Gold-Etched Silver Nanowire Endoscopy: Toward a Widely Accessible Platform for Surface-Enhanced Raman Scattering-Based Analysis in Living Cells

Abstract

Recently, our group introduced the use of silver nanowires (AgNWs) as novel non-invasive endoscopic probes for detecting intracellular Raman signals. This method, although innovative and promising, relies exclusively on the plasmonic waveguiding effect for signal enhancement. It, therefore, requires sophisticated operational tools and protocols, drastically limiting its applicability. Herein, an advanced strategy is offered to significantly enhance the performance of these endoscopic probes, making this approach widely accessible and versatile for cellular studies. By uniformly forming gold structures on the smooth AgNW surface via a galvanic replacement reaction, the density of the light coupling points along the whole probe surface is drastically increased, enabling high surface-enhanced Raman scattering (SERS) efficiency upon solely focusing the excitation light on the gold-etched AgNW. The applicability of these gold-etched AgNW probes for molecular sensing in cells is demonstrated by detecting site-specific and high-resolved SERS spectra of cell compartment-labeling dyes, namely, 4′,6-diamidino-2-phenylindole in the nucleus and 3,3′-dioctadecyloxacarbocyanine on the membrane. The remarkable spectral sensitivity achieved provides essential structural information of the analytes, indicating the overall potential of the proposed approach for cellular studies of drug interactions with biomolecular items.

Gold-Photodeposited Silver Nanowire Endoscopy for Cytosolic and Nuclear pH Sensing

“…Upon this process, AgNWs are attached in bundles to the W tip, providing the probe with the flexibility needed to penetrate the cell without breaking. 33,34 Afterward, AgNWs were fixed on the W tip by gluing the junctions with an epoxy resin to avoid detachment during probe insertion into the cell (Figure 3b). Finally, the as-obtained AgNW endoscopic probe was immersed in a HAuCl 4 aqueous solution and irradiated with a focused 488 nm laser for 120 s to form Au nanostructures (Figure 3c).…”

“…33 Subsequently, we have enhanced the SERS performance of AgNWs by etching their surface with a gold (Au) precursor via galvanic replacement reaction (GRR), and we proved the site specificity of our endoscopic technique by detecting the SERS signals of dyes from different cell compartments. 34 In these works, the noninvasivness of our technique has been evidently proven by calcium response tests. Thanks to its low invasiveness and high spatiotemporal resolution, this approach holds great potential for site-specific pH sensing in living cells.…”

“…The Au etching was performed according to the reported method with modification. 34 A total of 15 mL of Milli-Q water was heated at 80 °C for 10 min. A total of 450 μL of the AgNW solution was then added, followed by the addition of 1.8 mL of a 0.2 mM HAuCl 4 solution.…”

“…Most recently, nanoendoscopy using nanoscale endoscopes has gained increasing attention for intracellular investigations. , Among the pioneers of this approach, our group introduced the use of silver nanowires (AgNWs) as a noninvasive endoscopic probe to collect highly resolved Raman signals from the nuclei of living cells . Subsequently, we have enhanced the SERS performance of AgNWs by etching their surface with a gold (Au) precursor via galvanic replacement reaction (GRR), and we proved the site specificity of our endoscopic technique by detecting the SERS signals of dyes from different cell compartments . In these works, the noninvasivness of our technique has been evidently proven by calcium response tests.…”

In Situ SERS Monitoring of the Plasmon-Driven Catalytic Reaction by Using Single Ag@Au Nanowires as Substrates

“…SERS has the advantage of vibrational Raman spectroscopy in identifying various analytes with high sensitivity and selectivity based on the multiple narrow Raman spectral bands as the “vibration fingerprint”. It is well-known that silver nanostructures have unique advantages as SERS substrates, and various nano-silver materials have been prepared for SERS research. − For instance, the Schlücker group used the silver super structure to discover the hot-electron-induced reduction reaction on the silver surface by using in situ SERS . Fang and his co-workers synthesized a rough structure on the surface of the silver nanowires, which was used as a new SERS-active substrate to cause uniform and large surface plasmon resonance enhancement .…”