Enzymes are always considered as great gifts from nature since they are holding brilliant properties, including high activity, selectivity and specificity. Nowadays, a variety of enzymes have been applied to many industry processes. However, challenges are still needed to be addressed while applying enzymes. It is worth to point out that enzymes are sensitive to the change of ambient conditions. Most of enzymes are unstable and work under certain sort of temperature and pH conditions. Since enzymes could be denatured when subject to unnatural conditions, their work environment has to be controlled.

Researchers have been developed a variety of methods to improve the stability of bio-catalysts under various non-biological conditions. However, the immobilization process might harm the activity of enzymes. Therefore, even though immobilization approach has stabilized the stability of bio-catalysts, alternative strategies are still necessary to maintain the enzymes' activity during the encapsulation process.

In my research, two novel strategies were successfully developed to maintain enzymes' activity during encapsulation processes. Enzyme-based microgels and nanogels were successfully synthesized at cellular and enzymatic level for various applications, which are briefly outlined below:

Cellular level: An approach was envisioned in this section to improve biocatalyst stability, while maintaining their activities at the maximum during the encapsulation process. The new technology employs materials self-assembly to form a protective layer coating on cells surface. Enzymes are restricted within the cell all the time, without disturbing the structure during the encapsulation process. Therefore, this strategy maintains enzymes' activity at maximum. What's more, the protective polymer coating significantly increases biocatalyst viability in harsh thermal environment, different pH conditions, while allowing rapid transport of substrates into the biocatalyst without significant activity compromise. Compared with the conventional enzymes' encapsulation method, such robust microgels exhibit significantly improved activity and catalytic stability. Meanwhile, such robust single cells make the immobilized whole cells much cheaper to use than an immobilized enzyme.

Enzymatic level: In this section, surface coating with zwitterionic polymers was studied at the single enzymatic level without disturbing the enzyme structure during the encapsulation process in order to maintain enzymes' activity. The protective polymer coating can significantly increase biocatalyst viability while allowing rapid transport of substrates into the biocatalyst without significant activity compromise. Zwitterionic polymer shells have an efficient antibiofouling property which reduce the protein or cell adsorption, reduce immune response and prolong the circulation time of nanogels in blood circulation system.

Overall, my researches focus on maintaining enzymes' activity during the encapsulation process. Protective layers stabilize enzymes and create new surface functions. The encapsulation process is without disturbing enzymes' 3D structure. The resulted enzyme microgels or nanogels gain high activity and various new functionalities. With these technologies, we can envision a promising prospect in environmental, therapeutic and analytical applications of enzymes.

Radio communication is an integral part of wireless sensor networks. This dissertation focuses on improving the energy consumption of radio communication in sensor networks by proposing novel approaches in two key aspects of low-power wireless communication, namely, wireless link quality estimation and low duty-cycle data forwarding protocol. I first motivate the research with a comparative study of the routing performance and energy consumption with respect to existing link quality estimation protocols. Then, I propose 4C, a data-driven approach to build link quality prediction models based on empirical data collected from the deployment site in order to address the problems of link quality estimation in low-power sensor networks. Furthermore, I improve this novel data-driven approach to predict short temporal link quality variations without prior collected training data by employing online learning techniques. Analytical and empirical evaluations show that the proposed link quality prediction approach can significantly reduce the cost of radio transmissions by utilizing long links with variable quality. Moreover, I proposed SAF, an energy-efficient data forwarding protocol that can effectively utilize the short term link quality prediction models in duty-cycled networks. With the help of link quality prediction models, SAF not only minimizes the energy consumption spent on idle nodes, but also leverage the spatial diversity of wireless links via opportunistic routing. The dissertation concludes with a discussion of the potential improvements of the proposed approaches in low-power sensor networks as well as in other wireless networks.

Introduction: Among adult emergency department (ED) patients, we sought to examine how estimates of substance use prevalence and the need for interventions can differ, based on the type of screening and assessment strategies employed.

Methods: We estimated the prevalence of substance use and the need for interventions using the Alcohol, Smoking and Substance Involvement Screening Test (ASSIST) in a secondary analysis of data from two cross-sectional studies using random samples of English- or Spanish-speaking 18-64-year-old ED patients. In addition, the test performance characteristics of three simplified screening strategies consisting of selected questions from the ASSIST (lifetime use, past three-month use, and past three-month frequency of use) to identify patients in need of a possible intervention were compared against using the full ASSIST.

Results: Of 6,432 adult ED patients, the median age was 37 years-old, 56.6% were female, and 61.6% were white. Estimated substance use prevalence among this population differed by how it was measured (lifetime use, past three-month use, past three-month frequency of use, or need for interventions). As compared to using the full ASSIST, the predictive value and accuracy to identify patients in need of any intervention was best for a simplified strategy asking about past three-month substance use. A strategy asking about daily/near-daily use was better in identifying patients needing intensive interventions. However, some patients needing interventions were missed when using these simplified strategies.

Conclusion: Substance use prevalence estimates and identification of ED patients needing interventions differ by screening strategies used. EDs should carefully select strategies to identify patients in need of substance use interventions.

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Introduction: Urolithiasis causes severe acute pain and is commonly treated with opioid analgesics in the emergency department (ED). We examined opioid analgesic use after episodes of acute pain. 

Methods: Using data from a longitudinal trial of ED patients with urolithiasis, we constructed multivariable models to estimate the adjusted probability of opioid analgesic use 3, 7, 30, and 90 days after ED discharge. We used multiple imputation to account for missing data and weighting to account for the propensity to be prescribed an opioid analgesic at ED discharge. We used weighted multivariable regression to compare longitudinal opioid analgesic use for those prescribed vs not prescribed an opioid analgesic at discharge, stratified by reported pain at ED discharge. 

Results: Among 892 adult ED patients with urolithiasis, 79% were prescribed an opioid analgesic at ED discharge. Regardless of reporting pain at ED discharge, those who were prescribed an opioid analgesic were significantly more likely to report using it one, three, and seven days after the visit in weighted multivariable analysis. Among those who were not prescribed an opioid analgesic, an estimated 21% (not reporting pain at ED discharge) and 30% (reporting pain at discharge) reported opioid analgesic use at day three. Among those prescribed an opioid analgesic, 49% (no pain at discharge) and 52% (with pain at discharge) reported using an opioid analgesic at day three. 

Conclusion: Urolithiasis patients who received an opioid analgesic at ED discharge were more likely to continue using an opioid analgesic than those who did not receive a prescription at the initial visit, despite the time-limited nature of urolithiasis.