Surface-enhanced Raman spectroscopy (SERS) is considered a highly promising technology for different analytical purposes. The applications of SERS are still quite limited due its relatively poor quantitative repeatability and the fact that SERS is very sensitive to oxidation, which is a challenge especially with silver based SERS substrates. Here, the link between these phenomena is investigated by exposing silver SERS substrates to ambient laboratory air. We show that SERS intensity decreases exponentially after the exposure, which consequently leads to an increasing standard deviation (σ) in intensity. Within a five-hour measurement window, the SERS intensity already drops by 60%, while σ triples from 7% to 21%. The SERS results are supplemented by elemental analysis, which shows that oxidation and atmospheric carbon contamination coincide with the rapid SERS intensity decrease. The results emphasize how sensitive SERS is towards atmospheric contamination and how it can also reduce the measurement repeatability – even if the substrates are exposed to air just for a very short period of time.
Surface enhanced Raman scattering (SERS) fiber probes have enormous potential in optical sensing applications. However, their widespread use has been hindered by two major obstacles: the difficulty of fabricating the required silver nanostructures on optical fibers and the tarnishing of silver, rapidly degrading their sensing properties. Here we propose a solution to these dilemmas by abandoning the use of metallic silver and conventional nanofabrication procedures. Instead, we base our fabrication on chemically stable silver chloride and show that it can be directly grown on the optical fibers without any advanced fabrication equipment. As silver chloride itself is not SERS-active, we demonstrate how to “activate” the probes by turning the crystals into metallic silver nanostructures via photoreduction. We verify that if stored in the non-activated stage, the sensing properties of the structures remain unchanged. Finally, we demonstrate the high sensitivity (signal-to-noise ratio up to 42 ± 3 dB) of the probes in real-time in situ measurements at nanomolar analyte concentrations.
We propose direct synthesis of ultra-thin graphitic films on a dielectric substrate using sacrificial Ni catalyst layer, which significantly increases the crystallinity of the photoresist pyrolyzed at the temperature of 800 °C and above. A considerable amount of multilayer graphene in the photoresist film pyrolyzed in the presence of the Ni catalyst gives rise to an enhancement of the Raman signal of dye Sudan III molecules deposited on the substrate. We demonstrate comparable enhancement of the Raman signal from Sudan III molecules deposited on the fabricated graphitic substrate and those deposited on graphene, which was conventionally transferred to the silica substrate.
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