3D microelectrode C4D microfluidic chip helps soil nutrient analysis

A research group led by Prof. WANG Rujing and Assoc. Prof. CHEN Xiangyu from Hefei Institutes of Physical Science of Chinese Academy of Sciences, along with Prof. HONG Yan’s research group from Anhui University of Science and Technology, has recently developed a novel microfluidic chip with capacitively coupled contactless conductivity detection (C⁴D) integrated 3D microelectrodes. This is to rapidly and quantitatively determine abundant nutrient ions in soil.

"Farmers can use this chip to make sure their crops are getting all the nutrients they need to grow healthy and strong," explained Prof. WANG.

The research results were published in Computers and Electronics in Agriculture.

Nutrients such as nitrogen, phosphorus, and potassium are vital for crop growth and agricultural production. Hence, the rapid and precise determination of these nutrients on-site is crucial for guiding precise fertilization practices. Compared to traditional C⁴D microfluidic chips, integrating 3D microelectrodes enhances wall capacitance and improves signal response, while also being cost-effective and easy to produce.

In this study, the team developed a C⁴D microfluidic chip with integrated 3D microelectrodes, including a cross-over electrophoretic channel and a 3D channel, via the Micro-Electro-Mechanical System

process. Through a unique design with a single photolithography process, they successfully constructed 3D microelectrodes.

This 3D microelectrode system is composed of a side wall electrode and a bottom electrode, with the side wall electrode being realized by injecting liquid gallium into the electrode channel.
With this novel microfluidic chip, the on-site determination limits of ions such as K⁺, NH₄⁺, NO^3- and PO₄^3- were lower than 0.1 mg/L, with a relative standard deviation of less than 5% between multiple determinations. Additionally, the chip achieved high resolution in the separation between K⁺ and NH₄⁺ in soil samples.

The introduction of a new 3D microelectrode configuration scheme with excellent performance and low cost into the C⁴D microfluidic chip enables the on-site determination of soil abundant nutrient ions with multi-index, high sensitivity, and stability.

"Our finding will solve the need for rapid on-site determination of soil nutrients in farms effectively," said Assoc. Prof. CHEN Xi.

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