Abstract
Biogenic amines (BAs), such as putrescine and cadaverine, remain a persistent concern for food freshness and safety for human consumption. They are mainly from the breakdown of amino acids into protein-rich foods caused by enzymes released by pathogenic bacteria that contaminate food under poor storage conditions, acting as chemical indicators for spoilage. The Food and Drug Administration (FDA) has set the tolerable level of BAs for human health at ~100 mg/kg; above this, sensitive individuals can experience health issues triggered by BAs, with mass outbreaks of scombroid poisoning leading to severe symptoms such as nausea, headaches, heart problems, and even death. Therefore, there is a need for rapid, sensitive, and cost-effective detection methods. Metallic nanoclusters are useful in this regard because of their size-dependent optical properties, electron transfer capabilities, and compatibility with environmentally friendly protein-based synthesis approaches.
This work presents the synthesis of gold- and gold-palladium nanoclusters (AuNCs) and (AuPd NCs) using chicken egg white (CEW) as both reducing and stabilising agents under microwave heat. The materials were applied in both Fluorescence and electrochemical sensing of putrescine (PUT) and cadaverine (CAD). The NCs showed the expected orange-red emission under UV light. Photoluminescence (PL) lifetimes were 3.66 ns and 4.87 ns for AuNCs and AuPd NCs, with quantum yields (QY) of 9.88 and 4.39%, respectively. Structural characterisation confirmed face-centered cubic (FCC) metallic phases, and Fourier transform infrared spectroscopy (FTIR) confirmed protein functional groups in the CEW. Transmission electron microscope (TEM) showed ultrasmall spherical clusters with mean sizes of 2.11 ± 1.37 (AuNCs) and 1.69 ± 0.99 nm (AuPd NCs), consistent with lattice fringes of 0.24 nm, while Energy dispersive X-ray (EDX) confirmed elemental composition. Dynamic light Scattering (DLS) measurements yielded hydrodynamic diameters of 83.20 and 56.06 nm, and near-neutral zeta potentials. Fluorescence sensing exhibited measurable responses towards CAD and PUT, with LOD/LOQ values derived from regression and σ-based calculations being 0.6269/1.10 (AuNCs@CAD), 1.33/4.02 (AuPd NCs@CAD), 17.28/52.35 (AuNCs@PUT), and 12.71/38.51 μM (AuPd NCs@PUT). The NCs maintained selectivity even in the presence of common interferents. In electrochemical measurements, cyclic voltammetry revealed increasing anodic peak currents across bare GCE, AuNCs-GCE, and AuPd NCs-GCE, with the bimetallic NCs displaying the highest current due to synergistic effects. Electron Impedance Spectroscopy (EIS) confirmed reduced charge-transfer resistance for AuPd NCs. The electrooxidation of CAD/PUT produced anodic currents of 75.79 (AuPd NCs) and 46.68 μA (AuNCs). The electrochemical LOD and LOQ values were 0.557/1.856 for CAD and 0.0359/0.1197 μM for PUT, showing great improvement over previous reports.