Immunosensors label-free approaches

Tab e 9.2 Examples of electrochemical immunosensors related to food analysis with label-free approaches... 

Label-free impedance immunosensors have been developed, but in general these methods may require additional amplification to improve sensitivity [57,58]. Nevertheless, a capacitance method using a ferri/ferrocyanide probe and a potentiostatic step approach gave DL 10 pg mL (500 fM) for lL-6 in buffer [59]. Optimization of experimental protocols in flow injection impedance spectroscopy led to sensitivity in the low aM range for interferon-y in buffer [60]. Sensitivities have been enhanced using metal nanoparticle labels or AuNP labels that catalyze subsequent Ag deposition [57]. These methods may be promising for future point-of-care applications if NSB from non-analyte proteins in the patient samples can be minimized. 

A particularly useful ECL pathway for detecting low concentrations of proteins by immunosensors is initiated by oxidation at 0.9 V vs SCE of the sacrificial reductant TprA, whose products react in a complex pathway with RuCbpy) " to yield RuCbpy) ". We developed an immunosensor on a SWCNT forest platform for PSA in serum utilizing this approach with Ru(bpy)3Lsilica nanoparticles attached to secondary antibodies (RuBPY-silica-Ab2) as labels [99]. Addition of surfactants increases the hydrophobicity of the sensor surface via an adsorbed surfactant layer, which facilitates oxidation of TprA [1(X)]. Including Triton X-100 and Tween 20 in the electrolyte solution containing TPrA improved PSA sensitivity tenfold compared to TprA in surfactant-free solutions [99]. Surface... 

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