Novel Imprinted Metallic Nanozymes Based Nanosensor with Fast Catalytic Activity and Specificity for Cortisol
Authors: Pandey Indu , Sonawane Apurva , Bhansali Shekhar 
Published: May 2020

Introduction

Cost effective tailoring of inorganic nanoparticles (nanozymes) that mimics enzymatic reaction at diverse physiological condition needs a new approach for sensor development. Developing a feature of enzymes in nanozymes containing analyte selective pockets is challenging. Many reported methods using bio-ligands (aptamers, peptides, antibodies) are defeating the stability and cheap feature of nanozymes [1-3]. To address the challenges in synthesis of enzyme mimicked nanozymes, we proposed multifunctional imprinted metallic nanozymes for selective and catalytic sensing of cortisol. The improved biomimetic detection of cortisol at ppm level in artificial biological samples (blood, saliva) was performed by imprinted metallic nanozymes integrated sensor. Cortisol is the stress biomarker, and provides an option to monitor the physiological and emotional strain [4]. Thus, instant stress can be accurately measured by using the proposed nanosensor.

Synthesis of imprinted metallic nanozymes on gold electrode

Gold electrode was kept in 20 mL of acid mixture (0.05 mM sulphuric acid and 0.1 mM nitric acid) for 25 minutes. Cleaned gold electrode was used as working electrode, along with Silver electrode (reference electrode) and Platinum wire (counter electrode) for insitu synthesis of imprinted metallic nanozymes using electrochemical method. 50 mL solution containing copper sulphate 0.05 mM) along with aniline (0.05mM) solution at pH 7.4 was electropolymerized for 20 cycles in presence of cortisol (Fig.1 A section (I)). The decrease in the current indicates that the aggregation of nanoparticles increased with the number of scan cycles. Washing of cortisol was performed by ethanol solution to create selective binding pockets in metallic nanozymes. As a control in absence of cortisol, metallic nanozymes synthesis were named for non-imprinted metallic nanozymes (Fig. 1B, section (I)) was also synthesized keeping above mentioned identical experimental condition. Absence of well-defined cortisol peak in cyclic voltammogram (Fig. 1B, section (I)) indicates the formation of non-imprinted metallic nanozymes

Morphological Characterization

A typical SEM images of imprinted metallic nanozymes with cortisol at lower and higher magnification (Fig. 1A, B, section (II) and metallic nanozymes with binding pockets (Fig. 2C, section (II)) are shown. Gold electrode modified metallic nanoparticles appeared as white droplets with size (70-80 nm) (Fig. 1A section (II)). High magnified SEM image (Fig. 1B, section (II)) reveals the controlled coating of nanozymes on gold electrode. Imprinted metallic nanozyme surface exhibits pores, indicating binding pockets of cortisol.

Electrochemical analysis of cortisol in artificial human samples

Typical quantitative sensing of cortisol was performed in artificial sweat and blood samples of human in phosphate buffer solution (pH 7.4) using differential pulse voltammetry. The recovery percentage of cortisol on proposed sensor was calculated by standard addition method [5]. The obtained recovery results for both samples are tabulated in Table 1. Cortisol recovery % revealed that the proposed sensor could be used as wearable device for cortisol analysis in sweat.

Conclusions

Inorganic nanozymes could provide cost effective, scalable sensing platform with good selectivity towards cortisol. Selective binding pockets for cortisol were successfully developed in nanozymes with good catalytic property and recovery. Obtained results insights into easy monitoring of cortisol and enables the new approach of developing scalable sensor with improve accuracy. These excellent properties of proposed nanosensor could be useful for fabrication of a light weight flexible reusable wearable device.

References:

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[2] P. Zhang, D. Sun, A. Cho, S. Weon, S. Lee, J. Lee, J. W. Han, D.-P. Kim and W. Choi, Modified carbon nitride nanozyme as bifunctional glucose oxidase-peroxidase for metal-free bioinspired cascade photocatalysis, Nature Communications vol. 10, Article number: 940 (2019), DOI: 10.1021/jacs.7b00601.

[3] Z. Zhang, X. Zhang, B. Liu, and J. Liu, Molecular Imprinting on Inorganic Nanozymes for Hundred-fold Enzyme Specificity, J. Am. Chem. Soc., 139 (2017) 5412−5419. doi.org/10.1038/s41467-019-08731-y

[4] P. Manickam, S. K. Pasha, S. A. Snipes and S. Bhansali, A Reusable Electrochemical Biosensor for Monitoring of Small Molecules (Cortisol) Using Molecularly Imprinted PolymersJ. Electrochem. Soc. 2017 volume 164, issue 2, B54-B59. doi: 10.1149/2.0781702jes

[5] I. Pandey, S. S. Jha, Molecularly imprinted polyaniline-ferrocene-sulfonic acid-Carbon dots modified pencil graphite electrodes for chiral selective sensing of D-Ascorbic acid and L-Ascorbic acid: A clinical biomarker for preeclampsia, Electrochimica Acta, Volume 182, (2015) 917-928. doi.org/10.1016/j.electacta.2015.10.005

Figure 1