Oblique-incidence Reflectivity Difference On Polymer Modified Surfaces And Its Application In Biochemical Analysis

Oblique-incidence reflectivity difference?OIRD?is an intriguing optical technique capable of in situ and nondestructive monitoring the surface changes and surface processes by detecting the reflectivity changes of s/p composition in elliptically polarized light.In the past decade OIRD technology has been shown great potential in biochemical analysis such as biochip detection and biomolecular interaction research due to the advantages of being label-free,real-time,high-throughput,and compatible with arbitrary substrates.However,limited sensitivity of OIRD on solid/liquid interfaces is a main concern for its application in biochemical analysis,although it has exhibited high sensitivity in studies of different solid/gas interfaces.In order to improve the sensitivity of OIRD technology for biochemical analysis detection,this paper dedicates to investigating the OIRD signal on various polymer modified solid surfaces,where the properties of polymer layer,particular thickness was well controlled.The results reveal that the OIRD detection signal and its sensitivity are significantly influenced by the polymer thickness on the surface.Based on these findings,a general strategy was proposed and established for surface modification to essentially improve the sensitivity of OIRD technology for biochemical analysis.The contents are as follows:?1?Protein microarray chip is an important plarform for OIRD application.In order to quantitatively study the influence of polymer thickness on OIRD sensitivity,a model microarray chip was firstly developed by using polydopamine?PDA?as a universal and thickness-tunable layer to immobilize protein probes on standard glass slides.In this model chip,the surface density of the immobilized probe was kept constant while the thickness of the PDA layer was adjustable in a large range after systematic optimization of microarray printing parameters.Fluorescent images suggested that this microarray chip possesses uniform probe attachment,low spot-to-spot and chip-to-chip variations and high reproducibility,allowing for quantitative study of the influence of polymer thickness on OIRD sensitivity.?2?OIRD technology was used to detect the above-established microarray and the influence of the PDA thickness on the OIRD detection signal was quantitatively studied.Detection of a target at the same concentration suggested that the thickness of the PDA layer had a huge impact on the OIRD detection signal towards the same concentration of target.The OIRD detection signal increased with the increase of the PDA thickness from 0 to 90.15 nm;further increasing from 90.15 to 112.34 nm,the OIRD detection signal decreased;the protein microarray reached maximal sensitivity at 90.15 nm PDA thickness,where the target of anti-ZEN monoclonal antibody was successfully detected in a concentration range of 5.0-1000 ng mL^-11 with a detection limit of 5.0 ng mL^-1.The sensitivity was much better than that achieved on 24.55 nm PDA based microarray chip(detection limit of 100 ng mL^-1)and traditional GPTS based microarray(detection limit of 500 ng mL^-1).?3?Theoretical calculation was carried out to rationalize the experimental results by using a four-layer optical model.Mathematical relationship between the OIRD sensitivity and the thickness of the polymer layer was calculated.It shows that the polymer film as an optical interference layer could enhance the light-matter interaction to improve the sensitivity of OIRD technology;OIRD sensitivity has a periodic relationship with the film thickness and the maximum sensitivity is around 95 nm,which is in line with the experimental results.?4?By controlling the thickness of conductive polymer polyaniline?PANI?film to maximize the OIRD sensitivity,the electrochemical tunability of PANI film was successfully studied by OIRD technology.The results further demonstrate the effect of polymer thickness on OIRD detection sensitivity.Studies show that OIRD technology was able to detect the electrochemical tunability of PANI thin film with high spatial resolution at a suitable PANI thickness.Further,a hydrogen peroxide sensing chip was constructed to image the distribution of hydrogen peroxide on the PANI surface as hydrogen peroxide is able to change the oxidation state of PANI film.Preliminary results indicate this OIRD chip exhibits sensitive response towards hydrogen peroxide.This thesis systematically studies the OIRD detection signal on polymer modified surfaces.Based on these findings,a sensitive OIRD microarray chip was developed and its application in solid/liquid interface process detection was demonstrated.It may provide a new insight into the OIRD mechanismn on the solid/liquid interface,and promote the practical applications of OIRD technology in different fields.