4 research outputs found
Photon momentum enabled light absorption in bulk silicon
Photons do not carry sufficient momentum to induce indirect optical
transitions in semiconducting materials such as silicon, necessitating the
assistance of lattice phonons to conserve momentum. Compared to direct bandgap
semiconductors, this renders silicon a less attractive material for a wide
variety of optoelectronic applications. In this work, we introduce an
alternative strategy to fulfill the momentum-matching requirement in indirect
optical transitions. We demonstrate that when confined to scales below ~3 nm,
photons acquire sufficient momentum to allow electronic transitions at the band
edge of Si without the assistance of a phonon. Confined photons allow
simultaneous energy and momentum conservation in two-body photon-electron
scattering; in effect, converting silicon into a direct bandgap semiconductor.
We show that this less-explored concept of light-matter interaction leads to a
marked increase in the absorptivity of Si from the UV to the near-IR. The
strategy provides opportunities for more efficient use of indirect
semiconductors in photovoltaics, energy conversion, light detection and
emission
Novel Small Multilamellar Liposomes Containing Large Quantities of Peptide Nucleic Acid Selectively Kill Breast Cancer Cells
Peptide nucleic acid (PNA) may be used in various biomedical applications; however, these are currently limited, due to its low solubility in aqueous solutions. In this study, a methodology to overcome this limitation is demonstrated, as well as the effect of PNA on cell viability. We show that extruding a mixture of natural phospholipids and short (6–22 bases), cytosine-rich PNA through a 100 nm pore size membrane under mild acidic conditions resulted in the formation of small (60–90 nm in diameter) multilamellar vesicles (SMVs) comprising several (3–5) concentric lipid membranes. The PNA molecules, being positively charged under acidic conditions (due to protonation of cytosine bases in the sequence), bind electrostatically to negatively charged phospholipid membranes. The large membrane surface area allowed the encapsulation of thousands of PNA molecules in the vesicle. SMVs were conjugated with the designed ankyrin repeat protein (DARPin_9-29), which interacts with human epidermal growth factor receptor 2 (HER2), overexpressed in human breast cancer. The conjugate was shown to enter HER2-overexpressing cells by receptor-mediated endocytosis. PNA molecules, released from lysosomes, aggregate in the cytoplasm into micron-sized particles, which interfere with normal cell functioning, causing cell death. The ability of DARPin-functionalized SMVs to specifically deliver large quantities of PNA to cancer cells opens a new promising avenue for cancer therapy
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Photon momentum enabled light absorption in silicon
Photons do not carry sufficient momentum to induce indirect optical
transitions in semiconducting materials such as silicon, necessitating the
assistance of lattice phonons to conserve momentum. Compared to direct bandgap
semiconductors, this renders silicon a less attractive material for a wide
variety of optoelectronic applications. In this work, we introduce an
alternative strategy to fulfill the momentum-matching requirement in indirect
optical transitions. We demonstrate that when confined to scales below ~3 nm,
photons acquire sufficient momentum to allow electronic transitions at the band
edge of Si without the assistance of a phonon. Confined photons allow
simultaneous energy and momentum conservation in two-body photon-electron
scattering; in effect, converting silicon into a direct bandgap semiconductor.
We show that this less explored concept of light-matter interaction leads to a
marked increase of the absorptivity of Si from the UV to the near-IR. The
strategy provides opportunities for more efficient use of indirect
semiconductors in photovoltaics, energy conversion, light detection and
emission