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. 2018 Apr 17:13:2337-2347.
doi: 10.2147/IJN.S156932. eCollection 2018.

Sensitive determination of dopamine levels via surface-enhanced Raman scattering of Ag nanoparticle dimers

Xiantong Yu  1 , XiaoXiao He  1 , Taiqun Yang  1 , Litao Zhao  1 , Qichen Chen  1 , Sanjun Zhang  1   2 , Jinquan Chen  1 , Jianhua Xu  1   2
Affiliations

Sensitive determination of dopamine levels via surface-enhanced Raman scattering of Ag nanoparticle dimers

Xiantong Yu et al. Int J Nanomedicine. .

Abstract

Background: Dopamine (DA) is an important neurotransmitter in the hypothalamus and pituitary gland, which can produce a direct influence on mammals' emotions in midbrain. Additionally, the level of DA is highly related with some important neurologic diseases such as schizophrenia, Parkinson, and Huntington's diseases, etc. In light of the important roles that DA plays in the disease modulation, it is of considerable significance to develop a sensitive and reproducible approach for monitoring DA.

Purpose: The objective of this study was to develop an efficient approach to quantitatively monitor the level of DA using Ag nanoparticle (NP) dimers and enhanced Raman spectroscopy.

Methods: Ag NP dimers were synthesized for the sensitive detection of DA via surface-enhanced Raman scattering (SERS). Citrate was used as both the capping agent of NPs and sensing agent to DA, which is self-assembled on the surface of Ag NP dimers by reacting with the surface carboxyl group to form a stable amide bond. To improve accuracy and precision, the multiplicative effects model for surface-enhanced Raman spectroscopy was utilized to analyze the SERS assays.

Results: A low limits of detection (LOD) of 20 pM and a wide linear response range from 30 pM to 300 nM were obtained for DA quantitative detection. The SERS enhancement factor was theoretically valued at approximately 107 by discrete dipole approximation. DA was self-assembled on the citrate capped surface of Ag NPs dimers through the amide bond. The adsorption energy was estimated to be 256 KJ/mol using the Langmuir isotherm model. The density functional theory was used to simulate the spectral characteristics of SERS during the adsorption of DA on the surface of the Ag dimers. Furthermore, to improve the accuracy and precision of quantitative analysis of SERS assays with a multiplicative effects model for surface-enhanced Raman spectroscopy.

Conclusion: A LOD of 20 pM DA-level was obtained, and the linear response ranged from 30 pM to 300 nM for quantitative DA detection. The absolute relative percentage error was 4.22% between the real and predicted DA concentrations. This detection scheme is expected to have good applications in the prevention and diagnosis of certain diseases caused by disorders in the DA level.

Keywords: Ag NP dimers; MEMSERS; SERS; dopamine detection; multiplicative effects model for surface-enhanced Raman spectroscopy; surface-enhanced Raman scattering.

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Conflict of interest statement

Disclosure The authors report no conflicts of interest in this work.

Figures

Figure 1
Figure 1
Molecular structures of the main reagents used in the experiment. Note: Synthesis of Ag NP dimers. Abbreviation: NP, nanoparticle.
Figure 2
Figure 2
Schematic illustration of the preparation process of the Ag NP dimer hybrid structure and the detection of DA via SERS. Notes: (A) Ag NPs modified by citric acid; (B) Ag NP dimers further induced by the addition of HMD; (C) DA molecules adsorbed on Ag NPs surface by chemical adsorption; (D) the level of DA can be monitored via measuring the SERS signal enhanced by Ag NP dimers. Abbreviations: DA, dopamine; HMD, hexamethylenediamine; NP, nanoparticle; SERS, surface-enhanced Raman scattering.
Figure 3
Figure 3
The basic optical characterization obtained by the experiment. Notes: (A) Extinction spectra of Ag NPs. The inset displays the zoom of one Ag dimer nanostructure. (B) TEM of Ag NPs. (C) TEM of Ag NP dimers. Abbreviations: NP, nanoparticle; TE M, transmission electron microscopy.
Figure 4
Figure 4
(A) Simulated local electric field distributions of Ag NPs (top) and the Ag NP dimer (bottom). (B) Simulated extinction spectra of Ag NPs and Ag NP dimers. Note: (B) a and b indicate the regions of the hotspots of NP dimers and the vicinity of Ag NPs, respectively. Abbreviation: NP, nanoparticle.
Figure 5
Figure 5
SERS of DA adsorbed on the surface of Ag NPs dimers. Notes: (A) SERS of DA at 1.5 μM. (B) SERS of DA at different DA concentrations. (C) Main panel: SERS intensities of the peak at 767 cm−1 vs DA concentration. Inset: the line is fit by the Langmuir isotherm. (D) SERS intensity vs concentration of DA (20 pM–300 nM). Abbreviations: DA, dopamine; SERS, surface-enhanced Raman scattering.
Figure 6
Figure 6
The simulation analysis of DA SERS. Notes: (a) The Raman spectra of DA powders; (b) the simulated DA Raman spectra; (c) the Raman spectra of DA with the carboxyl groups; (d) the simulated SERS spectra; (e) the SERS spectra of DA at 1.5 μM. Abbreviations: DA, dopamine; SERS, surface-enhanced Raman scattering.
Figure 7
Figure 7
FT-IR absorption spectra of three different cases. Notes: Red curve represents Ag NP dimers, gray curve represents fresh DA, and blue curve represents DA adsorbed on the Ag NP dimers. The dotted circle signs the bond ~1,610 cm−1 which could be ascribed to the bending vibration of C=(N–H). Abbreviations: DA, dopamine; FT-IR, Fourier Transform Infrared; NP, nanoparticle.
Figure 8
Figure 8
Concentration predictions for DA through the MEMSERS method. Notes: (A) The multiplicative parameters qK vs DA concentrations. (B) The correlation between the real and predicted concentrations of DA. Abbreviations: DA, dopamine; MEMSERS, multiplicative effects model for surface-enhanced Raman spectroscopy.
Figure 9
Figure 9
Selectivity of the developed DA detection method, DA concentration is 300 nM; other substances are 1 μM. Abbreviations: BSA, bovine serum albumin; DA, dopamine; L-dopa, levodopa; MIX, mixture of all interfering chemicals; PEA, phenethylamine; Trp, tryptophan; Tyr, tyrosine.
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