The performance of low-cost, microgroove silicon (Si)-based internal reflection elements (μ-groove IREs) for infrared chemical imaging of microfluidic devices is described.

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Deep X-ray lithography processing of SU-8 negative resist layers with thicknesses of up to 1 mm and physical-chemical properties of SU-8 polymer structures were investigated to find the optimum conditions for the fabrication of X-ray refractive lenses. The exposure was carried out at the ANKA storage ring in Karlsuhe, Germany. Experimental tests of the lenses were performed at the ESRF in Grenoble, France. First lenses showed a gain in the range of 20, a full width at half maximum of the focal spot intensity of approximately 2 lm to 3 lm and unique radiation stability of the optical characteristics. IntroductionThe idea of refractive X-ray lenses proposed in [1] was for the first time realized in form of consecutive holes in an aluminum block [2]. Unlike in case of visible light such an X-ray lens has to be composed of several elements with a concave shape. Their radius of curvature is in the range of several hundreds down to tens of micrometers. The lens material is absorbing. Since the first publication search and development of suitable materials and technologies for the formation of this simplest and cheapest type of X-ray optics is going on [3][4][5][6][7][8][9].Materials consisting of light atoms allow to reduce X-ray absorption and to increase the gain in the focal spot of an X-ray lens compared to heavier materials. Minimizing the bridge distance between adjacent concave shapes of an element of an X-ray lens leads to the same result. Besides, the exact patterning of the lens element form with the possibility of a coaxial arrangement of the elements is necessary in order to obtain the minimal size of a focal spot. A high roughness of the surface of the lens elements and a crystallinity of the lens material needs also to be avoided because it reduces the gain in the focal spot. In addition, expensive and materials unstable under X-ray exposure under normal conditions can not be used for this application. Depending on these evident limitations, planar lithographic technologies, especially deep X-ray lithography and LIGA technique would be a suitable process to pattern these elements. Structure characteristics as aspect ratios up to 100, sub-micrometer tolerance, smooth side-walls, vertical and tilted structures, sub-micrometer precision and exact positioning of the structures on a substrate are achieved by deep X-ray lithography in thick resist layers [10]. In principle, polymer X-ray resist materials composed from C, O and H atoms mainly are from the point of absorption competitive against the known lens materials as Li, Be, diamond, Al and Si. However, positive X-ray resists like PMMA which is conventional for X-ray lithography are destroyed under X-ray exposure in case of an absorbed radiation of already 1 kJ/cm 3 . This is insufficient even for a 1 h monochromatic X-ray experiment.A while ago the multi-component highly sensitive negative photo-resist SU-8 [11] was firstly proposed for deep X-ray lithography [12]. In our previous works [13,14] it has been shown that microstructures with aspect ratios of m...

In deep X-ray lithography synchrotron radiation is applied to pattern several hundred micrometer thick resist layers. This technique has been used to obtain micro structures with an aspect ratio up to 100 and dimensions in the micrometer range. The structures are characterised by straight walls and a typical sidewall roughness of approximately 50 nm.To be able to fabricate n-coherent structures with any lateral shape and to have the possibility to use these resist microstructures in an additional electroforming process the resist is usually mounted on a ceramic or metallic substrate. Due to the different thermal expansion coefficients of the resist material and the substrate a developing temperature of 37°C produces cracks in the resist structures depending on the microstructure design. These defects are not observed if the developing temperature is reduced to 20°C. Better structure quality is obtained using the GG-developer instead of MIBK/IPA, but the developing rate is decreased. Measurements of the developing rate of PMMA in GG-developer at different temperatures show that the contrast of the developer-resist system is increased at 20°C compared to 37°C.

Extensive testing of populations against COVID-19 has been suggested as a game-changer quest to control the spread of this contagious disease and to avoid further disruption in our social, healthcare and economical systems. Nonetheless, testing millions of people for a new virus brings about quite a few challenges. The development of effective tests for the new coronavirus has become a worldwide task that relies on recent discoveries and lessons learned from past outbreaks. In this work, we review the most recent publications on microfluidics devices for the detection of viruses. The topics of discussion include different detection approaches, methods of signalling and fabrication techniques. Besides the miniaturization of traditional benchtop detection assays, approaches such as electrochemical analyses, field-effect transistors and resistive pulse sensors are considered. For emergency fabrication of quick test kits, the local capabilities must be evaluated, and the joint work of universities, industries, and governments seems to be an unequivocal necessity.

In the first step of the LIGA process a resist layer, typically PMMA (polymethylmethacrylate), is pattered by deep X-ray lithography. The exposed parts are subsequently dissolved by an organic developer. The quality and the achievable height of the microstructure is decisively determined by the development process. In order to increase the aspect ratio and maintain the quality of the microstructures the parameters influencing the development process were investigated. In the case of dip development and ultrasound development a strong dependency of the development rate on the temperature, dose value and depth of deposition has been noticed. The development rate increases with increasing dose value and temperature and decreases with increasing depth of deposition. In case of dip development the development course can be described by a phenomenological equation which considers the three mentioned parameters. In the case of ultrasound further parameters have to be taken into account: the geometry and the dimensions of the strucutres.

A custom-designed optical configuration compatible with the use of micromachined multigroove internal reflection elements (μ-groove IREs) for attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy and imaging applications in microfluidic devices is described. The μ-groove IREs consist of several face-angled grooves etched into a single, monolithic silicon chip. The optical configuration permits individual grooves to be addressed by focusing synchrotron sourced IR light through a 150 µm pinhole aperture, restricting the beam spot size to a dimension smaller than that of the groove walls. The effective beam spot diameter at the ATR sampling plane is determined through deconvolution of the measured detector response and found to be 70 µm. The μ-groove IREs are highly compatible with standard photolithographic techniques as demonstrated by printing a 400 µm wide channel in an SU-8 film spin-coated on the IRE surface. Attenuated total reflection FT-IR mapping as a function of sample position across the channel illustrates the potential application of this approach for rapid prototyping of microfluidic devices.

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