ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Ficin-functionalized gold nanoparticles for selective UV-Vis colorimetric detection of Hg²⁺, Cu²⁺, and Cr⁶⁺: optimization and RGB image-based quantification

Asraf Alif Rashidi, Mohd Mohd Izuan Effendi Halmi, Mohd Rizal Arifin, Khairul Hafiz Mohd Yusoff, Khairil Mahmud, Siti Salwa Abd Gani, and Mohd Yunus Abd Shukor

Faculty of Agriculture, Department of Land Management, University Putra Malaysia, Serdang, Malaysia

E-mail: m_izuaneffendi@upm.edu.my

Received: 18 February 2026  Accepted: 4 April 2026

Abstract:

Nowadays heavy metal pollution poses a critical environmental and public health challenge making affordable detection methods for water quality monitoring urgently needed. To address this issue, a novel colorimetric detection system based on ficin-functionalized gold nanoparticles (F-AuNPs) was developed and evaluated using UV-Vis spectrophotometry and smartphone-based RGB image analysis for the detection of Hg²⁺, Cu²⁺, and Cr⁶⁺. Response Surface Methodology using Box-Behnken Design optimized the functionalization conditions of Ficin to AuNPs resulting in an excellent model fit (R² = 0.9818, adequate precision = 26.992). The optimized F-AuNPs exhibited selective aggregation with Hg²⁺, Cu²⁺, and Cr⁶⁺ causing a visible color transition from red to blue gray but remained dispersed in the presence of nine other tested metal ions. UV-Vis spectrophotometry demonstrated strong linearity with LOD/LOQ values of 0.02/0.06 ppm for Hg²⁺, 0.05/0.17 ppm for Cu²⁺, and 0.10/0.33 ppm for Cr⁶⁺. RGB image analysis yielded comparable sensitivity across all three metals, with LOD/LOQ values of 0.02/0.06 ppm for Hg²⁺, 0.06/0.17 ppm for Cu²⁺, and 0.11/0.33 ppm for Cr⁶⁺. Spike-recovery tests in tap and lake water confirmed feasibility of the F-AuNPs with spiked samples validating the method’s applicability for environmental monitoring. Thus, the F-AuNPs colorimetric platform provides a low-cost operation-minimal sample preparation that functions as practical field-ready tool for future near real time monitoring of these heavy metals.

Keywords: Ficin; Gold-nanoparticle; Heavy metals; Colorimetric; Optimization; UV-Vis spectrophotometry; Digital Image Analysis

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04886-3

Chemical Papers 80 (7) 8267–8280 (2026)