Hybridization of two or more DNA or RNA strands is well documented for the process taking place with all strands free in solution or when one strand is immobilized on a substrate. This study contributes to the investigation of the hybridization process when two single DNA strands (ssDNA) are in close proximity. We took advantage of an X sensor in which hybridization of four DNA strands enables the formation of a DNA four-way junction (crossover or X) structure. We immobilized multiple layers of crossover structures to study its hybridization being triggered by short ssDNA coming from solution and further investigate how many layers of these structures can hybridize by the addition of only one ssDNA (called input). Using a molecular beacon as reporter, we combined crossover DNA strands that recognize the reporter sequence at one side and at the other, the sequence of its input or downward crossover layer. Fluorescent signal was detected by separation of the molecular beacon’s fluorophore and quencher, as it hybridizes with the system of layers. Immobilization of the X structures into the scaffold proved to increase their communication, in comparison to being free in solution. This evidence gives us significant information for the communication of hybridized layers in a localized system, showing a promising standard for development of multilayered logic gates. The potential of these crossover DNA strands using X structure include applications in the future of biological systems, nanotechnology, and target DNA recognition for its ability to quickly recognize a signal and propagate it through extended DNA nanostructure in a controlled manner.

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Thesis advisor: Jon Wargo / This research study investigates how young Brazilian immigrant students (ages 5-9) experience their education in a Two-Way Immersion (TWI) program (Portuguese-English) at one elementary school in the U.S. Northeast. TWI is a bilingual education model that has become popular in recent years but has also come under scrutiny with growing concerns for equity. This multi-year ethnographic study examined students’ roles as thinkers and knowers who contribute to the social world of schooling in a bilingual program that was originally envisioned to serve their needs. Data sources are: participant observations in classrooms and schoolwide and program-specific meetings; interviews with school staff members, children, and caregivers; and a collection of in-class assignments.Findings from this study point to the paradoxical relationship that the focal school had with young immigrant children. First, children of Brazilian descent contributed to the successful implementation and survival of the new bilingual strand in their school through daily language practices and by leveraging their lived experiences and memories during instruction. Second, Brazilian immigrant students carved out spaces in their TWI classrooms to deploy and co-construct subalternized knowledges based on their transborder experiences. At the same time, they faced conflicting orientations concerning their role and participation in the TWI program as well as dynamics of in/visibility. Third, following these students at the height of the Covid-19 pandemic, during fully remote learning, revealed how the children negotiated compounded constraints. I show how young students humanized their virtual TWI classrooms, made space for playfulness, and centered their care-full lives in their formal schooling during remote learning. Investigating the educational realities of Brazilians, a rapidly growing but understudied segment of the U.S. Latinx population, not only sheds light on unique facets of their experience, but also generates insights as to how to (re)think educational models, programs, and responses to minoritized populations in the U.S. Precisely, together, the findings advocate for a holistic focus on childhoods, as opposed to the current emphasis on language-as-subject, in TWI education. / Thesis (PhD) — Boston College, 2023. / Submitted to: Boston College. Lynch School of Education. / Discipline: Teacher Education, Special Education, Curriculum and Instruction.