Elsevier

Biosensors and Bioelectronics

Volume 51, 15 January 2014, Pages 286-292
Biosensors and Bioelectronics

Molecularly imprinted quartz crystal microbalance sensor based on poly(o-aminothiophenol) membrane and Au nanoparticles for ractopamine determination

https://doi.org/10.1016/j.bios.2013.07.043Get rights and content

Highlights

  • This research combined the advantages of nanoparticle synergy, molecular imprinting technology and piezoelectric sensing.

  • The integration of Au nanoparticles into the electrodeposited membrane has enhanced the sensor's sensitivity for ractopamine analysis.

  • This work provides a promising method for enhancing the performance of MIP-based chem- and bio-sensors.

Abstract

A molecularly imprinted quartz crystal microbalance (QCM) sensor for ractopamine (RAC) detection was developed by electrodepositing a poly-o-aminothiophenol membrane on an Au electrode surface modified by self-assembled Au nanoparticles (AuNPs). The modified electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. This molecularly imprinted QCM sensor showed good frequency response in RAC binding measurements and the introduction of AuNPs demonstrated performance improvements. Frequency shifts were found to be proportional to concentration of RAC in the range of 2.5×10−6 to 1.5×10−4 mol L−1 with a detection limit of 1.17×10−6 mol L−1 (S/N=3). The sensor showed a good selective affinity for RAC (selectivity coefficient >3) compared with similar molecules and good reproducibility and long-term stability. This research has combined the advantages of high specific surface area of AuNPs, high selectivity from molecularly imprinted electrodeposited membrane and high sensitivity from quartz crystal microgravimetry. In addition, the modified electrode sensor was successfully applied to determine RAC residues in spiked swine feed samples with satisfactory recoveries ranging from 87.7 to 95.2%.

Introduction

The development of chemical and biological sensors for specific molecule analysis at low concentration has received considerable attention with research efforts in various fields (Wang et al., 2009a, Wang et al., 2009b, Du et al., 2008, Qu et al., 2009, Li et al., 2005). Different recognition elements have been introduced into these sensors to meet various application requirements. Receptors derived from living organisms (enzyme, microbes, and antibodies) have high selectivity towards target molecules (Dickert et al., 2004, Shakhmaeva et al., 2011), however biological products are often expensive, and suffer from poor temperature and chemical stability. Molecularly imprinted polymers (MIPs), also known as artificial receptors, are biomimetic materials that may be prepared easily and cheaply with good stability under extreme conditions (Haupt, 2003, Asanuma et al., 2000, Wulff, 2002). These materials may be used to overcome the drawbacks of biological molecules in the fabrication of biomimetic sensors (Malitesta et al., 2012, Meng et al., 2011, Ebarvia et al., 2004). For construction of MIP-based sensors, electropolymerization is one promising but underused method (Liao et al., 2004, Li et al., 2009, Kim and Yoo, 2011), in which a polymeric membrane can be easily grown onto a transducer surface with control over the membrane shape, size and thickness through control of the amount of charge transferred (Malitesta et al., 1999). This method is often adopted to prepare special MIP-based sensors that have fast response and potential to be miniaturized. However, because of the relatively high density of electropolymerized membranes, fewer imprinted sites are formed during the electrodeposition process, reducing the performance of the proposed MIP-based sensor.

Au nanoparticles (AuNPs) have been widely used as a signal amplification medium to increase sensitivity of sensors because of their unique chemical and physical features (Taylor et al., 2000, Li et al., 2006). For a MIP-based sensor, assembled AuNPs can increase the sensor surface area, and thus increase the total number of imprinted sites formed in the polymer matrix. This in turn produces more sensitive assays.

Quartz crystal microbalances (QCMs) are a type of mass-sensitive chemical sensor that allow dynamic monitoring of mass changes at the ng level, using an oscillating crystal electrode (Nunalee et al., 2006, Park et al., 2004). QCM devices are considered to be highly suitable sensing platforms to combine with molecular imprinting technique for the development of effective MIP-based sensors (Thoelen et al., 2008).

Ractopamine (RAC), a typical β-adrenergic agonist, was widely introduced into animal feed as a growth promoting agent because it can increase the percentage of lean meat and improve feed conversion ratios (Tang et al., 2011). However its persistence in animal tissues and meat products is potentially hazardous to human health (Blanca et al., 2005). Until recently, many analytical methods based on molecular imprinting technique have been reported for the determination of RAC residues (Zhang et al., 2012, He et al., 2011, Hu et al., 2010). In our group, a MIP-based integrated method for RAC analysis was constructed that included online SPE-HPLC (Wang et al., 2009a, Wang et al., 2009b), biomimetic ELISA (Fang et al., 2011) and amperometric sensors (Kong et al., 2012).

In this work, we fabricated a MIP-based QCM sensor for RAC determination by electrodepositing a molecularly imprinted poly-o-aminothiophenol (PoAT) membrane on an Au electrode surface modified by self-assembled AuNPs. The resultant QCM sensor demonstrated that integration of AuNPs into the molecular imprinting electropolymerization process can improve the performance of imprinted electrodeposited membrane. This enhanced sensor provided a more sensitive analysis of RAC.

Section snippets

Reagents and chemicals

The RAC and other analytes tested including isoproterenol (ISOP), terbutaline (TER), and isoxsuprine (ISOX) were purchased from Sigma-Aldrich (St. Louis, MO, USA). The o-aminothiophenol (o-AT), tetrabutylammonium perchlorate, trisodium citrate, gold chloride (HAuCl4) and 1,6-hexanedithiol were obtained from Alfa Aesar (Tianjin, China). Potassium ferricyanide (K3[Fe(CN)6]) and other chemicals used in the experiments were purchased from Tianjin No. 1 Chemical Reagent Factory (Tianjin, China) and

Molecular imprinting electropolymerization

An o-AT self-assembled monolayer (SAM) was formed on the AuNPs surface during the immersion of the AuNP-Au electrode in an o-AT/ethanol solution overnight because of the Au–S bonds, which can serve as an initial polymerizable monolayer to improve polymer membrane stability and drive the selective occurrence in electropolymerization (Sabatani et al., 1995).

In addition, the monomer o-AT and RAC template molecules could be protonated using HCl and attracted to the electrode surface at negative

Conclusions

In this study, the AuNPs were introduced into the molecularly imprinted electrodeposited membrane to develop a sensitive MIP-based QCM sensor for RAC determination. It was found that the sensitivity was improved by assembly AuNPs on the electrode surface because of an increase in the number of imprinted recognition sites in the membrane. This novel MIP-based QCM sensor exhibited good frequency response and high selectivity toward the template molecular RAC. The sensor also showed good

Acknowledgments

This work was supported by National Basic Research Program (973) of China (project No. 2012CB720803) and the National Natural Science Foundation of China (project No. 31171683) and Tianjin Municipal Science and Technology Commission (project No. 12TXSYJC33600) and General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China (project No. 201210053).

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