Novelly SERS Analytical Methods Based On Gold Nanostars

Due to its high sensitivity,high throughput and molecular specificity,surfaceenhanced Raman scattering(SERS)technology has been developed rapidly in analytical chemistry.The detection and structural analysis of biomacromolecules,and design of high-quality SERS substrates for utilizing in various practical detection environments are still popular in the study of SERS analytical methodology.Using gold nanostars(AuNSs)as the main SERS substrate,this work firstly developed the highefficiency methods for DNA conformation regulation and DNA subtle structure detection based on the AuNS dispersed system.Then,a series of easy-to-handle SERS sensors were designed for the analysis of various practical samples based on AuNS selfassembly system.These new SERS detection methods provide powerful tools for disease diagnosis,food safety and environmental monitoring.This work includes the following six parts:1.Polyadenine-Modulated DNA Conformation Monitored by SERS on Multibranched Gold Nanoparticles and Its Sensing ApplicationWe proposed a new method for modulating the DNA conformation on the surface of AuNSs.In this strategy,a length-adjustable polyadenine(polyA)sequence was designed at the end of the DNA sequence.PolyA could not only attach DNA sequences to AuNSs,but also electrostatically and spatially repel to the DNA sequence,which made the sequence bias to "stand up" on the surface.A SERS reporter molecule was combined to the other end of the DNA.When the DNA sequence changed the distance between the reporter and the AuNSs during the process from "lie down" to "stand up",in situ monitoring of this conformational regulation process could be achieved by detecting the SERS signal change of the reporter.In addition,if the DNA sequence was designed as a probe to specifically recognize the target DNA,this method could be used to improve the recognition efficiency,therefore achieving efficiently specific nucleic acid detection.This method not only realized the conformational regulation of single/double-stranded DNA sequences from "lie down" to "stand up" on the AuNS surface,but also quantitatively detected target DNA ranging from 0.1 nM to 500 nM with limit of detection as low as 45.7 pM,which could also identify target DNA from mismatched sequences.This work provides a new way for SERS-based nucleic acid detection.2.Probing the Subtle Structural Distinction of the Same Topological Gquadruplexes Coordinated with Different Cations by SERSWe proposed a new method for in situ detecting structure differences of Gquadruplexs coordinated with different cations.In this strategy,AuNSs were used as SERS substrate,which were added into the cationic environment containing Gquadruplexs.The metal cations will reduce the negative charge on AuNS surface and promote nanoparticles aggregation.The G-quadruplexs will be located in "hot spots" of the aggregation to produce in situ SERS signals.The difference in SERS signals of G-quadruplexes coordinated with different cations could be used to identify their subtle structure difference.The structural difference between the known sequence Oxy-1.5 coordinated with Na+ or K+was firstly obtained by this SERS method,and the result was consistent with the existing consequence from nuclear magnetic resonance and X-ray crystallography.Then,the structural difference between the unknown sequence T30695-D coordinated with Na+or K+was also detected,and the result are supported by molecular dynamics simulation.This study not only makes people deeply understand the cation-dependent effect of G-quadruplex structure,but also opens a new avenue to distinguish the subtle structure of nucleic acid.3.A Self-calibrated 2D Nanoarchitecture for Label-free SERS Quantitation and Distribution Imaging of TargetWe designed a 2D ultra-thin and soft SERS device containing internal standard(IS).The device consisted of a self-assembled AuNS layer sandwiched by two pieces of single-layer graphene(1LG).The presence of 1LG could not only separate the AuNSs from the external environment to prevent interference,but also allow the analyte to be uniformly interacted with the device,which could improve the uniformity and stability of produced SERS signals.The IS was implanted on the surface of the upper 1LG,and the nether 1LG was used to contact with targets,therefore the SERS signals of the IS and targets could be simultaneously obtained and the reliable SERS quantitative detection was realized by the internal standard method.After immobilizing the entire structure by polymethyl methacrylate(PMMA),its soft and freestanding properties made it applicable to arbitrary target detection by conveniently floating on solution or covering on solid surface.Therefore,the device realized detection of carcinogenic dye in aqueous solution from 0 to 5 ?M and image of the thiabendazole distribution on apple surface,indicating the great potential in point-of-care testing(POCT).4.A Multifunctional SERS Sticky Note for Real-time Quorum Sensing Tracing and Inactivation of Bacterial BiofilmsWe designed a versatile SERS "sticky note" for in situ monitoring quorum sensing and inactivating bacteria.The sticky note consisted of a self-assembled multi-sized AuNS layer sandwiched by two pieces of single-layered hexagonal boron nitride(hBN),which the AuNS layer offered high SERS sensitivity and the hBN could further enhance the SERS signals.The IS was implanted on the surface of the upper hBN,and the nether hBN was used to contact with targets.After immobilizing the whole structure by PMMA,the accurate SERS quantitative detection could be realized by the internal standard method.When the sticky note was pasted on the living biofilm of Pseudomonas aeruginosa,the signal molecule of quorum sensing secreted by the bacteria could be detected within 1 hour,and real-time monitoring was also achieved within 0-24 hours.When antibiotics were loaded on the sticky note,the in-situ sterilization and monitoring of bactericidal effect were realized,and the sterilization rate could reach 85.6%.The reusability and ease of operation made the sticky note become a promising platform in bacterial physiology monitoring and the development of antibacterial agents.5.A "Three-in-One" SERS adensive tape for Rapid Sampling,Release and Detection of Wound Infectious PathogensWe designed a photo-controlled adhesive tape as a " three-in-one" platform for rapid sampling,photo-controlled release and SERS detection of wound infectious pathogens.This IS-implanted tape was constructed by encapsulating densely packed multi-sized AuNS layer between two pieces of 1LG and modifying with the synthetic photoresponsive molecule.The molecule made the tape able to capture pathogens through electrostatic interaction and release the pathogens under UV light irradiation.In this way,the tape could be directly attached to wound surface to quickly sample the pathogens,and then peeled off to past on culture medium.After irradiating by the UV light,the pathogens were released for growth followed by detection via their characteristic SERS signals.The SERS adhesive tape could capture up to 1.2 × 107 cm-2 of pathogens on its surface within 5 minutes,and release up to 83.9%of them after 2 minutes irradiation by a mini-UV flashlight.When it was pasted on the surface of mouse burn wound infected with Pseudomonas aeruginosa and Staphylococcus aureus,the ahesive tape realized sampling,release for culturing and SERS detection of these two kinds of pathogens with 8 h.Considering the easy operations and short analysis time,such tape showed great potential for POCT of pathogens.6.A Facile SERS Paper Nose for Point-of-Care Monitoring of Bacterial Airborne Metabolites in Food SpoilageWe designed a handy SERS system for real-time monitoring of bacterial airborne metabolites.A facile SERS "paper nose" is used as SERS substrate constructed by simple suction filtration of AuNSs on an anodic aluminum oxide filter membrane,which represented high SERS sensitivity,reproducibility and quantitative ability.Taking the Escherichia coli,Staphylococcus aureus or Pseudomonas aeruginosa contaminated pork as model analyte,this robust paper nose can collect their respective SERS signals from the sample headspace using a handheld Raman spectrometer,which only costed few seconds in signal collection.Furthermore,the real-time monitoring of pork spoilage degree via detecting airborne metabolites is also realized and the bacterial presence can be detected in the first day of culture,which is much more sensitive than human senses.The use of miniaturized equipment with rapid and easy operations make this POCT method suitable for using in daily scenes,indicating great potential in food safety and healthcare applications.