Rapid and sensitive detection of biomolecules is crucial for supporting early disease diagnosis. This study developed a giant magnetoresistance (GMR)-based biosensor using a commercial chip. This sensor detection was integrated with machine learning (ML) analysis to detect bovine serum albumin (BSA) and creatinine. The magnetite/reduced graphene oxide (Fe3O4/rGO) nanocomposite as nanotag labels was synthesized via a green approach. The Fe3O4/rGO nanocomposite was functionalized with glutaraldehyde (GA) as a linker for biomolecule immobilization. Characterization results show that the magnetic labels exhibit superparamagnetic properties and generate a stray field sufficient for detection at an optimal bias field of 3.6 Oe. The biosensor demonstrates good linearity with an R2 value of 0.98 for BSA and 0.95 for creatinine. The highest sensitivity was obtained for BSA detection at 23.02 mV/(mg/mL) with a limit of detection (LoD) of 0.8 mg/mL, while creatinine yielded a sensitivity of 10.84 mV/(mg/mL) and an LoD of 1.5 mg/mL. Repeated measurements show good repeatability, with relative standard deviation ranges of 0.4–3.4% for BSA and 0.5–9.2% for creatinine. Furthermore, the ML approach using principal component analysis and linear discriminant analysis at a biomolecule concentration of 1 mg/mL shows that feature extraction improved discrimination between BSA and creatinine. These findings highlight the potential of the Fe3O4/rGO-GA-based GMR biosensor as a simple and sensitive platform for biomolecule detection and differential recognition.
The neutralization of organophosphates and the reduction of nitrophenols remain significant challenges for chemical safety and wastewater treatment, requiring efficient and selective catalysts. Herein, a multifunctional catalyst based on highly oxidized graphene oxide (GO10d), functionalized with cysteamine via epoxide ring opening (GOSH10) and decorated with silver nanoparticles (Ag-rGOSH10), was developed to promote the sequential degradation of a paraoxon simulant (DEDNPP) through two consecutive steps: (i) nucleophilic cleavage of the organophosphate PO bond and (ii) reduction of the nitrophenol generated as a byproduct. Prolonged oxidation increased the structural disorder and interlayer spacing of graphene oxide, indicating a higher degree of oxidation and a greater abundance of oxygen-containing functional groups. After functionalization, the incorporation of nitrogen and sulfur confirmed the successful anchoring of cysteamine. GOSH10 exhibited enhanced catalytic performance towards the nucleophilic degradation of DEDNPP compared with analogous materials based on conventionally oxidized graphene oxide. Decoration with silver nanoparticles preserved the nucleophilic activity while enabling efficient catalytic reduction of 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP). In a one-pot system, Ag-rGOSH10 enabled the sequential conversion of DEDNPP into 2,4-diaminophenol, demonstrating the complete detoxification of the paraoxon simulant. These findings show that increasing the oxidation degree of graphene oxide enhances cooperative effects in nucleophilic catalysis, while silver nanoparticle incorporation provides bifunctional catalytic activity, offering a promising strategy for the detoxification of hazardous organophosphates and nitrophenols.
