Abstract
We have reported the in situ surface–enhanced Raman spectroscopy (SERS) monitoring of repetitive surface plasmon–mediated chemical transformation cycles in a conjugate nanobiological system. The nanobiological conjugate comprised a gold-coated plasmonic substrate biofunctionalized with thiolated single–stranded DNA carrying a reduction-oxidation indicator methylthioninium chloride, which is also known as methylene blue (MB), in buffer solution at a neutral pH. Exposure to a 523-nm laser excitation produced pronounced SERS bands of oxidized MB. Continued exposure to the laser resulted in disappearance of the SERS bands, which can be interpreted as a reduction of MB. This occurred in the absence of electrochemical stimulation, chemical agents, or catalysts, suggesting a surface plasmon–mediated mechanism of the transformation. The oxidized form of MB was recovered by an addition of fresh buffer solution on the surface of the sample. Continued laser exposure with periodical addition of the buffer resulted in repetitive cycles of changes in the SERS pattern, which were monitored in situ. The chemical transformations of MB were preceded by a buildup of an intermediate SERS pattern, which was attributed to a transient form of MB created by selective surface plasmon-driven excitation.
Highlights
Engineering of multifunctional nanobioelectronic materials is a rapidly advancing interdisciplinary field of research and innovation
Most plasmonic substrates that show a strong SERS enhancement are efficient as photocatalysts and vice versa. This multifunctional nature of plasmonic substrates enables a unique platform that combines the capabilities of energy harvesting from visible light, photocatalytic functions, and Plasmonics (2020) 15:427–434 ultrasensitive characterization of molecular events in the same design [4, 11,12,13,14,15]
We have developed a conjugate nanobiological system interfacing plasmonic gold nanostructures with thiolated single-stranded DNA carrying an important reduction-oxidation indicator, methylthioninium chloride C16H18ClN3S, which is known as methylene blue (MB)
Summary
Engineering of multifunctional nanobioelectronic materials is a rapidly advancing interdisciplinary field of research and innovation. When a proper nanostructure (plasmonic substrate) is exposed to light, highly efficient absorption of incoming photons is possible, which is accompanied by a buildup of Bhot-spots^—nano-sized regions This multifunctional nature of plasmonic substrates enables a unique platform that combines the capabilities of energy harvesting from visible light, photocatalytic functions, and Plasmonics (2020) 15:427–434 ultrasensitive characterization of molecular events in the same design [4, 11,12,13,14,15]. The integration of plasmonic substrates with stimuli-responsive biological materials promises countless self-powered nanobiological systems with precise positional control of selectively stimulated molecular events For this potential to be realized, specific conjugate architectures that allow for combined surface plasmon-driven photocatalytic stimulation and monitoring need to be designed and investigated. We have investigated the evolution of SERS spectra of DNA-bound MB in our conjugate system under laser exposure in aquatic environment and captured a reversible reduction-oxidation process mediated by surface plasmons during the laser excitation
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