Analyte-restrained silver coating of gold nanostructures: an efficient strategy to advance multicolorimetric probes

Abstract

Visual detection based on gold nanorods (AuNRs) has gained tremendous attention in sensing applications owing to the potential for simple, inexpensive, instrument-free, and on-site detection. The proper selection of the mechanism involved in the interaction between the analyte and the nanostructure plays a significant role in designing a selective and multicolorimetric probe for visual purposes. A winning mechanism to develop multicolorimetric probes is the silver metalization of AuNRs. Herein, an unprecedented idea is presented to expand the variety of multicolorimetric sensors relying on the mechanism of silver deposition. We introduce the anti-silver deposition mechanism in which the analyte directly or indirectly restrains the silver coating of AuNRs. To ascertain the anti-silver deposition mechanism, we have exploited the proposed idea for the direct detection of nitrate. The presence of nitrate (as restrainer agent), which was firstly treated with ascorbic acid (as reducing agent), induced a decrease in the spectral blueshift of AuNRs along with diverse sharp color transitions from reddish-orange (blank) to maroon, wine, berry/purple, dark blue, teal, green, seafoam, and mint. The difference in the spectrum area of the probe in the absent (S o) and presence (S) of nitrate were linearly proportional to nitrate concentration in the range of 0.5–5.5 mmol l−1 and the limit of detection was calculated to be 465 μmol l−1. Furthermore, the practicability of the multicolor probe was assessed by the determination of nitrate in complex environmental samples.

Colorimetric Silver Ion Detection Based on Silver Metallization of Gold Nanorods

“…In this mechanism, silver ions (Ag + ) with a determined concentration are added to the detection solution. Ag + is reduced to Ag o in the presence of ascorbic acid and by inducing metallization are grown in the form of a shell on AuNRs to finally form the Au@Ag core‐shell nanorods [33,37, 38] …”

“…Ag + is reduced to Ag o in the presence of ascorbic acid and by inducing metallization are grown in the form of a shell on AuNRs to finally form the Au@Ag core-shell nanorods. [33,37,38] Absorption spectra of the detection solution in the absence and presence of silver ions were determined by UV-Vis spectroscopy. As shown in Figure 1a, the SPR peak of AuNRs is located at 680 nm wavelength.…”

“…In addition, with the induction of anisotropy, these properties show significant changes. [15,32] Gold nanorods (AuNRs) are one of the most practical anisotropic structures that are used as diagnostic particles in colorimetric sensors due to their unique optical features.. [32][33][34] In this research, a colorimetric probe was designed to detect silver ions based on the formation of gold@silver core-shell NRs. During this process, silver ions are reduced by a reductant and deposited on the surface of AuNRs.…”

Effect of Light Irradiation on Hot Electron-Mediated Photoreduction of Silver Ions on Single Gold Nanorods without a Reducing Agent

“…In particular, Au@Ag core@shell structures have been widely used for surface-enhanced Raman scattering because of the high plasmonic efficiency and large electromagnetic enhancement introduced by Ag atoms . As a result of recent advances in the chemical synthesis of these heterostructures, the extinction spectrum can be adjusted over the entire visible range by controlling the thickness of the Ag shell. , In addition, the shape of the Ag shell can be controlled by changing the reaction conditions, such as the concentration of AgNO 3 , cetyltrimethylammonium bromide (CTAB), and the reductant, aging time, pH, and temperature. − …”

Machine Learning-Assisted Colorimetric Assay Based on Au@Ag Nanorods for Chromium Speciation

“…While there are multifarious plasmonic NPs of various shapes and compositions, the implementation of gold nanorods (AuNRs) as extraordinary color labels and signal producers in the development of multicolorimetric sensors has attracted recurring interest in recent years. ,− On account of structural anisotropy, the extinction spectrum of AuNRs displays two bands emanating from the transversal and longitudinal plasmonic modes; that of the latter mode can be tuned over a broad spectral range depending on the length-to-diameter aspect ratio and the dielectric constant of the surrounding medium . Therefore, the minute alterations of the surface composition or aspect ratio of AuNRs are followed by a significant blue/red shift of the longitudinal peak along with elegant and high-contrast multicolor variations. , Interestingly, the overgrowth of AuNRs with a silver nanoshell through the reduction of silver ions in an aqueous medium changes the aspect ratio and refractive index of AuNRs, thereby leading to the gradual blue shift of the longitudinal peak, as well as the appearance of a new peak at ∼420 nm attributed to the formation of spherical AgNPs. , Controlling this phenomenon underlies a series of sharp-contrast rainbow colors providing ample opportunities for the design of highly accurate visual assessments.…”