannels to examine dynamic chemical events (to a time resolution of <10 ms). This article also discusses the optical basis of this method. The simultaneous resolution of wavelength, time, and space at a scale <10 m provides additional capabilities for chemical and biological analysis.poly(dimethylsiloxane) ͉ array of microlenses ͉ spectrophotometer ͉ image processing T his article describes an optical method that resolves wavelength, time, and location simultaneously for samples in microsystems. This technique, which we call micropattern spectrophotometry (PS), analyzes a continuous spectrum of wavelengths (with best performance, in the system described here, in the range of 450 to 700 nm) at multiple positions in the field of view of a microscope. This procedure provides a flexible method for analyzing the composition of samples at a number of points, or in a number of samples, simultaneously and continuously.Microsystems are now ubiquitous in chemistry and biology (1). Applications include analysis of chemical reactions (2), sorting of cells (3), and high-throughput screening (4). Because these systems often require separation (5), mixing (6, 7), and reaction (8) of components with distinct optical profiles, they would benefit from a method that allows the components to be characterized optically in space and time. Advances in miniaturization of components used in spectrophotometric systems have produced a number of useful microsystems: these systems typically work at a single wavelength at any one time (9, 10) or perform measurements at a single spatial location (11-15), and most cannot be easily interfaced with microfluidic systems (16-18). Miniaturized systems for integrating microspectrometers and microfluidics have been proposed but not demonstrated (19,20). Although fiber optic-based microspectrophotometers (21) have been described and microscope-based spectrophotometers (22) are available, they are capable of analyzing only one or only a few samples at a time, and they scan the spectrum one wavelength at a time. Also, they require alignment of a fiber optic cable to the sample region.The method described here collects spectral information at many wavelengths and for many samples simultaneously. Materials and MethodsSetup of the Micropattern Spectrophotometer. We fabricated an array of microlenses in an opaque background by reflowing photoresist (with an index of refraction of 1.59) followed by electroplating of nickel around the mi...

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