ORIGINAL PAPER Fluorescent turn-on detection of cysteine using a molecularly imprinted polyacrylate linked to allylthiol-capped CdTe quantum dots Mu-Rong Chao & Chiung-Wen Hu & Jian-Lian Chen Received: 15 December 2013 /Accepted: 13 February 2014 /Published online: 11 March 2014 # Springer-Verlag Wien 2014 Abstract CdTe quantum dots capped with thioglycolic acid (TGA) display a strong turn-on fluorescence response if ex- posed to solutions of cysteine (Cys). In order to exploit this effect, a molecularly imprinted polymer (MIP) for Cys was covalently linked to the QDs via allyl mercaptan. The resulting nanomaterials (QDs, MIP-coated QDs, and nonimprint-coated QDs) were characterized by FTIR and scanning electron mi- croscopy. The adsorption of Cys was studied in phosphate buffer (pH 7.4) with respect to equilibration times (5, 15, and 40 min, respectively), binding constants [2.98, 2.42, and 0.96 (×10 4 M -1 )], and Langmuir isotherms (R 2 =0.9995, 0.9999, and 0.9983) in the Cys concentration range between 3.33 μM to 500 μM. The method has a detection limit of 0.85 μM (3σ, blank, for n =10). The selectivity of the MIP-coated QDs for Cys over 19 other amino acids is similar to that of bare QDs, but MIP-QDs afford better recoveries of Cys from solutions also containing bovine serum albumin (90 %) and fetal bovine serum (97 %), respectively, when compared to the recoveries that are obtained with bare (non-imprinted) QDs (135 % and 120 %). This is probably due to the fact that the outer MIP shell largely reduces protein wrapping, dot aggregation, and matrix inclusion. Keywords Cysteine . Fluorescence . Molecularly imprinted polymer . CdTe nanocrystal . Polyacrylate . Quantum dot Introduction Many quantum dots (QDs), which are most often composed of metal chalcogenides and their derivatives, have been used as fluorescence probes to detect ions, molecules, proteins, en- zymes, and cells [1–4]. The effective recognition of target constituents in a variable biomatrix is the key to developing successful QD probes and is usually achieved using receptor- specific molecules as the recognition materials coupled to QD surfaces, such as ion-selective ligands [5], ionophores [6], cyclodextrins [7], dendrimers [8], and biomolecules, includ- ing enzymes [9], antibodies [1], and aptamers [10]. Molecular imprinting also creates a receptor-specific poly- meric network with specific three-dimensional recognition and binding sites that are complementary to the template analyte [11]. In contrast to bulk monoliths, molecularly imprinted polymers (MIP) on nanoparticles have higher sur- face area-to-volume ratios and thus the imprinted cavities are more easily accessible by templates and the binding kinetics is improved [12]. Composites of MIPs and chalcogenide QDs have been successfully applied as sensing materials for mo- lecular and biomolecular Templates. A biocompatible poly- mer, poly(ethylene-co-ethylene alcohol), was used to couple QDs and biotemplates with the phase inversion method [13]. Additionally, a sol-gel technique was utilized in MIP-QD Electronic supplementary material The online version of this article (doi:10.1007/s00604-014-1209-6) contains supplementary material, which is available to authorized users. J.<L. Chen (*) School of Pharmacy, China Medical University, No. 91 Hsueh-Shih Road, Taichung 40402, Taiwan e-mail: cjl@mail.cmu.edu.tw M.<R. Chao Department of Occupational Safety and Health, Chung Shan Medical University, Taichung 402, Taiwan M.<R. Chao Department of Occupational Medicine, Chung Shan Medical University Hospital, Taichung 402, Taiwan C.<W. Hu Department of Public Health, Chung Shan Medical University, Taichung 402, Taiwan C.<W. Hu Department of Family and Community Medicine, Chung Shan Medical University Hospital, Taichung 402, Taiwan Microchim Acta (2014) 181:1085–1091 DOI 10.1007/s00604-014-1209-6