Title：Electron Transfer-Driven Nanozymes Boost Biosensor Sensitivity via a Synergistic Signal Amplification Strategy
Journal: ACS Nano
IF: 16
Original link：DOI: 10.1021/acsnano.5c00430
Reporter：Shaohe Chang-23-master
The conventional gold nanoparticles (AuNPs) with insufficient brightness face substantial challenges in developing a sensitive lateral flow immunoassay (LFIA). Herein, multibranched manganese−gold (Mn−Au) nanoparticles (MnAuNPs) with a Au core−Mn shell nanostructure were synthesized by a one-pot method. The Mn shell of valence-rich and Au core of high electron transfer efficiency endowed MnAuNPs with oxidase-like activity, which oxidized 3,3′,5,5′-tetramethylbenzidine (TMB) only by electron transfer. Ox-TMB, which was the oxidation product ofTMB, is an excellent photothermal agent. Furthermore, the synergistic photothermal effect of ox-TMB and MnAuNPs significantly enhanced the photothermal conversion efficiency. The synergistic photothermal effect of multibranched MnAuNPs and ox-TMB has enabled highly sensitive quantitative detection. The LFIA based on MnAuNPs (cascade LFIA) has achieved sensitive detection of Escherichia coli O157:H7. The entire detection process was completed in 25 min. The limit of detection of cascade LFIA was 239 CFU mL−1, which was 37.21-fold lower than that of AuNPs-LFIA (8892 CFU mL−1). The recoveries of cascade LFIA were 82.63−111.67%, with coefficients of variation of 4.28−14.19%. Overall, this work suggests the potential of MnAuNPs and ox-TMB in the development of sensitive LFIA and broadens the biosensing strategies for point-of-care testing.
Point-of-care testing (POCT) is frequently employed across disease diagnosis, environmental monitoring, and food safety testing.1,2 Among the existing POCT, lateral flow immunoassay (LFIA) is widely used owing to its strong alignment with the ASSURED criteria (affordable, sensitive, specific, userfriendly, rapid and robust, equipment-free or simple, and deliverable to end user).3 However, the sensitivity of conventional LFIAs, which are based on colorimetric nanoparticles like gold nanoparticles (AuNPs)4,5 and latex beads,6 remains limited due to the inadequate brightness of these nanoparticles. Currently, two kinds of key strategies are employed to improve the sensitivity of LFIA. One strategy is the introduction of more sensitive signal output modalities (such as fluorescence, surface-enhanced Raman scattering, and photothermal signal).7−9 The other strategy is to amplify colorimetric signals (nanozyme amplification, metal in situ growth, and nanomaterial accumulation) of LFIA.10−12 Prior investigations have demonstrated that the LFIA based on photothermal signals could significantly enhance detection sensitivity. For example, Zhang et al. synthesized bimetallic Ag−Au urchin-like hollow nanospheres and used them in photothermal LFIA, which achieved highly sensitive detection of Escherichia coli O157:H7 (E. coli O157:H7).13 Atta et al. developed a photothermal LFIA based on gold nanostars for the detection of troponin I, achieving a limit of detection (LOD) of 5.5 pg mL−1, which was 1000-fold more sensitive than the AuNPs-LFIA.14 Therefore, the introduction of a photothermal signal in LFIA is beneficial in terms of improving detection sensitivity.
Recently, nanozymes have garnered significant attention for in vitro diagnostics and in vivo therapy due to their strong catalytic ability, good biocompatibility, and optical proper ties.15,16 They exhibit enormous potential as the colorimetric signal label for improving the sensitivity and application range of conventional LFIAs because of their remarkable colorimetric and catalytic properties.17 3,3′,5,5′-Tetramethylbenzidine (TMB) could be served as a substrate for simulating peroxidase.18,19 Interestingly, ox-TMB, which is the oxidation product of TMB, could be served as a type of near-infrared (NIR) photothermal agent and employed in some photothermal sensors.20,21 Therefore, it is feasible to develop nanozymes that exhibit superior photothermal performance to improve detection sensitivity. Previous studies have shown that multibranched nanoparticles possessed superior photothermal performance and colorimetric ability.22,23 Consequently, the development of multibranched nanoparticles has the potential to improve the sensitivity of LFIA. The LFIA based on nanozymes significantly enhances the detection sensitivity of LFIA through the synergistic colorimetric effect of nanozymes and ox-TMB. Inspired by this synergistic signal amplification, the coexistence of multibranch nanozymes with excellent photothermal performance and NIR photothermal agent ox-TMB in LFIA may be beneficial for enhancing the detection sensitivity of photothermal LFIA.
Herein, we synthesized multibranched manganese−gold nanoparticles (MnAuNPs) by a one-pot method. The structure of the Mn shell of valence-rich and Au core of high electron transfer efficiency conferred MnAuNPs with oxidase-like activity, which oxidized the TMB exclusively through electron transfer. The oxidation product ox-TMB not only displayed a colorimetric property but also possessed photothermal performance. Furthermore, the multibranched structure endowed MnAuNPs with photothermal performance. The synergistic photothermal effect of ox-TMB and multibranched MnAuNPs was conducive to improving the photothermal conversion efficiency. Subsequently, MnAuNPs were employed to construct photothermal LFIA for the sensitive detection of E. coli O157:H7, which was one of the major foodborne pathogenic bacteria and posed a serious threat to human health and the global economy.24 The MnAuNPs might serve as a promising signal label in LFIA, offering valuable insights into the development of sensitive LFIA.
1. Synthesis and Characterization of the MnAuNPs.
2. Investigation of Oxidase-like Activity of the MnAuNPs.
3. Investigation of the Photothermal Performance of MnAuNPs and ox-TMB.
4. Feasibility and Principle of Cascade LFIA.
5. Analytical Performance of the Cascade LFIA.
In summary, we successfully synthesized MnAuNPs nanozymes with a core−shell nanostructure, which oxidated TMB by triggering electron transfer from the inner Au core to the outer Mn shell. MnAuNPs exhibited a higher antibody conjugation capability, superior oxidase-like activity, and excellent photothermal performance. Furthermore, the synergistic photothermal effect of ox-TMB and MnAuNPs could significantly enhance the photothermal performance of MnAuNPs@ox-TMB. Subsequently, MnAuNPs were applied to the LFIA platform for the detection of E. coli O157:H7. The LOD of cascade LFIA was 239 CFU mL−1, which was 37.21fold lower than that of AuNPs-LFIA (8892 CFU mL−1). The recoveries of E. coli O157:H7 in actual samples detected by cascade LFIA were 82.63−111.67%, and the coefficient of variations was 4.28−14.19%. This study confirmed the viability of employing the synergistic photothermal effect of ox-TMB and MnAuNPs to significantly improve the sensitivity of LFIA and broaden the biosensing strategies for point-of-care testing.