Highly sensitive electrochemical detection of cholesterol based on Au-Pt NPs/PAMAM-ZIF-67 nanomaterials

Abstract

A cholesterol biosensor was constructed by bimetallic (Au and Pt) and poly(amidoamine)-zeolite imidazole framework (PAMAM-ZIF-67). First, PAMAM-ZIF-67 nanomaterial was immobilized onto the electrode, and then Au and Pt were modified on the electrode by the electro-deposition method. Subsequently, cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) were fixed on the electrode. The stepwise modification procedures were recorded by impedance spectroscopy and voltammetry. The current response presented a linear relation to the logarithm of cholesterol content when content ranged between 0.00015 and 10.24 mM, and the minimum detection concentration reached 3 nM. The electrode was also used for the cholesterol assay in serum, which hinted at its potentially valuable in clinical diagnostics. An electrochemical biosensor based on gold nanoparticles, platinum nanoparticles, and polyamide-zeolitic imidazolate frameworks was developed for detection of cholesterol. First, polyamide-zeolitic imidazolate frameworks nanomaterial was fixed onto the electrode modified of mercaptopropionic acid by Au-S bond. Then, gold nanoparticles and platinum nanoparticles were electrodeposited on the above electrode. Subsequently, cholesterol oxidase and cholesterol esterase were co-immobilized on the surface of the modified electrode to fabricate the cholesterol biosensor. The biosensor has also been used for the measurement of cholesterol in human serum, which implied potential applications in biotechnology and clinical diagnostics.

Keywords: Biosensor; Cholesterol; Nanoparticles; Zeolitic imidazolate frameworks.

Fig. 1

Principle of the ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67 biosensor for the detection of cholesterol

Fig. 2

Characterization of PAMAM–ZIF-67. A ¹H NMR spectra of PAMAM, B SEM image of ZIF-67, C SEM image of PAMAM–ZIF-67, D FT-IR spectra of (a) ZIF-67, (b) PAMAM, (c) PAMAM–ZIF-67

Fig. 3

Electrochemical behaviors of the biosensor. A CV response of (red curve a) bare GE, (blue curve b) MPA/GE, (cyan curve c) PAMAM–ZIF-67/MPA/GE, (brown curve d) Au–Pt NPs/PAMAM–ZIF-67/MPA/GE, (green curve e) ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67/MPA/GE, (pink curve f) Ag/ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67/MPA/GE in an [Fe(CN)₆]^3−/4− solution from -0.4 to 0.8 V with a 100 mV/s scanning rate. B EIS of (red curve a) bare GE, (blue curve b) MPA/GE, (cyan curve c) PAMAM–ZIF-67/MPA/GE, (brown curve d) Au–Pt NPs/PAMAM–ZIF-67/MPA/GE, (green curve e) ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67/MPA/GE, (pink curve f) Ag/ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67/MPA/GE in PBS containing 5 mM Fe(CN)₆³⁻/⁴⁻ at 0.24 V (versus SCE) with a frequency range of 0.1–100 kHz. C Current response with the different modifications, including ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67/GE, ChOx&ChEt/PAMAM–ZIF-67/GE, ChOx&ChEt/Au NPs/GE, bare GE and ChOx&ChEt/GE. (The error bars represent the standard error of the mean (n = 3 electrodes)

Fig. 4

SEM images of A the bare electrode, B PAMAM–ZIF-67/GE, C Au–Pt NPs/PAMAM–ZIF-67/GE, D ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67/GE, E Ag/ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67/GE, F EDS images of Ag/ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67/GE

Fig. 5

A Effect of the electro-deposition time of Au–Pt NPs on the electrode. B Optimization of the concentration of Ag⁺ in the glycine buffer. C Optimization of the temperature of the deposition reaction on the electrode. D Effect of the ratio of Au and Pt on the current response. The current was recorded using LSV measurements in 0.1 M HNO₃ solution containing 0.6 M KNO₃. The error bars are the standard error of the mean (n = 3 electrodes)

Fig. 6

A Current response of the ChOx&ChEt/Au–Pt NPs/PAMAM–ZIF-67 biosensor toward cholesterol ranging from 0.3 × 10⁻⁵ to 10.24 mM. The concentration of cholesterol (0–400 nM) is given in the inset in (A). B Linear relation between current response and logarithm of cholesterol concentration. The error bars are the standard error of the mean (n = 3 electrodes)

Fig. 7

Current response of the biosensor toward cholesterol and interfering substances. The error bars are the standard error of the mean (n = 3 electrodes)