A simple, selective and sensitive method is proposed for determination of cysteine (Cys) in milk samples using ionic liquid functionalized silver nanoparticles (ILs-AgNPs) as a colorimetric probe. ILs-AgNPs was synthesized by simple reduction method using silver nitrate as a precursor and sodium borohydride as a reducing agent and functionalized with ILs to prevent particles from self-aggregation. The sensing mechanism has been dependent on the color change of ILs-AgNPs and red shift of absorption band from 395 nm to 560 nm in the visible region, which is found proportional to the concentration of target analyte in sample. ILs-AgNPs was characterized in absence and presence of Cys by UV–vis, Fourier transform-infrared (FTIR) spectroscopy, transmission electron microscope (TEM) and dynamic light scattering (DLS). The linear range was acquired in the range of 0–100 ng mL⁻¹, with correlation coefficient (R²) of 0.996 and limit of detection (LOD) of 4.0 nM. The binding mechanism and interactions between Cys and ILs-AgNPs was confirmed by calculating the binding constant and thermodynamic parameters such as enthalpy (∆H), entropy (∆S) and Gibb's free energy (∆G). The use of ILs-AgNPs exhibited high colorimetric selectivity for Cys in milk samples in presence of other amino acids. This proposed strategy possessed the advantages of simplicity and selectivity, hence is applied for analysis of Cys in milk samples.

提出了一种简单，选择性和灵敏的方法，使用离子液体功能化的银纳米颗粒（ILs-AgNPs）作为比色探针，测定牛奶样品中的半胱氨酸（Cys）。ILs-AgNPs是通过简单的还原方法合成的，其中硝酸银为前体，硼氢化钠为还原剂，并用ILs进行功能化以防止颗粒自聚集。感测机制取决于ILs-AgNPs的颜色变化以及可见区吸收带从395 nm到560 nm的红移，这与样品中目标分析物的浓度成正比。通过紫外可见，傅里叶变换红外（FTIR）光谱，透射电子显微镜（TEM）和动态光散射（DLS）表征了不存在Cys的ILs-AgNPs。^-1，相关系数（R ²）为0.996，检测极限（LOD）为4.0 nM。通过计算结合常数和热力学参数，如焓（ΔH），熵（ΔS）和吉布斯自由能（ΔG），可以确定Cys与ILs-AgNPs的结合机理和相互作用。ILs-AgNPs的使用对牛奶样品中存在其他氨基酸的Cys具有较高的比色选择性。所提出的策略具有简便，选择性强的优点，因此可用于牛奶样品中半胱氨酸的分析。