Measuring ion concentration in solutions for clinical and environmental research

June 28, 2018, Okayama University
Measuring ion concentration in solutions for clinical and environmental research
Schematic of the sensing plate when it is illuminated by the femtosecond laser. Inset is the microphotograph of the microsolution wells. Credit: Okayama University

Okayama University researchers describe in the journal Optics Express the use of Terahertz (THz) chemical microscopy to measure the pH of water-based solutions with a volume as small as 16 nL. The findings are important to be able to measure pH concentrations in small-volume solutions for clinical and environmental analyses.

For clinical and environmental research and monitoring it is important to be able to measure pH concentrations in small-volume solutions. However, conventional systems used to measure the of ions require the use of reference electrodes that end up reducing the volume of the , setting a limit on the minimum volume that it is possible to analyze.

Now, Dr.Toshihiko Kiwa and colleagues at the Graduate School of Natural Science and Technology in Okayama University, Japan, demonstrated the use of Terahertz (THz) chemical microscopy to measure the pH of water-based solutions with a volume as small as 16 nL. The results are published in Optics Express. This type of microscope has a sensing plate with patterned micro wells hosting the solution; an ultrafast laser pulse directed on the sensing plate generates a photocurrent with ultrafast modulation that, in turn, emits THz radiation into free space. Because the amplitude of the THz radiation depends on the concentration of ions in the micro wells, this method opens up the possibility of imaging the concentration of ions without the need of using electrodes. This enables the measurement of volumes of solution that would be too small for conventional methods.

The THz chemical microscope, which was developed by this same group in 2007, features a semiconducting (silicon) thin film mounted on a sapphire substrate that acts as the sensing plate. A layer of oxide naturally forms on the silicon film, providing an insulating layer between the silicon surface and the solution. The researchers added a resin on top of the oxide layer and used conventional photolithographic techniques to pattern micro wells in it, obtaining wells with a volume of 16 nL. They also optimized the laser pulses to stabilize the signal, and integrating this method into the microscope is part of the next steps the researchers intend to take.

Thinking about the future directions the team is interested to explore, the author say that "we will attempt the integration for multi-ion sensing and reducing the laser spot size to improve the accuracy of THz chemical microscopy."

Explore further: A simple method etches patterns at the atomic scale

More information: Toshihiko Kiwa et al. pH measurements in 16-nL-volume solutions using terahertz chemical microscopy, Optics Express (2018). DOI: 10.1364/OE.26.008232

Related Stories

A simple method etches patterns at the atomic scale

April 26, 2018

A precise, chemical-free method for etching nanoscale features on silicon wafers has been developed by a team from Penn State and Southwest Jiaotong University and Tsinghua University in China.

A micro-thermometer to record tiny temperature changes

May 14, 2018

Scientists at Tokyo Institute of Technology (Tokyo Tech) and their collaborators have developed a micrometer-wide thermometer that is sensitive to heat generated by optical and electron beams, and can measure small and rapid ...

Recommended for you

Reducing the impact forces of water entry

November 20, 2018

When professional divers jump from a springboard, their hands are perpendicular to the water, with wrists pointed upward, as they continue toward their plunge at 30 mph.

Tiny lasers light up immune cells

November 20, 2018

A team of researchers from the School of Physics at the University of St Andrews have developed tiny lasers that could revolutionise our understanding and treatment of many diseases, including cancer.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.