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A multifunctional surface-enhanced Raman scattering (SERS) platform integrating sensitive detection and drug resistance analysis was developed for Gram-positive bacteria. The substrate was based on self-assembled Ti3C2Tx@Au NPs films and capture molecule phytic acid (IP6) to achieve specific capture of Gram-positive bacteria and different bacteria were analyzed by fingerprint signal. It had advantages of good stability and homogeneity (RSD = 8.88%). The detection limit (LOD) was 102 CFU/mL for Staphylococcus aureus and 103 CFU/mL for MRSA, respectively. A sandwich structure was formed on the capture substrate by signal labels prepared by antibiotics (penicillin G and vancomycin) and non-interference SERS probe molecules (4-mercaptobenzonitrile (2223 cm−1) and 2-amino-4-cyanopyridine (2240 cm−1)) to improve sensitivity. The LOD of Au NPs@4-MBN@PG to S. aureus and Au NPs@AMCP@Van to MRSA and S. aureus were all improved to 10 CFU/mL, with a wide dynamic linear range from 108 to 10 CFU/mL (R2 ≥ 0.992). The SERS platform can analyze the drug resistance of drug-resistant bacteria. Au NPs@4-MBN@PG was added to the substrate and captured MRSA to compare the SERS spectra of 4-MBN. The intensity inhomogeneity of 4-MBN at the same concentrations of MRSA and the nonlinearity at the different concentrations of MRSA revealed that MRSA was resistant to PG. Finally, the SERS platform achieved the determination of MRSA in blood. Therefore, this SERS platform has great significance for the determination and analysis of Gram-positive bacteria. [ABSTRACT FROM AUTHOR]

The proliferation of drug-resistant bacteria and infections such as methicillin-resistant Staphylococcus aureus (MRSA) pose a serious challenge to global healthcare. Photothermal therapy (PTT) is becoming a highly effective antimicrobial method. Compared with near infrared I (NIR-I), near infrared II (NIR-II) has deeper penetration depth, less light scattering and higher maximum permissible exposure (MPE). The selection of a photothermal agent (PTA) and laser parameters is important. Three kinds of MXenes, Nb2C, Ti3C2 and V2C, were prepared in this paper, and the extinction coefficient and photothermal conversion efficiency (PCE) of NIR-I and NIR-II were compared. The extinction coefficient of Ti3C2 (26.23 L g−1 cm−1) at 808 nm was greater than those of Nb2C (24.38 L g−1 cm−1) and V2C (19.43 L g−1 cm−1). However, V2C had a higher temperature than Nb2C at 808 nm due to its high PCE (49.26%). Nb2C had a higher extinction coefficient (24.99 L g−1 cm−1) and PCE (45.55%) at 1064 nm, resulting in the highest temperature change. High extinction coefficient and high PCE are the two important factors for an excellent PTA. To reduce laser power used in the treatment, NIR-II laser and a gelation strategy for MXenes were used. The prepared Nb2C/Gel could be rapidly heated to 62 °C at a laser power of 0.112 W (lower than MPE), and the sterilization rate for MRSA was 92.48%. A NIH-3T3 cell activity study showed that the prepared Nb2C had good biocompatibility. Nb2C/Gel has excellent antibacterial properties and it is expected that a rapid, efficient and safe biological antimicrobial strategy against bacterial infections can be established using Nb2C/Gel, especially for drug-resistant bacterial infections. [ABSTRACT FROM AUTHOR]