Colorimetric protein sensing using catalytically amplified sensor arrays

Abstract

Catalytically active iron oxide nanoparticles are used as recognition elements and signal amplifiers for the array-based colorimetric sensing of proteins. Interactions between cationic monolayers on the Fe(3) O(4) NPs and analyte proteins differentially modulates the peroxidase-like activity of Fe(3) O(4) NPs, affording catalytically amplified colorimetric signal patterns that enable the detection and identification of proteins at 50 nM.

Figure 1

a. Illustration of the Fe₃O₄ NP enzyme mimetic amplified colorimetric sensing of proteins. b. Structures of Dop-Fe₃O₄ and TMA-Fe₃O₄. c. Hydrodynamic diameter and zeta potential of Fe₃O₄ NPs in 5 mM CH₃COONa buffer at pH 5.0.

Figure 2

Normalized OD at 420 nm upon protein addition with fixed NPs concentration (25 μg/mL). a. Concentration dependent OD curve of lipase. Inset is the hydrodynamic diameter of functionalized Fe₃O₄ NPs and lipase-NP complexes. b. Normalized OD curve of lysozyme with modest permutation. Inset: hydrodynamic diameter of functionalized Fe₃O₄ NPs and lysozyme-NP complexes. Results are average of three measurements and error bars are standard deviation. The NP concentration used in the size measurement is 250 μg/mL and the protein is at a concentration of 500 nM.

Figure 3

Array-based sensing of ten proteins. a. Photograph of the color change upon addition of protein solutions at 50 nM. b. OD response (OD/OD₀ at 420 nm) patterns in the presence of proteins at 50 nM (responses are an average of five measurements and the error bars are the standard deviation). c. Canonical score plot for the OD response patterns as obtained from LDA with 95% confidence ellipses.