title: Observation of molecular diffusion in polyelectrolyte-wrapped SERS nanoprobes.
abstract: The popularity of nanotechnology-based sensing technologies has rapidly expanded within the past decade. Surface-enhanced Raman spectroscopy (SERS) is one such technique capable of chemically specific and highly sensitive measurements. The careful preparation of SERS-active nanoprobes is immensely vital for biological applications where nanoprobes are exposed to harsh ionic and protein rich microenvironments. Encapsulation of optical reporter molecules via layer-by-layer (LbL) polyelectrolyte wrapping is an emerging technique that also permits facile modification of surface chemistry and charge. LbL wrapping can be performed within a few hours and does not require the use of organic solvents or hazardous silanes. Nonetheless, the stability of its products requires further characterization and analysis. In this study, Raman-active methylene blue molecules were electrostatically encapsulated within alternating layers of cationic and anionic polyelectrolytes surrounding gold nanospheres. We observed molecular diffusion of methylene blue through polyelectrolyte layers by monitoring the change in SERS intensity over a period of more than 5 weeks. To minimize diffusion and improve the long-term storage stability of our nanoprobes, two additional nanoprobe preparation techniques were performed: thiol coating and cross-linking of the outer polyelectrolyte layer. In both cases, molecular diffusion is significantly diminished.
authors.affiliation: Department of Electrical and Computer Engineering, ‡Department of Materials Science and Engineering, §Department of Bioengineering, ∥Beckman Institute for Advanced Science and Technology, ⊥Department of Chemistry, and #Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Brent M
authors.initials: BM
authors.lastname: DeVetter
authors.forename: Sean T
authors.initials: ST
authors.lastname: Sivapalan
authors.forename: Dwani D
authors.initials: DD
authors.lastname: Patel
authors.forename: Matthew V
authors.initials: MV
authors.lastname: Schulmerich
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Murphy
authors.forename: Rohit
authors.initials: R
authors.lastname: Bhargava
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D015374:Biosensing Techniques / Q000379:methods; D003432:Cross-Linking Reagents / Q000737:chemistry; D004058:Diffusion; D004339:Drug Compounding; D005976:Glutaral / Q000737:chemistry; D006046:Gold / Q000737:chemistry; D053768:Metal Nanoparticles / Q000737:chemistry*; D008751:Methylene Blue / Q000737:chemistry*; D054118:Nanospheres / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods; D011073:Polyamines / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods*; D055672:Static Electricity; D013439:Sulfhydryl Reagents / Q000737:chemistry; D013499:Surface Properties
chemical_list: D000180:Acrylic Resins; D003432:Cross-Linking Reagents; D011073:Polyamines; D013439:Sulfhydryl Reagents; C063994:polyallylamine; C006903:carbopol 940; D006046:Gold; D005976:Glutaral; D008751:Methylene Blue