Polydopamine Thin Film-based Label-free Photoelectrochemical Immunoassay

Photoelectrochemical(PEC)immunoassay is a newly established biosensor technique by rationally combining PEC process and specific antibody-antigen bio-recognition and has demonstrated compelling applications in different fields.A PEC immunoassay device typically consists of a photo-electricity conversion interface and a bio-recognition layer.For successful PEC immunoassay,the PEC interface incorporating immunosensing surface and light-electricity conversion interface is supposed to achieve photo-electricity conversion with high stability and reproducibility and capture of targets with high sensitivity and selectivity.To date,the architecture of most PEC immunosensors is complicated and involved multistep modification and possible signal amplification for high photocurrent.However,the reproducibility and reliability of sensors may be questionable and the label-free advantage of PEC immunoassay may be completely ruined.In this regard,it is worth clarifying that the high photoelectric conversion efficiency does not warrant high performance of PEC immunosensor because PEC immunosensor uses the change of photocurrent but not photocurrent itself as the detection signal.Therefore,rational construction of a simple and efficient light-electricity conversion interface/immunosensing surface with architecture as simple as possible is highly desirable for high reliability and stability immunoassay.In this thesis,polydopamine(PDA)thin film was used to construct PEC immunosensor owing to its electric-optical property and bio-conjugation activity.The details as follows:(1)Bifunctional polydopamine thin film coated zinc oxide nanorods for label-free(1)Bifunctional polydopamine thin film coated zinc oxide nanorods for label-free photoelectrochemical immunoassayA novel yet simple PEC immunosensor based on bio-inspired PDA thin film-coated zinc oxide(Zn O)nanorods was developed.Zn O nanorods were firstly grown by low-temperature chemical bath deposition method.Then the PDA thin film was introduced to coat the Zn O nanorods via spontaneous oxidative polymerization of dopamine under alkaline condition.In this architecture,PDA thin film serves simultaneously as a unique sensitizer for stable light-electricity conversion interface as well as a functional layer for probe antibody attachment via covalent bonding.Thus PDA-Zn O photoelectrode offers a simple and reliable platform for PEC label-free immunoassay.By using an antibody-antigen pair as a model,successful label-free immunoassay was achieved with a detection limit of 10 pg m L-1.This work demonstrates intriguing electric-optical property and bio-conjugation activity of PDA film and may pave the way toward advanced PEC immunoassay.(2)Polydopamine-assisted Cd S modified Zn O nanorods for photoelectrochemical immunoassayIn this part,a novel label-free photoelectrochemical immunosensor was developed,in which Cd S nanoparticles were uniformly deposited on the surface of Zn O nanorods with the assist of PDA thin film.Zn O nanorods were firstly prepared by low-temperature chemical bath deposition method,followed by deposition of Cd S nanoparticles via successive ionic layer adsorption and reaction with the assistance of PDA thin film to construct Zn O-(Cd S/PDA)n photoelectrodes.It was found that with the present of PDA,Cd S nanoparticles distribute evenly on the surface of Zn O-(Cd S/PDA)n photoelectrode,which possesses improved stability of photon-to-electron conversion interface.By using anti-Mouse Ig G as a target protein,successful label-free immunoassay was achieved with a detection limit of 100 pg m L-1.In this thesis,PDA thin film is a multifunctional layer to serve as a sensitizer for light absorption,assisting evenly distribution of Cd S nanoparticles and as a functional matrix for probe immobilization.Due to the simple architecture and reliable stable light-electricity conversion interface/immunosensing surface,these immunosensors might show promising applications in various fields.