Fariborz Taghipour

High-throughput analysis of single hematopoietic stem cell proliferation in microfluidic cell culture arrays

Heterogeneity in cell populations poses a major obstacle to understanding complex biological processes. Here we present a microfluidic platform containing thousands of nanoliter-scale chambers suitable for live-cell imaging studies of clonal cultures of nonadherent cells with precise control of the conditions, capabilities for in situ immunostaining and recovery of viable cells. We show that this platform mimics conventional cultures in reproducing the responses of various types of primitive mouse hematopoietic cells with retention of their functional properties, as demonstrated by subsequent in vitro and in vivo (transplantation) assays of recovered cells. The automated medium exchange of this system made it possible to define when Steel factor stimulation is first required by adult hematopoietic stem cells in vitro as the point of exit from quiescence. This technology will offer many new avenues to interrogate otherwise inaccessible mechanisms governing mammalian cell growth and fate decisions.

Large-Scale Synthesis of TiO2 Microspheres with Hierarchical Nanostructure for Highly Efficient Photodriven Reduction of CO2 to CH4

In this study, a simple and reproducible synthesis strategy was employed to fabricate TiO2 microspheres with hierarchical nanostructure. The microspheres are macroscopic in the bulk particle size (several hundreds to more than 1000 μm), but they are actually composed of P25 nanoparticles as the building units. Although it is simple in the assembly of P25 nanoparticles, the structure of the as-prepared TiO2 microspheres becomes unique because a hierarchical porosity composed of macropores, larger mesopores (ca. 12.4 nm), and smaller mesopores (ca. 2.3 nm) has been developed. The interconnected macropores and larger mesopores can be utilized as fast paths for mass transport. In addition, this hierarchical nanostructure may also contribute to some extent to the enhanced photocatalytic activity due to increased multilight reflection/scattering. Compared with the state-of-the-art photocatalyst, commercial Degussa P25 TiO2, the as-prepared TiO2 microsphere catalyst has demonstrated significant enhancement in photodriven conversion of CO2 into the end product CH4. Further enhancement in photodriven conversion of CO2 into CH4 can be easily achieved by the incorporation of metals such as Pt. The preliminary experiments with Pt loading reveal that there is still much potential for considerable improvement in TiO2 microsphere based photocatalysts. Most interestingly and significantly, the synthesis strategy is simple and large quantity of TiO2 microspheres (i.e., several hundred grams) can be easily prepared at one time in the lab, which makes large-scale industrial synthesis of TiO2 microspheres feasible and less expensive.

Application of ultraviolet light-emitting diodes (UV-LEDs) for water disinfection: A review.

Ultraviolet (UV) disinfection is an effective technology for the inactivation of pathogens in water and is of growing interest for industrial application. A new UV source - ultraviolet light-emitting diode (UV-LED) - has emerged in the past decade with a number of advantages compared to traditional UV mercury lamps. This promising alternative raises great interest in the research on application of UV-LEDs for water treatment. Studies on UV-LED water disinfection have increased during the past few years. This article presents a comprehensive review of recent studies on UV-LEDs with various wavelengths for the inactivation of different microorganisms. Many inconsistent and incomparable data were found from published studies, which underscores the importance of establishing a standard protocol for studying UV-LED inactivation of microorganisms. Different UV sensitivities to UV-LEDs and traditional UV lamps were observed in the literature for some microorganisms, which requires further investigation for a better understanding of microorganism response to UV-LEDs. The unique aspects of UV-LEDs improve inactivation effectiveness by applying LED special features, such as multiple wavelengths and pulsed illumination; however, more studies are needed to investigate the influencing factors and mechanisms. The special features of UV-LEDs offer the flexibility of novel reactor designs for a broad application of UV-LED reactors.

Simulation of UV Photoreactor for Degradation of Chemical Contaminants: Model Development and Evaluation

Models simulating the performance of UV reactors enhance our understanding of the fundamental principles governing the operation of these units. When modeling the performance of UV reactors, governing equations for all related phenomena are derived and solved. This research presents a step-by-step methodology to setup and solve the governing equations determining the performance of UV reactors and to evaluate the results. A computational fluid dynamic (CFD) model was developed in order to simulate UV photoreactors in the Eulerian framework for chemical removal using a UV-based hydroxyl radical initiated oxidation process. Verifying the results of the integrated CFD model, a novel method was developed using a modified planar laser-induced fluorescence technique for measuring tracer concentration profiles inside the UV reactor. In addition, the components of the CFD model--hydrodynamics and radiation--were evaluated using experimental profile throughout the entire reactor. This verified procedure can be applied to the simulation and optimization of UV photoreactors with various geometries and operating conditions.

Development of a method for the characterization and operation of UV-LED for water treatment

Tremendous improvements in semiconductor technology have made ultraviolet light-emitting diodes (UV-LEDs) a viable alternative to conventional UV sources for water treatment. A robust and validated experimental protocol for studying the kinetics of microorganism inactivation is key to the further development of UV-LEDs for water treatment. This study proposes a protocol to operate UV-LEDs and control their output as a polychromatic radiation source. In order to systematically develop this protocol, the results of spectral power distribution, radiation profile, and radiant power measurements of a variety of UV-LEDs are presented. A wide range of UV-LEDs was selected for this study, covering various UVA, UVB, and UVC wavelengths, viewing angles from 3.5° to 135°, and a variety of output powers. The effects of operational conditions and measurement techniques were investigated on these UV-LEDs using a specially designed and fabricated setup. Operating conditions, such as the UV-LED electrical current and solder temperature, were found to significantly affect the power and peak wavelength output. The measurement techniques and equipment, including the detector size, detector distance from the UV-LED, and potential reflection from the environment, were shown to influence the results for many of the UV-LEDs. The results obtained from these studies were analyzed and applied to the development of a protocol for UV-LED characterization. This protocol is presented as a guideline that allows the operation and control of UV-LEDs in any structure, as well as accurately measuring the UV-LED output. Such information is essential for performing a reliable UV-LED assessment for the inactivation of microorganisms and for obtaining precise kinetic data.

UV-LED Photo-activated Chemical Gas Sensors: A Review

ABSTRACT Metal oxide semiconductor gas sensors operating under UV irradiation have been validated for detection of variety of chemicals in wide ranges of concentrations at room temperature. This article reviews recent advances in UV-activated metal oxide gas sensors in general and outlines the operating principles and sensing performance of UV-LED based sensors in particular. The sensing properties of several metal oxide semiconductors such as ZnO, TiO2, SnO2, In2O3, and metal oxide composites under UV-LED irradiation are individually presented and their advantages and shortcomings toward various gases are compared. Moreover, it is demonstrated that for the UV-LED based gas sensors, the performance can be improved by optimizing the sensor platform design and UV source parameters such as wavelength and power intensity. Further, it is illustrated that the gas sensing selectivity can be tuned by modifying the semiconductor layer structure or adjusting appropriate wavelength to an optimal value.

Iodine Behavior Under Conditions Relating to Nuclear Reactor Accidents

Abstract The short-term radiological impact of some serious reactor accidents may be governed by the release of airborne radioiodine to the environment. The impacts of parameters affecting iodine volatility, including radiation, iodine concentration, and solution pH, were investigated under a range of postaccident chemical conditions expected in a reactor containment structure. A bench-scale apparatus, installed in the irradiation chamber of a Gammacell, was used to measure the rate of iodine volatilization from dilute, 10-6 to 10-4 M, CsI solutions with pH values from 5 to 9. Iodine volatilization dramatically increased in the presence of radiation. The volatilization rates were nearly proportional to iodine concentration over the range of concentrations and pH values examined. Volatilization rate increased significantly with a decrease in pH. A kinetic-based model containing a mechanistic description of iodine chemistry was developed to simulate the radiation chemistry of iodine. The majority of the model prediction and experimental results of iodine volatilization rates were in agreement, although some divergence was evident.

Radioiodine Volatilization in the Presence of Organic Compounds

Abstract The impact of organic compounds on iodine volatility was investigated under a range of postaccident chemical conditions expected in a reactor containment structure. The rate of production of volatile iodine was evaluated in the presence of 10-3 M concentrations of carbonyl, alkyl halide, and aromatic compounds. A bench-scale apparatus, installed in the irradiation chamber of a Gammacell, was used to measure the rate of iodine volatilization from 10-6 to 10-4 M CsI solutions with pH values from 5 to 9. The results indicated that organic compounds could be classified into groups, based on their distinct effects on iodine volatility. Iodine volatilization increased significantly, up to two orders of magnitude, in the presence of carbonyl compounds and alkyl chlorides, while it decreased in the presence of aromatic compounds. Gas phase speciation indicated that organic iodides dominate the airborne iodine species in the presence of carbonyl compounds and alkyl halides.

Development of a CFD-Based Model for Photo-Reactor Simulation

Publisher Summary This chapter discusses the computational fluid dynamics (CFD)-based model development for photo-reactor simulation. A CFD-based model that integrates reactor hydrodynamics, kinetics, and radiation intensity was developed in order to simulate the performance of photo-reactors for fluid treatment. The flow paths of chemical species were computed from the CFD generated velocity profiles, using a particle-tracking algorithm. The path of each chemical species was integrated with the intensity and kinetic models to calculate the overall conversion of the target compounds in the reactor. The model was applied to the simulation of various conceptual reactor designs. The performance of photo-reactor systems is strongly affected by the flow and UV intensity distribution within the reactors. As a result of the complexity of these systems and interaction of many parameters, design optimization of photo-reactors can best be achieved through modeling and reactor performance simulation. It is capable of providing insight into reactor design and studying the effect of geometry parameters (e.g. inlet/outlet positions, and lamp configurations) on reactor performance.

Protocol for Determining Ultraviolet Light Emitting Diode (UV-LED) Fluence for Microbial Inactivation Studies

Determining fluence is essential to derive the inactivation kinetics of microorganisms and to design ultraviolet (UV) reactors for water disinfection. UV light emitting diodes (UV-LEDs) are emerging UV sources with various advantages compared to conventional UV lamps. Unlike conventional mercury lamps, no standard method is available to determine the average fluence of the UV-LEDs, and conventional methods used to determine the fluence for UV mercury lamps are not applicable to UV-LEDs due to the relatively low power output, polychromatic wavelength, and specific radiation profile of UV-LEDs. In this study, a method was developed to determine the average fluence inside a water suspension in a UV-LED experimental setup. In this method, the average fluence was estimated by measuring the irradiance at a few points for a collimated and uniform radiation on a Petri dish surface. New correction parameters were defined and proposed, and several of the existing parameters for determining the fluence of the UV mercury lamp apparatus were revised to measure and quantify the collimation and uniformity of the radiation. To study the effect of polychromatic output and radiation profile of the UV-LEDs, two UV-LEDs with peak wavelengths of 262 and 275 nm and different radiation profiles were selected as the representatives of typical UV-LEDs applied to microbial inactivation. The proper setup configuration for microorganism inactivation studies was also determined based on the defined correction factors.