Plasmonic Rare-Earth Nanosheets as Surface Enhanced Raman Scattering Substrates with High Sensitivity and Stability for Multicomponent Analysis

Thermoelectrically Driven Dual-Mechanism Regulation on SERS and Application Potential for Rapid Detection of SARS-CoV-2 Viruses and Microplastics

Electric-induced surface-enhanced Raman scattering (E-SERS) has been widely studied for its flexible regulation of SERS after the substrate is prepared. However, the enhancement effect is not sufficiently high in the E-SERS technology reported thus far, and no suitable field of application exists. In this study, a highly sensitive thermoelectrically induced SERS substrate, Ag/graphene/ZnO (AGZ), was fabricated using ZnO nanoarrays (NRs), graphene, and Ag nanoparticles (NPs). Applying a temperature gradient to the ZnO NRs enhanced the SERS signals of the probe molecules by a factor of approximately 20. Theoretical and experimental results showed that the thermoelectric potential enables the simultaneous modulation of the Fermi energy level of graphene and the plasma resonance peak of Ag NPs, resulting in a double enhancement in terms of physical and chemical mechanisms. The AGZ substrate was then combined with a mask to create a wearable thermoelectrically enhanced SERS mask for collecting SARS-CoV-2 viruses and microplastics. Its SERS signal can be enhanced by the temperature gradient created between a body heat source (∼37 °C) and a cold environment. The suitability of this method for virus detection was also examined using a reverse transcription-polymerase chain reaction and SARS-CoV-2 virus antigen detection. This work offers new horizons for research of E-SERS, and its application potential for rapid detection of the SARS-CoV-2 virus and microplastics was also studied.

Fe and Cu Intercalations Enhance SERS of MoO3 through Different Mechanistic Pathways

Surface Enhanced Raman spectroscopy (SERS) is a molecular-specific analytical technique with various applications. Although electromagnetic (EM) and chemical (CM) mechanisms have been proposed to be the main origins of SERS, exploring highly sensitive SERS substrates with well-defined mechanistic pathways remains challenging. Since surface and electronic structures of substrates were crucial for SERS activity, zero-valent transition metals (Fe and Cu) were intercalated into MoO3 to modulate its surface and electronic structures, leading to unexceptional high enhancement factors (1.0×108 and 1.1×1010 for Fe-MoO3 and Cu-MoO3 , respectively) with decent reproducibility and stability. Interestingly, different mechanistic pathways (CM and EM) were proposed for Fe-MoO3 and Cu-MoO3 according to mechanistic investigations. The different mechanisms of Fe-MoO3 and Cu-MoO3 were rationalized by the electronic structures of the intercalated Fe(0) and Cu(0), which modulates the surface and electronic structures of Fe-MoO3 and Cu-MoO3 to differentiate their SERS mechanisms.

Plasmonic Coupling of Au Nanoclusters on a Flexible MXene/Graphene Oxide Fiber for Ultrasensitive SERS Sensing

High sensitivity, good signal repeatability, and facile fabrication of flexible surface enhanced Raman scattering (SERS) substrates are common pursuits of researchers for the detection of probe molecules in a complex environment. However, fragile adhesion between the noble-metal nanoparticles and substrate material, low selectivity, and complex fabrication process on a large scale limit SERS technology for wide-ranging applications. Herein, we propose a scalable and cost-effective strategy to a fabricate sensitive and mechanically stable flexible Ti₃C₂T_x MXene@graphene oxide/Au nanoclusters (MG/AuNCs) fiber SERS substrate from wet spinning and subsequent in situ reduction processes. The use of MG fiber provides good flexibility (114 MPa) and charge transfer enhancement (chemical mechanism, CM) for a SERS sensor and allows further in situ growth of AuNCs on its surface to build highly sensitive hot spots (electromagnetic mechanism, EM), promoting the durability and SERS performance of the substrate in complex environments. Therefore, the formed flexible MG/AuNCs-1 fiber exhibits a low detection limit of 1 × 10^-11 M with a 2.01 × 10⁹ enhancement factor (EF_exp), signal repeatability (RSD = 9.80%), and time retention (remains 75% after 90 days of storage) for R6G molecules. Furthermore, the l-cysteine-modified MG/AuNCs-1 fiber realized the trace and selective detection of trinitrotoluene (TNT) molecules (0.1 μM) via Meisenheimer complex formation, even by sampling the TNT molecules at a fingerprint or sample bag. These findings fill the gap in the large-scale fabrication of high-performance 2D materials/precious-metal particle composite SERS substrates, with the expectation of pushing flexible SERS sensors toward wider applications.

Two-dimensional MBenes with ordered metal vacancies for surface-enhanced Raman scattering

As an emerging class of two-dimensional (2D) materials, MBenes show enormous potential for optoelectronic applications. However, their use in molecular sensing as surface-enhanced Raman scattering (SERS)-active material is unknown. Herein, for the first time, we develop a brand-new high-performance MBene SERS platform. Ordered vacancy-triggered highly sensitive SERS platform with outstanding signal uniformity based on a 2D Mo_4/3B₂ MBene material was designed. The 2D Mo_4/3B₂ MBene presented superior SERS activity to most of the semiconductor SERS substrates, showing a remarkable Raman enhancement factor of 3.88 × 10⁶ and an ultralow detection limit of 1 × 10^-9 M. The underlying SERS mechanism is revealed from systematic experiments and density functional theory calculations that the ultrahigh SERS sensitivity of 2D Mo_4/3B₂ MBene is derived from the efficient photoinduced charge transfer process between MBene substrates and adsorbed molecules. The abundant electronic density of states near the Fermi level of 2D Mo_4/3B₂ MBene enables its Raman enhancement by a factor of 100 000 times higher than that of the bulk MoB. Consequently, the 2D Mo_4/3B₂ MBene could accurately detect various trace chemical analytes. Moreover, with ordered metal vacancies in the 2D Mo_4/3B₂ MBene, uniform charge transfer sites are formed, resulting in an outstanding signal uniformity with a relative standard deviation down to 6.0%. This work opens up a new horizon for the high-performance SERS platform based on MBene materials, which holds great promise in the field of chemical sensing.

Recent Advances in Responsive Membrane Functionalization Approaches and Applications

In recent years, significant advances have been made in the field of functionalized membranes. With the functionalization using various materials, such as polymers and enzymes, membranes can exhibit property changes in response to an environmental stimulation, such as heat, light, ionic strength, or pH. The resulting responsive nature allows for an increased breadth of membrane uses, due to the developed functionalization properties, such as smart-gating filtration for size-selective water contaminant removal, self-cleaning antifouling surfaces, increased scalability options, and highly sensitive molecular detection. In this review, new advances in both fabrication and applications of functionalized membranes are reported and summarized, including temperature-responsive, pH-responsive, light-responsive, enzyme-functionalized, and two-dimensional material-functionalized membranes. Specific emphasis was given to the most recent technological improvements, current limitations, advances in characterization techniques, and future directions for the field of functionalized membranes.