It is impossible for infrared (IR) imaging, so called thermography, to obtain temperature images of aqueous solutions inside a microchip because IR radiation from the liquid is overwhelmed by radiation from the microchip’s materials such as glass and poly-dimethyl siloxane (PDMS). In addition, IR imaging is a passive method, which means that signal intensity from a micro-area would become too small to be detected. Our study presents a novel method for temperature imaging using near-infrared light. The principle is based on the temperature dependence of the absorption band of water. This method would be useful for temperature measurement applications and control of aqueous solutions in microchips.

Keywords: Temperature imaging, Aqueous solution, Near-infrared spectroscopy, Microchip.


Figure: Temperature image of 0.5 mm-thick water heated by a nichrome wire with a diameter of 0.05 mm.

Infrared spectroscopy (IRS) is a noncontact method to measure solute concentration, water content, and temperature of aqueous solutions. To apply IRS to microchip analyses, it is important to investigate the characteristics of IR absorption of extremely thin water, which must be different from that of bulk water. Since water strongly absorbs mid-infrared light (wavelength from 2500 nm to 5000 nm), an attenuated total reflection (ATR) method is commonly used in spectral analyses. However, our study focuses on a transmission method, considering usability with existing microchips and the development of imaging.
Keywords: Infrared spectroscopy, Thin-film water, Temperature, Microchip.












Figure: Temperature dependence of mid-infrared absorption spectrum of 10 µm-thick water.

Micropipette electrode is a glass micropipette coated with metal film. When high voltage (1-2 kV) is applied to the electrode in atmospheric air, corona discharge occurs from the tip to a counter plate electrode. Although the corona discharge takes low electric power, strong electric field is formed in the vicinity of the tip, which could decompose or ionize various substances.
Keywords: Micropipette electrode, Corona discharge, Microplasma.








Figure: SEM image of the tip of a micropipette electrode. The tip diameter is 1 um. The surface (except the tip) is coated with diamond-like carbon for electrical insulation.

Keywords: Cell, Micropipette, Electrometry, Injection.








Figure: micropipette electrode and cell.