# Fluorescent Imprinted Nanoparticles for Sensing of Chlorogenic Acid in Coffee Extracts
## 1 Introduction
The receptor can be composed of distinct molecular units called recognition receptors or, alternatively, it can be a material that includes in its composition recognition sites. Therefore, MIPs can be considered as biomimetic receptors,  
Figure 1: Chemical structures of analyte **1**, template **2**, monomers **3** and **7**, co-monomer **6** and cross-linkers **4** and **5**. since these materials can show specificities and affinities perfectly comparable with the natural ones and their advantages, such as chemical and physical stability, making them compatible with several detection conditions and conferring relatively long life times [4]. The use of MIPs as receptors greatly depends on the immobilization methods and different immobilization techniques which have been reported in the literature, such as physical entrapment, adsorption, covalent binding, and cross-linking. MIPs based on non-covalent interactions have been mostly used in solid phase extraction and sample concentration for the analysis of CGAs. MIP for CGA was successfully applied for the extraction of CGA in the leaves of _Eurommia ulmodies_ using methacrylic acid as a functional monomer, divinylbenzene as a crosslinker, and methanol or dimethylsulfoxide as a co-solvent. The prepared MIPs were microspheres with a narrow particle size distribution. The MIP had a specific molecular-recognition ability for CGA, while other related compounds, such as caffe acid, gallic acid, protocatechuic acid, and vanillic acid, could not be recognized by the MIP [5]. Another approach was the development of a modified bisphenol A molecularly imprinted polymer sorbent used in the hollow fiber solid phase microextraction of CGA. The pre-polymerization solution containing the template was introduced into the polypropylene hollow fiber segment for in situ polymerization. The system was used for selective extraction of CGA in _Echinacea purpurea_, a medicinal plant. The obtained solid phase microextraction (SPME) device exhibits excellent characteristics, such as high porosity and chemical stability, with a limit of detection of 0.08 ng/mL [6]. A rapid and accurate approach was established for simultaneous purification of theophylline and CGA in green tea by coupling hybrid molecularly imprinted solid-phase extraction with HPLC. Satisfactory extraction recoveries for theophylline (96.7%) and CGA (95.8%) were afforded, and the detection limits were 0.01 mg/mL for theophylline and 0.05 mg/mL for CGA [7]. In the same way, some other MIP-based electrochemical sensors have been developed for CGA detection [8; 9; 10; 11; 12]. For instance, a sensitive molecularly imprinted electrochemical sensor was constructed by deposition of a molecularly imprinted siloxane (MIS) film. The MIS-imprinted film was electrochemically characterized using different pulse voltammetry. The MIS/Au sensor was tested in a solution of the CGA template and other similar molecules, showing excellent selectivity towards CGA when compared with structurally similar molecules. The detection limit was 1.48 \(\times\) 10\({}^{-7}\) M, and the sensor was successfully applied for the determination of CGA in coffee and tea samples [12]. Most recently, a promising technique for the enrichment and determination of chlorogenic acids from herbal medicines was proposed. The system consists of a solid-phase extraction adsorbent based on MIPs made of 4-vinylpyridine (4 VP) as the functional monomer and hydrogenated 5-CQA (H-5-CQA) as the mimic template. Selective extraction and determination of three isomers of caffeoylquinic acids (CQAs), considered as quality markers for _Lonicra japonica_ and _Lianhua qingwen_ granules, was successfully achieved. The adsorption isotherms, kinetics, and selectivity of the MIPs were systematically compared with those of non-molecularly imprinted polymers. The MIPs showed high selectivity towards chlorogenic acid, cryptochlorogenic acid, and neochlorogenic acid.