Preparation And Research Of Silk Fibroin-Based SERS Materials

Surface-enhanced Raman scattering(SERS)spectroscopy has the advantages of high detection sensitivity,no moisture interference,and in-situ nondestructive detection,and has been widely used in the analysis of the chemical composition and structural characteristics of target molecules as well as identification of molecular adsorption behavior and surrounding environment properties.Electromagnetic field "hot spots" with unique nanostructures are the key factor for the enhanced performance of SERS substrates.The special nanostructure of silk fibroin aggregates has the natural advantage of forming "hot spots",which can combine silk fibroin nanofiber ribbons(SNR)and Au nanoparticles(AuNPs)to form a sandwich "hot spot" structure for sensitive SERS detection.However,the nano-aggregates have the disadvantage that the number of sandwich "hot spots" is small and the distribution is not uniform.Therefore,through the optimized design of the structure,the sensitivity,uniformity and reproducibility of Raman signals can be continuously improved,which is beneficial to the understanding of the SERS performance of aggregates nanostructures and can be used to develop new SERS materials for biological detection,and is of great value in both basic research and application fields.Based on this,this work achieved the improvement of SERS performance by optimizing the spatial combination of silk fibroin aggregate nanostructures and silk fibroin-nanoparticle complexes in the system,studying the relationship between structure and performance,and exploring applications in the field of biomedicine and SERS detection.First,the size of silk fibroin aggregates was regulated by ultrasonic treatment,which reduced the adsorption steric hindrance of AuNPs,thereby increasing the density of "hot spot" structures,and then evaluated the SERS performance of nano-aggregates.The research results showed that with the reduction of the size of silk fibroin aggregates,the adsorption of AuNPs in the nano-aggregates increases and the density of "hot spots" increases,the sensitivity and uniformity of SERS detection are significantly improved(The detection sensitivity was improved from 10-13 mol/L to 10-15 mol/L,and the RSD value was improved from 11.2%to 9.5%),and the trace concentration SERS detection of probe molecules is successfully achieved.At the same time,fast SERS imaging of tumor cells could also be achieved with the SERS material.Subsequently,considering the difference in charge density of silk fibroin-Au aggregates with different structures,the separation of silk fibroin-Au aggregates was achieved by an electric field-induced method to obtain silk fibroin-Au nanocomposites with better performance.The optimized nano-aggregates were modified with pH-sensitive molecules to obtain high-sensitivity pH nanosensors with good biocompatibility and stable performance(The pH detection sensitivity is 0.089 pH units),which could realize pH distribution imaging in different types of cells.Finally,the SERSactive metal nanoparticles were reduced in situ by the tyrosine residues on the surface of silk fibroin.The in situ formed silk-metal nanoparticle composites exhibited enhanced SERS signs of silk fibroin and could be used to detect Hg2+ density quantitatively with silk fibroin as Raman probe(10 ng/mL).In summary,silk fibroin nano-aggregates were used to prepare silk fibroin-metal SERS materials in this study.The continuous improvement of SERS performance was achieved by optimizing the sandwich "hot spot" structure.While studying the relationship between the structure of silk fibroin aggregates and SERS performance,the above-mentioned SERS materials were used to realize the detection of biological signals and Hg2+ concentration,broadening the application of silk fibroin in the field of biomedicine and SERS detection.