Nanoparticles, whose size is 1-100 nm, easily aggregate as their size becomes smaller. Therefore, it is difficult to
produce solution in which nanoparticles are dispersed. We have, as a way to disperse aggregated particles, for example, a
media-typed disperse machine. During the procedures, however, we have to deal with some complicating operations;
separation of the media from the solution, the defacement of the media into the solution, and so on. Furthermore, it is not
an effective method for particles whose size is less than 50 nm. We tried to find an easier and more effective method for
producing solution in which we re-disperse aggregated nanoparticles to still smaller particles. The aggregated particles
were put into a machine with a pinhole small needle valve, and they were re-dispersed by "sheering stress". The
estimation of re-dispersion was carried out by the measurement of their size distribution and surface z-average. With the
utility of the machine, the re-dispersions of aggregated particles were observed. Furthermore, the increase of the pressure
and of the velocity of the flow caused the decrease of particle size, which makes the surface area larger and therefore the
surface z-average larger. It become clear that it is possible to re-disperse aggregated nanoparticles by adding shearing
stress. We can regulate shearing stress by controlling the pressure and flow, and therefore we can control the
effectiveness and the yield.
Carbon group quantum dots (QDs) such as carbon, silicon and germanium, have potential for biomedical applications
such as bio-imaging markers and drug delivery systems and are expected to demonstrate several advantages over
conventional fluorescent QDs such as CdSe, especially in biocompatibility. We assessed biocompatibility of newly
manufactured silicon QDs (Si-QDs), by means of both MTT assay and LDH assay for HeLa cells in culture and thereby detected the cellular toxicity by administration of high concentration of Si-QD (>1000 μg/mL), while we detected the high toxicity by administration of over 100 μg/mL of CdSe-QDs. As a hypothesis for the cause of the cellular toxicity, we measured oxy-radical generation from the QDs by means of luminol reaction method. We detected generation of oxy-radicals from the Si-QDs and those were decreased by radical scavenger such as superoxide dismutase (SOD) and N-acetyl cysteine (NAC). We concluded that the Si-QD application to cultured cells in high concentration led cell membrane damage by oxy-radicals and combination usage with radical scavenger is one of the answers.
Gene therapy is an attractive approach to supplement a deficient gene function. Although there has been some success
with specific gene delivery using various methods including viral vectors and liposomes, most of these methods have a
limited efficiency or also carry a risk for oncogenesis.
Fluorescent nanoparticles, such as nanocrystal quantum dots (QDs), have potential to be applied to molecular biology
and bioimaging, since some nanocrystals emit higher and longer lasting fluorescence than conventional organic probes
do. We herein report that quantum dots (QDs) conjugated with nuclear localizing signal peptides (NLSP) successfully
introduced the gene-fragments with promoter elements, which promoted the expression of the enhanced green
fluorescent protein (eGFP) gene in mammalian cells. The expression of eGFP protein was observed when the QD/geneconstruct
was added to the culture media. The gene-expression efficiency varied depending on multiple factors around
QDs, such as 1) the reading direction of gene fragments, 2) the quantity of gene fragments attached on the surface of
QD-constructs, 3) the surface electronic charges varied according to the structure of QD/gene-constructs, and 4) the
particle size of QD/gene complex varied according to the structure and amounts of gene fragments. Using this QD/geneconstruct
system, eGFP protein could be detected 28 days after the gene-introduction whereas the fluorescence of QDs
was disappeared. This system therefore provides another method for the intracellular delivery of gene-fragments without
using either viral vectors or specific liposomes.
These results suggest that inappropriate treatment and disposal of QDs may still have risks to the environmental
pollution including human health under certain conditions. Here we propose the further research for the immune and
physiological responses in not only immune cells but also other cells, in order to clear the effect of all other nanoscale
products as well as nanocrystal QDs.
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 clinical 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 of CdSe core should be considered. To overcome the problem, silicon nanocrystals, which have the potential of biocompatibility, could be a candidate of alternate probes. Silicon nanoparticles have been synthesized using several techniques. Recently, novel silicon nanoparticles were reported to be synthesized with the combination methods, radio frequency sputtering method and hydrofluoric-etching method In order to assess the biocompatibility of the Silicon nanoparticles, we performed two different cytotoxicity assays, cell iability/proliferation assay using the mitochondrial activity assay and cell membrane damage assay using the lactate dehydrogenase assay. At the 112 μg/mL of silicon nanoparticles (the maximum concentration in this study), we could detected the cell membrane damage of HeLa cells and the decrease of hepatocytes viability. We concluded that we could use the silicon nanoparticles as bioimaging marker but the attention should be given when Silicon nanoparticles were applied to cells in high concentration.
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.
We developed the smaller sized quantum dots covered with sodium 2-mercaptoethanesulfonate which has a sulfonyl group (QDs-SO<sub>3</sub>-), and compared its stability in acid, salt and buffer solutions with that of the quantum dots covered with the mercaptoundecanoic acid (QDs-MUA) and covered with the NH<sub>2</sub> group (QDs-NH<sub>2</sub>). We found that the QD-SO<sub>3</sub>- well disperses in these solutions without quenching and this stability holds on 24 hours. Next, we observed the cell damage caused by the quantum dots. In the evaluation of cell damage, QD-SO<sub>3</sub>- did not show noticeable cell damage in the 0.2mg/mL by the comet assay as well as QD-MUA and QD-NH<sub>2</sub> in the same concentration. All these results could suggest that SO<sub>3</sub>- might be useful for the biomedical engineering.
Photo-luminescent semiconductor quantum dots are nanometer-size probes that have the potential to be applied to the fields of the bio-imaging and the study of the cell mobility inside the body. At the same time, on the other hand, quantum dots are expected to carry some kind of molecules to the local organ inside of the animal body, which leads to the expectation that they can be used as a medicine-carrier. For this purpose, we conjugate (2S)-1-[(2s)-2-Methyl-3-sulfanylpropionyl]pyrrolidine-2-carboxylic acid (cap) with the quantum dot. Cap has the effect as an anti-hypertension drug, which inhibits angiotensin 1 converting enzyme. We conjugated the quantum dot with cap by the exchange reaction avoiding the regions which holds medicinal effect. Quantum dot conjugated with cap (QD-cap) were 3-times brighter than thioglycerol-coated quantum dots (QD-OH). The particle size of cap was 1.1nm and that of QD-cap was 12nm. QD-cap was permeated into the HeLa cells, while QD-MUA were taken into the HeLa cells by endocytosis. In addition, no apoptosis was detected against the cells that permeated QD-cap, because there was no damage to DNA. These results indicated that QD-conjugated medicines (QD-medicine) could be safe in the experiment on the level of the cell. More over, when QD-cap was intravenously injected into Stroke-prone Spontaneously Hypertensive Rats (SHRSP), they reduced blood pressure at systole. Therefore, the anti-hypertension effect of cap remained after conjugated with the quantum dot. These results suggested that QD-medicine were effective on the animal level.