Cost-effective SERS-based detection of chlorpyrifos residues in honey

Abstract

The presence of pesticide residues in honey which are a consequence of bees foraging habits and hive treatments, pose a threat to consumer safety. While the European Commission (EC) has banned certain harmful pesticides like chlorpyrifos (CPY), their continued global use necessitates frequent testing to safeguard citizens within the European Common Market. Traditional analytical methods, like gas chromatography coupled with tandem mass spectrometry, offer high accuracy but are hindered by their time-consuming and expensive nature. Consequently, the development of more efficient and cost-effective screening alternatives is crucial. This study addresses this challenge by developing a cost-effective and effective pesticide detection method using Surface Enhanced Raman Spectroscopy (SERS) coupled with QuEChERS extraction. To enhance SERS performance, cost effective metallic foils with localized surface plasmon resonance (LSPR) activity were explored as substrates. A key contribution of this work is the demonstration that LSPR-active surfaces, specifically cost-effective aluminum foil (ALF) coupled with deposited gold nanoparticles (AuNPs), significantly enhance Raman signals when compared to LSPR-inactive substrates including silicon (Si) under the same conditions. The ALF@AuNPs platform, combined with QuEChERS extraction, enabled the detection of CPY in honey down to a concentration of 4.8×10⁻⁷ M. Further enhancements to the ALF@AuNP substrate through omniphobic surface modification reduced the limit of detection (LOD) to 1.1×10⁻⁹ M, well below the EU maximum residue limit (MRL). Notably, this represents the first successful application of an instantaneous omniphobic coating as a cost-effective SERS substrate coupled with QuEChERS extraction. Additionally, SERS substrate fabrication techniques were compared, demonstrating that a three-phase Marangoni approach and a 532 nm incident wavelength significantly improved performance over simple deposition and a 785 nm wavelength. Using a gold foil SERS substrate fabricated via the Marangoni approach and measured using a 532 nm incident wavelength, CPY detection in honey was reduced to an LOD of 2.3×10⁻⁸ M, which is below the EU MRL. In each approach, a principal component analysis (PCA) model was developed, successfully distinguishing CPY in honey samples containing multiple pesticides, thereby enhancing selectivity and reliability. To assess the practical applicability of the developed method, an industry survey was conducted, revealing a strong demand for faster and more affordable pesticide screening solutions. This reinforces the significant commercial potential of the research.

Thesis is embargoed until 31 July 2026.

Date of Award	Jul 2025
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Cuong Cao (Supervisor) & Tassos Koidis (Supervisor)