Tandeep S. Chadha

Linker-free deposition and adhesion of Photosystem I onto nanostructured TiO2 for biohybrid photoelectrochemical cells.

Photosystem I (PSI) from oxygenic photosynthetic organisms is an attractive sensitizer for nano-biohybrid solar cells as it has a combined light-harvesting and reaction center in one protein complex and operates at a quantum yield close to one in biological systems. Using a linker-free deposition technique enabled by an electrospray system, PSI was coupled to 1-D nanostructured titanium dioxide thin films to fabricate an electrode for a photoelectrochemical cell. After deposition, the surfactant in the PSI aggregate was dissolved in the surfactant-free electrolyte, ensuring that partly hydrophobic PSI was not resuspended and stayed in contact with titanium dioxide. A maximum current density of 4.15 mA cm(-2) was measured after 10 min of electrospray deposition, and this is the highest current density reported so far for PSI-based photoelectrochemical cells. The high current is attributed to 1D nanostructure of titanium dioxide and orientation of the PSI onto the surface, which allows easy transfer of electrons.

Measurement of sub-2 nm clusters of pristine and composite metal oxides during nanomaterial synthesis in flame aerosol reactors.

Measuring stable clusters to understand particle inception will aid the synthesis of well-controlled nanoparticles via gas-phase aerosol routes. Using a Half Mini differential mobility analyzer, the presence of monomers, dimers, trimers, and tetramers was detected for the first time in a flame aerosol reactor during the synthesis of pristine TiO2 and TiO2/SiO2 nanocomposites. Atomic force microscopy confirmed the presence and the size of sub-2 nm clusters. The detection of these clusters elucidated the initial stages of particle formation during combustion synthesis and supported previous hypotheses that collisional growth from stable monomers of metal oxides is the first step of particle growth.

Perspective on Nanoparticle Technology for Biomedical Use.

This review gives a short overview on the widespread use of nanostructured and nanocomposite materials for disease diagnostics, drug delivery, imaging and biomedical sensing applications. Nanoparticle interaction with a biological matrix/entity is greatly influenced by its morphology, crystal phase, surface chemistry, functionalization, physicochemical and electronic properties of the particle. Various nanoparticle synthesis routes, characterization, and functionalization methodologies to be used for biomedical applications ranging from drug delivery to molecular probing of underlying mechanisms and concepts are described with several examples (150 references).

Study of the Charge Distribution on Liposome Particles Aerosolized by Air-Jet Atomization

BACKGROUND Air-jet atomization is a common technique used for the generation of therapeutic aerosols from liposome suspensions for drug delivery to the lungs. Although the technique does not use an electric field, the aerosols generated by this technique are still charged, and this may affect respiratory drug deposition. METHODS In this study, the charge distribution of liposomes aerosolized by an air-jet atomizer was measured using a tandem differential mobility analyzer (TDMA) technique. The liposomes, composed of a mixture of two amphiphilic lipids and cholesterol, were synthesized by the dehydration-rehydration vesicle method. The effect of the precursor suspension properties, such as medium composition, pH, conductivity, and lipid mass concentration, on the charge distribution of the liposome aerosols was studied. RESULTS AND CONCLUSIONS Results showed that the atomized liposomes have a bipolar charge distribution, and the number-fraction of charged liposome aerosols was influenced strongly by properties of the precursor solution under investigation. Liposomes synthesized in deionized water were observed to carry much higher charges than those synthesized in phosphate-buffered saline (PBS). Increasing the lipid mass concentration in the precursor suspension resulted in a decrease in the charge on the aerosols. Thus, the precursor suspension properties--composition, pH, and conductivity--can be used to control the magnitude of charge on liposome aerosols and to synthesize engineered liposome particles for the pulmonary delivery of drugs with controlled alveolar deposition and controlled delivery to alveolar macrophages.

Non-invasive aerosol delivery and transport of gold nanoparticles to the brain

Targeted delivery of nanoscale carriers containing packaged payloads to the central nervous system has potential use in many diagnostic and therapeutic applications. Moreover, understanding of the bio-interactions of the engineered nanoparticles used for tissue-specific delivery by non-invasive delivery approaches are also of paramount interest. Here, we have examined this issue systematically in a relatively simple invertebrate model using insects. We synthesized 5 nm, positively charged gold nanoparticles (AuNPs) and targeted their delivery using the electrospray aerosol generator. Our results revealed that after the exposure of synthesized aerosol to the insect antenna, AuNPs reached the brain within an hour. Nanoparticle accumulation in the brain increased linearly with the exposure time. Notably, electrophysiological recordings from neurons in the insect brain several hours after exposure did not show any significant alterations in their spontaneous and odor-evoked spiking properties. Taken together, our findings reveal that aerosolized delivery of nanoparticles can be an effective non-invasive approach for delivering nanoparticles to the brain, and also presents an approach to monitor the short-term nano-biointeractions.

Growth of single crystal, oriented SnO2 nanocolumn arrays by aerosol chemical vapour deposition

A single-step, template-free aerosol chemical vapor deposition (ACVD) method is demonstrated to grow well-aligned SnO2 nanocolumn arrays. The ACVD system parameters, which control thin film morphologies, were systematically explored to gain a qualitative understanding of nanocolumn growth mechanisms. Key growth variables include feed rates, substrate temperature, and deposition time. System dynamics relating synthesis variables to aerosol characteristics and processes (collision and sintering) are elucidated. By adjusting system parameters, control of the aspect ratio, height, and crystal structure of columns is demonstrated. A self-catalyzed (SnO2 particles) vapor–solid (VS) growth mechanism, whereby a vapor–particle deposition regime results in the formation of nanocrystals that act as nucleation sites for the preferential formation and growth of nanocolumns, is proposed and supported. Density functional theory (DFT) calculations indicate that the preferential orientation of thin films is a function of the system redox conditions, further supporting the proposed VS growth mechanism. When taken together, these results provide quantitative insight into the growth mechanism(s) of SnO2 nanocolumn thin films via ACVD, which is critical for engineering these, and other, nanostructured films for direct incorporation into functional devices.

Carbon elimination from silicon kerf: Thermogravimetric analysis and mechanistic considerations

40% of ultrapure silicon is lost as kerf during slicing to produce wafers. Kerf is currently not being recycled due to engineering challenges and costs associated with removing its abundant impurities. Carbon left behind from the lubricant remains as one of the most difficult contaminants to remove in kerf without significant silicon oxidation. The present work enables to better understand the mechanism of carbon elimination in kerf which can aid the design of better processes for kef recycling and low cost photovoltaics. In this paper, we studied the kinetics of carbon elimination from silicon kerf in two atmospheres: air and N2, under a regime of no-diffusion-limitation. We report the apparent activation energy in both atmospheres using three methods: Kissinger, and two isoconversional approaches. In both atmospheres, a bimodal apparent activation energy is observed, suggesting a two stage process. A reaction mechanism is proposed in which (a) C-C and C-O bond cleavage reactions occur in parallel with polymer formation; (b) at higher temperatures, this polymer fully degrades in air but leaves a tarry residue in N2 that accounts for about 12% of the initial total carbon.

Sustainable one step process for making carbon-free TiO 2 anodes and sodium-ion battery electrochemistry

Electrodes with a carbon-free architecture impart a sustainable solution by eliminating side reactions. Such designs are required for anode systems, especially for sodium-ion batteries where the capacity contribution from carbon is noticed. Herein, carbon-free TiO2 is prepared in the monolithic dendritic form via a facile single-step aerosol vapor deposition technique, grown onto a stainless steel current collector. The single crystalline nature of the anatase dendrites explicitly provides detailed crystallographic analysis. Herein, we have realized an escalation of the rutile phase with the existing anatase phase upon cycling, which is depicted as a moire pattern, while evaluating the structure through TEM studies. As the anode is carbon and binder-free, the overall material is electrochemically active, and hence appreciably improves the volumetric energy-density. Here, we observe a long cycle life of 1000 cycles from the additive-free anatase dendrites with an adequate capacity retention of 85.1%. Therefore, we believe that our single-step fabrication process to procure additive-free monolithic electrodes is a forthcoming paramount technique to produce sodium-ion batteries on mass.

Production and performance of a Photosystem I-based solar cell using nano-columnar TiO 2

To meet the worlds growing energy demands in a renewable and cost-effective manner, Photosystem I has been studied as a model for solar energy capture. Previous work has demonstrated the ability to construct low cost biohybrid solar cells using Photosystem I and specialty surfactants onto metal oxide surfaces. Electrospray deposition has also been used for adsorption of plant proteins onto metal oxide surfaces. Attachment of Photosystem I onto nanostructured materials increases the surface area and activity of biohybrid solar cells. Recent work has shown that Photosystem I can be attached to metal oxide surfaces without using linkers and maintain high current density. However, the current density of the surface decreases over the course of weeks (unpublished data). This work investigated the performance of Photosystem I-based solar cells manufactured using electrospray deposition. Photosystem I was successfully deposited onto metal oxide surfaces, and current densities of up to 6.84 mA/cm2 were measured. Different amounts of protein were deposited and the solar performance was tested for each cell. It was shown that very small and very large amounts of PS I increase the current density, but there is an intermediate regime where performance drops. This intermediate regime was attributed to a shading effect of the protein on the surface and self-assembly effects of the protein on the surface.