Low-cost and highly sensitive colorimetric and visual detection of amikacin in milk using melamine functionalized gold nanoparticles

This study developed a rapid, low-cost and highly sensitive analytical method using melamine functionalized gold nanoparticles (MA-Au NPs) as a colorimetric sensor to detect amikacin in milk. The MA-Au NPs were synthesized using a self-assembly process and analyzed using absorption spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. The MA-Au NPs exhibited a distinct surface plasmon resonance (SPR) absorption peak at 520 nm and demonstrated excellent spherical dispersion. The reaction parameters were optimized, with a Au NP concentration of 2.0 × 10⁻⁷ mol L⁻¹, MA concentration of 1.0 × 10⁻⁶ mol L⁻¹, pH of 4.0, and reaction time of 15 minutes. In the optimization experiment, the effects of unmodified Au NPs and MA-Au NPs as colorimetric sensors for amikacin determination were compared. As a specific amount of amikacin was added to the Au NP solution, the reaction solution showed a visible change from wine red to purple and then to blue gray; a red-shift in the absorption spectrum of the solutions was observed, which could also be analyzed using the A₆₄₀/A₅₂₀ value, and the color changes were recorded using smartphones for visual detection through RGB (red–green–blue) data image analysis, which made the detection easy and fast. As a result, two approaches were devised using visible absorption spectra and smartphones. A linear correlation was established between the A₆₄₀/A₅₂₀ value and the concentration of amikacin in the range of 4.0 to 16.0 × 10⁻⁸ mol L⁻¹. The minimal limit of detection (LOD) for absorption spectrum analysis was 3.75 × 10⁻⁹ mol L⁻¹, whereas for smartphone analysis, it was 6.0 × 10⁻⁸ mol L⁻¹. The recoveries ranged from 103.09% to 104.51%, while the relative standard deviations (RSDs) ranged from 3.76% to 4.25%. The proposed method was used to detect actual milk samples. The results showed that the method is simple, selective, and practical.