DOI: 10.1002/chem.201102188 Synthesis of Fe 3 O 4 @Phenol Formaldehyde Resin Core–Shell Nanospheres Loaded with Au Nanoparticles as Magnetic FRET Nanoprobes for Detection of Thiols in Living Cells Ping Yang, [a, b] Qi-Zhi Xu, [a] Sheng-Yu Jin, [a] Yang Zhao, [a] Yang Lu, [a] Xue-Wei Xu, [a] and Shu-Hong Yu* [a] Introduction Glutathione (GSH), homocysteine (Hcy), and cysteine (Cys) are three primary biological thiols (biothiols) in the cell which play crucial roles in physiological systems. [1] The amount of glutathione (GSH) in tissues is a key indicator of human health. [2] Epidemiological investigations demonstrat- ed a correlation between the level of Hcy in blood plasma and coronary heart disease, stroke, and peripheral vascular diseases. [3] Similarly, if the physiological system is devoid of Cys many diseases, such as decreased hematopoiesis, leuko- cyte loss, and psoriasis, occur. [4] Thus, it is essential to detect thiols in biological systems. Up to now, many methods have been applied for monitoring thiols in vivo. [5] Among them, fluorescent probes have drawn great attention for the detec- tion of thiols or imaging owing to their evident advantages over other methods in terms of sensitivity and conve- ACHTUNGTRENNUNGnience. [6] However, development of low-toxicity fluorescent probes for assaying intracellular components is uncom- mon. [7] By strongly oxidizing relative cellular components, some of the fluorescence probes were designed for live imaging of cellular thiols. [8] Therefore, it is of significant in- teresting to develop a novel, selective, and efficient fluores- cent probe based upon low-toxicity nanomaterials without injury to cells for the detection of total thiols. Traditional organic dyes are often used as a part of bio- logical probes due to their excellent luminescence proper- ties. [9] However, the shortcomings of high toxicity, easy pho- tobleaching, weak biocompatibility, and multichromaticity limits their extensive application in bioassays. [10] Compared with traditional organic dyes, semiconductor quantum dots with many excellent optical properties such as high quantum yield of photoluminescence, tunable size, size-dependent emission, broad excitation spectra, and narrow emission peaks have been widely utilized in analytical chemistry and biochemistry. [11] However, the inherent toxicity and chemical instability limit their application in detection of samples in vivo. Thus, exploiting a novel, biocompatible, sensitive, and easily synthesized fluorescent probe is still highly attractive. Among a variety of possible methods, fluorescence reso- nance energy transfer (FRET) is a powerful technique for biosensing. [12] The FRET-based probe systems have the ad- vantage of selectivity, sensitivity, and efficiency for desired Abstract: A magnetic, sensitive, and se- lective fluorescence resonance energy transfer (FRET) probe for detection of thiols in living cells was designed and prepared. The FRET probe consists of an Fe 3 O 4 core, a green-luminescent phenol formaldehyde resin (PFR) shell, and Au nanoparticles (NPs) as FRET quenching agent on the surface of the PFR shell. The Fe 3 O 4 NPs were used as the core and coated with green-luminescent PFR nanoshells by a simple hydrothermal approach. Au NPs were then loaded onto the surface of the PFR shell by electric charge ab- sorption between Fe 3 O 4 @PFR and Au NPs after modifying the Fe 3 O 4 @PFR nanocomposites with polymers to alter the charge of the PFR shell. Thus, a FRET probe can be designed on the basis of the quenching effect of Au NPs on the fluorescence of Fe 3 O 4 @PFR nanocomposites. This magnetic and sensitive FRET probe was used to detect three kinds of pri- mary biological thiols (glutathione, ho- mocysteine, and cysteine) in cells. Such a multifunctional fluorescent probe shows advantages of strong magnetism for sample separation, sensitive re- sponse for sample detection, and low toxicity without injury to cellular com- ponents. Keywords: analytical methods · bioACHTUNGTRENNUNGthiols · fluorescent probes · FRET · nanostructures [a] P. Yang, Q.-Z. Xu, S.-Y. Jin, Dr. Y. Zhao, Dr. Y. Lu, X.-W. Xu, Prof. Dr. S.-H. Yu Division of Nanomaterials & Chemistry Hefei National Laboratory for Physical Sciences at Microscale Department of Chemistry The National Synchrotron Radiation Laboratory University of Science and Technology of China Hefei, Anhui 230026 (P.R. China) Fax: (+ 86) 551-3603040 E-mail : shyu@ustc.edu.cn [b] P. Yang Department of Chemistry and Chemical Engineering Huainan Normal University Huainan, Anhui 232001 (P.R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201102188.  2012 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim Chem. Eur. J. 2012, 18, 1154 – 1160 1154