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

Abstract

Because of the sharp distance dependence of surface-enhanced Raman spectroscopy (SERS), analyte molecules that do not exhibit strong affinity for Au/Ag often elude detection. New methods of integrating such analytes with SERS substrates are required to circumvent this limitation and expand the sensitivity of SERS to new molecules and applications. We communicate here a solution-phase, capture agent-free method of aggregating Au nanospheres in the presence of five neurotransmitters (dopamine, epinephrine, norepinephrine, serotonin, and histamine) and preventing sedimentation by encapsulating the aggregated nanospheres with polyvinylpyrrolidone, thereby trapping the neurotransmitters in close proximity to the Au nanospheres and enabling SER detection. The primary advantages of this physicochemical trapping method, which is generalizable to analytes beyond the scope of this work, are the high signal-to-noise ratio and spectral consistency down to nM levels. Normal Raman spectra and density functional theory calculations corroborate the accuracy of the spectra. Spectra collected over a wide range of concentrations were used to construct adsorption isotherms for all five neurotransmitters, from which adsorption dissociation constants were calculated, spanning from 5.7 × 10–4 M to 1.7 × 10–10 M. We expect this method to produce high quality SER spectra of any molecule with an Au affinity known or expected (based on functional groups) to be within that range. Our results have implications for plasmonic detection of these neurotransmitters, particularly for mixtures of those that exhibited disparate Au affinity in our study. We also present evidence that this method produces spectra of sufficient resolution to explore hypotheses related to surface adsorption behavior.

The highly sensitive determination of serotonin by using gold nanoparticles (Au NPs) with a localized surface plasmon resonance (LSPR) absorption wavelength in the visible region

“…80 There were no peaks from ascorbic acid due to its lack of affinity for Au. 81 In general, 5-HT can be detected by our SERS substrate in a complex mixture. A schematic diagram showing the direct APTES [(3-aminopropyl)triethoxysilane] functionalization of Au NPs is shown in Fig.…”

Nanopipette‐based electrochemical SERS platforms: Using electrodeposition to produce versatile and adaptable plasmonic substrates

“…[46][47][48] Fast electrodeposition at high overpotentials is expected to generate structures which fulfill these requirements, as it favors nucleation over growth, leading to a corrugated surface with sharp features, nanoscale gaps, and defects, with potential to act as plasmonic hotspots. [49,50] The inherently self-similar resulting morphology ensures a high density of such hotspots, improving SERS performance. [51][52][53] An example is shown in Figure 1b, obtained after cycling a nanoelectrode two times between 0 and −0.9 V at 20 mV/s in a 0.2 mM HAuCl 4 and 50 mM KCl solution.…”

“…This is expected, as the electrodeposited structures are analogous to aggregated particles, for which the plasmon mode is broad and redshifted with respect to the LSPR of well dispersed individual nanoparticles. [50,53] Based on these measurements, we selected 785 nm as the laser excitation wavelength for SERS experiments.…”

Strong histamine torsion Raman spectrum enables direct, rapid, and ultrasensitive detection of allergic diseases

“…Complex sample preparation, expensive instrumentation, and long inspection time are the main drawbacks of these techniques. Surface-enhanced Raman scattering (SERS) is a useful tool to achieve high-precision detection of small molecules ( Giancane et al., 2016 ; Vander Ende et al., 2019 ). Determination of histamine concentration in food by SERS in the high-frequency side (>200 cm −1 ) has been reported recently ( Bettini et al., 2019 ; Huynh et al., 2020 ).…”