Porous Au–Ag Nanoparticles from Galvanic Replacement Applied as Single‐Particle SERS Probe for Quantitative Monitoring

Abstract

Especially, the porous plasmonic NPs present significant larger tunability in terms of porosity, composition, and larger specific surface area and higher hot spots density compared to the nonporous nanostructures. [3] As their plasmonic peaks can be tuned in the biological transparent window located in NIR region, the porous NPs may be implemented efficiently in biomedical applications, including bioimaging, biodetection, and drug delivery, as well as the surface-enhanced Raman scattering (SERS) based applications. [4] For biosensing and diagnostics, SERS sensing probes are outstanding among various methods. [5] By highly enhancing "finger-print" Raman signal, SERS substrates and probes show promises in analytical chemistry and biochemistry detection with low detection limits. [6] The growing demand for accurate, personalized diagnosis and therapy is opening up new areas of biomedical application with SERS individual nanoprobes, [7] such as, multiplex Raman cellular detection and differentiation, or ultrasensitive multiplex quantitation of microorganisms. [8] In addition, single NPs exhibit great potential in the use of SERS nanoprobes for cyto-and histopathological diagnostics, where they can give an improvement over the existing tissue imaging system using Raman spectroscopy, [9] by providing local enhancement in spatial Raman mapping studies at the cellular and subcellular level. [10] Plasmonic NPs, especially Au-Ag NPs, provides adjustable SERS probes with high enhancement, due to their LSPR behaviors and their designable structures with high hot spots density. The rough surface, assemblies, nanoscale curvature and gap are promising structures for SERS. [11] However, the reproducibility and the stability remain as the main challenge for practical applications. Therefore, it becomes important to have a controllable synthetic strategy for plasmonic NPs with designed nanostructure, clean surface and aqueous dispersibility, to facilitate the wide application in biosensing.Porous and hollow plasmonic structures have been widely explored using the galvanic replacement reaction (GRR) approach, which removes the less noble metal from the template and replaces it with more noble metal via redox process, while forming vacancies in the multimetallic structure. [12] In Plasmonic nanostructures have raised the interest of biomedical applications of surface-enhanced Raman scattering (SERS). To improve the enhancement and produce sensitive SERS probes, porous Au-Ag alloy nanoparticles (NPs) are synthesized by dealloying Au-Ag alloy NP-precursors with Au or Ag core in aqueous colloidal environment through galvanic replacement reaction. The novel designed core-shell Au-Ag alloy NP-precursors facilitate controllable synthesis of porous nanostructure, and dealloying degree during the reaction has significant effect on structural and spectral properties of dealloyed porous NPs. Narrow-dispersed dealloyed NPs are obtained using NPs of Au/Ag ratio from 10/90 to 40/60 with Au and Ag core to produce solid core@porous shell and po...

Semiconductor-based surface enhanced Raman scattering (SERS): from active materials to performance improvement

“…71 Some metal nanostructures with rough surface or tiny nanogaps also contain abundant "hot spots". [72][73][74] Similar to noble metal nanostructures, the plasmon resonance of semiconductors can be manipulated by morphology design and optimization to enhance the SERS performance. 75 Benefiting from the abundant species and mature synthesis technology, various semiconductor nanostructures ranging from 0D (quantum dot, nanocrystalline), 68,76 1D (nanowire, nanorod, nanocone), 77,78 and 2D (nanoplate, nanodisk) 79,80 to 3D (nanocage, nanoflower, nanoarray) 81,82 have been developed.…”

State of the Art on Green Route Synthesis of Gold/Silver Bimetallic Nanoparticles

“… GRR on Au@Au/Ag and Ag@Au/Ag, resulting in porous shell with solid core (porous NP) or hollow interior (porous nanoshell), respectively. Reprinted from Reference [ 19 ]. …”

“…The GRR of Ag NPs in the presence of HAuCl 4 is depicted in Figure 1 [ 19 ]. The driving force of this phenomenon is the favorable difference in electrochemical potential between Ag + /Ag (0.80 V) and AuCl 4 − /Au (1.00 V) [ 20 ].…”

Near-infrared II plasmonic porous cubic nanoshells for in vivo noninvasive SERS visualization of sub-millimeter microtumors

“…The plasmon absorption of Au NSs with hollow interiors could be also pushed into the NIR region by tailoring the geometry, but currently limited to the NIR-I region 31 . In addition, the dealloying process has been utilized for the fabrication of porous Au nanostructures, but it only produced porous structures with plasmon absorption limited in the visible region 32 – 34 . Our recent work developed a class of Au@Au-Ag dot-in-cubic nanoframe structures with excellent NIR-II plasmonic properties, which exhibits remarkable spectral tunability by the edge length and wall pore size 35 .…”