Electric field-engineered bimetallic MXene for ultra-sensitive SERS sensors

Abstract

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  An electric-field modulation strategy to activate non-metallic SERS
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  Electric field gating couples PEICT and PESP pathways via electronic tailoring
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  Ti₂TaC₂ enables 10⁻¹³ M detection with a 10³-fold sensitivity gain
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  The electric-tunable SERS response can extend to diverse molecular probes

Surface-enhanced Raman scattering (SERS) is a powerful technique for trace molecular analysis, yet many non-metallic substrates are still limited by insufficient enhancement capability, making reproducible order-of-magnitude gains in sensitivity difficult to achieve. A key challenge in this field is how to cooperatively and controllably regulate the charge transfer and plasmon-associated electromagnetic enhancement, thereby overcoming the SERS performance bottleneck of conventional non-metallic substrates. In this work, we introduce external electric-field modulation as an active enhancement strategy for bimetallic MXenes. The applied field enables the near-Fermi electronic structure, carrier distribution, and surface plasmon response to be tuned after the fabrication of non-metallic SERS substrates, thereby cooperatively amplifying the photoelectric charge transfer and electromagnetic enhancement. This work establishes an electrically programmable design paradigm for SERS substrates by introducing electrical tunability, through which the charge-transfer and electromagnetic enhancement pathways can be modulated. More broadly, the developed electric-field modulation strategy could be extended to other quasi-metallic or semiconductor materials, providing a practical route to the tunable, high-sensitivity, non-noble-metal SERS sensors and advancing their trace analysis in chemical sensing, environmental monitoring, and biomedical detection.

Advances in ultra-sensitive surface-enhanced Raman scattering (SERS) substrates and SERS enhancement strategies are the two fundamental pillars for the development of SERS technology. However, broadly applicable strategies that reproducibly achieve order-of-magnitude improvements in SERS sensitivity remain scarce. Herein, we propose an electric-field modulation strategy to simultaneously stimulate photo-electric-induced charge transfer (PEICT) and surface-plasmon enhancement (PESP). This strategy increases the density of states near the E_F and induces an upward shift of E_F, thereby lowering inter-band transition barriers and promoting surface electron localization. Guided by this strategy, a series of bimetallic MXene SERS-active substrates are theoretically predicted and experimentally reported for the first time. Under cooperative excitation with a 532-nm laser and a 300-V field, Ti₂TaC₂ achieves a limit of detection (LOD) of 10⁻¹³ M and a SERS performance factor (SPF) of 2.3 × 10⁵, a three-orders-of-magnitude gain over laser-only excitation. This strategy provides a broadly applicable route to substantially enhance SERS sensitivity in non-metallic substrates.

Advances in ultra-sensitive surface-enhanced Raman scattering (SERS) substrates and SERS enhancement strategies are the two fundamental pillars for the development of SERS technology. However, broadly applicable strategies that reproducibly achieve order-of-magnitude improvements in SERS sensitivity remain scarce. Herein, we propose an electric-field modulation strategy to simultaneously stimulate photo-electric-induced charge transfer (PEICT) and surface-plasmon enhancement (PESP). This strategy increases the density of states near the E_F and induces an upward shift of E_F, thereby lowering inter-band transition barriers and promoting surface electron localization. Guided by this strategy, a series of bimetallic MXene SERS-active substrates are theoretically predicted and experimentally reported for the first time. Under cooperative excitation with a 532-nm laser and a 300-V field, Ti₂TaC₂ achieves a limit of detection (LOD) of 10⁻¹³ M and a SERS performance factor (SPF) of 2.3 × 10⁵, a three-orders-of-magnitude gain over laser-only excitation. This strategy provides a broadly applicable route to substantially enhance SERS sensitivity in non-metallic substrates.

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