Gold Nanorods-Based Novel Photoacoustic Probes For In Vitro Detection

Photoacoustic detection as an emerging detection method has attracted increasing attention,recently.In this method,the target analyte was detected by capturing and analyzing the intensity changes of the ultrasound signal,which was produced by thermal expansion of the laser energy absorbed by the endogenous or exogenous probes.Compared with traditional optical-related detection methods,photoacoustic detection mainly reveals information of light absorption and is insensitive to light-scattering signals.Furthermore,its analytical samples do not require pre-processing.The probes currently used for photoacoustic detection are usually organic dye molecules,while these small molecules are poor in light stability,easy to photobleach and photodegrade,and the synthesis steps are relatively complicated.In contrast,inorganic nanomaterials-gold nanorods?GNRs?as a good photoacoustic contrast agents,have the advantages of good light stability and simple and controllable synthesis.Therefore,the new photoacoustic probes based on GNRs have potential application prospect in the field of in vitro detection.The aggregation or etching of GNRs can change their surface plasmon resonance,resulting in the change of their optical absorption,and ultimately leading to changes of their photoacoustic signal.Therefore,in this thesis,two novel photoacoustic probes based on GNRs were synthesized for the detection of different targets.The main contents are as follows:?1?A novel photoacoustic probe based on?11-decyl undecyl?-trimethylammonium?MTA?molecules modified GNRs?MTA-GNRs?was developed for photoacoustic detection of mercury ion(Hg²⁺).The MTA molecules were attached to the surface of the GNRs via ligand exchange and acted as a ligand protector to make GNRs disperse evenly.The affinity of Hg²⁺to the sulfhydryl group in the MTA molecule is greater than the interaction between the sulfhydryl group and the GNRs.When Hg²⁺is present in the solution,the MTA molecules rapidly fell off from the surface of the GNRs,causing the aggregation of uniformly dispersed GNRs,followed by the enhanced photoacoustic signal for the detection of Hg²⁺.It is worth to mention that the detection system not only shows good stability in the complex water samples?such as high salt environment?,but also has strong anti-interference performance for some complex or actual test samples.Therefore,MTA-GNRs have great potential for the detection of actual Hg²⁺-contaminated water samples.?2?The GNR@Ag@SiO₂ nanoparticles were prepared and combined with a glucose oxidase?GOx?-labeled enzyme-linked immunosorbent assay?ELISA?system for colorimetric/fluorescent/photoacoustic thri-output detection of cancer biomarker.The detection principle is as follows:?a?The prepared GNR@Ag@SiO₂ nanoparticles as good photoacoustic probe,have almost no absorption at 680-970 nm.When the target exists in the system,the adsorbed GOx on magnetic beads?MBs?can catalyze the production of hydrogen peroxide?H₂O₂?by glucose,and the silver layer of the nanoparticles is etched by H₂O₂produced by the enzymatic process.The remaining GNR@SiO₂ nanoparticles have strong absorption at 680-970 nm,thus realizing the"OFF"-"ON"of photoacoustic signals.?b?At the same time,because of the silver etching,the color of GNR@Ag@SiO₂ changes from green to red,which can realize colorimetric detection of cancer biomarkers.?c?In addition,the Ag⁺produced by the etched silver layer can be detected by the synthesized fluorescent probe of Ag⁺to realize the fluorescence detection of cancer biomarkers.This detection system has a two-step signal amplification design:one is to load a large amount of GOx molecules on the surface of the MBs,and the other is to etch a silver layer to form a large amount of Ag⁺by H₂O₂ generated by enzyme catalysis.Therefore,the detection system has high sensitivity to the target analyte and is expected to be used for early detection of prostate cancer.In summary,two novel photoacoustic probes based on GNRs were designed and synthesized for the detection of Hg²⁺and cancer biomarker.This study provides some results for the development of photoacoustic probes with potential application prospects.