Arsenic is a toxic metalloid that occurs naturally in the Earth's crust. Its widespread distribution and mobility have led to extensive environmental contamination and adverse human health effects across numerous regions worldwide. Monitoring arsenic concentrations in ecosystems is crucial for mitigating potential hazards and minimizing human exposure. This research outlines the synthesis, characterization, and application of an innovative Schiff base Quinazoline ligand and its corresponding ternaryMn(II) complex for arsenic sensing. A manganese (II) coordination compound featuring a principal ligand denoted (WMS) and an auxiliary ligand Glycine (GLY) was synthesized and comprehensively characterized using analytical techniques such as FT-IR, UV-Vis, mass spectrometry, elemental analysis, and electrical conductance measurements. Thermal analysis (TGA) of the Manganese(II) complex corroborated well with the proposed formula derived from the analytical data. The molecular formula of the complex was determined to be [Mn(WMS)(GLY)H2O].Cl.H2O, with the (WMS) ligand exhibiting tridentate chelation behavior by coordinating with the central Mn(II) ion through its two azomethine nitrogen atoms and one pyridine nitrogen. The (Gly) ligand bound to Mn (II) via deprotonated carboxylate oxygen and the (NH2) nitrogen, resulting in a distorted Octahedral geometry. In addition, Density Functional Theory (DFT) calculations are performed to determine the optimal structure of the Schiff base (WMS) and its Mn (II) complex. The HOMO-LUMO energy gaps, chemical hardness, and dipole moments of the (WMS) and its Manganese complex were also investigated. The study examined the biological roles of the (WMS) and its Mn (II) complex, specifically focusing on its antibacterial, antifungal, and anticancer properties. To understand the molecular interactions, we conducted molecular docking simulations to determine the potential binding orientations of the (WMS) and its Mn (II) complex with active sites on the receptor (3HB5). The docking analyses were conducted meticulously utilizing the MOE program, renowned for its robust, stiff molecular docking capabilities. Extensive characterization of the nano-sized Quinazoline Manganese complex involved dynamic light scattering (DLS), zeta potential analysis, x-ray diffraction (XRD), atomic force microscopy (AFM), BET surface area determination, and pore size analysis. The possible application of this nano-complex as a quartz crystal microbalance (QCM) sensor for detecting arsenic contamination in water was investigated. The sensor exhibited rapid response times (less than 2 minutes), excellent mechanical stability (confirmed by contact angle measurements), and consistent performance across varying pH and temperature conditions. This research highlights the synthesis of new arsenic-sensing material and its promising application in continuous environmental monitoring. Given the widespread prevalence of arsenic contamination, particularly in groundwater sources used for drinking and irrigation, developing sensitive and selective arsenic sensors is paramount for safeguarding public health and ecosystem integrity.