Size Selection Of Nanoparticles Research Articles

Indicator Supraparticles for Smart Gasochromic Sensor Surfaces Reacting Ultrafast and Highly Sensitive

AbstractThe detection of toxic gases, such as NH3 and CO, in the environment is of high interest in chemical, electronic, and automotive industry as even small amounts can display a health risk for workers. Sensors for the real‐time monitoring of these gases should be simple, robust, reversible, highly sensitive, inexpensive and show a fast response. The indicator supraparticles presented herein can fulfill all of these requirements. They consist of silica nanoparticles, which are assembled to supraparticles upon spray‐drying. Sensing molecules such as Reichardt's dye and a binuclear rhodium complex are loaded onto the microparticles to target NH3 and CO detection, respectively. The spray‐drying technique affords high flexibility in primary nanoparticle size selection and thus, easy adjustment of the porosity and specific surface area of the obtained micrometer‐sized supraparticles. This ultimately enables the fine‐tuning of the sensor sensitivity and response. For the application of the indicator supraparticles in a gas detection device, they can be immobilized on a coating. Due to their microscale size, they are large enough to poke out of thin coating layers, thus guaranteeing their gas accessibility, while being small enough to be applicable to flexible substrates.

Ultra-High Vacuum Fabrication of Ordered Nanoparticles and Their Device Applications

Nanoparticles are important for the implementation of a variety of photonic and electronic devices with new functionalities and improved performances. While multiple photonic devices using nanoparticles have been successfully implemented, the use of nanoparticles in electronic devices have significantly lagged; one of the primary reasons being the more stringent material and surface purity requirements for such devices. While the feasibility of a variety of electronic devices based on nanoparticles have been demonstrated in the laboratory, such as nanoparticle flash memory and single electron transistors, the fabrication technique employed is electron-beam lithography, which unfortunately is not suitable for large scale manufacturing. For most electronic devices, it is typically required that the nanoparticle dimensions be in the 1 nm to 10 nm range with size variations of 10% or less. Current photolithographic techniques are not suitable for the implementation of such nanoparticles, and nonlithographic techniques are typically used for their fabrication. However, most nonlithographic techniques are based on natural self-organization processes and suffer from a lack of flexibility or a lack of engineering control. Among the various nonlithographic techniques, the predominant ones are solution based, examples of which include sol-gel synthesis, chemical synthesis, and electrochemical synthesis inside self-organized nanoporous templates. While such solution based techniques can produce nanoparticles with the required dimensions and size distributions, they also need complex surface passivation involving capping molecules to prevent aggregation. These capping molecules modify the electrical surface properties of the nanoparticles making charge injection/extraction difficult. In addition, the solution based synthesis techniques are not compatible with the silicon integrated circuit (IC) process, in particular the Complementary Metal Oxide Silicon (CMOS) process, which is the predominant manufacturing process for electronic devices. It is widely believed that the availability of a CMOS compatible nanoparticle fabrication technique can greatly increase the viability of nanoparticle based electronic devices. We have developed a CMOS compatible ultra-high vacuum system for the implementation of nanoparticle based electronic devices that addresses the above issues. The system consists of (i) a nanoparticle unit that provides the capability to deposit nanoparticles of any metal, semiconductor or insulator of diameters as low as 1 nm with less than 5% size variation on an arbitrary substrate, (ii) a 4-pocket electron-beam evaporation unit that allows the in-situ deposition of four different materials (metals or insulators) with less than 5% thickness uniformity, and (iii) a UHV pulsed DC sputter source that allows the in-situ deposition of thick layers of insulators (semiconductors or metals) including isolation dielectrics. The nanoparticle deposition unit, the ohmic contact metallization unit and the isolation dielectric deposition unit are all housed inside an ultra-high vacuum (10-10 torr) chamber to ensure high purity and good surface properties of the nanoparticles. The nanoparticle deposition system is based on sputtering, thus making it possible to deposit nanoparticles of any material that can be sputtered. In addition, nanoparticle deposition can be carried out at room temperature, making it possible to deposit the nanoparticles on a variety of substrates including flexible substrates. Size selection of nanoparticles is achieved by using a quadrupole mass filter with the capability to provide as low as 2% size control. One advantage of the system is that ohmic contacts and isolation dielectrics can be formed in an integrated manner without breaking vacuum, which is important for electrical continuity. In addition, the deposited nanoparticles can be embedded in, or coated with, metallic, semiconducting or insulating layers without breaking vacuum, thus making complex multi-layered structures possible that can have applications in a variety of fields including nanoscale detectors, nano-optics, nano-sensors, field-emitters etc. For nanoparticle based electronic devices to function properly, it is essential that the nanoparticles are physically separated from each other. In addition, if the nanoparticles can be ordered in a periodic manner, it can significantly improve device reliability and performance. To address these issues, we have developed a technique for the electrical ordering of the nanoparticles that can be carried out in-situ without breaking vacuum. The ordering process is rapid, does not require physical contact with nanoparticles and thus prevents contamination. We have used the system and technique for the deposition of a variety of nanoparticles of metals and semiconductors including Ni, Fe, Co, Au, Ag, Cu, Si, CdTe, CdSe, ZnS on a variety of substrates including silicon, silicon dioxide coated Si, metal coated silicon, quartz, sapphire. We have also fabricated complex structures containing nanoparticles for various applications In this presentation, we will provide details of the apparatus, fabrication process, experimental results as well some of the nanoparticle based electronic devices currently being developed.

Field Induced Ordering of Nanoparticles

Nanoparticles of semiconductors and metals are promising for the implementation of a variety of photonic and electronic devices with new functionalities and improved performance. For the implementation of nanoparticle based devices it is essential that the nanoparticles are electrically isolated from each other, otherwise the benefits such as quantum confinement or Coulomb blockade, can be lost. A convenient way to achieve such isolation is by ordering the nanoparticles in a periodic fashion, which ensures inter-particle separation as well as improvement in reliability and device performance. There is thus significant interest in the fabrication of ordered nanoparticles. For most electronic and photonic devices, it is typically required that the nanoparticle dimensions be in the 1-20 nm range with size variations of 10% or less. Current lithographic techniques are not suitable for the implementation of such nanoparticles, and nonlithographic techniques are typically used for their fabrication. However, many of the nonlithographic techniques are based on natural self-organization processes and suffer from a lack of flexibility or a lack of engineering control. Among the various nonlithographic techniques, the predominant ones are solution based. While such solution based techniques can produce nanoparticles with the required dimensions and size distributions, and in some cases periodicity, they require complex surface passivation involving organic capping molecules. These capping molecules modify the electrical surface properties of the nanoparticles making charge injection/extraction difficult. In addition, the solution based synthesis techniques are not compatible with solid-state device technology, the primary manufacturing process for electronic and photonic devices. The problems associated with solution based methods can be addressed to some extent by using nonlithographic fabrication techniques based on physical vapor deposition such as Stransky-Krastanov growth by epitaxial process. However, most of these techniques have severe constraints in terms of nanoparticle size, material, periodicity and the choice of substrate. A versatile nanofabrication technique that can produce high purity nanoparticles with flexibility in terms of particle size, nanoparticle material, periodicity and the choice of substrate, together with the capability for in-situ deposition of ohmic contact and isolation dielectric materials, will be an important step towards the realization of a variety of nanoparticle based electronic and photonic devices. Our research group has developed a cluster tool system that addresses the above issues. The system consists of a nanoparticle deposition unit, an electron-beam evaporation unit for the deposition of thin films, and a pulsed DC sputtering unit for the deposition of thick layers of metals and insulators. The nanoparticle deposition system is based on sputtering, thus allowing the deposition of nanoparticles of any material that can be sputtered. In addition, nanoparticle deposition can be carried out at room temperature, making it possible to deposit the nanoparticles on a variety of substrates including flexible substrates. Size selection of nanoparticles is achieved by using a quadrupole mass filter with the capability to provide as low as 2% size control. The nanoparticle deposition unit, the electron beam evaporation unit and the DC sputtering unit are all housed inside an ultra-high vacuum chamber to ensure high purity and good surface properties of the nanoparticles. We have used this technique to fabricate nanoparticles of a variety of metals and semiconductors with sizes ranging from 2 nm to 30 nm with less than 5% size variation and demonstrated the viability of the system for the fabrication of nanoparticle based electronic and photonic devices. The nanoparticles deposited in this system are not uniformly distributed, however, most show physical separation from each other. This is due to the charged nature of the nanoparticles creating inter-particle repulsion. In order to create ordered nanoparticles, we have developed a system where the charged nanoparticles can be physically manipulated through the application of an external electric field. The system consists of an electrode mounted on a platform with x,y,z motion and rotation capability. The displacement in the z-direction (vertical) is of nanometer sensitivity which allows the probe to be placed in close proximity to the substrate. The ordering of the nanoparticles is achieved through x,y or rotational scanning of the electrode with an applied voltage, We have demonstrated various ordering of nanoparticles using this technique. We have also extended the technique to order neutral nanoparticles by inducing image charge on the nanoparticles through the electrode and then manipulating the particles. We have also demonstrated that the technique can be used to order magnetic nanoparticles by using a magnetic tip instead of an electrode. In this poster, we will present details of the nanoparticle ordering system, describe the mechanisms affecting the ordering and present experimental results.

Harnessing Photovoltage: Effects of Film Thickness, TiO2 Nanoparticle Size, MgO and Surface Capping with DSCs.

High photovoltage dye-sensitized solar cells (DSCs) offer an exceptional opportunity to power electrocatalysts for the production of hydrogen from water and the reduction of CO2 to usable fuels with a relatively cost-effective, low-toxicity solar cell. Competitive recombination pathways such as electron transfer from TiO2 films to the redox shuttle or oxidized dye must be minimized to achieve the maximum possible photovoltage (Voc) from DSC devices. A high Voc of 882 mV was achieved with the iodide/triiodide redox shuttle and a ruthenium NCS-ligated dye, HD-2-mono, by utilizing a combined approach of (1) modulating the TiO2 surface area through film thickness and nanoparticle size selection, (2) addition of a MgO insulating layer, and (3) capping available TiO2 film surface sites post film sensitization with an F-SAM (fluorinated self-assembled monolayer) treatment. The exceptional Voc of 882 mV observed is the highest achieved for the popular NCS containing ruthenium sensitizers with >5% PCE and compares favorably to the 769 mV value observed under common device preparation conditions.

Synthesis and characterization of multifunctional hybrid-polymeric nanoparticles for drug delivery and multimodal imaging of cancer.

In this study, multifunctional hybrid-polymeric nanoparticles were prepared for the treatment of cultured multicellular tumor spheroids (MCTS) of the PANC-1 and MIA PaCa-2 pancreatic carcinoma cell lines. To synthesize the hybrid-polymeric nanoparticles, the poly lactic-co-glycolic acid core of the particles was loaded with Rhodamine 6G dye and the chemotherapeutic agent, Paclitaxel, was incorporated into the outer phospholipid layer. The surface of the nanoparticles was coated with gadolinium chelates for magnetic resonance imaging applications. This engineered nanoparticle formulation was found to be suitable for use in guided imaging therapy. Specifically, we investigated the size-dependent therapeutic response and the uptake of nanoparticles that were 65 nm, 85 nm, and 110 nm in size in the MCTS of the two pancreatic cancer cell lines used. After 24 hours of treatment, the MCTS of both PANC-1 and MIA PaCa-2 cell lines showed an average increase in the uptake of 18.4% for both 65 nm and 85 nm nanoparticles and 24.8% for 110 nm nanoparticles. Furthermore, the studies on therapeutic effects showed that particle size had a slight influence on the overall effectiveness of the formulation. In the MCTS of the MIA PaCa-2 cell line, 65 nm nanoparticles were found to produce the greatest therapeutic effect, whereas 12.8% of cells were apoptotic of which 11.4% of cells were apoptotic for 85 nm nanoparticles and 9.79% for 110 nm nanoparticles. Finally, the study conducted in vivo revealed the importance of nanoparticle size selection for the effective delivery of drug formulations to the tumors. In agreement with our in vitro results, excellent uptake and retention were found in the tumors of MIA PaCa-2 tumor-bearing mice treated with 110 nm nanoparticles.

DMA를 이용한 나노 입자의 크기 분류법에 대한 이해와 성능개선

DMA를 이용한 나노 입자의 크기 분류법에 대한 이해와 성능개선

USPIO‐loaded red blood cells as a biomimetic MR contrast agent: a relaxometric study

Red blood cells (RBCs) loaded with iron oxide nanoparticles have been proposed as biomimetic constructs with long half-life (ca. 20 days) in the blood compartment and potentially interesting properties (such as relaxivity) as intravascular contrast agents for magnetic resonance imaging. However, the encapsulation of nanoparticles into RBCs might affect their magnetic properties and relaxivity, which may be significantly different from the native suspension. Here, we present a relaxometric study of P904, a novel ultra small iron oxide nanoparticle developed by Guerbet, enclosed in human RBCs. We measured longitudinal (r1 ) and transverse (r2 ) relaxivity over a wide range of Larmor frequencies (0.01-300 MHz) in samples of P904-loaded RBCs, and in control samples with P904 nanoparticles dispersed in blood. Internalization of P904 into RBCs resulted in smaller r1 , and in a very high r2 /r1 ratio (232) at the highest field. Moreover, a shift of the Curie peak to high fields was observed in P904-loaded RBCs, possibly the result of nanoparticle size selection caused by the internalization process. High r2 relaxivity together with a high r2 /r1 ratio and a very long blood half-life make P904-loaded RBCs a promising blood-pool negative contrast agent for MR diagnostic applications.

Organometallic approach to polymer-protected antibacterial silver nanoparticles: optimal nanoparticle size-selection for bacteria interaction

The optimal size-specific affinity of silver nanoparticles (Ag NPs) towards E. coli bacteria has been studied. For this purpose, Ag NPs coated with polyvinylpyrrolidone (PVP) and cellulose acetate (CA) have been prepared using an organometallic approach. The complex NBu4[Ag(C6F5)2] has been treated with AgClO4 in a 1:1 molar ratio giving rise to the nanoparticle precursor [Ag(C6F5)] in solution. Addition of an excess of PVP (1) or CA (2) and 5 h of reflux in tetrahydrofuran (THF) at 66 °C leads to Ag NPs of small size (4.8 ± 3.0 nm for PVP-Ag NPs and 3.0 ± 1.2 nm for CA-Ag NPs) that coexist in both cases with larger nanoparticles between 7 and 25 nm. Both nanomaterials display a high antibacterial effectiveness against E. coli. The TEM analysis of the nanoparticle–bacterial cell membrane interaction shows an optimal size-specific affinity for PVP-Ag NPs of 5.4 ± 0.7 nm in the presence of larger size silver nanoparticles. An organometallic approach permits the synthesis of small size silver nanoparticles (ca 5 nm) as a main population in the presence of larger size nanoparticles. Optimal silver nanoparticle size-selection (5.4 nm) for the interaction with the bacterial membrane is achieved.

A Differential Mobility Analyzer (DMA) for Size Selection of Nanoparticles at High Flow Rates

This article demonstrates the feasibility of scaling-up the technique for particle size selection in the gas phase based on differential mobility analysis. Nano-DMAs used to select the particle size in processes for the synthesis of nanomaterials in the laboratory operate at aerosol flow rates of a few liters per minute. A new DMA capable of classifying nanoparticles of up to 30 nm in size at aerosol flow rates as high as 100 l· min −1 will be presented (HF-DMA). A major advantage of the HF-DMA over current nano-DMAs covering the same particle size is that its resolution is almost unaffected by Brownian diffusion for particles as small as 3 nm. Monodisperse nanoparticles in the 5 to 25 nm size range have been produced at flow rates of up to 90 l· min −1 . The spread in particle size and the particle number concentration were studied with respect to their dependency on the flow rates in the HF-DMA. The measurements reflect the behavior predicted by the theory. The HF-DMA makes it possible to deliver nanoparticles of a well-defined size at yields two orders of magnitude higher than with current nano-DMAs.

Absorption Properties of Hybrid SnO2 Nanocrystal-Carbon Nanotube Structures

Tin oxide (SnO 2 ) nanocrystals of a few nanometers are of great interest for electronic applications. Here we present a mini-arc plasma method to produce aerosol tin oxide nanocrystals at atmospheric pressure. The product SnO 2 nanocrystals are then assembled onto the external surface of carbon nano-tubes (CNTs) to form hybrid SnO 2 -CNT structures. The absorption properties of both the SnO 2 nanocrystals and the SnO 2 -CNT hybrid structures have been characterized. Quantum size effects have been observed for as-produced SnO 2 nanocrystals. The intrinsic nanoparticle size selection during the assembly process results in a blue shift of the absorption spectrum for hybrid nano-structures.

Nanoparticle ordering by dewetting of Co on SiO2

Most metals on SiO2 have a finite contact angle and are therefore subject to dewetting during thermal processing. The resulting dewetting morphology is determined primarily by nucleation and growth or instabilities. The dewetting mechanism implies a disordered spatial arrangement for homogeneous nucleation, but an ordered one for instabilities such as spinodal decomposition. Here, we show that the morphology of laser-melted ultrathin Co film (4-nm thick) can be attributed to dewetting via an instability. Dewetting leads to breakup of the continuous Co film into nanoparticles with a monomodal size distribution with an average particle diameter of 75 nm±23 nm. These nanoparticles have short-range order (SRO) of 130 nm in their separation. This result has important implications for nanomanufacturing with a robust spacing or size selection of nanoparticles in addition to spatial ordering.

Controlled decoration of carbon nanotubes with nanoparticles

We present an efficient gas-phase route to decorate both single-walled and multiwalledcarbon nanotubes with nanoparticles based on electrostatic force directed assembly. Weshow that, in addition to an intrinsic nanoparticle size selection, the packingdensity and the final size distribution of nanoparticles docking on nanotubes can becontrolled during the assembly process. Our method enables in situ coating ofnanotubes with nanoparticles. Due to the inherent material-independent nature of theelectrostatic force, various compositions of such nanoparticle–nanotube structurescan be produced using this new technique. These novel structures will enablenew opportunities for exploring nanoscience, nanotechnology, and biotechnology.