Herein is presented a proof-of-concept study of protease sensing that combines nontoxic silicon quantum dots (SiQDs) with Förster resonance energy transfer (FRET). The SiQDs serve as the donor and an organic dye as the acceptor. The dye is covalently attached to the SiQDs using a peptide linker. Enzymatic cleavage of the peptide leads to changes in FRET efficiency. The combination of interfacial design and optical imaging presented in this work opens opportunities for use of nontoxic SiQDs relevant to intracellular sensing and imaging.
In this paper we present recent advances in Förster resonance energy transfer (FRET) sensing and bioimaging using nontoxic silicon quantum dots. (SiQDs) In our work, we prepare SiQDs-dye conjugates, with SiQDs serving as the donor which are covalently attached to organic dye acceptors via self-assembled monolayer linkers. Enzymatic cleavage of the peptide leads to changes in FRET response which was monitored using fluorescence lifetime imaging microscopy (FLIM-FRET). The combination of interfacial design and optical imaging presented in this work opens new opportunities for bio-applications using nontoxic silicon quantum dots.
Current ‘gold standard’ staging of breast cancer and melanoma relies on accurate in vivo identification of the sentinel lymph node. By replacing conventional tracers (dyes and radiocolloids) with magnetic nanoparticles and using a handheld magnetometer probe for in vivo identification, it is believed the accuracy of sentinel node identification in nonsuperficial cancers can be improved due to increased spatial resolution of magnetometer probes and additional anatomical information afforded by MRI road-mapping. By using novel iron core/iron oxide shell nanoparticles, the sensitivity of sentinel node mapping via MRI can be increased due to an increased magnetic saturation compared to traditional iron oxide nanoparticles. A series of in vitro magnetic phantoms (iron core vs. iron oxide nanoparticles) were prepared to simulate magnetic particle accumulation in the sentinel lymph node. A novel handheld magnetometer probe was used to measure the relative signals of each phantom, and determine if clinical application of iron core particles can improve in vivo detection of the sentinel node compared to traditional iron oxide nanoparticles. The findings indicate that novel iron core nanoparticles above a certain size possess high magnetic saturation, but can also be produced with low coercivity and high susceptibility. While some modification to the design of handheld magnetometer probes may be required for particles with large coercivity, use of iron core particles could improve MRI and magnetometer probe detection sensitivity by up to 330 %.
Quantum dots (QDs) have brighter and longer fluorescence than organic dyes. Therefore, QDs can be applied to biotechnology, and have capability to be applied to medical technology. Currently, among the several types of QDs, CdSe with a ZnS shell is one of the most popular QDs to be used in biological experiments. However, when the CdSe QDs were applied to clinical technology, potential toxicological problems due to CdSe core should be considered. To eliminate the problem, silicon nanocrystals, which have the potential of biocompatibility, could be a candidate of alternate probes.
Silicon nanocrystals have been synthesized using several techniques such as aerosol, electrochemical etching, laser pyrolysis, plasma deposition, and colloids. Recently, the silicon nanocrystals were reported to be synthesized in inverse micelles and also stabilized with 1-heptene or allylamine capping. Blue fluorescence of the nanocrystals was observed when excited with a UV light. The nanocrystals covered with 1-heptene are hydrophobic, whereas the ones covered with allylamine are hydrophilic. To test the stability in cytosol, the water-soluble nanocrystals covered with allylamine were examined with a Hela cell incorporation experiment. Bright blue fluorescence of the nanocrystals was detected in the cytosol when excited with a UV light, implying that the nanocrystals were able to be applied to biological imaging.
In order to expand the application range, we synthesized and compared a series of silicon nanocrystals, which have variable surface modification, such as alkyl group, alcohol group, and odorant molecules. This study will provide a wider range of optoelectronic applications and bioimaging technology.
Silicon quantum dots have been synthesized in micelles. Particle sizes have been ascertained by transmission electron microscopy and UV-Vis absorption and photoluminescence spectroscopy. The surface of the silicon and germanium particles produced have been modified to produce hydrophobic and hydrophilic particles by reaction with either with 1-heptene or allylamine respectively. For biological applications control of the surface character of the nanocrystals is essential. FTIR spectra show the surface modification of the particles by 1-heptene or allylamine.
Photoluminescent water-soluble silicon nanocrystals were synthesized using solution-phase wet chemistry techniques. Adjustment of the mean size and size distribution was achieved by adjusting the rate of addition of the hydride reducing agent. When the reducing agent was added slowly the mean size of the silicon nanocrystals was 1.4nm with a monodisperse size distribution. However, when the reducing agent was added rapidly the size distribution enlarged and concomitantly the
mean sized also increased. The photoluminescence and photoluminescence excitation spectra from the monodisperse sample show narrower features when compared to the solution with the large size distribution. This provides direct evidence for size dependant effects on the photoluminescence of silicon nanocrystals.
Silicon quantum dots have been synthesized in micelles. Particle sizes have been ascertained by transmission electron microscopy and UV-Vis absorption and photoluminescence spectroscopy. The
surface of the silicon particles produced have been modified to produce hydrophobic and hydrophilic particles by reaction with either with 1-heptene or allylamine respectively. For biological applications
control of the surface character of the nanocrystals is essential. FTIR spectra show the surface modification of the particles by 1-heptene or allylamine.