Decoupled in-plane Dipole Resonance Modulated Colorimetric Assay-Based Optical Ruler for Ultra-Trace Gold (Au) Detection

Abstract

Decoupling of different plasmon resonance modes (in-plane, and out-of-plane dipole and quadrupole resonances) by tuning nanoparticle’s size and shape offers a new field of plasmonics as colorimetric assay-based optical-ruler for ultra-trace sensing. Driven by its low cost, easy to perform and efficient way to measure trace level (up to 30 ppt in presence of common mining elements in natural gold ore) abundance, this study develops a highly selective and ultrasensitive turn-on colorimetric sensor to detect gold-ion from environmental samples. Different level of gold-ion tracer makes size variable spherical- and disc-shaped silver nanoparticles when added to a ‘growth solution’ which results decoupling of in-plane dipole resonance from in-plane quadrupole and out-of-plane dipole resonances with a wide range of in-plane dipole plasmon tunability to generate different colors. This color-coded sensing of gold-ion shows high selectivity and ultrasensitivity over other metal ions in the ppt level with an impurity aberration limit of 1 ppm. A plausible explanation explains the possible role of catalytic gold-ion to initiate unfavorable silver ion (Ag+) reduction by ascorbic acid to generate silver nanoparticles. Proposed technology has been applied in real mining sample (Bugunda Gold Deposit, Tajikistan) to detect gold concentration from ores to find potential application in mining technology.

Zone-Specific Crystallization and a Porosity-Directed Scaling Marker for the Catalytic Efficacy of Au–Ag Alloy Nanoparticles

“…The role of Au­(III) and the amount of seed in controlling the size and crystallinity of the central cavity can be explained by considering the reduction potentials of the component redox systems (Au 3+ /Au 0 , Ag + /Ag 0 , and AA 2+ /AA) present in the reaction mixture. The reduction potentials reported for Au 3+ /Au 0 , Ag + /Ag 0 , and AA 2+ /AA are 1.5, 0.81, and −0.066 V (at pH 7), respectively. , As explained before in our previous report, the presence of Au­(III) enhances the differential reduction potential of AA from 0.8 V (between Ag + /Ag 0 and AA 2+ /AA) to 1.5 V (between Au 3+ /Au 0 and AA 2+ /AA), which forces AA to act as an efficient reducing agent and results in all of the available AA being used in the reduction of Au­(III) and Ag­(I) to form seed-mediated alloy structures. When we add a small amount of seed, the volume-to-surface ratio, i.e., π R 2 h /2π R 2 , of the nucleation zone to accommodate all of the Au 0 and Ag 0 in the prismatic geometry should be very small compared to the total surface of the HNPr and vice versa for a large amount of seed.…”

“…This gradual increment of strain along the (111) plane indicates that the reactivity on the {111} facet increases gradually with Ag doping. This results in transformation from the prismatic shape to HNPr to achieve the desired stability by reducing their vibrational entropy , in the form of developed strain. On the other hand, the more reactive (220) plane, which comprises the faces of HNPrs, acts as the active facet for effective UA oxidation.…”

Silver Nanoplates for Colorimetric Determination of Xanthine in Human Plasma and in Fish Meat via Etching/Aggregation/Fusion Steps

“…Regardless of the ratio of PVP to AgNO 3 , the characteristic absorption peaks appeared at 672–703 nm, 460–486 nm, and 331 nm, and were ascribed to the in-plane dipole mode, in-plane quadrupole mode, and out-of-plane quadrupole mode, respectively ( Figure 1 f). The characteristic absorptions of the in-plane dipole mode and in-plane quadrupole mode, especially for 460–486 nm, in UV-visible spectra of AgP were correlated to the edge lengths [ 21 , 22 ]. Simultaneously, the relative particle population of AgP peaked at a molar ratio of the PVP–AgNO 3 solution of 7:1 (mM:M), which was chosen as the optimized synthesis condition for Xan sensing.…”