Publication: Junctionless silicon nanowire transistor for in-situ detection of ballast water pollution.
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Date
2025-01
Authors
Abdullah, Ahmad Makarimi
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Abstract
The discharge of ballast water from ships is a major concern for the marine environment. While it is needed for ship stability, ballast water often carries pollutants, including cadmium (Cd²⁺), a toxic heavy metal that threatens marine life and human health. With shipping activity increasing worldwide, there is an urgent need for fast, reliable, and affordable sensors to detect cadmium in seawater. Existing detection methods are often too slow, costly, or unsuitable for real-time use. This study presents a silicon nanowire transistor (SiNWT) sensor designed for cadmium detection in ballast water. The device was fabricated on a silicon-on-insulator (SOI) wafer, chosen for its excellent electrical properties. Nanowire structures were patterned using atomic force microscopy (AFM) lithography with local anodic oxidation (LAO). The etching process used a mixture of 30 wt% potassium hydroxide (KOH) and 10 vol% isopropyl alcohol (IPA) at 65°C for 22 seconds, followed by diluted hydrofluoric acid (HF), producing well-defined nanowire structures. To enhance selectivity, the nanowire surface was functionalised with 3-mercaptopropyl trimethoxysilane (MPTMS), which provides thiol (-SH) groups that strongly bind cadmium ions. Electrical testing showed
stable current–voltage responses for nanowire gaps between 100.5 nm and 435.6 nm. Seawater tests at West Port, Selangor, and Labuan Port, Sabah confirmed cadmium detection at 7.31 ppm and 21.11 ppm. The results demonstrate that the SiNWT sensor offers a compact, sensitive, and practical tool for real-time monitoring of ballast water.