micro-Hotplate enhanced optical heating by infrared light for single cell treatment.

In this study we present a simple approach for fast and localised heating that relies on the strong absorbance of infrared light by microsized patterned surfaces ("micro-hotplates"). Two different materials, micro-arrays of carbon and gold, were tested with respect to their absorbance of the 830 nm diode laser light and their applicability. Both materials were found to be suitable for inducing controlled heating to a temperature increase of more than 10 degrees C within less than a second. The effect of optical heating on living cells (colon cancer cell line SW 480) was investigated with a modified fluorescence microscope. The temperature was controlled by varying the intensity and the exposure time of the laser light. Depending on temperature, induced death of cells in direct contact with the absorbent material was observed, or otherwise cells were kept alive. Cells survive the direct exposure of IR light without the use of the micro-hotplates. In contrast to common heating systems, the optical heating does not need direct contact to a temperature control device. Therefore, it is a very flexible method that can easily be implemented within any microchip. We believe that it will be a versatile tool for initiation and modulation of biochemical or cellular reactions, reversible cell membrane opening, and for control of cell growth.

Formation of surface-attached responsive gel layers via electrochemically induced free-radical polymerization.

We report on the formation of hydrogel layers on conducting substrates via a simple electrochemical route. Free-radical polymerization is initiated by an electron transfer from the substrate to a redox-active initiator. Gels of the thermally responsive material poly-N-isopropylacrylamide (p-NIPAM) with a thickness between 25 and 250 nm were produced and characterized. The gels adhere well to the substrate. They show the characteristic swelling transition at 32 degrees C. Although the films appear homogeneous in optical microscopy, AFM images reveal a slightly heterogeneous, globular structure. The gels are permeable to small ions as evidenced by electrochemical experiments with gel-covered electrodes.