Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Chemistries that Facilitate Nanotechnology Kim E. Sapsford,† W. Russ Algar, Lorenzo Berti, Kelly Boeneman Gemmill,‡ Brendan J. Casey,† Eunkeu Oh, Michael H. Stewart, and Igor L. Medintz*,‡ †Division of Biology, Department of Chemistry and Materials Science, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, Maryland 20993, United States ‡Center for Bio/Molecular Science and Engineering Code 6900 and Division of Optical Sciences Code 5611, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States College of Science, George Mason University, 4400 University Drive, Fairfax, Virginia 22030, United States Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Sacramento, California 95817, United States Sotera Defense Solutions, Crofton, Maryland 21114, United States

Functionalizing nanoparticles with biological molecules: developing chemistries that facilitate nanotechnology.

Colloidal nanocrystals (NCs, i.e., crystalline nanoparticles) have become an important class of materials with great potential for applications ranging from medicine to electronic and optoelectronic devices. Today’s strong research focus on NCs has been prompted by the tremendous progress in their synthesis. Impressively narrow size distributions of just a few percent, rational shape-engineering, compositional modulation, electronic doping, and tailored surface chemistries are now feasible for a broad range of inorganic compounds. The performance of inorganic NC-based photovoltaic and light-emitting devices has become competitive to other state-of-the-art materials. Semiconductor NCs hold unique promise for near- and mid-infrared technologies, where very few semiconductor materials are available. On a purely fundamental side, new insights into NC growth, chemical transformations, and self-organization can be gained from rapidly progressing in situ characterization and direct imaging techniques. New phenom...

Prospects of Nanoscience with Nanocrystals

SnO2: A comprehensive review on structures and gas sensors

The size of C-nanodots can be electrochemically tuned by changing the applied potential during their preparation. The higher the applied potential, the smaller the resulting C-nanodots. Moreover, the surface oxidation degree of the C-nanodots can also be electrochemically tuned. The red-shift of emission independent of the size provides an insight into the luminescence mechanism of C-nanodots.

Electrochemical Tuning of Luminescent Carbon Nanodots: From Preparation to Luminescence Mechanism

Using electrochemical etching of a polycrystalline 3$C$-SiC target and subsequent ultrasonic treatment in water solution, we have fabricated suspensions of 3$C$-SiC nanocrystallites that luminesce. Transmission electron microscope observations show that the 3$C$-SiC nanocrystallites, which uniformly disperse in water, have sizes in the range of 1\char21{}6 nm. Photoluminescence and photoluminescence excitation spectral examinations show clear evidence for the quantum confinement of 3$C$-SiC nanocrystallites with the emission band maximum ranging from 440 to 560 nm. Tunable, composite polystyrene/SiC film can be made by adding polystyrene to a toluene suspension of the 3$C$-SiC nanocrystallites and then coating the resulting solution onto a Si wafer.

Experimental evidence for the quantum confinement effect in 3C-SiC nanocrystallites.

In this review, the emerging roles of group IV nanoparticles including silicon, diamond, silicon carbide, and germanium are summarized and discussed from the perspective of biologists, engineers, and medical practitioners. The synthesis, properties, and biological applications of these new nanomaterials have attracted great interest in the past few years. They have gradually evolved into promising biomaterials due to their innate biocompatibility; toxic ions are not released when they are used in vitro or in vivo, and their wide fluorescence spectral regions span the near-infrared, visible, and near-ultraviolet ranges. Additionally, they generally have good resistance against photobleaching and have lifetimes on the order of nanoseconds to microseconds, which are suitable for bioimaging. Some of the materials possess unique mechanical, chemical, or physical properties, such as ultrachemical and thermal stability, high hardness, high photostability, and no blinking. Recent data have revealed the superiority of these nanoparticles in biological imaging and drug delivery.

Group IV nanoparticles: synthesis, properties, and biological applications.

Ultra-long rutile tin dioxide nanowires and nanobelts are synthesized by thermal oxidation of tin powder using gold film as the catalyst. Nanowire or nanobelts can be selectively produced by tuning the reaction temperature. The vapour-liquid-solid growth mechanism is proposed. The band gaps of the nanowires and nanobelts are 3.74 and 3.81 eV respectively, determined from UV/visible absorption spectral results. The SnO2 nanowires show stable photoluminescence with two emission peaks centred at around 470 and 560 nm. Their wavelengths stay almost fixed while their intensities depend sensitively on the temperatures within the examination ranges from 10 to 300 K. The SnO2 nanobelts show similar photoluminescence behaviours and the origin of the luminescence is discussed.

https://iopscience.iop.org/article/10.1088/0957-4484/17/6/025/pdf

Synthesis and low-temperature photoluminescence properties of SnO2 nanowires and nanobelts.

Quantum dots are superior to dye molecules in many aspects from size-tunable fluorescence and resistance to photobleaching and they have thus been widely used in biology as fluorescent probes. However, the cytotoxicity of some quantum dots limits their use in biological systems, and exploiting green nanoparticles with low cytotoxicity has become one major concern in this field. Silicon carbide, one well-known power electronic semiconductor material, is considered one of the best biocompatible materials, especially to blood. In addition, it has superior properties such as low density, high hardness, high strength, and chemical inertness. In recent years, much effort has been made to synthesize nanocrystalline SiC and study its photoluminescence (PL) properties. Some synthesized SiC nanostructures showed emission in the blue-to-UV range with their properties depending sensitively on the fabrication method and even on specific experiments. Although some variations have been reported, in general the observed emissions can be ascribed to some surface or defect states in the SiC nanostructures. However, owing to their relatively large size, low emission intensity, lack of controlled synthesis, and variable optical properties, these interconnected SiC nanostructures can hardly be used as fluorescent biological labels. Kassiba and co-workers synthesized SiC nanoparticles with diameters of tens of nanometers

3C-SiC nanocrystals as fluorescent biological labels.

We synthesize the colloidal carbon/graphene quantum dots 1–9 nm in diameter and study their photoluminescence properties. Surprisingly, the luminescence properties of a fixed collection of colloidal carbon quantum dots can be systematically changed as the concentration varies. A model based on photon reabsorption is proposed which explains well the experiment. Infrared spectral study indicates that the surfaces of the carbon quantum dots are substantially terminated by oxygen atoms, which causes their ultra-high hydrophilicity. Our result clarifies the mystery of distinct emission colors in carbon quantum dots and indicates that photon reabsorption can strongly affect the luminescence properties of colloidal nanocrystals.

Jiyang Fan

Papers

Experimental evidence for the quantum confinement effect in 3C-SiC nanocrystallites.

Group IV nanoparticles: synthesis, properties, and biological applications.

Synthesis and low-temperature photoluminescence properties of SnO2 nanowires and nanobelts.

3C-SiC nanocrystals as fluorescent biological labels.

Red shift in the photoluminescence of colloidal carbon quantum dots induced by photon reabsorption