Size Control Synthesis of Monodisperse, Quasi-Spherical Silver Nanoparticles To Realize Surface-Enhanced Raman Scattering Uniformity and Reproducibility

Abstract

In this work, we reported the synthesis of monodisperse, quasispherical Ag nanoparticles (NPs) with sizes of 40–300 nm by using ascorbic acid reduction of a silver–ammonia complex onto preformed, 23 nm Ag-NP seeds in the aqueous solution with an optimal pH of about 9.6 at room temperature. The as-prepared Ag NPs with such a large size span (from 40 to 300 nm) and high quality by one-pot seeded growth method are reported for the first time to the best of our knowledge. It is found that the key in the present seed-mediated growth method is to introduce a proper amount of ammonia water for the formation of a stable complex with a silver precursor (silver–ammonia complex) while maintaining the pH value of the growth solution simultaneously. By using rhodamine 6G molecules as probes, the surface-enhanced Raman scattering (SERS) activities of the as-prepared Ag NPs in ethanol solution are highly dependent on the sizes of Ag NPs at the fixed 633 nm laser and at the fixed particle number, which show a volcano-like curve. Moreover, 125 nm Ag NPs bear the largest SERS activity among them. Furthermore, Ag NPs with narrow distributions in shape and size (say, less than 10%) can achieve the uniformity and reproducibility of their SERS signals in solution; their relative standard deviations can be as low as 5% in space and temporal scale.

Two-dimensional Au & Ag hybrid plasmonic nanoparticle network: broadband nonlinear optical response and applications for pulsed laser generation

“…The extinction spectra of the mixing solution of Au NPs and Ag NPs obtained at different standing time shown in Figure S2 (a) verifies the formation of short chains made up of Au NPs and Ag NPs. Figure S2b and c shows the extinction spectra of as-synthesized Au and Ag NPs separately [36,37]. After 3 h standing, Au & Ag HPNN formed in the ethanol solution were then transferred onto a CaF 2 substrate by spin-coating method.…”

Physicochemical Aspects of Metal Nanoparticle Preparation

“…The process of "seed-mediated" preparation of nanoparticles is based on the preparation of seeds, in diameter of nanometers, using strong reducing agents. The nuclei are, in the next step, let to grow into their required diameter, thanks to the addition of new portion of the metal ions reduced by using weaker reducing agent [11,230,231]. Reasonable adjustment of both steps, nanoparticles in a wide range of diameters, can be prepared.…”

“…As it is a stronger acid than H 2 Q , a certain reducing ability can be observed already at pH lower than 7 (approximately pH = 6), but it does not behave as an effective reducing agent until pH 9 is reached. In such a case, the reduction is completed within several minutes, and the generated silver nanoparticles (AgNPs) have the diameter smaller than 50 nm [11,196,197]. Weak reducing agents, e.g., reducing saccharides, are able to reduce silver ions only under pH higher than 7.…”

“…Silver and gold nanoparticles have found their targeted applications in the enhancement of Raman scattering due to the optical properties that are associated with the existence of localized surface plasmon resonance (LSPR) [4][5][6][7][8] with the absorption maximum in visible part of the electromagnetic part of the spectra. Thanks to this fact the particles provide a significant enhancement of the Raman signal used in the highly sensitive analytical method of surface-enhanced Raman spectroscopy (SERS) [9][10][11][12] used in biology and medicine [13][14][15][16][17]. Transitional metals are commonly known for their high catalytic activity, which is even amplified by the nanodimension of the metal nanoparticles with high ratio between the surface area and the volume of the particle because the catalytic process is located on the surface [18][19][20].…”

Facile Surfactant‐, Reductant‐, and Ag Salt‐free Growth of Ag Nanoparticles with Controllable Size from 35 to 660 nm on Bulk Ag Materials

“…Therefore, numerous synthetic recipes were developed to fabricate Ag nanocrystals of various shape and dimension [8,9] . Typically, Ag salts were reduced to drive the crystal nucleation and growth in a solution containing steric surfactants or capping agents [10–14] . For size control, strong reductants (e. g., borohydride) were chosen to obtain small Ag nanocrystals (<10 nm), while weak reductants (e. g., citrate or ascorbic acid) lead to large Ag nanocrystals (30–80 nm) [15–17] .…”