Semiconductor SERS of diamond

Snowflake Cu2S@ZIF-67: A novel heterostructure substrate for enhanced adsorption and sensitive detection in BPA

Developing semiconductor substrates with superior stability and sensitivity is challenging in surface-enhanced Raman scattering (SERS) research. Here, a snowflake Cu2S@ZIF-67 heterostructure was fabricated using a straightforward method, exhibiting a notable enhancement factor of 9.0 × 109 and a limit of detection (LOD) of 10-14 M for methylene blue (MB). In addition, the Cu2S@ZIF-67 heterostructure substrate demonstrates outstanding homogeneity (relative standard deviation (RSD) = 9.2%) and stability (120 days). Employing Cu2S generates highly sensitive hotspots via an electromagnetic (EM) mechanism, and the growth of ZIF-67 on its surface augments the adsorption capacity and charge transfer capability (chemical mechanism, CM), thereby enhancing the SERS detection sensitivity. Furthermore, the Cu2S@ZIF-67 heterostructure, which was used as a SERS substrate, facilitated the detection of bisphenol A (BPA) with an LOD of 10-11 M. The Cu2S@ZIF-67 heterostructure substrate has excellent selectivity and anti-interference, which is very suitable for BPA detection in complex environment applications. The accuracy of the Cu2S@ZIF-67 heterostructure as a SERS substrate for detecting BPA in real water samples (water bottles, tap water, and pure milk) was confirmed by comparison with high-performance liquid chromatography (HPLC). These results demonstrate that through the rational design of heterostructures can achieve the quantitative and accurate detection of hazardous substances in food and the environment can be achieved.

Resonance-Assisted Surface-Enhanced Raman Spectroscopy Amplification on Hierarchical Rose-Shaped MoS2/Au Nanocomposites

Surface-enhanced Raman spectroscopy (SERS) has emerged as a highly sensitive trace detection technique in recent decades, yet its exceptional performance remains elusive in semiconductor materials due to the intricate and ambiguous nature of the SERS mechanism. Herein, we have synthesized MoS2 nanoflowers (NFs) decorated with Au nanoparticles (NPs) by hydrothermal and redox methods to explore the size-dependence SERS effect. This strategy enhances the interactions between the substrate and molecules, resulting in exceptional uniformity and reproducibility. Compared to the unadorned Au nanoparticles (NPs), the decoration of Au NPs induces an n-type effect on MoS2, resulting in a significant enhancement of the SERS effect. This augmentation empowers MoS2 to achieve a low limit of detection concentration of 2.1 × 10-9 M for crystal violet (CV) molecules and the enhancement factor (EF) is about 8.52 × 106. The time-stability for a duration of 20 days was carried out, revealing that the Raman intensity of CV on the MoS2/Au-6 substrate only exhibited a reduction of 24.36% after undergoing aging for 20 days. The proposed mechanism for SERS primarily stems from the synergistic interplay among the resonance of CV molecules, local surface plasma resonance (LSPR) of Au NPs, and the dual-step charge transfer enhancement. This research offers comprehensive insights into SERS enhancement and provides guidance for the molecular design of highly sensitive SERS systems.

Surfactant-free interfacial growth of graphdiyne hollow microspheres and the mechanistic origin of their SERS activity

As a two-dimensional carbon allotrope, graphdiyne possesses a direct band gap, excellent charge carrier mobility, and uniformly distributed pores. Here, a surfactant-free growth method is developed to efficiently synthesize graphdiyne hollow microspheres at liquid‒liquid interfaces with a self-supporting structure, which avoids the influence of surfactants on product properties. We demonstrate that pristine graphdiyne hollow microspheres, without any additional functionalization, show a strong surface-enhanced Raman scattering effect with an enhancement factor of 3.7 × 107 and a detection limit of 1 × 10-12 M for rhodamine 6 G, which is approximately 1000 times that of graphene. Experimental measurements and first-principles density functional theory simulations confirm the hypothesis that the surface-enhanced Raman scattering activity can be attributed to an efficiency interfacial charge transfer within the graphdiyne-molecule system.

Nb2C MXene self-assembled Au nanoparticles simultaneously based on electromagnetic enhancement and charge transfer for surface enhanced Raman scattering

Recent years, two-dimensional transition metal carbonitrides (MXene) have attracted much attention in the field of surface-enhanced Raman scattering (SERS). However, the relatively low enhancement of MXene is a major challenge. Herein, Nb₂C-Au NPs nanocomposites were prepared by electrostatic self-assembly method, which have a synergistically conjugated SERS effect. The EM hot spots of Nb₂C-Au NPs are significantly enlarged and expanded, while the surface Fermi level is decreased. This synergistic effect could improve the SERS performance of the system. Consequently, for the dye molecules CV and MeB, the detection limits reach 10^-10 M and 10^-9 M, respectively, while for biomolecule adenine, the detection limit is as low as 5 × 10^-8 M. The results also show the good concentration-dependent linearity, uniformity, reproducibility and stability of SERS substrate. Nb₂C-Au NPs could be a fast, sensitive and stable SERS platform for label-free and non-destructive detection. This work may expand the application of MXene based materials in the field of SERS.

Surface enhanced Raman scattering of adsorbates on Au-CsPbIBr2 perovskite-based nanocomposites: charge-transfer and electromagnetic enhancement

In this study, perovskite-based nanocomposites as surface enhanced Raman scattering substrates were designed by physically sputtering Au nanoparticles onto fabricated all-inorganic CsPbIBr₂ perovskite films, which provide much stronger SERS signals as compared to normal Au or perovskite substrates. Their synergism enhancement mechanisms and influence factors, including hybrid layer sequence, fabrication parameters and excitation source, are discussed. In addition, the prepared composite substrate exhibits excellent uniformity, reproducibility and time stability. This study promotes an easily prepared perovskite-based substrate for SERS-related applications and develops further understanding of molecule-semiconductor-noble metal nanostructure interfacial interactions.

A universal strategy for the incorporation of internal standards into SERS substrates to improve the reproducibility of Raman signals

The uneven distribution of metal nanoparticles is a vital influencing factor in the poor uniformity of surface-enhanced Raman scattering (SERS) substrates, which is a challenge in SERS quantitative analysis. Recent reports showed that the reproducibility of a nonuniform SERS substrate can be effectively improved by the use of an internal standard (IS). However, most of these approaches require the investment of time for precise regulation, and those approaches based on the addition of an IS are specific to a certain substrate. In this work, we proposed a simple, rapid and universal method to incorporate an IS into a SERS substrate for improving the reproducibility of Raman signals based on the systematic evaluation of the influencing factors of the competitive adsorption between the IS and the target analytes. Following the proposed pressure drop-coating (PDC) method, an IS-modified gold nanobipyramids (Au NBPs)/anodic aluminum oxide (AAO) SERS substrate was fabricated within 1 min, showing high reproducibility of Raman signals. In addition, the IS-modified Au NBPs/AAO SERS substrate was successfully applied to analyze thiram in freshly squeezed apple juice and the result showed a stable Raman signal with a relative standard deviation of less than 6.00%. What is more, three different commercial SERS chips were modified with an IS molecule using the PDC method. Compared to the traditional SERS chips, the Raman signal reproducibility of the functionalized SERS chips was improved significantly. Since the addition of an IS is not based on a certain substrate, the proposed approach could be useful for all the researchers working in the field of SERS.

Plasmonic hollow fibers with distributed inner-wall hotspots for direct SERS detection of flowing liquids

Plasmonic hollow fibers are fabricated by coating silver-/ gold-alloyed nanoparticles (Ag-Au-ANPs) onto the inner walls of hollow fibers. In this Letter, the Ag-Au-ANPs were synthesized chemically and dissolved in acetone to prepare a colloidal solution, flowed subsequently through the hollow fiber multiple times so that a thin layer of colloidal Ag-Au-ANPs was produced on the inner wall. Annealing at 400°C enabled melting/aggregation of the metallic nanoparticles and consequent formation of closely arranged plasmonic nanostructures fixed solidly on the inner wall. A surface-enhanced Raman scattering (SERS) mechanism was thus established for the liquids flowing through the hollows. The SERS measurements show an enhancement factor >10⁴ for such plasmonic hollow fibers in the direct detection of R6G/ethanol solutions. Confinement of the excitation laser energy inside the hollow space represents an additional contribution to the enhancement mechanism. This is a promising design for the direct on-site SERS detection of molecules in flowing liquids with low concentrations.

A mixed valence state Mo-based metal–organic framework from photoactivation as a surface-enhanced Raman scattering substrate

In this work, a facile method for a mixed valence state Mo-base metal-organic framework from photo activation (UV Mo-MOF) was proposed and employed as a SERS substrates with molecule enrichment property.

Substrates for Surface-Enhanced Raman Scattering Formed on Nanostructured Non-Metallic Materials: Preparation and Characterization

The efficiency of the generation of Raman spectra by molecules adsorbed on some substrates (or placed at a very close distance to some substrates) may be many orders of magnitude larger than the efficiency of the generation of Raman spectra by molecules that are not adsorbed. This effect is called surface-enhanced Raman scattering (SERS). In the first SERS experiments, nanostructured plasmonic metals have been used as SERS-active materials. Later, other types of SERS-active materials have also been developed. In this review article, various SERS substrates formed on nanostructured non-metallic materials, including non-metallic nanostructured thin films or non-metallic nanoparticles covered by plasmonic metals and SERS-active nanomaterials that do not contain plasmonic metals, are described. Significant advances for many important applications of SERS spectroscopy of substrates based on nanostructured non-metallic materials allow us to predict a large increase in the significance of such nanomaterials in the near future. Some future perspectives on the application of SERS substrates utilizing nanostructured non-metallic materials are also presented.

Recent Development of SERS Technology: Semiconductor-Based Study

As a new analytical technology, surface-enhanced Raman scattering (SERS) has received increasing attention, and researchers have discovered the importance of SERS-active materials. Considerable effort has been made by researchers to develop multiperformance and multipurpose SERS-active substrates ranging from coinage metals to transition metals and semiconductor materials. SERS-active substrates are critical for obtaining accurate and reproducible spectral information. Among all the substrate materials, semiconductors are considered one of the most promising materials, as they exhibit high chemical stability, good biocompatibility, high carrier mobility, and good controllability during fabrication. Here, we provide an overview of SERS enhancement mechanisms based on semiconductor materials, such as inorganic semiconductors, metal/semiconductor composites, and organic semiconductors.

Si1-xGex nanoantennas with a tailored Raman response and light-to-heat conversion for advanced sensing applications

Active light-emitting all-dielectric nanoantennas recently have demonstrated great potential as highly efficient nanoscale light sources owing to their strong luminescent and Raman responses. However, their large-scale fabrication faces a number of problems related to productivity limits of existing lithography techniques. Thus, high-throughput fabrication strategies allowing in a facile way to tailor of the nanoantenna emission and thermal properties in the process of their fabrication are highly desirable for various applications. Here, we propose a cost-effective approach to large-scale fabrication of Si1-xGex alloyed Mie nanoresonators possessing an enhanced inherent Raman response which can be simply tailored via tuning the Ge concentration. Moreover, by tailoring the relative Ge composition one can gradually change a complex refractive index of the produced Si1-xGex alloy, which affects the ratio between radiative and nonradiative losses in Si1-xGex nanoantennas, which is crucial for optimization of their optical heating efficiency. Composition-tunable Si1-xGex nanoantennas with an optimized size, light-to-heat conversion and Raman response are implemented for non-invasive sensing of 4-aminothiophenol molecules with a temperature feedback modality and high subwavelength spatial resolution. The results are important for advanced multichannel optical sensing, providing information on analyte's composition, analyte-nanoantenna temperature response and spatial position.