# A Cost-Effective Reference-Less Semiconductor Ion Sensor with Anodic Aluminum Oxide Film

## TL;DR

A low-cost, miniaturized ion sensor using anodic aluminum oxide film was developed for applications like food safety and diagnostics.

## Contribution

A reference-less semiconductor ion sensor using anodic aluminum oxide film is introduced, eliminating the need for expensive reference electrodes.

## Key findings

- The sensor achieved 57.8 mV/pH sensitivity with low hysteresis.
- It enabled non-destructive, real-time monitoring of milk freshness.
- The fabrication process is cost-effective and compatible with semiconductor manufacturing.

## Abstract

What are the main findings?

Developed a low-cost reference-less ion sensor using AAO films.

Achieved 57.8 mV/pH sensitivity and demonstrated non-destructive monitoring for milk freshness.

What are the implications of the main findings?

Enables miniaturized, cost-effective ion sensors.

Promises portable, disposable platforms for food safety and diagnostics.

The detection and monitoring of ions are essential for a broad range of applications, including industrial process control and biomedical diagnostics. Traditional ion-sensitive field-effect transistors require bulky and expensive reference electrodes, which face several limitations, including device miniaturization, high fabrication costs, and incompatibility with semiconductor manufacturing processes. Here, we introduce a reference-less semiconductor ion sensor (RELESIS) that utilizes anodic aluminum oxide film as both the sensitive and dielectric layer. The RELESIS is composed of a metal-oxide-semiconductor field-effect transistor and an interdigital electrode, which fundamentally eliminates the need for a reference electrode, thereby enabling device miniaturization. During fabrication, the anodic oxidation process is employed in place of the expensive atomic layer deposition method, significantly reducing manufacturing costs while maintaining high surface quality. In practical measurements, the RELESIS device demonstrated an excellent pH sensitivity of 57.8 mV/pH with a low hysteresis of 7 mV. As a proof-of-concept application, the RELESIS device was employed for real-time, non-destructive monitoring of milk freshness, accurately detecting pH changes from fresh to spoiled in milk samples. The combination of reference-less structure, low-cost fabrication, and superior sensing performance positions this technology as a promising platform for next-generation portable ion sensing systems in food safety, environmental monitoring, and point-of-care diagnostics.