Stable SERS substrate based on highly reflective metal liquid-like films wrapped hydrogels for direct determination of small molecules in a high protein matrix

SERS detection of thiram using polyacrylamide hydrogel-enclosed gold nanoparticle aggregates

The development of sensitive and long-term signal-stable plasmonic substrates is vital to the in-field application of the surface-enhanced Raman spectroscopy (SERS) technique. The colloidal gold nanoparticles (AuNPs) system is commonly used in SERS detection, but it shows less signal stability and reproducibility due to the uncontrollable aggregation of nanoparticles by adding aggregating agents in SERS detection. In this study, we developed a new SERS detection platform based on polyacrylamide hydrogel-enclosed plasmonic gold nanoparticle aggregates (PAH-AuANs). In the system, the formation of PAH can rapidly stabilize the gold nanoparticle aggregates, avoiding the over-aggregation or precipitation of AuNPs. With the PAH concentration in the range of 6-10 % and AuNPs at the concentration of 0.2 nM, the resulting PAH-AuNAs platform exhibited both sensitive SERS activity and excellent SERS signal stability. The relative standard deviation of the 4-MBA probe SERS signal collected from the PAH-AuNAs platform was lower than 3 %. The limit of detection for the pesticide thiram was down to 0.38 μg/L with a handheld Raman spectrometer. Moreover, the procedure for preparing the PAH-AuNAs platform was easy to handle, offering a new strategy for in-field detection of environmental contaminants with a handheld Raman spectrometer in the future.

SERS and EC-SERS detection of local anesthetic procaine using Pd loaded highly reduced graphene oxide nanocomposite substrate

The localized surface plasmon resonance (LSPR) excitations are critical towards achieving sizable spectral enhancements of the Raman scattered light. Herein, the synthesis of palladium-based highly reduced graphene oxide (Pd-HRG) with LSPR properties as an effective surface-enhanced Raman scattering (SERS) substrate and its utility in the highly sensitive detection of procaine are reported. The concentration detection of procaine samples was optimized by applying a set of pre-concentration parameters. The Pd-HRG nanocomposite showed a remarkable LSPR response with a Raman enhancement factor of 8.7 × 10². The Pd-HRG is employed to modify fluorine doped tin oxide electrode (Pd-HRG/FTO), resulted with an enhancement factor of 7.5 × 10⁴ corresponding to the EC-SERS technique. The electronic and surface properties of synthesized Pd-HRG and functionalized FTO electrode were evaluated using Raman, infrared, EIS, XRD, FESEM and EDX techniques. Quantum chemical calculations were carried out to elaborate on the nature of interaction of procaine molecules with a nanostructured surface model. Pd-HRG, with an efficient and cost-effective fabrication, can be considered as a promising EC-SERS substrate for the detection of organic therapeutic drugs.

MOF-Derived hierarchical porous 3D ZnO/Ag nanostructure as a reproducible SERS substrate for ultrasensitive detection of multiple environmental pollutants

The three-dimensional (3D) surface-enhanced Raman scattering (SERS) substrate for trace molecule detection has recently attracted considerable interest; however, these substrates generally either show poor sensitivity or require a complex preparation process. In this work, we have fabricated a 3D ZnO/Ag substrate using porous zeolite imidazole frameworks (ZIF-8) derived ZnO nanoparticles (NPs) followed by evaporation-induced self-assembly of Ag NPs over it, which can detect multiple environmental pollutants by a facile and cost-effective method. This 3D porous substrate showed an ultra-sensitivity for detecting various types of molecules, e.g., rhodamine 6G (R6G), crystal violet (CV), tetracycline, and thiram, simultaneously suggesting its generality. Notably, the lowest detectable concentration (LDC) attained for R6G is 10^-13 M, and the enhancement factor (EF) reaches up to 1.8 × 10⁸. The most important reason for ultra-sensitivity is that ZnO derived from ZIF-8 has a hierarchical porous structure and large surface area to provide more "hot spots" and absorb more probe molecules. Consequently, the ZnO/Ag nanostructures show excellent photocatalytic performance. The detected probe molecules could be completely degraded in situ within a short UV exposure time (<30 min), thereby enabling outstanding reusability of this substrate. Finite-different time-domain (FDTD) simulations were used to understand the underlying mechanism of the substrate by calculating electric fields and hot spot distributions. The simulations suggested that the widespread hot spots structures on the substrate are the main reason for its SERS ultra-sensitivity.

Simultaneous and ultra-sensitive SERS detection of SLPI and IL-18 for the assessment of donor kidney quality using black phosphorus/gold nanohybrids

Due to the global challenge of donor kidney shortage, expanding the pool of deceased donors has been proposed to include expanded criteria donors. However, the lack of methods to precisely measure donor kidney injury and predict the outcome still leads to high discard rates and recipient complications. As such, evaluation of deceased donor kidney quality is critical prior to transplantation. Biomarkers from donor urine or serum provide potential advantages for the precise measure of kidney quality. Herein, simultaneous detection of secretory leukocyte peptidase inhibitor (SLPI) and interleukin 18 (IL-18), two important kidney injury biomarkers, has been achieved, for the first time, with an ultra-high sensitivity using surface enhanced Raman scattering (SERS). Specifically, black phosphorus/gold (BP/Au) nanohybrids synthesized by depositing Au nanoparticles (NPs) onto the BP nanosheets serve as SERS-active substrates, which offer a high-density of inherent and accessible hot-spots. Meanwhile, the nanohybrids possess biocompatible surfaces for the enrichment of target biomarkers through the affinity with BP nanosheets. Quantitative detection of SLPI and IL-18 were then achieved by characterizing SERS signals of these two biomarkers. The results indicate high sensitivity and excellent reproducibility of this method. The limits of detection reach down to 1.53×10^-8 mg/mL for SLPI and 0.23×10^-8 mg/mL for IL-18. The limits of quantification are 5.10×10^-8 mg/mL and 7.67×10^-9 mg/mL for SLPI and IL-18. In addition, simultaneous detection of these biomarkers in serum was investigated, which proves the feasibility in biologic environment. More importantly, this method is powerful for detecting multiple analytes inheriting from excellent multiplexing ability of SERS. Giving that the combined assessment of SLPI and IL-18 expression level serves as an indicator of donor kidney quality and can be rapidly and reproducibly conducted, this SERS-based method holds great prospective in clinical practice.