Probeless and label-free impedimetric biosensing of D-dimer using gold nanoparticles conjugated with dihexadecylphosphate on screen-printed carbon electrodes

D-dimer (DD) is a clinical biomarker of emerging significance. Its fast analysis and quantification, preferably by the bedside, helps a medical doctor make crucial decisions. Electrochemical biosensors are point-of-care technologies that can address such issues. Herein, it is developed a probeless and label-free impedimetric DD biosensor. Gold nanoparticles (AuNPs) are dispersed along with dihexadecylphosphate (DHP) on the surface of screen-printed carbon electrodes (SPCEs) to attach anti-DD monoclonal antibody as sensing recognition element, and the measurements are performed using electrochemical impedance spectroscopy (EIS). Two different analytical models are used to interpret raw impedance spectra. The first model is based on the capacitive response within the DHP monolayer and its electrochemical occupancy described by the complex capacitance value at the frequency of 200 mHz, noted as M1. The second model is based on the charge transfer resistance changes (Rct) occurring upon the mAb-DD binding event, fitted by two different Randles types of the equivalent circuits (noted as M2a and M2b). The models are compared, and with the obtained high linearity in the clinically relevant range (up to 500 ng mL−1) and low levels of detection (as low as 8.92 ng mL−1), a potential POC sensor is demonstrated. Additionally, the proposed sensor is applied in real whole blood samples showing good recovery values with certain discrepancies from the standard laboratory assay result, making a cheap and straightforward way for semi-quantitative bedside clinical evaluation.