Block Copolymer Brush Layer-Templated Gold Nanoparticles on Nanofibers for Surface-Enhanced Raman Scattering Optophysiology

Abstract

A nanothin block copolymer (BCP) brush-layer film adsorbed on glass nanofibers is shown to address the longstanding challenge of forming a template for the deposition of dense and well-dispersed nanoparticles on highly curved surfaces, allowing the development of an improved nanosensor for neurotransmitters. We employed a polystyrene-block-poly(4-vinylpyridine) BCP and plasmonic gold nanoparticles (AuNPs) of 52 nm in diameter for the fabrication of the nanosensor on pulled fibers with diameters down to 200 nm. The method is simple, using only solution processes and a plasma cleaning step. The templating of the AuNPs on the nanofiber surprisingly gave rise to more than 1 order of magnitude improvement in the surface-enhanced Raman scattering (SERS) performance for 4mercaptobenzoic acid compared to the same AuNPs aggregated on identical fibers without the use of a template. We hypothesize that a wavelength-scale lens formed by the nanofiber contributes to enhancing the SERS performance to the extent that it can melt the glass nanofiber under moderate laser power. We then show the capability of this nanosensor to detect the corelease of the neurotransmitters dopamine and glutamate from living mouse brain dopaminergic neurons with a sensitivity 1 order of magnitude greater than with aggregated AuNPs. The simplicity of fabrication and the far superior performance of the BCP-templated nanofiber demonstrates the potential of this method to efficiently pattern nanoparticles on highly curved surfaces and its application as molecular nanosensors for cell physiology.

Physicochemical Trapping of Neurotransmitters in Polymer-Mediated Gold Nanoparticle Aggregates for Surface-Enhanced Raman Spectroscopy

“…Representative high-concentration SER spectra of each neurotransmitter are shown in Figure . Although the clean subtraction of PVP contributions from the neurotransmitter SER spectra provides confidence in labeling those spectra as being highly representative of the neurotransmitters, because direct SERS results for these molecules vary in the literature (dopamine, ,,− epinephrine, , norepinephrine, , serotonin, ,,− histamine , ), additional steps were taken to confirm their identity and gauge the robustness of the AuNP/PVP method. NR spectra (in solution and of the solid salts of the neurotransmitters) and neutral species gas-phase DFT-calculated Raman spectra of the neurotransmitters were collected for comparison.…”

“…Thus, it is of interest to circumvent the need for a capture agent and find ways to directly sense molecules that are weakly Ag/Au-affinitive. The direct detection of neurotransmitters has been demonstrated with templated Au nanoparticles, aggregated Au and Ag nanoparticles (dried or concentrated via centrifugation), , and with electrochemical SERS, but the spectra from these different studies are insufficiently consistent when compared to each other to conclude that direct sensing of neurotransmitters cannot be improved upon. We view solution-phase physicochemical trapping as an alternative to other SERS substrates and to capturing a molecule with a capture agent as an internally consistent and reproducible method.…”

Human metabolite detection by surface-enhanced Raman spectroscopy

“… The preparation of nanostructures with engineered hotspots. This can be fulfilled through forming particle aggregations, enlarging the surface area, and fabricating plasmon-coupling structures [ [124] , [125] , [126] ]. For example, colloidal aggregates are preferred in liquid phase, and nanopillar patterns [ 127 ], film layers [ 100 ] as well as porous structures [ 100 ] are frequently reported on a planar substrate.…”

Raman Scattering: From Structural Biology to Medical Applications

“…SERS was also applied to detect and quantify three types of bacterial meningitis pathogens in the cerebral spinal fluid [256]. Masson group developed plasmonic nanosensors to detect metabolites that were secreted from cells, such as pyruvate, lactate, ATP, and urea [257,258], or neurotransmitters (dopamine and glutamate) [259] near living cell surface. SERS-detectors may provide quantitative estimation of the analyte or can give qualitative information regarding analyte presence in the studied medium.…”