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Surface-enhanced Raman scattering (SERS) is highly dependent on the adsorption of target molecules onto metallic surfaces, such as colloidal metallic nanoparticles. The selection of suitable substrates is crucial for optimizing SERS performance. Herein, we investigated the dependence of two pesticide SERS signals, thiabendazole (TBZ) and carbendazim (MBC), on both Ag nanoparticles (reduced by hydroxylamine—AgH or citrate—AgCT) and the aggregation conditions induced by adding different salts (NaCl, KCl or KNO3). In addition to SERS experiments, in order to assess the induced aggregation of the Ag nanoparticles, UV-Vis absorption spectroscopy, dynamic light scattering (DLS) and zeta potential were employed. For AgH, the use of salts did not yield the greatest effect in the presence of TBZ, as only with the pesticide was it possible to achieve the highest aggregation and greater intensity of the SERS signal. In contrast, with the MBC pesticide, the KNO3 salt promoted the greatest aggregation state and was crucial for obtaining the most amplified SERS signal. The thicker coating layer of AgCT prevented the adsorption of both pesticides on the surface of the nanoparticles, which was achievable using salts containing Cl− ions. Additionally, to obtain the SERS signal of MBC with AgCT, besides the presence of chlorinated salts, other adjustments were necessary, such as changing both the pH of the medium (from pH 5.8 to pH 8, for which MBC is in its neutral form) and the laser lines (from 785 to 514.5 nm). These findings demonstrated that although the pesticide molecules belong to the same chemical functional group, their detection was strongly influenced by the surface of the silver nanoparticles and the salts added. This highlights the specific nuances in detection depending on the method of Ag synthesis and the nature of the aggregating agents used. [ABSTRACT FROM AUTHOR]

Carbendazim (MBC), a commonly used fungicide from the benzimidazole group, was applied in this study as a probe molecule to understand the influence of sample preparation on the SERS (surface-enhanced Raman scattering) signal. We applied the external standard method (ESM), preparing fresh Ag colloid samples (reduced by hydroxylamine) for each concentration and measuring with and without potassium nitrate (KNO₃) as an aggregation-inducing salt. The impact of sample dilution before or after the addition of the salt to the Ag colloid was also explored. SERS signals were correlated with Ag colloid aggregation observed via transmission electron microscopy (TEM), UV-Vis extinction, dynamic light scattering (DLS), and zeta potential, examining diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA) mechanisms. The optimal results were achieved without KNO₃, with more compact aggregates at lower concentrations and more branched ones at higher concentrations. Dilution of the Ag colloid before salt addition enabled lower detection limits than without any dilution. No SERS signal was observed when the salt was added before dilution. These findings emphasize that a consistent relationship between aggregate morphology and the SERS signal cannot be generalized across analytes. Analyte-specific properties play a crucial role in determining optimal aggregation conditions for SERS analysis. [ABSTRACT FROM AUTHOR]

The excessive use of pesticides has detrimental effects on the ecosystem, leading to soil contamination and the spread of pollution beyond the targeted areas. Concerns arise regarding the permissible limits of pesticides, typically around 10−8 mol/L. In this study, we employed surface‐enhanced Raman spectroscopy (SERS), a highly sensitive and selective technique, to investigate the behavior of the pesticide ametrine (AMT) on silver colloids. The Ag nanoparticles (AgNPs) exhibited an average size of (26 ± 2) nm and a zeta potential of (−30 ± 1) mV in the absence of AMT, which decreased to (−24 ± 1) mV in the presence of AMT, resulting in mild AgNPs aggregation, with the average diameter of AgNPs increasing to approximately 300 nm. This aggregation is advantageous, as they provide active sites for pesticide detection. Besides, the purification method employed ensured that AMT remained undegraded, and various conformations of AMT were simulated using Ag clusters to study the SERS effect. Comparison with the experimental spectra indicated that the SERS‐4 conformer closely resembled the experimental spectrum, suggesting simultaneous interaction between the Ag surface and the sulfur (S) and nitrogen (N) atoms of the AMT triazine ring. Notably, changes in the AMT molecule were observed with pH variations: at pH below 5, hydroxylation occurred, resulting in an Ag–Cl stretching at 241 cm−1 in the SERS spectra. Conversely, at pH above 5 (pH 6–13), the presence of bands at 230 and 219 cm−1 in the SERS spectra indicate the formation of Ag–N and Ag–S bonds, respectively, between the AMT and the AgNPs. Furthermore, the study successfully detected AMT at pH 7, establishing a limit of detection (LOD) of 1.36 × 10−8 mol/L (3 ppb) based on the SERS spectra. These findings underscore the applicability of the SERS technique in the sensitive and selective detection of AMT, offering a promising approach for monitoring the presence of this pesticide in environmental samples. [ABSTRACT FROM AUTHOR]

The development of materials for multiple applications is a challenge in the fields of technology and materials science. In this work, screen-printed carbon electrodes (SPCEs) were modified with an electropolymerized nickel tetrasulfonated phthalocyanine film (polymeric-NiTsPc = p-NiTsPc) decorated with gold nanoparticles (AuNP). The modified SPCEs were applied as a sensing platform for analysis via electrochemical and surface-enhanced Raman scattering (SERS) spectroscopy. The SPCEs modification was based on the potential cycling firstly in a NiTsPc solution and then in an AuHCl4 solution, with the fast formation of spherical AuNP through the p-NiTsPc film surface. The modified electrode based on SPCE/p-NiTsPc/AuNP showed a synergetic effect in voltammetric measurements in [Fe(CN)6]3−/[Fe(CN)6]4− probe as well as an electrocatalytic effect in the presence of dopamine. The calibration curve towards dopamine detection presented a linear range from 1 to 10 μmol/L with a limit of detection of 0.73 μmol/L. The spectroelectrochemistry measurements combining SERS and the applied potential of −60 mV showed that the SPCE/p-NiTsPc/AuNP and SPCE/AuNP can be powerfully used as a dual sensing platform for dopamine detection. In the case of SPCE/p-NiTsPc/AuNP, p-NiTsPc plays an important role in facilitating electron transfer during the electrochemical reaction, while AuNP is crucial for obtaining SERS signals for dopamine detection. [ABSTRACT FROM AUTHOR]

Usually, electronic tongues (e-tongue) do not require specific interactions to discriminate aqueous solutions. Among the several factors which determine the electrical properties of sensing units, the interactions between liquids and interfaces have a crucial role. Here, we explore the interaction between dioctadecyldimethylammonium bromide (DODAB) lipid and carbendazim (MBC) pesticide in an e-tongue to discriminate different MBC concentrations in aqueous solutions. The sensing units were fabricated of gold interdigitated electrodes (IDEs) coated with layer-by-layer (LbL) films of DODAB and nickel tetrasulfonated phthalocyanine (NiTsPc), perylene and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (DPPG), namely (DODAB/NiTsPc)5 and (Perylene/DPPG)5, respectively. Besides, a bare electrode also constituted the e-tongue to distinguish MBC concentrations from 1.0 × 10−7 up to 1.0 × 10−10 mol L−1, by impedance spectroscopy. In addition, the experiment was optimized using two IDE geometries. The LbL films were manually fabricated obtaining linear growth monitored via UV-Vis absorption spectroscopy. Optical images associated with chemical mapping reveals the presence of small aggregates in the DODAB/NiTsPc LbL film surface. Although the e-tongue was able to discriminate all MBC concentrations by means of the interactive document map (IDMAP), only the sensing unit covered with DODAB/NiTsPc LbL film presented a satisfactory response. According to the equivalent circuit, the main contribution arises from the bulk and film surface due to the interaction between DODAB and MBC, indicating THE sensitivity of the sensing unit. Finally, the adsorption of MBC molecules onto the film surface induced an irreversible process, although there are some frequencies at which the sensing unit response seems to be reversible, as shown by parallel coordinates. [ABSTRACT FROM AUTHOR]