Andrew Michael Leach

Dynamic nuclear polarization polarizer for sterile use intent.

A novel polarizer based on the dissolution‐dynamic nuclear polarization (DNP) method has been designed, built and tested. The polarizer differs from those previously described by being designed with sterile use intent and being compatible with clinical use. The main features are: (1) an integral, disposable fluid path containing all pharmaceuticals constituting a sterile barrier, (2) a closed‐cycle cryogenic system designed to eliminate consumption of liquid cryogens and (3) multi‐sample polarization to increase throughput. The fluid path consists of a vial with the agent to be polarized, a pair of concentric inlet and outlet tubes connected to a syringe with dissolution medium and a receiver, respectively. The fluid path can operate at up to 400 K and 2.0 MPa and generates volumes as high as 100 mL. An inline filter removes the amount of electron paramagnetic agent in the final product by more than 100‐fold in the case of [1‐13C]pyruvate. The system uses a sorption pump in conjunction with a conventional cryocooler. The system operates through cycles of pumping to low temperature and regeneration of the sorption pump. The magnet accommodates four samples at the same time. A temperature of less than 1 K was achieved for 68 h (no sample heat loads) with a liquid helium volume of 2.4 L. The regeneration of the liquid helium could be achieved in less than 10 h, and the transition to cold (< 1.2 K) was achieved in less than 90 min. A solid state polarization of 36 ± 4% for [1‐13C]pyruvic acid was obtained with only 10 mW of microwave power. The loading of a sample adds less than 50 J of heat to the helium bath by introducing the sample over 15 min. The heat load imposed on the helium bath during dissolution was less than 70 J. The measured liquid state polarization was 18 ± 2%. Copyright

Selective gas nanosensors with multisize CdSe nanocrystal/polymer composite films and dynamic pattern recognition

We introduce a concept for selective chemical sensing based on different size semiconductor nanocrystals incorporated into a preselected polymer matrix. When CdSe nanocrystals of different sizes (2.8 and 5.6nm diam) were incorporated into a polymer film, each size of the nanocrystals demonstrated a distinct photoluminescence response pattern (excitation at λ=407nm) upon exposure to polar and nonpolar vapors in air at atmospheric pressure. When this composite response was processed using a multivariate analysis, a single film with different size CdSe nanocrystals served as a selective sensor.

Theory and practice of ubiquitous quantitative chemical analysis using conventional computer optical disk drives.

We demonstrate a new attractive approach for ubiquitous quantitative chemical or biological sensing when analog signals are acquired from conventional optical disk drives, and these signals are used for quantitative detection of optical changes of sensing films deposited on conventional CD and DVD optical disks. Our developed analytical model of the operation of this Lab-on-DVD system describes the optical response of sensing films deposited onto the read surface of optical disks by taking into account the practical aspects of system performance that include possible reagent leaching effects, water sampling (delivering) efficiency, and possible changes of the film morphology after water removal. By applying a screen-printing process, we demonstrated a laboratory-scale automated production of sensing films with an average thickness of approximately 10 microm and a thickness relative standard deviation of <3% across multiple films. Finally, we developed a system for delivery of water-sample volumes to sensing films on the disk that utilized a multifunctional jewel case assembly.

Jet Impingement Melting With Vaporization: A Numerical Study

The objective of this work was to develop a computational model for better understanding of the process of producing contrast agent, used in Magnetic Resonance Imaging (MRI). Contrast agents are used to provide high-resolution anatomical and functional information to identify tumor growth for prostrate and breast cancers. The production process for the contrast agents involves melting and dissolution of the imaging agent (maintained at very low temperature ∼1K to retain its polarization capability) by injecting the jet of alkaline solvent. Dissolution should happen in minimum time to allow for time required to inject contrast agent into the patient with sufficient time to travel to the targeted organ. This process involves multi-phase, multi-species and chemically reacting fluid dynamics. The intricacy and complexity of the melting process and very small time scales (order of a few milliseconds) poses practical challenges of collecting enough experimental data for the better understanding of such processes. It creates a need for looking at these kinds of processes from a numerical point of view. A computational model was developed in commercial software to capture the relevant physics involved in the flow-thermal process. System was analyzed to guide design changes with the objective of minimizing the melting time of imaging agent. Model predictions were validated against experiments and sensitivity studies were carried out pertaining to operating parameters such as solvent flow rate, temperature and other geometrical parameters. The predictions from model gave an insight into the process. It was found that melting time is not only a function of operating conditions and geometrical parameters but also a function of nature of the multiphase flow. Other than solid and molten phase, vapor phase (vaporization of the alkaline solvent) also coexist in the system under certain operating conditions; which further complicates the process. Desired operating conditions and geometrical changes were recommended to minimize the melting time. It is believed that current findings and numerical modeling approach could be utilized in other similar processes.Copyright

High-Throughput Screening of Vapor Selectivity of Multisize CdSe Nanocrystal/Polymer Composite Films

We have achieved selective gas sensing based on different size semiconductor nanocrystals incorporated into rationally selected polymer matrices. From the high-throughput screening experiments, we have found that when CdSe nanocrystals of different size (2.8 and 5.6 nm diameter) were incorporated into different types of polymer films, the photoluminescence (PL) response patterns upon laser excitation at 407-nm and exposure to polar and nonpolar solvent vapors were dependent on the nature of polymer. We analyzed the spectral PL response from both sizes of CdSe nanocrystals using multivariate analysis tools. Results of this multivariate analysis demonstrate that a single film with different size CdSe nanocrystals serves as a selective sensor. The stability of PL response to vapors was evaluated upon 16 h of continuous exposure to laser excitation.

Gas Sensor Materials Based on Semiconductor Nanocrystal / Polymer Composite Films

We introduce here a new concept for selectivity improvement in chemical sensing. We have found that when semiconductor CdSe nanocrystals of different size were incorporated into a polymer film and photoactivated, each size of CdSe nanocrystals unexpectedly demonstrated its own photoluminescence (PL) response pattern upon exposure to polar and nonpolar vapors. When this composite response was processed using multivariate analysis, a single film with different size CdSe nanocrystals served as a selective sensor.