In situ synthesis of label-free electrochemical aptasensor-based sandwich-like AuNPs/PPy/Ti3C2Tx for ultrasensitive detection of lead ions as hazardous pollutants in environmental fluids

The monitoring of hazardous pollutants in environmental fluids is one of main stretaegy in investigation of water and soil quality. Metal ions are one of main and dangerius materials in water sampels and one of the main causes of environmental problems. Therefore, many of environmental researchers focused on fabrication of highly sensitive sensor to ion hazardous pollutants environmental fluids. The encapsulation of 2D MXenes with other stable materials has proven to be an effective method for enhancing their stability and electrochemical properties. In this work, a sandwich-like nanocomposite structure, AuNPs/PPy/Ti₃C₂T_x, was designed and synthesized via a facile method of one-step layer-by-layer self-assembly. The morphology and structure of the prepared nanocomposites are characterized with various methods such as scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Ti₃C₂T_x as a substrate played a significant role in the synthesis and alignment of PPy and AuNPs growth. The nanocomposites have maximized the benefits of the inorganic AuNPs and organic PPy materials, enhancing their stability and electrochemical performance. Meanwhile, AuNPs have given the nanocomposite the ability to form covalent bonds with biomaterials via the Au–S bond. Thus, a novel electrochemical aptasensor was developed based on AuNPs/PPy/Ti₃C₂T_x for the sensitive and selective detection of Pb²⁺. It demonstrated a wide linear range from 5 × 10⁻¹⁴ to 1 × 10⁻⁸ M with a low LOD of 1 × 10⁻¹⁴ M (S/N = 3). Additionally, the developed aptasensor exhibited excellent selectivity and stability and successfully used to sensing of Pb²⁺ in environmental fluids such as NongFu Spring and tap water.