Immunosensors are used to provide simple, quick and effective ways to detect analytes for the diagnosis of a number of diseases. This work reports on a novel optical immunosensor based on thyroxine antibody labeled gold nanoparticles (anti-T4/C-AuNPs) for the sensitive detection of the thyroxine (T4) hormone. T4 hormone is a reliable diagnostic biomarker present in the human blood serum that is necessary for normal neural development and cellular metabolism. The free T4 hormone, a major key player of the total biologically active T4 hormone, in serum regulates the patient's thyroid function. The immunosensor was synthesized by using amine functionalized cysteamine capped gold nanoparticles (C-AuNPs) of size 36 nm approximately. The T4 specific antibody (anti-T4) was covalently attached to C-AuNP by EDC-NHS (1-ethyl-3-(-3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide) cross-linking chemistry. This anti-T4/C-AuNP bioconjugate was used for the analysis of the free thyroxine hormone in samples. The proposed method exhibited high performance immunosensors having a linear range of 0.52 to 65.1 pg/mL and the detection limit of 9.11 pg/mL.

A label‐free electrochemical immunosensor was fabricated for the detection of thyroxine hormone by immobilizing thyroxine‐specific monoclonal antibody (Ab) onto copper metal‐oxide framework (Cu‐MOF) and polyaniline (PANI) composite modified screen‐printed carbon electrode (SPCE). The Cu‐MOF@PANI@Ab‐modified SPCE was used as a sensing platform. Cu‐MOF and its composite were characterized by field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy, RAMAN spectroscopy, X‐ray diffraction, cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The immunosensor possessed a dynamic linear range (10–105 pM) with a low limit of detection (LOD) of 0.33 pM (0.25 pg/mL) for CV and 0.17 pM (0.13 pg/mL) for DPV. The evaluation study of immunosensor displayed a good analytical recovery of ≥90%, when different concentrations of thyroxine were added in the serum sample. In addition, to determine the reproducibility for working electrode between and within batch, the relative standard deviation calculated were 3.87% and 6.04%, respectively, and represent its good reproducibility. The immunosensor retained 90% of its initial activity after its regular use for 40 days, while being stored at 4 °C.

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