Nastaran Hashemi

Optofluidic characterization of marine algae using a microflow cytometer

The effects of global warming, pollution in river effluents, and changing ocean currents can be studied by characterizing variations in phytoplankton populations. We demonstrate the design and fabrication of a Microflow Cytometer for characterization of phytoplankton. Guided by chevron-shaped grooves on the top and bottom of a microfluidic channel, two symmetric sheath streams wrap around a central sample stream and hydrodynamically focus it in the center of the channel. The lasers are carefully chosen to provide excitation light close to the maximum absorbance wavelengths for the intrinsic fluorophores chlorophyll and phycoerythrin, and the excitation light is coupled to the flow cytometer through the use of an optical fiber. Fluorescence and light scatter are collected using two multimode optical fibers placed at 90-degree angles with respect to the excitation fiber. Light emerging from these collection fibers is directed through optical bandpass filters into photomultiplier tubes. The cytometer measured the optical and side scatter properties of Karenia b., Synechococcus sp., Pseudo-Nitzchia, and Alexandrium. The effect of the sheath-to-sample flow-rate ratio on the light scatter and fluorescence of these marine microorganisms was investigated. Reducing the sample flow rate from 200 μL/min to 10 μL/min produced a more tightly focused sample stream and less heterogeneous signals.

Three-Dimensional Paper-Based Microfluidic Device for Assays of Protein and Glucose in Urine

The first step in curing a disease is being able to detect the disease effectively. Paper-based microfluidic devices are biodegradable and can make diagnosing diseases cost-effective and easy in almost all environments. We created a three-dimesnional (3D) paper device using wax printing fabrication technique and basic principles of origami. This design allows for a versatile fabrication technique over previously reported patterning of SU-8 photoresist on chromatography paper by employing a readily available wax printer. The design also utilizes multiple colorimetric assays that can accommodate one or more analytes including urine, blood, and saliva. In this case to demonstrate the functionality of the 3D paper-based microfluidic system, a urinalysis of protein and glucose assays is conducted. The amounts of glucose and protein introduced to the device are found to be proportional to the color change of each assay. This color change was quantified by use of Adobe Photoshop. Urine samples from participants with no pre-existing health conditions and one person with diabetes were collected and compared against synthetic urine samples with predetermined glucose and protein levels. Utilizing this method, we were able to confirm that both protein and glucose levels were in fact within healthy ranges for healthy participants. For the participant with diabetes, glucose was found to be above the healthy range while the protein level was in the healthy range.

Microflow Cytometer for optical analysis of phytoplankton

Analysis of the intrinsic fluorescence profiles of individual marine algae can be used in general classification of organisms based on cell size and fluorescence properties. We describe the design and fabrication of a Microflow Cytometer on a chip for characterization of phytoplankton. The Microflow Cytometer measured distinct side scatter and fluorescence properties of Synechococcus sp., Nitzschia d., and Thalassiosira p.; measurements were confirmed using the benchtop Accuri C6 flow cytometer. The Microflow Cytometer proved sensitive enough to detect and characterize picoplankton with diameter approximately 1 μm and larger phytoplankton of up to 80 μm in length. The wide range in size discrimination coupled with detection of intrinsic fluorescent pigments suggests that this Microflow Cytometer will be able to distinguish different populations of phytoplankton on unmanned underwater vehicles.

The nonlinear dynamics of tapping mode atomic force microscopy with capillary force interactions

We study the nonlinear dynamics of a tapping mode atomic force microscope with tip-surface interactions that include attractive, repulsive, and capillary force contributions using numerical techniques tailored for hybrid or discontinuous dynamical systems that include forward-time simulation with event handling and numerical pseudo-arclength continuation. We find four branches of periodic solutions that are separated by windows of complex and irregular dynamics. The branches of periodic solutions end where the cantilever comes into grazing contact with event surfaces in state space, corresponding to the onset of capillary interactions and the onset of repulsive forces associated with contact. These windows of irregular dynamics are found to coexist with the periodic branches of solutions as well as exist beyond the termination of the periodic solution. Finally, we show that these details can be overlooked unless one is careful to sample the dynamics appropriately.

The single-band red upconversion luminescence from morphology and size controllable Er3+/Yb3+ doped MnF2 nanostructures

Er3+/Yb3+ doped MnF2 nanostructures have been prepared via a solvothermal method. The morphology of the nanocrystals could be well controlled from nanoparticles to nanoclusters and nanolanterns by varying the volume ratio between oleic acid and ethanol in the solvent. Moreover, the size is tuned from 200 nm to 1.5 μm with the increase of reaction temperature from 110 to 200 °C. It is shown that controlling the doping concentration (Yb3+ ≤ 20 mol%) is essential to preserve the single phase and morphology of the MnF2 host. Single-band red upconversion (UC) emission can be generated in Er3+ single and Er3+/Yb3+ codoped MnF2 nanoclusters due to the energy transfer between host Mn2+ and dopant Er3+ ions. The detailed studies suggest that our MnF2:Er3+/Yb3+ nanocrystals have the strongest single-band luminescence feature at the dopant concentrations of Er3+ (2 mol%) and Yb3+ (20 mol%). The brighter red emission from the current nanostructure compared with those from NaYF4:Er3+/Yb3+ has shown its suitability as an efficient UC luminescence host. It is expected that the achieved intense pure red emission may have potential application in in vivo bioimaging.

In Situ Phytoplankton Analysis: There’s Plenty of Room at the Bottom

In Situ Phytoplankton Analysis: There’s Plenty of Room at the Bottom Jeffrey S. Erickson, Nastaran Hashemi, James M. Sullivan, Alan D. Weidemann, and Frances S. Ligler* Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Code 6900, Washington, D.C. 20375-5438, United States WET Laboratories, Inc., Department of Research, 70 Dean Knauss Drive, Narragansett, Rhode Island 02882, United States Hydro-Optics, Sensors, and Systems Section, Naval Research Laboratory, Code 7333, Stennis Space Center, Mississippi 39529-5004, United States

Artificial neural network as a predictive tool for emissions from heavy-duty diesel vehicles in Southern California

Abstract An artificial neural network (ANN) was trained on chassis dynamometer data and used to predict the oxides of nitrogen (NO x ), carbon dioxide (CO2), hydrocarbons (HC), and carbon monoxide (CO) emitted from heavy-duty diesel vehicles. Axle speed, torque, their derivatives in different time steps, and two novel variables that defined speed variability over 150 seconds were defined as the inputs for the ANN. The novel variables were used to assist in predicting off-cycle emissions. Each species was considered individually as an output of the ANN. The ANN was trained on the Highway cycle and applied to the City/Suburban Heavy Vehicle Route (CSHVR) and Urban Dynamometer Driving Schedule (UDDS) with four different sets of inputs to predict the emissions for these vehicles. The research showed acceptable prediction results for the ANN, even for the one trained with only eight inputs of speed, torque, their first and second derivatives at one second, and two variables related to the speed pattern over the last 150 seconds. However, off-cycle operation (leading to high NO x emissions) was still difficult to model. The results showed an average accuracy of 0.97 for CO2, 0.89 for NO x , 0.70 for CO, and 0.48 for HC over the course of the CSHVR, Highway, and UDDS.

On-chip development of hydrogel microfibers from round to square/ribbon shape

We use a microfluidic approach to fabricate gelatin fibers with controlled sizes and cross-sections. Uniform gelatin microfibers with various morphologies and cross-sections (round and square) are fabricated by increasing the gelatin concentration of the core solution from 8% to 12%. Moreover, the increase of gelatin concentration greatly improves the mechanical properties of gelatin fibers; the Youngs modulus and tensile stress at break of gelatin (12%) fibers are raised about 2.2 and 1.9 times as those of gelatin (8%) fibers. The COMSOL simulations indicate that the sizes and cross-sections of the gelatin fibers can be tuned by using a microfluidic device with four-chevron grooves. The experimental results demonstrate that the decrease of the sheath-to-core flow-rate ratio from 150 : 1 to 30 : 1 can increase the aspect ratio and size of ribbon-shaped fibers from 35 μm × 60 μm to 47 μm × 282 μm, which is consistent with the simulation results. The increased size and shape evolution of the cross-section can not only strengthen the Youngs modulus and tensile stress at break, but also significantly enhance the tensile strain at break.

Investigation of spray-coated silver-microparticle electrodes for ionic electroactive polymer actuators

We have employed the easy-to-scale-up method of spray-coating in combination with layer-by-layer self-assembly technique to fabricate ionic electroactive polymer actuators (IEAPAs). IEAPAs with spray-coated silver microparticle electrodes demonstrate enhanced strain and response time when compared to nearly identical, optimized conventional IEAPA with gold leaf electrodes. The results demonstrate that strain of these IEAPAs increases with the decrease of thickness of the outer silver microparticle electrodes. In addition, the response time of the actuators at frequencies of 1 and 10 Hz improves compared to optimized conventionally fabricated IEAPA. It was found that samples consisting of spray-coated silver electrodes can charge up to ∼3 times faster than conventional actuators at 1 Hz frequency. Faster charging/discharging results in higher mobility of ions within the actuator and thus, faster actuation. Given the relatively large thickness of the silver microparticle electrodes (∼50× gold leaf), similar...

A paper-based microbial fuel cell operating under continuous flow condition

Microbial fuel cells have gained popularity as a viable, environmentally friendly alternative for the production of energy. However, the challenges in miniaturizing the system for application in smaller devices as well as the short duration of operation have limited the application of these devices. Here, the capillary motion was employed to design a self-pumped paper-based microbial fuel cell operating under continuous flow condition. A proof-of-concept experiment ran approximately 5 days with no outside power or human interference required for the duration of operation. Shewanella oneidensis MR-1 was used to create a maximum current of 52.25 µA in a 52.5 µL paper-based microfluidic device. SEM images of the anode following the experiment showed biofilm formation on the carbon cloth electrode. The results showed a power density of approximately 25 W/m3 and proved unique capabilities of the paper-based microbial fuel cells to produce energy for an extended period of time.