Biocompatible Casein Silver Nanoparticles: An Efficient Nanosensor for Rapid Nitazoxanide Detection in Biological and Environmental Samples

The widespread usage of polluted water containing drug residues leading to an increased negative impact on living organisms. Therefore, a growing need to identify commonly available drugs in real samples. In this work, a very sensitive and selective method was developed for the detection of nitazoxanide (NTZ) by casein silver nanoparticles (CasAgNPs). CasAgNPs were synthesized by green chemical reduction approach with sodium borohydride serving as reducing agent, while casein functionalization provides excellent colloidal stability to nanoparticles (R_H = 66.3 nm; PDI = 5%; zeta potential = + 18 mV). CasAgNPs were extensively characterized by UV–visible, circular dichroism (CD), Fourier transform infrared (FTIR), fluorescence spectroscopy, dynamic light scattering (DLS), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) measurements. Synthesized CasAgNPs was established as highly sensitive and selective probe for the detection of NTZ with significant linearity (2.5–25 µM; R² = 0.998) and detection limits (LOD/LOQ = 1.1/3.3 µM, respectively). Likewise, Job’s plot revealed the presence of a 1:3 binding stoichiometric ratio, while the free energy of binding calculated (− 26.2 kJ/mol) suggests that the formed complex was energetically favorable. The proposed sensor worked effectively, and excellent recoveries (> 96%) were found in real samples. The sensing mechanism was established by FTIR and DLS measurements, suggesting that NTZ induces a time-dependent CasAgNPs aggregation. Synthesized CasAgNPs also demonstrated excellent antimicrobial and antibiofilm activities and were found absolutely nontoxic in hemolysis assay. Cumulatively, a facile, nontoxic, eco-friendly, and biocompatible nanosensor was established for NTZ sensing in biological and environmental samples.