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RNA in situ hybridization (RNA-ISH) based on the mechanism of hybridization chain reaction (HCR) enables multiplexed, quantitative, high-resolution RNA imaging in highly autofluorescent samples including whole-mount vertebrate embryos, thick brain slices, and formalin-fixed paraffin-embedded (FFPE) tissue sections. Here, we extend the benefits of 1-step, multiplexed, quantitative, isothermal, enzyme-free HCR signal amplification to immunohistochemistry (IHC), enabling accurate and precise protein relative quantitation with subcellular resolution in an anatomical context. More-over, we provide a unified framework for simultaneous quantitative protein and RNA imaging with 1-step HCR signal amplification performed for all target proteins and RNAs simultaneously.

In situ hybridization based on the mechanism of hybridization chain reaction (HCR) enables multiplexed quantitative mRNA imaging in the anatomical context of whole-mount vertebrate embryos. Third-generation in situ HCR (v3.0) provides automatic background suppression throughout the protocol, dramatically enhancing performance and ease of use. In situ HCR v3.0 supports two quantitative imaging modes: (1) qHCR imaging for analog mRNA relative quantitation with subcellular resolution in an anatomical context and (2) dHCR imaging for digital mRNA absolute quantitation with single-molecule resolution in an anatomical context. Here, we provide protocols for qHCR and dHCR imaging in whole-mount zebrafish, chicken, and mouse embryos.

In situ hybridization based on the mechanism of hybridization chain reaction (HCR) enables high-throughput expression profiling of mammalian or bacterial cells via flow cytometry. Third-generation in situ HCR (v3.0) provides automatic background suppression throughout the protocol, dramatically enhancing performance and ease of use. In situ HCR v3.0 supports analog mRNA relative quantitation via qHCR flow cytometry. Here, we provide protocols for multiplexed qHCR flow cytometry for mammalian or bacterial cells in suspension.

In situ hybridization based on the mechanism of hybridization chain reaction (HCR) enables multiplexed quantitative mRNA imaging in diverse sample types. Third-generation in situ HCR (v3.0) provides automatic background suppression throughout the protocol, dramatically enhancing performance and ease of use. In situ HCR v3.0 supports two quantitative imaging modes: (1) qHCR imaging for analog mRNA relative quantitation with subcellular resolution and (2) dHCR imaging for digital mRNA absolute quantitation with single-molecule resolution. Here, we provide protocols for qHCR and dHCR imaging in mammalian cells on a slide.

In situ hybridization methods enable the mapping of mRNA expression within intact biological samples. With current approaches, it is challenging to simultaneously detect multiple target mRNAs in vertebrate embryos and tissue sections – a significant limitation in attempting to study interacting regulatory elements in systems most relevant to human development and disease. This thesis presents a multiplexed fluorescent in situ hybridization method based on orthogonal amplification with hybridization chain reaction (HCR). Using this approach, RNA probes complementary to mRNA targets trigger chain reactions in which fluorophore-labeled RNA hairpins self-assemble into tethered fluorescent amplification polymers. Robust performance and high signal-to-background are achieved when imaging five target mRNAs at the same time in fixed whole-mount zebrafish embryos. The programmability and sequence specificity of these amplification cascades enable all five amplifiers to operate orthogonally at the same time in the same sample. The fact that amplification polymers are triggered to self-assemble in situ results in excellent sample penetration and high signal-to-background. These properties suggest the broad applicability of fluorescent in situ HCR amplification to multiplexed imaging of mRNA expression in normal and pathological cells, embryos, and tissue sections.

In situ hybridization methods enable the mapping of mRNA expression within intact biological samples. With current approaches, it is challenging to simultaneously detect multiple target mRNAs in vertebrate embryos and tissue sections – a significant limitation in attempting to study interacting regulatory elements in systems most relevant to human development and disease. This thesis presents a multiplexed fluorescent in situ hybridization method based on orthogonal amplification with hybridization chain reaction (HCR). Using this approach, RNA probes complementary to mRNA targets trigger chain reactions in which fluorophore-labeled RNA hairpins self-assemble into tethered fluorescent amplification polymers. Robust performance and high signal-to-background are achieved when imaging five target mRNAs at the same time in fixed whole-mount zebrafish embryos. The programmability and sequence specificity of these amplification cascades enable all five amplifiers to operate orthogonally at the same time in the same sample. The fact that amplification polymers are triggered to self-assemble in situ results in excellent sample penetration and high signal-to-background. These properties suggest the broad applicability of fluorescent in situ HCR amplification to multiplexed imaging of mRNA expression in normal and pathological cells, embryos, and tissue sections.

A theoretical examination of kinetic mechanisms for forming knots and links in nucleic acid structures suggests that molecules involving base pairs between loops are likely to become topologically trapped in persistent frustrated states through the mechanism of ‘helix-driven wrapping’. Augmentation of the state space to include both secondary structure and topology in describing the free energy landscape illustrates the potential for topological effects to influence the kinetics and function of nucleic acid strands. An experimental study of metastable complementary ‘kissing hairpins’ demonstrates that the topological constraint of zero linking number between the loops effectively prevents conversion to the minimum free energy helical state. Introduction of short catalyst strands that break the topological constraint causes rapid conversion to full duplex.

A theoretical examination of kinetic mechanisms for forming knots and links in nucleic acid structures suggests that molecules involving base pairs between loops are likely to become topologically trapped in persistent frustrated states through the mechanism of ‘helix-driven wrapping’. Augmentation of the state space to include both secondary structure and topology in describing the free energy landscape illustrates the potential for topological effects to influence the kinetics and function of nucleic acid strands. An experimental study of metastable complementary ‘kissing hairpins’ demonstrates that the topological constraint of zero linking number between the loops effectively prevents conversion to the minimum free energy helical state. Introduction of short catalyst strands that break the topological constraint causes rapid conversion to full duplex.

A study program is presented on the effects of strong electric fields on condensation heat transfer and two-phase flow. It has been confirmed that significant changes in the flow regimes and heat transfer are possible with negligible electrical power expenditure. Over 100 per cent increase in heat transfer has been attained with pressure drop increases which are of the order of 15 per cent in the annular flow regime. These investigations were performed on two separate apparatus: one at Tufts University in which heat transfer phenomena in condensation were investigated and one at the Massachusetts Institute of Technology in which hydrodynamic phenomena in two-phase flow were studied. Results show that the slug flow regime is substantially suppressed. In essence, slug flow occurs only in the region of very low gas flows in which the system is almost entirely gravity dependent. The increase in heat transfer rates is gradual up to a certain threshold value of the applied voltage; beyond this value, the increase is steep. Some progress has been made in analytical and physical modeling of the phenomenon both from the viewpoint of determining pressure drop and heat transfer and of aiding in the determination of the fluid configuration at the heat transfer surface. (Author), In cooperation with Massachusetts Institute of Technology, Cambridge.