Aliyyul Wafa, Rizqi A'mal Hibatullah Tabrani, Pinaka Elda Swastika, Larrisa Jestha Mahardhika, Nurul Imani Istiqomah, Harlina Ardiyanti, Husna Ajrina, Rafiqa Wulandani, Adhistinka Jiananda, Citra Dwi Lestari, Zurnansyah, Edi Suharyadi
The detection of protein, including bovine serum albumin (BSA), is crucial in the initial diagnosis of diseases due to the common use of BSA as a model for human serum albumin. Therefore, this study aimed to develop a giant magnetoresistance (GMR) biosensor integrated with green-synthesized Fe3O4/Ag ferrofluid for protein detection. The ferrofluid was selected because of the superior dispersibility compared to powder-based labels, producing a more homogeneous stray magnetic field across the sensor surface. The analysis of structural, optical, and magnetic characterizations confirmed the successful preparation of Fe3O4/Ag ferrofluid through a green synthesis method using oleic acid as a surfactant and castor oil as a dispersion medium, which showed stable superparamagnetic behavior. Meanwhile, the sensor performance was evaluated at protein concentrations of 1–5 mg/mL, corresponding to normal human blood albumin levels, with gelatin used as a non-target molecule to assess the sensor's discrimination capability. The sensor showed high accuracy for both analytes (R2 = 0.99), with gelatin presenting higher sensitivity (13.8 mV/(mg/mL)) and a lower limit of detection (0.11 mg/mL) than BSA (6.57 mV/(mg/mL) and 0.48 mg/mL). Meanwhile, the limit of quantification for BSA was 1.45 mg/mL, suggesting that reliable quantitative measurements could be achieved in the investigated concentration range. This difference is attributed to molecular architecture, where the random-coil fibrous structure of gelatin enables multipoint interactions with Ag nanoparticles and the castor oil medium, leading to more effective magnetic field modulation than the predominantly single-point Ag-BSA interaction. This selectivity study represents an initial step toward the development of selective albumin detection strategies, indicating the promising applicability of green-synthesized Fe3O4/Ag ferrofluid-enhanced GMR sensor as a selective platform for BSA detection and separation from non-specific protein including gelatin. © 2026 Elsevier B.V.
Department of Physics, Universitas Gadjah Mada, Yogyakarta, Indonesia; Department of Physics Education, Universitas Negeri Yogyakarta, Yogyakarta, Indonesia; Department of Physics, Institut Teknologi Sumatera, Lampung, Indonesia
