Mixed valence Ce-doped TiO2 with multiple energy levels and efficient charge transfer for boosted SERS performance

A novel three-dimensional porous Ag/TiO2 hybrid aerogels with high dense hot spot as effective SERS substrate for ultrasensitive detection

This research focuses on preparing a series of new TiO2/Ag hybrid aerogels with varying TiO2 contents, and demonstrates their application as ultrasensitive SERS substrates. The synthesized TiO2/Ag hybrid aerogels exhibited excellent SERS behavior when detecting 4-Mercaptobenzoic acid (4-MBA), and the calculated SERS enhancement factor (EF) was 6.34 × 106. 3D structured aerogels can create more hot spots and adsorption sites, and multiple interband chemical transfer (CT) pathways emerged and enhanced CT efficiency because of the large number of surface oxygen vacancies of meso-TiO2 NPs. Therefore, the synergy of electromagnetic field enhancement and chemical enhancement leads to SERS enhancement. In addition, the composite SERS substrate has high sensitivity, and the detection limit of adsorbed 4-MBA probe molecules reaches 10-11 M. Furthermore, the TiO2/Ag hybrid aerogels demonstrate good reproducibility with minimal standard deviation in terms of SERS signals. In addition, even after standing for 6 months, there is almost no attenuation in the SERS signal intensity, which highlights the excellent stability of this substrate. Therefore, these highly sensitive TiO2/Ag hybrid aerogels SERS substrates have important practical value in environmental monitoring, medical inspection and food supervision.

A double defects-dominated flexible TiO2 matrix for in-situ SERS sensing of antibiotic residues in aquatic ecosystem (fish & fishpond water) and their on-site degradation in flowing water

High-performance flexible semiconductor material can be used as an excellent multifunctional matrix for in-situ ultrasensitive surface-enhanced Raman scattering (SERS) detection and synchronous photocatalytic degradation of antibiotic residues in aquatic ecosystem. Here, a calcium-doped TiO2 flexible matrix with double defects (surface oxygen vacancy defect and Ti3+ energy level defect) was developed by its "in-situ one-step" hydrothermal synthesis on cotton fabric for the above purposes. Due to the joint contribution of double defects, a multi-channel charge transfer mode and a high-efficiency carrier separation are achieved, which endows flexible cotton fabric/Ca-doped TiO2 (Cot/Ca-TiO2) substrate with the greatly boosted SERS effect for in-situ detection of antibiotic residues on fish body surface and in fishpond water by a simple wiping or dipping sampling method, even for simultaneous identification of multi-component residues. The detection limits of three antibiotic residues (enrofloxacin, ciprofloxacin and enoxacin) are as low as 10-9 M, which are far lower than the EU standard. More meaningfully, the flexible Cot/Ca-TiO2 can be used as a multifunctional filter-membrane type photocatalyst for efficient on-site degradation of antibiotic residues in flowing fishpond water by a multi-grade photocatalysis means. Moreover, the flexible matrix exhibits good recyclability in both actual detection and photocatalysis.

A flexible semiconductor SERS substrate by in situ growth of tightly aligned TiO2 for in situ detection of antibiotic residues

Semiconductor materials have become a competitive candidate for surface-enhanced Raman scattering (SERS) substrate. However, powdered semiconductors are difficult to execute a fast in situ detection for trace analytes. Here, we developed a new flexible semiconductor SERS substrate by in situ densely growing anatase TiO2 nanoparticles on the surface of cotton fabric through a filtration-hydrothermal method, in which TiO2 exhibits excellent controllability in size and distribution by regulating the ratio of water to alcohol in synthesis and the number of filtration-hydrothermal repetitive cycle. Cotton fabric/TiO2 (Cot/TiO2) substrate exhibits a high SERS activity and excellent spectral repeatability. The developed substrate has an ultra-high stability that can withstand long-term preservation; it can even resist the corrosions of strong acid and alkali, as well as high temperature up to 100 °C and low temperature down to - 20 °C. The flexible substrate can be used to carry out a rapid in situ detection for quinolone antibiotic (enrofloxacin and enoxacin) residues on the fish body surface by using a simple swabbing method, with high quantitative detection potential (up to an order of magnitude of 10-7 M), and even for the simultaneous detection of both drug residues. The flexible substrate also exhibits an excellent recyclability up to 6 recycles in the actual SERS detection.

A new semiconductor heterojunction SERS substrate for ultra-sensitive detection of antibiotic residues in egg

Antibiotic residues in animal-derived food (egg) are threatening human health. Semiconductor heterojunction surface-enhanced Raman scattering (SERS) substrates can be used for ultra-sensitive detection of antibiotic residues in egg. Here, a TiO2/ZnO heterojunction was developed as a new SERS substrate based on an interface engineering strategy. Due to strong interfacial coupling and efficient carrier separating in heterostructure, utilization rate of photo-induced electrons in substrate was improved greatly, which realized the efficient charge transfer in substrate-molecule system, resulting in a prominent SERS enhancement. Taking the detection of enrofloxacin residue in egg as an example, the limit of detection (LOD) is only 13.1 μg/kg, which is far below the European Union standard, and lower than LODs of other conventional analytical methods and existing noble metal-based SERS methods. More importantly, benefiting from high sensitivity and selectivity of heterojunction and fingerprint characteristics of SERS, multiple antibiotic residues in egg can be identified simultaneously.

Controllable preparation of Ti3C2Tx/Ag composite as SERS substrate for ultrasensitive detection of 4-nitrobenzenethiol

Currently, metal carbonitride (MXene) has been identified as a hot research topic in the research area of surface-enhanced Raman scattering (SERS). In this study, Ti3C2Tx/Ag composite was fabricated as SERS substrate with different Ag contents. The fabricated Ti3C2Tx/Ag composites show good SERS behavior by detecting 4-Nitrobenzenethiol (4-NBT) probe molecules. Through calculation, the SERS enhancement factor (EF) of the Ti3C2Tx/Ag substrate was as high as 4.15 × 106. It is worth noting that the detection limit of 4-NBT probe molecules can be achieved ultralow concentration of 10-11 M. In this system, electromagnetic enhancement mechanism and chemical enhancement mechanism have synergistic effects on SERS phenomenon. Meanwhile, the Ti3C2Tx/Ag composite substrate exhibited good SERS reproducibility. In addition, the SERS detection signal hardly changed after 6 months of natural standing, and the substrate showed good stability. This work suggests that the Ti3C2Tx/Ag substrate could be used as a sensitivity SERS sensor for practical application, and could be applied in the field of environmental monitoring.