title: Reporter-Embedded SERS Tags from Gold Nanorod Seeds: Selective Immobilization of Reporter Molecules at the Tip of Nanorods.
abstract: Reporter-embedded (RE) tags are a new generation of sensitive, stable surface enhanced Raman scattering (SERS) tags with Raman reporters embedded between gold nanoparticle (NP) cores and gold (or silver) shells. Most of the reported RE tags have been designed using Au nanospheres as a seed material. Herein, we investigated the synthesis and SERS properties of AuNR/reporter/Ag tags by using gold nanorod (AuNR) seeds with anisotropic physical and optical features. Several highlighted points were discovered, including the following: (1) The cetyltrimethylammonium bromide (CTAB) layer induced the coexistence of chemically and physically adsorbed Raman reporters on AuNR. Conventional washing of the AuNR-reporter complex with water results in the formation of an "internal-external" mixed tag. To obtain a "pure" RE structure, an additional extraction step involving a CTAB solution was essential. (2) The anisotropic distribution of CTAB on AuNR resulted in the preference of the Raman reporters to adsorb to the hotspot at the AuNR tip, which made it a perfect match for improving the SERS signal of the tag. (3) An anisotropic silver coating occurred with the shell thickness on the AuNR side growing much faster than the shell thickness at the tip. This feature ensured that the tag grew to a suitable size with enough silver for SERS enhancement without shadowing the effective Raman reporters at the tip too much. (4) RE tags showed better in vitro and in vivo signal stabilities compared with their external labeling counterparts. Moreover, a novel pH-sensitive SERS peak test was proposed by using 4-mercaptobenzoic acid as the Raman reporter to verify thin coverage by a silver layer. We believe this tag can be broadly applied for molecular detection and bioimaging, and the proposed preparation and structure verification methods can provide universal guidance in the design of novel RE tags.
authors.affiliation: School of Pharmacy, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Yantai University , Yantai 264005, China.|Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences , Yantai 264003, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences , Yantai 264003, China.
authors.forename: Yunqing
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences , Yantai 264003, China.
authors.forename: Wenhai
authors.initials: W
authors.lastname: Wang
authors.affiliation: School of Pharmacy, Collaborative Innovation Center of Advanced Drug Delivery System and Biotech Drugs in Universities of Shandong, Key Laboratory of Molecular Pharmacology and Drug Evaluation (Yantai University), Ministry of Education, Yantai University , Yantai 264005, China.
authors.forename: Kaoxiang
authors.initials: K
authors.lastname: Sun
authors.affiliation: Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences , Yantai 264003, China.
authors.forename: Lingxin
authors.initials: L
authors.lastname: Chen
keywords: SERS tags; anisotropic property; core−shell nanoparticle; gold nanorod; internal standard