Poly-l-lysine-Coated Silver Nanoparticles as Positively Charged Substrates for Surface-Enhanced Raman Scattering

Abstract

Positively charged nanoparticles to be used as substrates for surface-enhanced Raman scattering (SERS) were prepared by coating citrate-reduced silver nanoparticles with the cationic polymer poly-l-lysine. The average diameter of the coated nanoparticles is 75 nm, and their zeta potential is +62.3 ± 1.7 mV. UV-vis spectrophotometry and dynamic light scattering measurements show that no aggregation occurs during the coating process. As an example of their application, the so-obtained positively charged coated particles were employed to detect nanomolar concentrations of the anionic chromophore bilirubin using SERS. Because of their opposite charge, bilirubin molecules interact with the coated nanoparticles, allowing SERS detection. The SERS intensity increases linearly with concentration in a range from 10 to 200 nM, allowing quantitative analysis of bilirubin aqueous solutions.

Bimodal Sintered Silver Nanoparticle Paste with Ultrahigh Thermal Conductivity and Shear Strength for High Temperature Thermal Interface Material Applications

“…On the basis of a previous study, the principal band is assigned to the carboxylate antisymmetric stretching mode (v as (COO)), and its dominant intensity reflects the interaction between one carboxylate and the Ag surface. 52 The relatively intense bands at 1328 and 1518 cm −1 are assigned to the carboxylate symmetric stretching mode (v s (COO)) and another v as (COO) mode, 32,53 and the relatively low intensities of these two bands indicate that they may not bond directly to the Ag surface. Because the difference in frequency between the two v as (COO) modes is only 18 cm −1 , this finding can be best rationalized by the binding of one terminal carboxylate to the Ag surface, while the other terminal carboxylate and the tertiary carboxylate remain unbound.…”

Synthetic Routes for the Preparation of Silver Nanoparticles

“…7 Illustration of the stabilized capped-AgNP synthesized using GA as proposed in Ref. [33] nitrate by dimethylformamide (DMF) and using 3-(aminopropyl)trimethoxysilane (APS) to stabilize the particles.…”

Fabrication of stable network-like gold nanostructures in solution and their assessment as efficient NIR-SERS platforms for organic pollutants detection

“…The presence of the same spectral features in both Raman and SERS spectra clearly identify the presence of citrate molecules onto the gold network surface. The prominent band at 1018 cm À1 observed in the SERS spectrum corresponds to the C-O stretching of the tertiary alcohol [24][25][26]. The bands between 1300 and 1500 cm À1 are due to symmetric carboxylate stretching mode, and those between 800 and 1000 cm À1 are caused by C-COO and C-OH stretching modes [24][25][26].…”

“…Previous studies [ ( F i g . _ 1 ) T D $ F I G ] demonstrate the applicability of sodium citrate molecules used for nanoparticles stabilization as internal Raman probe [24][25][26]. Considering this the first assessment of the SERS activity of the fabricated network-like gold nanostructures was conducted using this molecule.…”

“…The prominent band at 1018 cm À1 observed in the SERS spectrum corresponds to the C-O stretching of the tertiary alcohol [24][25][26]. The bands between 1300 and 1500 cm À1 are due to symmetric carboxylate stretching mode, and those between 800 and 1000 cm À1 are caused by C-COO and C-OH stretching modes [24][25][26]. It is worth mentioning that no specific Raman signal was detected from citrate molecules when the dispersed colloidal spherical gold nanoparticles were used as a SERS substrate (result not shown).…”