University of Central Florida Orlando, Florida, United States
Introduction: In vitro diagnostics (IVDs) play a pivotal role in modern healthcare. About two-thirds of medical decisions are made based on IVD test results. Yet labs and industries are continually pressed to lower costs, maintain test simplicity, and do more with less. Among various IVDs, colorimetric IVDs are broadly recognized as a class of accessible technology for medical diagnostics, owing to their great simplicities and low costs. Currently, the bottleneck of colorimetric IVD development is the relatively low detection sensitivity primarily because of the weak color signal yielded from transducers (i.e., components that are conjugated to bioreceptors and specifically generate color signal).
Materials and
Methods: In this research, the central objective is to break through the detection limit barrier of colorimetric IVDs, without compromising their simplicities and increasing costs. The key strategy is to develop unique catalytic nanoparticles (NPs) as sensitive signal transducers for IVDs. The NPs are engineered by creating a special bimetallic core-shell structure for the particles (see Figure 1). Herein, the bimetallic NPs possess strong enzyme-like catalytic activities, allowing them to generate ultra-intense color signal by catalyzing chromogenic substrates. We hypothesize that the catalytic efficiency of the NPs can be maximized through careful control over the particle morphology and elemental composition. The NPs offer facile surface modification of bioreceptors such as antibodies and display excellent stabilities, making them extremely suitable for IVDs. Significantly, the NPs can be straightforwardly applied to various colorimetric IVD platforms in similar fashions as conventional signal transducers, without involvement of additional instrument, materials and assay procedures.
Results, Conclusions, and Discussions: As showed in our preliminary work with Ni-Pt NP (J. Am. Chem. Soc., 2021, 143, 2660), an individual NP can yield ≥E7 colored products per second (i.e., catalytic constant - Kcat ≥E7 s-1), which is 10,000 times greater than Kcat of horseradish peroxidase (HRP, a typical peroxidase). This represents a record-high catalytic efficiency among all the already reported peroxidase mimics of 1-100 nm in sizes. Significantly, unlike conventional signal transducers, the activities of our NPs can be tuned and optimized by carefully controlling the elemental composition and particle morphology (e.g., size and shape). This assumption has been partially validated by our previous experimental results and calculation data (Nano Letters, 2017, 17, 5572). After surface modifications of bioreceptors, the NPs can be straightforwardly used as transducers for various colorimetric IVDs, including enzyme-linked immunosorbent assay (ELISA), lateral flow assay (LFA, also known as strip test), immunohistochemistry (IHC). For instance, we demonstrated that Ni-Pt NPs can substantially improve the sensitivity of ELISA (see Figure 2). The limit of detection of Ni-Pt NPs-based ELISA was over 300-fold lower than that of conventional HRP-based ELISA using the same antibodies. The catalytic NPs can also be used for other IVD platforms such as lateral flow assay and immunohistochemistry, providing substantially improved detection sensitivities. Notably, just like the case of gold nanoparticles used in commercial IVDs, material costs of the bimetallic NPs in this study should not be an issue in the particular application of IVD because the utilized amount of NPs is tiny (nano gram level per test), and the costs of metals (e.g., Pt and Pd) are comparable to or cheaper than Au. Furthermore, the NPs are chemically and thermally stable primarily because they are encased by inert noble metals on the surface. Such superior stabilities of transducers ensure good reliability for resultant IVDs.
