Core–Shell Gold Nanorod@Zirconium-Based Metal–Organic Framework Composites as in Situ Size-Selective Raman Probes

Abstract

Nanoparticle encapsulation inside zirconium-based metal-organic frameworks (NP@MOF) is hard to control and the resulting materials often have non-uniform morphologies with NPs on the external surface of MOFs and NP aggregates inside the MOFs. In this work, we report the controlled encapsulation of gold nanorods (AuNRs) by a scu-topology Zr-MOF, via a room-temperature MOF assembly. This is achieved by functionalizing the AuNRs with polyethylene glycol (PEG) surface ligands, allowing them to retain colloidal stability in the precursor solution and to seed the MOF growth. Using this approach, we achieve core-shell yields exceeding 99%, tuning the MOF particle size via the solution concentration of AuNRs. The functionality of AuNR@MOFs is demonstrated by using the AuNRs as embedded probes for selective surface-enhanced Raman spectroscopy (SERS). The AuNR@MOFs are able to both take-up or block molecules from the pores, thereby facilitating highly-selective sensing at the AuNR ends. This proofof-principle study serves both to present the outstanding level of control in the synthesis as well as the high potential for AuNR@Zr-MOF composites for SERS.

Surface-enhanced Raman spectroscopy: benefits, trade-offs and future developments

“…Their sizes fall within the range of that of the analyte molecules and allow the selective permeation of small molecules via the molecular sieving effect. [84][85][86][87][88] These materials can be used as a coating layer over the SERS substrates for trapping the analytes within their pores or channels and driving them to the hot spots. This strategy is suitable for the analysis of samples, like small molecules and gas samples (i.e., aldehydes), that can easily diffuse away from the metal surface.…”

Metal‐Organic Frameworks and Metal‐Organic Cages – A Perspective

“…[114] As MOFs are solid-state materials it is also possible to grow MOFs around large guests including proteins, [115] nanoparticles [116] and nanorods. [117] One of the most interesting new directions of MOF hostguest chemistry is their use as crystalline sponges. [118] As MOFs are typically crystalline in nature it is possible to use the order of the framework to arrange guest molecules into crystalline arrangements.…”

Tailoring optical cross sections of gold nanorods at a target plasmonic resonance wavelength using bromosalicylic acid

“…The LSPR of AuNRs with small size below the quasi static limit can be well described by the Gans theory, where the optical cross section and the LSPR wavelength hold linear dependence on the volume and R of the nanorod, respectively. For larger AuNRs, however, the dependence becomes implicit 36,37 due to phase retardation and dynamic depolarization effects. 38,39 One has to take this into account when performing the overgrowth of AuNRs at xed LSPR wavelengths.…”