High‐Performance Hydrogel SERS Chips with Tunable Localized Surface Plasmon Resonance for Coordinated Electromagnetic Enhancement with Chemical Enhancement

Abstract

throughput, and rapid response, SERS has great potential in applications including surface science, [2,3] material science, [4] biological medicine, [5] drug analysis, [6] food safety, [7,8] environmental testing, [9] and so on. It is well known that SERS tests require the target molecules to be adsorbed on the surface of certain special materials (so-called SERS substrate), and the SERS response is greatly dependent on the nature of the substrate. The present SERS substrates usually suffer from the major disadvantages of low sensitivity, poor stability, poor uniformity, and weak anti-interference ability. [10,11] Electromagnetic enhancement (EM) and chemical enhancement (CM) are two widely accepted processes involved in the SERS mechanism. Usually, EM is considered to play a greater role than CM. [12,13] Accordingly, many SERS substrates have been designed based on the strong localized surface plasmon resonance (LSPR) of noble metals. [14] In particular, various silver (Ag) based nanostructures have been developed for SERS substrate due to their strong LSPR. [15,16] However, the constructed Ag based SERS substrates tend to be only responsive to certain specific molecules but are insensitive to many important molecules to be tested. [17] Thus, improving the SERS activity of Ag-based substrates is still greatly necessary. The contribution of CM in Ag-based substrates is usually covered up by the CM, and is usually ignored. Recently, increasing research results suggest a non-negligible role of CM in SERS. [18] In particular, many semiconductor-based nanomaterials have been found to have high enhancement factors (EFs) up to 10 5 -10 6 relying only on the CM. Can Ag based substrates also have such a strong CM? If yes, how to coordinate efficiently the CM and EM to gain the strongest SERS activity? To gain the maximum CM effect, a laser with matched energy should be applied according to the energy level of the target molecule and the Fermi level of Ag to ensure the efficiency of charge transfer (CT). [19] Thus, lasers of different wavelengths may be selected for different target molecules. At the same time, to achieve an optimal EM effect, Hydrogel surface-enhanced Raman scattering (SERS) chips with tunable localized surface plasmon resonance (LSPR) wavelength are prepared to coordinate the chemical enhancement (CM) and electromagnetic enhancement (EM) effects for molecules. When detecting different molecules, a laser with matched energy is selected according to energy intervals between the molecular energy levels and the Fermi level of Ag nanoparticles to obtain the strongest CM effect. Meanwhile, a hydrogel SERS chip with the LSPR wavelength matching with the laser is selected to gain the strongest EM effect. As a result, the constructed hydrogel SERS chips show outstanding activity to many molecules. Amoxicillin, pymetrozine, and chlorpyrifos are used as the model molecules to demonstrate the great importance of CM effect and the working principle of the obtained hydrogel SERS chips. Besides the ultrahigh activity,...

Ordered Anodic Aluminum Oxide-Based Nanostructures for Surface-Enhanced Raman Scattering: A Review

“…On the other hand, the CM mechanism originates from the interaction between probe molecules and the substrate, altering the charge distribution of the adsorbed molecules and then resulting in a smaller Raman EF ranging from 10 2 to 10 3 . 59,60 SERS enhancement critically relies on surface plasmons, which represent the resonant oscillation of conduction electrons at the substrate interface, and these surface plasmons are able to amplify the surface electromagnetic field, consequently enhancing the intensity of Raman scattering. 13,61 There are mainly two classes of surface plasmons including surface plasmon polaritons (SPPs) and localized surface plasmon resonance (LSPR).…”

“…The EM mechanism, considered the primary mechanism, arises from the high-density electric field in localized surface plasmon resonance (LSPR), resulting in an exceptionally high Raman enhancement factor (EF) ranging from 10 6 to 10 12 . On the other hand, the CM mechanism originates from the interaction between probe molecules and the substrate, altering the charge distribution of the adsorbed molecules and then resulting in a smaller Raman EF ranging from 10 2 to 10 3 . , …”

MoS2 Nanosheets as Substrates for SERS-Based Sensing

“…CM is relatively complex but can generally be induced by charge transfer between molecules and substrates. Recently, increasing research results suggest that the CM effect cannot be ignored. − For instance, many carbon and semiconductor materials have only CM effect, without any EM effect, and can also exhibit very high SERS activity. − The enhancement factor (EF) of some semiconductor-based nanomaterials can even reach above 10 7 , which is equivalent to that of many metal nanostructures with EM effects. ,− More importantly, the CM effect is the key to achieve the specific enhancement. Therefore, investigating the CM effect of a semiconductor is of great significance for promoting the development of SERS.…”

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