Title：Block-Polymer-Restricted Sub-nanometer Pt Nanoclusters Nanozyme-Enhanced Immunoassay for Monitoring of Cardiac Troponin I

Journal：《Analytical chemistry》

IF：7.4

Original link：https://pubs.acs.org/doi/full/10.1021/acs.analchem.3c03249

Reporter：Qingzhe Zhang, Master of Grade 2022

This paper presents an organic block surfactant (polyvinylpyrrolidone, PVP) to construct monodisperse water-stable Pt nanoclusters (Pt NCs) for an enhanced immunoassay of cardiac troponin I (cTnI). The PVP modified Pt NC nanozyme exhibited up to 16.3 U mg−1 peroxidase-mimicking activity, which was mainly attributed to the ligand modification on the surface and the electron-absorbing effect of the ligand on the Pt NCs. The PVP-modified Pt NCs have a lower OH-transition potential, as determined by density functional theory. Under optimized experimental conditions, the enhanced nanozyme immunoassay strategy exhibited an ultrawide dynamic response range of 0.005−50 ng mL−1 for cTnI targets with a detection limit of 1.3 pg mL−1 , far superior to some reported test protocols. This work provides a designable pathway for the design of artificial enzymes with high enzyme-like activity to further expand the practical range of enzyme alternatives.

Nanozymes, as nanomaterials that simulate enzyme activity under physiologically relevant conditions, are gradually becoming star products that can replace natural enzymes for biocatalysis. However, the aggregation of single-particulate nanoparticles can severely affect their exposed catalytically active sites, so that they exhibit weak enzyme-like activity. Acute myocardial infarction (AMI) has been an important global health problem for nearly two decades. In our previous report, although some low-cost integrated systems have been developed for flexible detection of cardiac troponin I (cTnI) targets in plasma samples, low sensitivity and poor working range limited their clinical use. further development in the environment.

1.Figure 1 shows the synthesis strategy, morphology, particle size, etc. of the PVP-PtNCs designed in this study, proving the successful synthesis of the material.

Figure 1.(A) Schematic synthesis of sub-nanometer Pt NCs nanozymes confined by block polymers. (B) TEM images of PVP−Pt NCs. (C) Histogram of particle size distribution of PVP−Pt NCs. (D) HRTEM image of PVP−Pt NCs, where the enlarged well-crystallized Pt (111) crystal surface in the lower right corner was illustrated. (E) Characteristic XRD images of PVP−Pt NCs. (F) Pt 4f fine XPS spectra of PVP−Pt NCs. (G) EDS spectra of PVP−Pt NCs.

2.Figure 2 explores the nature and mechanism of peroxisome-like nanoenzymes, and the three synthesized PtNC nanoenzymes were tested for activity based on TMB chromogenic reaction. The results show that 4.0 nm PtNPs are one of the candidate materials for efficient enzyme reaction immunization strategies.

Figure 2. (A) Characterization of POD-like activity of Pt NCs in a TMB−H2O2 system. (B) Catalytic activity comparison chart. (C) EPR spectra of Pt−H2O2−DMPO in the presence of antioxidant (AA) conditions. Kinetic parameters of the PVP−Pt NCs1−3 nanozyme for TMB (D) and H2O2 (E) substrates. (F) Effect of pH value on POD-like activity of Pt NCs.

3.Figure 3 shows that the developed test protocol is capable of accurately determining the concentration of cTnI in actual human samples.

Figure 3. (A) Schematic illustration of the enhanced immunoassay strategy for the colorimetric reaction catalyzed by an enzyme immunoassay protocol coupled with nanozyme catalysis. (B) Immunoincubation colorimetric response curves with different concentrations (0.005−50 ng mL−1 ) of the target cTnI protein. (C) Regression curves of colorimetric values for different concentrations of targets. (D) Selectivity of the colorimetric biosensor for cTnI (0.1 ng mL−1 ) versus CEA (10 ng mL−1 ), PSA (10 ng mL−1 ), AFP (10 ng mL−1 ), and IgG (10 ng mL−1 ). (E) In the gradient concentration (0.02−20 ng mL−1 ) plus standard recovery test, the test results of this method were compared with the recovery values of commercially available ELISA kits. (F) Contrast plots on the dynamic response range of the target through our work and the reported.

In conclusion, this paper reported herein a proof-of-concept strategy based on enzymatic product-induced free-radical elimination for nanozymes involved in a low-cost naked-eye colorimetric realization of a sensitive test for cTnI. PVP−Pt nanozymes with high POD-like activity (16.3 U mg−1 ) were synthesized by a surface engineering strategy. Moreover, charge transfer from Pt (111) to surface ligands was considered a key factor to improve the catalytic efficiency, elucidating how surface engineering modulates the mechanism of nanozyme properties identified by DFT. This strategy presents distinct advantages: (i) the reaction involves enzyme amplification of a multienzyme reaction, which can be used to improve the assay sensitivity and working range; (ii) the splitting reaction reduces the occurrence of false positives in complex reaction environments; and (iii) the sensing strategy is characterized by portability and low-cost scalability, which can be adapted to meet the needs of community-based point-of-care assays. This approach provides an effective way to develop efficient nanozyme-enhanced immunosensing strategies and provides a theoretical guidance for the construction of efficient nanocatalysts.