Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
A nanocomposite optosensor containing carboxylic functionalized multiwall carbon nanotubes and quantum dots incorporated into a molecularly imprinted polymer for highly selective and sensitive detection of ciprofloxacin
Graphical Abstract
Introduction
Ciprofloxacin is a fluoroquinolone antibiotic which is widely used for the treatment of respiratory and digestive infections in humans and livestock [1]. This drug also misused in the livestock industry since treating animals with these agents can increase productivity. However, this can become a serious problem, since the antibiotics can be expressed in meat and milk leading to potential toxicity [2] or allergic hypersensitivity reactions in humans. There is also a further serious issue that this practice may lead to the generation of antibiotic resistant human pathogens. Therefore, the European Union has set the maximum residue limit (MRL) for ciprofloxacin at 100 μg kg−1 in milk, chicken and pig muscle [3]. Thus, it is necessary to develop a convenient, rapid and cost-effective method for the monitoring of ciprofloxacin in food samples. Several analytical techniques have been reported for ciprofloxacin detection such as high performance liquid chromatography [[4], [5], [6]], capillary electrophoresis [7] and electrochemical techniques [[8], [9], [10], [11]]. However, these techniques can be complicated, may require expensive instrumentation and highly skilled personnel. To overcome these drawbacks, spectrofluorimetry can be considered as an alternative method due to its simplicity, rapidity and cost effectiveness. The sensitivity of this method can be improved using high sensitive fluorescence probes such as quantum dot nanoparticles (QDs). QDs have been used for the determination of various target analytes at trace levels typical analytes include salicylic acid [12], glucose [13], H2O2 [14], 6-mercaptopurine [15], ochratoxin A [16], kaempferol [17] and copper (II) ion [18]. In addition, QDs have many unique optical properties such as tunable size-dependent photoluminescence, good photostability and narrow symmetric emissions [19,20]. The determination of trace target analytes in real samples with high matrix interferences normally requires highly selective methods. To further improve the selectivity of these methods, molecularly imprinted polymers (MIPs) have received considerable study due to their high specificity and facile preparation. MIPs are normally prepared by a co-polymerization process of cross-linker moieties with functional monomers that form complexes with analytes (template molecule) prior to polymerization. After the template molecules were eluted from the polymer, specific recognition sites which are complementary in size, shape and functional groups to the template can be obtained, leading to the ability to rebind template molecules with high specificity. MIPs not only provide highly selective binding material but also have high stability meaning they can be used under extreme condition such as extreme pH, high temperature and in organic solvents. Since MIPs are cost-effective and robust materials, they have been extensively used in many fields such as an adsorbent material [21], solid phase microextraction [[22], [23], [24]] and chemosensors and biosensors [[25], [26], [27]]. For sensor applications, the composite fluorescence probes using QDs incorporated into MIPs have been developed as highly selective fluorescence probes for the determination of some target compounds such as salbutamol [28], patulin [29], sulfadiazine [30], sulfadimidine [31], malachite green [32], tetracycline [33], cocaine [34] and amoxicillin [35]. To improve the kinetic adsorption or affinity binding of ciprofloxacin, addition of carboxylic acid functionalized multiwall carbon nanotubes is an interesting alternative approach since they contain an extended π structure which can adsorb aromatic compounds via π-π interactions [36]. The carboxylic acid functionalisation of multiwall carbon nanotubes can improve their dispersibility in aqueous media and it is easy to achieve further covalent functionalisation with other materials [37].
In this work, nanocomposite optosensor COOH functionalized MWCNTs and CdTe quantum dots embedded in a MIPs were synthesized for trace ciprofloxacin detection. The determination of ciprofloxacin is based on the fluorescence quenching when target analyte is bound to the binding sites on the developed fluorescence probes. This integrated the desirable optical properties of the quantum dots with the high specificity of MIPs and high adsorption affinity of COOH@MWCNT to produce a rapid, highly sensitive optosensor for the determination of ciprofloxacin with good selectivity. The developed optosensor was applied to determine ciprofloxacin in chicken muscle and milk and the accuracy of the method was investigated by comparing with a HPLC technique.
Section snippets
Chemicals and Reagents
Tellurium powder (99.8%), sodium borohydride (NaBH4), thioglycolic acid (TGA), 3-aminopropyltriethoxysilane (APTES), cadmium chloride (CdCl2·H2O) and tetraethylorthosilicate (TEOS) were from Sigma-Aldrich (St. Louis, MO, USA). Ciprofloxacin was supplied by Tokyo Chemical Industry (Tokyo, Japan), Tris (hydroxymethyl) aminomethane and methanol were obtained from Merck (Darmstadt, Germany), 25% NH3·H2O was from QReC (New Zealand). MWCNTs were purchased from Shenzhen Nano-Technologies Port Co.,
The Synthesis of Nanocomposite COOH@MWCNT-MIP-QDs Optosensors for Ciprofloxacin Detection
The nanocomposite COOH@MWCNT-MIP-QDs optosensor were prepared via copolymerization process incorporating COOH@MWCNT, TGA-capped CdTe QDs, APTES (functional monomer), TEOS (cross-linker), ciprofloxacin (template) and NH3 (catalyst). The carboxylic groups of TGA-capped CdTe QDs and COOH@MWCNT can interact with amino groups (-NH2) of APTES to facilitate incorporation of the CdTe QDs into the sol-gel via hydrogen bonding. Also, non-covalent interaction between APTES and ciprofloxacin (template)
Conclusion
A nanocomposite COOH@MWCNT-MIP-QDs optosensor was developed for the determination of ciprofloxacin based on the electron transfer induced fluorescence quenching. The developed optosensor combined the high specificity of MIPs with the excellent optical properties of QDs with the high affinity of COOH@MWCNT to ciprofloxacin, thereby demonstrating a highly selective, sensitive and rapid method for the determination of trace ciprofloxacin. This rapid, convenient and cost-effective hybrid
Acknowledgements
This work was supported by the budget revenue of Prince of Songkla University (SCI600559S), the Thailand research fund, Center of Excellence for Innovation in Chemistry (PERCH-CIC). Naphat Yuphintharakun was supported by the faculty of Science Research Fund, Prince of Songkla University, Hat Yai, Thailand, Contract no. 1-2559-02-009.
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