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In this work, a mussel-inspired polydopamine (PDA) nanoparticle with biocompatible and reactive surface characteristics was desirably incorporated with high loading capacity and pH-induced disassembly-releasing behavior toward Fe(III) ions to develop an enzyme-free colorimetric immunoassay. The catechol functional network of PDA can act as a scaffold to coordinate with large amounts of Fe(III) ions to form the PDA-Fe(III) NPs whose coordination state can be tailored by changing the pH values. In detail, PDA-Fe(III) NPs can be maintained in a disassembled tri-coordinate state under alkaline conditions while the highly loaded Fe(III) ions can be easily released under acid conditions to react with ferrocyanide for the in situ generation of Prussian blue (PB) NPs. The detection sensitivity of prostate-specific antigen (PSA) was significantly improved, owing to the high peroxidase-like activity of PB NPs that triggered excellent catalytic effect by the colorimetric reaction. In addition, favorable linearity was found in the range of 0.0005-20 ng mL

In this paper, GaON with excellent photoelectrochemical (PEC) performance was adopted in PEC immunosensor for the first time. Based on CdS sensitized BiVO4/GaON composite material, a label-free PEC immunosensor was successfully developed for determination of procalcitonin (PCT). Firstly, BiVO4 nanoarray was prepared by electrodeposition. Then GaON was added to form the BiVO4/GaON composite material, due to the greatly increasing charge transfer efficiency, the PEC signal increased by about 3 times. At last, CdS grew in situ on BiVO4/GaON composite that further expanded the light absorption range and improved the light utilization, and the PEC signal further increased again. This PEC immunosensor has a good linear relationship of 0.1 pg mL−1 - 50 ng mL−1 and the detection limitation of 0.03 pg mL−1 is calculated. Importantly, the BiVO4/GaON/CdS immunosensor platform showed good specificity and stability, and serum sample analysis have been performed with satisfactory results.

In this work, biomimetic polydopamine nanospheres (PDANSs) were easily prepared and were firstly exploited as an electrochemiluminescence (ECL) nanoquencher for the development of a sandwich type immunosensor. The PDANSs with abundant active functional groups can facilely label the detection antibody and show remarkable quenching effect towards the ECL of the tris-(2,2'-bipyridine)ruthenium (Ru(bpy)32+). The amino-modified multiwall carbon nanotubes/Nafion (MWCNTs-NH2@N) composite-film was adopted as a matrix to incorporate the luminophor Ru(bpy)32+ and immobilize the capture antibody. The prominent decrease of ECL signal intensity was obtained on account of the unique quenching ability of the labeled PDANSs. The quenching mechanism is believed that the excited states of Ru(bpy)32+ can be annihilated by quinone units in PDANSs via energy transfer. The ECL quenching efficiency was logarithmically related to the concentration of the prostate specific antigen (PSA) in the range from 0.1 pg mL-1 to 20 ng mL-1 with a detection limit of 35 fg mL-1. Furthermore, the proposed ECL immunosensor presented good stability, repeatability and selectivity.