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WIREs Nanomed Nanobiotechnol
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Catalyst‐functionalized nanomaterials

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Abstract With rapid development in both nanotechnology and biotechnology, it is now possible to combine these two exciting fields to modulate the physical properties of nanomaterials with the molecular recognition and catalytic functional properties of biomolecules. Such research efforts have resulted in a larger number of sensors that can detect a broad range of analytes ranging from metal ions, small molecules, and nucleic acids down to proteins. These sensors will find important applications in nanomedicine. In this article, the design of sensors with four classes of nanomaterials (metallic, semiconductor, magnetic, and carbon nanotube nanoparticles) is reviewed. Metallic nanoparticles possess distance‐dependent optical properties and are useful for designing colorimetric sensors. Semiconductor nanoparticles or quantum dots (QDs) appear to be superior alternatives to traditional organic fluorophores in many aspects, such as broad excitation range, narrow emission peaks, and high photo stability. QD sensors based on either energy transfer or charge transfer are summarized. Furthermore, magnetic nanoparticles are shown to be useful as smart magnetic resonance imaging (MRI) contrast agents. Finally, some carbon nanotubes show near‐IR emission properties, and thus, are potentially useful for in vivo sensing. Sensors based on either tuning the emission intensity or wavelength are discussed. Copyright © 2008 John Wiley & Sons, Inc. This article is categorized under: Diagnostic Tools > In Vitro Nanoparticle-Based Sensing

(a) Maltose detection based on a displacement reaction with Cy3.5 labeled β‐cyclodextrin. MBP, maltose binding protein. (b) Detection of proteases by conjugating a quencher‐labeled peptide to QDs. (c) Detection of thrombin based on the structure‐switching property of a thrombin aptamer. A quencher‐labeled DNA was released due to aptamer binding to thrombin.

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(a) Secondary structure of a DNA aptamer that can bind hemin (denoted as the diamond shape). This aptamer/hemin complex is a DNAzyme that can catalyze conversion of luminal. (b) Schematic presentation of DNA detection with DNAzyme‐functionalized gold nanoparticles (AuNPs). (c) Secondary structure of a thrombin‐binding DNA aptamer. (d) Schematic presentation of thrombin detection with Pt nanoparticles acting as a catalyst for signal generation. (e) Schematic presentation of AuNP as wiring for electron relay redrawn from Ref. 59.

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Aptamer and gold nanoparticles (AuNP)‐based lateral flow device. (a) Left: adenosine‐induced disassembly of AuNP aggregates into red‐colored dispersed particles. Biotin is denoted as a black star. Right: lateral flow devices loaded with the aggregates (on the conjugation pad) and streptavidin (on the membrane in cyan color) before use (left strip), in a negative (middle strip), or a positive (right strip) test. (b) Test of the adenosine lateral flow device with varying concentrations of nucleosides. A, adenosine; C, cytidine; U, uridine. (c) Test of the cocaine lateral flow device with varying concentrations of cocaine in undiluted human blood serum. Coc, cocaine; Ade, adenosine.

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The secondary structure of the native (a) and mutated (b) DNAzyme. The position of mutation is shown in blue. The extinction spectra of DNAzyme‐assembled gold nanoparticles (AuNPs) in the presence (red) or absence (blue) of Pb2+ for the native DNAzyme (c) and the mutated DNAzyme (d). (e) Pb2+‐dependent color change of AuNPs with 100% native DNAzyme and with only 5% native DNAzyme and 95% mutated DNAzyme .

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The secondary structure of the native (a) and mutated (b) DNAzyme. The position of mutation is shown in blue. The extinction spectra of DNAzyme‐assembled gold nanoparticles (AuNPs) in the presence (red) or absence (blue) of Pb2+ for the native DNAzyme (c) and the mutated DNAzyme (d). (e) Pb2+‐dependent color change of AuNPs with 100% native DNAzyme and with only 5% native DNAzyme and 95% mutated DNAzyme .

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(a) Detection of maltose based on modulation of charge transfer from a labeled ruthenium compound to quantum dots (QDs). (b) Detection of thrombin based on the charge transfer from thrombin to QDs.

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The secondary structure of the native (a) and mutated (b) DNAzyme. The position of mutation is shown in blue. The extinction spectra of DNAzyme‐assembled gold nanoparticles (AuNPs) in the presence (red) or absence (blue) of Pb2+ for the native DNAzyme (c) and the mutated DNAzyme (d). (e) Pb2+‐dependent color change of AuNPs with 100% native DNAzyme and with only 5% native DNAzyme and 95% mutated DNAzyme .

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Colorimetric sensing with functional nucleic acids and gold nanoparticles (AuNPs). (a) The secondary structure of a Pb2+‐specific DNAzyme. (b) Schematic presentation of cleavage of the substrate by the enzyme in the presence of Pb2+. (c) In the presence of Pb2+, the DNAzyme‐assembled AuNPs are dispersed with a blue‐to‐red color transition. (d) A TLC plate with the sensor solutions spotted. The sensor shows a red color only in the presence of Pb2+. (e) Schematics of the adenosine aptamer binding to its target. (f) Schematic presentation that the aptamer can be either a random coil or in a complexed structure upon binding to its target. (g) The adenosine aptamer‐linked AuNPs change color from blue to red in the presence of adenosine through a structure‐switching process. (h) Color of the sensor in the presence of different nucleosides. (i) An adenosine‐dependent aptazyme constructed on the basis of the Pb2+‐specific DNAzyme and the adenosine aptamer. The aptazyme is active only in the presence of adenosine. (j) Color of the aptazyme‐based adenosine sensor spotted on a TLC plate.

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(a) Glucose detection with glucose oxidase‐immobilized carbon nanotubes. [Fe(CN)6]3– strongly quenches nanotube emission, while [Fe(CN)6]2– has much lower quenching efficiency. (b) Hg2+‐ induced DNA B‐Z conformational change for Hg2+ detection. Nanotubes emit at different wavelengths depending on the DNA conformation. (Some parts of the figure are adapted from Ref. 76).

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