Surface-enhanced Raman spectroscopy is widely used for rapid and sensitive molecular detection in chemistry and biology, but typically relies on noble metals. Here the authors report a non-stoichiometric semiconducting material with defect-rich surface that displays excellent detection limits and enhancement factors.

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Noble metal-comparable SERS enhancement from semiconducting metal oxides by making oxygen vacancies.

Dielectrics represent a new frontier for surface-enhanced Raman scattering. They can serve as either a complement or an alternative to conventional, metal-based SERS, offering key advantages in terms of low invasiveness, reproducibility, versatility, and recyclability. In comparison to metals, dielectric systems and, in particular, semiconductors are characterized by a much greater variety of parameters and properties that can be tailored to achieve enhanced Raman scattering or related effects. Light-trapping and subwavelength-focusing capabilities, morphology-dependent resonances, control of band gap and stoichiometry, size-dependent plasmons and excitons, and charge transfer from semiconductors to molecules and vice versa are a few examples of the manifold opportunities associated with the use of semiconductors as SERS-active materials. This review provides a broad analysis of SERS with dielectrics, encompassing different optical phenomena at the basis of the Raman scattering enhancement and introducing...

Enhanced Raman Scattering with Dielectrics.

Photocatalysis fundamentals and surface modification of TiO2 nanomaterials

Semiconductor-based surface-enhanced Raman spectroscopy (SERS) substrates represent a new frontier in the field of SERS. However, the application of semiconductor materials as SERS substrates is still seriously impeded by their low SERS enhancement and inferior detection sensitivity, especially for non-metal-oxide semiconductor materials. Herein, we demonstrate a general oxygen incorporation-assisted strategy to magnify the semiconductor substrate–analyte molecule interaction, leading to significant increase in SERS enhancement for non-metal-oxide semiconductor materials. Oxygen incorporation in MoS2 even with trace concentrations can not only increase enhancement factors by up to 100,000-fold compared with oxygen-unincorporated samples but also endow MoS2 with low limit of detection below 10−7 M. Intriguingly, combined with the findings in previous studies, our present results indicate that both oxygen incorporation and extraction processes can result in SERS enhancement, probably due to the enhanced charge-transfer resonance as well as exciton resonance arising from the judicious control of oxygen admission in semiconductor substrate. The application of non-metal-oxide semiconductor materials as surface-enhanced Raman spectroscopy (SERS) substrates is impeded by their low SERS enhancement and detection sensitivity. Here, the authors develop a general oxygen incorporation strategy to magnify these parameters.

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Semiconductor SERS enhancement enabled by oxygen incorporation

A Cu2 O superstructure is constructed through a recrystallization-induced self-assembly strategy. Single Cu2 O superstructure particle exhibits an outstanding surface-enhanced Raman spectroscopy performance with the limit of detection as low as 10-9 mol L-1 and metal comparable enhancement factor (8 × 105 ) due to the synergetic effect of vacancies defect-facilitated charge-transfer process and copper vacancies defect-induced electrostatic adsorption.

Ultrasensitive SERS Detection by Defect Engineering on Single Cu2O Superstructure Particle

Highly sensitive surface-enhanced Raman scattering (SERS) detection was achieved on plasmon-free TiO2 photonic artificial microarray, which can be quickly recovered under simulated solar light irradiation and repeatedly used. The sensitive detection performance is attributed to the enhanced matter-light interaction through repeated and multiple light scattering in photonic microarray. Moreover, the SERS sensitivity is unprecedentedly found to be dependent on the different light-coupling performance of microarray with various photonic band gaps, where microarray with band gap center near to laser wavelength shows a lower SERS signal due to depressed light propagation, while those with band gap edges near to laser wavelength show higher sensitivity due to slow light effect.

Improved SERS Sensitivity on Plasmon-Free TiO2 Photonic Microarray by Enhancing Light-Matter Coupling

A range of TiO 2 inverse opals with tunable macroporous size were synthesized using different sized PS (polystyrene sphere) arrays as hard templates. After a simple heating treatment in vacuum, Ti 3+ doped TiO 2 inverse opals were obtained. The materials were characterized and verified by XRD, XPS, UV–vis DRS, EPR, and SEM. The result indicated that the optical responses of TiO 2 and Ti 3+ doped TiO 2 inverse opals could be enhanced by choosing PS arrays with appropriate size as hard templates due to the slow light effect of inverse opal structure. The photocatalytic efficiency was evaluated by the photo degradation of AO7, and it is proved that the cooperation of slow light effect and Ti 3+ doping is an effective way to improve visible-light driven photocatalytic performance of TiO 2 photocatalyst.

Enhanced photocatalytic performance of TiO2 based on synergistic effect of Ti3+ self-doping and slow light effect

Ag nanowires confined in mesoporous SBA-15 show improved SERS activity towards organics detection compared with Ag nanospheres. The mild chemical transformation reaction between Ag and AgCl and photocatalytic elimination of analyte were utilized to recycle the SERS detection.

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Dianyu Qi

Papers

Improved SERS Sensitivity on Plasmon-Free TiO2 Photonic Microarray by Enhancing Light-Matter Coupling

Enhanced photocatalytic performance of TiO2 based on synergistic effect of Ti3+ self-doping and slow light effect

Sensitive and easily recyclable plasmonic SERS substrate based on Ag nanowires in mesoporous silica