We report on monodisperse fluorescent core-shell silica nanoparticles (C dots) with enhanced brightness and photostability as compared to parent free dye in aqueous solution. Dots containing either tetramethylrhodamine or 7-nitrobenz-2-oxa-1,3-diazole dyes with diameters ranging from tens of nanometers to microns are discussed. The benefits of the core-shell architecture are described in terms of enhanced fluorescent yield of the fluorophores in the quasi-solid-state environment within the particle as compared with parent free dye in water. Several applications of these particles in the fields of photonics and the life sciences are discussed. Specifically, fluorescent core-shell silica nanoparticles are investigated as an active medium for photonic building blocks assembled on zinc sulfide-based seed particles. Initial assembly results for these composite raspberry structures are shown. Finally, applications in the life sciences are explored, including targeting of specific antibody receptors using these single-emission nanoparticles. We expand on single-emission core-shell architecture to incorporate environmentally-sensitive fluorophores to create quantitative ratiometric nanoscale sensors capable of interrogating chemical concentrations on the sub-cellular to molecular levels and demonstrate initial results of intracellular pH imaging. The concept of a single particle laboratory (SPL) is introduced as an active investigator of its environment.

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.

We present the growth of efficient infrared light-emitting quantum dots directly on DNA. The nanoparticles emit in the second biological window 1050-1200 nm with photoluminescence quantum efficiencies of 11% in aqueous solution. The infrared fluorophores are stable for over a week in blood plasma at 37°C.

We have synthesized high quality type-II CdTe/CdSe near infrared quantum dots using successive ion layer adsorption and reaction chemistry. Transmission electron microscopy reveals that CdTe/CdSe can be synthesized layer by layer yielding quantum dots of narrow size distribution. Excitation and photoluminescence spectra reveal discrete type-II transitions, which correspond to energy lower that type-I bandgap. We have used a peptide coating technique on type-II and commercial near infrared quantum dots for delivery in live animals and cultured cells.

InP quantum dots (QDs) with zinc blende structure and InN QDs with hexagonal structure were synthesized from appropriate organometallic precursors in a noncoordinating solvent using myristic acid as a ligand. In2O3 nanospheres and quantum rods were synthesized under reflux conditions in a coordinating methyl imizadole (MeIm) solvent. The QDs were characterized by TEM, the associated energy dispersive spectroscopy (EDS), electron diffraction, and steady state UV-VIS optical absorption and photoluminescence spectroscopy.

We have developed hybrid light responsive TiO₂ nanoparticles electronically linked to PNA oligonucleotides that site specifically bind to double stranded target DNA. This opens a new opportunity for the development of a highly efficient "artificial restriction enzyme" whose activity can be controlled by using light. The work focuses on the use of TiO₂ nanocomposites as analogs of restriction enzymes with unique specificity that does not exist in current biological approaches. TiO₂ nanoparticles electronically linked to DNA or PNA adapters have been site-specifically attached along double stranded λ DNA vectors. Illumination of this assembly results in selective oxidation of DNA at the deepest "thermodynamic traps" located closest to the nanoparticle surface, causing DNA cleavage. We investigate the effect of the sequence and length of DNA and PNA adapters on the specificity of DNA cleavage. Related to this issue, the potential use of TiO₂/DNA nanocomposites as "rare cutters" that cleave DNA in the places not achieved with existing protein-based enzymes is investigated.

Fluorescent nanocrystals (quantum dots or QDs) have a number of unique properties that overcome the limitations of conventional organic dyes. However, the optical properties of QDs have been observed to be strongly dependent upon their local chemical environment including novel surface coatings, which have been developed to render QDs water soluble and conjugation ready leading to their use as fluorescent tags and optical sensors for a variety of biological and biomedical applications. The quantitative utility of QDs in complex biological systems requires that their optical properties be well understood and interrelated with their chemical functionalization on the surface and their interactions with surface-conjugated materials. In this report, quantitative measurement of adhesion forces between a hydrophilic or a hydrophobic AFM probe and an amine-functionalized single QD or a hydrophilic substrate were obtained to demonstrate the utility of the atomic force microscopy (AFM) as a tool to probe surface functionalities of single functionalized QDs. We also present procedures to combine AFM and confocal fluorescence microscopy in an effort to simultaneously probe optical characteristics and physical/chemical properties of single or clustered functionalized QDs at the nanoscale.

Colloidal quantum dots (QDs) possess numerous physical and optical properties that are ideal for biosensing and multiplexing applications. Fluorescence resonance energy transfer (FRET) is a well-established technique for detecting molecular-scale interactions due to proximity-driven changes in fluorescence. We have shown that QDs are excellent energy donors where dye labeled proteins serve as acceptors, and developed a number of prototype nanosensors for small molecules in solution. Among the more promising potential uses of QD-based FRET nanosensors is the ability to "multiplex" signal channels for parallel detection. Because of their very broad absorption and narrow symmetric emission spectra, QDs are ideal fluorophores for multiplexing applications. In this paper, we describe the benefits of QDs in FRET-based assays (as donors and acceptors) and the potential for signal multiplexing in nanoscale biosensors.

We have demonstrated fluorescence resonance energy transfer (FRET) between lanthanide-ion doped oxide nanoparticles acting as donors and organic acceptor molecules (Cy5). Due to the long nanoparticle lifetime and the large Stokes shift between nanoparticle absorption and emission, unambiguous and precise FRET measurements can be performed despite the presence of large free acceptor oncentrations. We determined FRET efficiencies as a function of Cy5 concentration which are in very good agreement with a multiple acceptor-multiple donor calculation.

We have previously assembled QD-based fluorescence resonance energy transfer (FRET) sensors specific for the sugar nutrient maltose and the explosive TNT. These sensors utilize several inherent benefits of QDs as FRET donors. In this report, we show that QD-FRET based sensors can also function in the monitoring of proteolytic enzyme activity. We utilize a QD with multiple dye-labeled proteins attached to the surface as a substrate for a prototypical protease. We then demonstrate how this strategy can be extended to detect protease activity by utilizing a dye-labeled peptide attached to the QD as a proteolytic substrate. Self-assembly of the peptide-dye on the QD brings the dye in close proximity to the QD and result in efficient FRET. Addition of a proteolytic enzyme that specifically recognizes and cleaves the peptide alters the FRET signature of the sensor in a concentration-dependent manner. Both qualitative and quantitative data can be derived from these sensors. The potential benefits of this type of QD sensing strategy are discussed.

The photoluminescence spectrum of a quasi-monodisperse semiconductor quantum dot (QD) population is composed of a continuum of extremely narrow single QD spectra. This is due to inhomogeneities in nanocrystal size within a population and the color-size dependency imposed by effects of carrier quantum confinements. We take advantage of this population heterogeneity to gain a unique insight into the fluorescence resonant energy transfer (FRET) process between a QD donor and proximal dye-labeled protein acceptors. Our ensemble and single-QD studies demonstrate that the spectral dependency of the energy transfer rate matches the acceptor absorption spectrum as predicted by Forster formalism. This allows ratiometric FRET measurements based on the QD donor emission.

Semiconductor quantum dots (QDs) possess highly reactive electrons and holes after photoexcitation. The energy of these electrons and holes can be deliberately modulated by attaching the QD to an electron donor or acceptor. This eliminates (quenches) QD fluorescence, as well as affecting the ability of the QD to oxidize or reduce common biomolecules such as glutathione and DNA. This greatly alters the fluorescent properties and toxicity of such QDs inside cells. In this work, we show that a specific electron donor, the neurotransmitter dopamine, yields redox-sensitive conjugates when attached to at least some colors of CdSe/ZnS QDs. The potential for the use of such conjugates as sensors, and the implications for enhanced toxicity in such conjugates are discussed.

Innovations in fluorescence microscopy of live cells involving new reagents and techniques reveal dynamic processes that were not previously observable and therefore unknown. Water soluble, biofunctionalized semiconductor quantum dots (QDs) provide advantages of much greater photostability compared to conventional fluorescent dyes, and, as a consequence, single QDs can be easily detected. QDs coupled to growth factor ligands behave similarly as the natural ligand and serve as highly fluorescent probes of the erbB family of tyrosine kinase receptors in living cells. Continuous confocal laser scanning microscopy and flow cytometry measurements of QDs combined with visible fluorescent fusions of the receptors have elucidated individual steps in the signaling cascades initiated by these receptors. This report highlights advantages and some disadvantages of QDs, such as size and blinking behavior that complicate some live cell imaging applications. The new class of noble metal nanodots constitute an attractive alternative to QDs in that they are not only highly fluorescent and photostable, but also, much smaller and nontoxic. We present a new synthesis method for the production of Au nanodots. We demonstrate that electrochemical synthesis allows the reproducible control of cluster size. The resulting clusters are more monodisperse than those formed by other methods and are stable over many months. We report their characterization using MALDI-TOF mass spectrometry and UV-VIS spectroscopy.

Quantum dots promise to revolutionize the way fluorescence imaging is used in the Cell Biology field. The unique fluorescent spectral characteristics, high photostability, low photobleaching and tight emission spectra of quantum dots, position them above traditional dyes. Here we will address the ability of EviTags, which are water stabilized quantum dot products from Evident Technologies, to behave as effective FRET donors in cells. EviTag-Hops Yellow (HY; Emission 566nm; Donor) conjugated to biotin were bound to stretapvidin-Alexa568 (Acceptor) conjugates. These HYbiotin-streptavidin-Alexa568 FRET EviTag conjugates were then internalized by fluid-phase into non-polarized MDCK cells. Confocal microscopy detects these FRET EviTag conjugates in endocytic compartments, suggesting that EviTags can be used to track fluid-phase internalization and trafficking. EviTags are shown here to be effective FRET donors when internalized into cells. Upon pairing with the appropriate acceptor dyes, quantum dots will reduce the laborious data processing that is required to compensate for bleed through contamination between organic dye donor and acceptor pair signals. The EviTag technology will simplify and expand the use of FRET in the analysis of cellular processes that may involve protein-protein interactions and other complex cellular processes.

We report the use of antibody-conjugated quantum dots (QDs) to monitor the expression dynamics of the membrane bound cytokine receptor interleukin-2 receptor-α (IL-2Rα) throughout the course of Jurkat T cell activation. Maximal receptor expression is observed 32-48 hours after activation, followed by a sharp decrease subsequent to 48 hours consistent with IL-2R internalization. Fluorescence microscopy, ELISA, and FACS analyses were used to verify controlled activation and specificity of QD labeling. Additionally, confocal microscopy demonstrated receptor internalization subsequent to expression and QD labeling. Antibody-conjugated QDs provide a convenient means to rapidly determine cell state and interrogate end products of cell signaling pathways. Interrogation of other signaling pathways can eventually be carried out in a similar manner upon identification of relevant membrane associated receptors. Ultimately, the multiplexing capabilities of QDs will allow the examination of several signaling pathways simultaneously and aid in toxin detection and discrimination.

We report the synthesis of high quality ZnS nanoparticles using sulfur and zinc acetate as the S and Zn source, respectively. It was found that sulfur and zinc acetate could be easily dissolved in the mixture of trioctylphosphine oxide (TOPO) and hexadecylamine (HDA) at a temperature of about 65°C and ZnS nanoparticles were generated at temperatures above 150°C. These reactive species of sulfur and zinc were also used for an epitaxial growth of ZnS shell around a CdSe core. The formation of ZnS nanoparticles was confirmed by powder X-ray diffraction (XRD). Particle size and size distribution were studied by transmission electron microscopy (TEM). Optical properties were characterized by a combination of UV-vis and photoluminescence (PL) spectroscopy. The PL quantum yield of the CdSe/ZnS nanoparticles reached about 66% compared with the dye, Rhodamine 6G (R6G). The present synthetic strategy is a "greener" and simpler synthetic scheme due to the use of air-stable and environmentally benign reagents of sulfur and zinc acetate instead of air-sensitive ones such as dimethylzinc and bis(trimethylsilyl) sulfide.

Colloidal semiconductor quantum dots (QDs) have become common fluorescent probes in biology. Their optical properties not only facilitate spectrally multiplexed detection but also enable single molecule measurements with high signal to noise ratio. This is of particular interest in cell biology since it allows individual QD-tagged biomolecules to be tracked with good spatial and temporal resolution over long durations. Recent measurements on membrane proteins have validated this approach and serve as a basis for more complex experiments in which the motion of different biomolecules, located in various cell compartments (membrane, cytosol, nucleus,...) and tagged with QDs having distinct emission colors, is recorded in real time and with a nanometer resolution. The development of these new imaging methods, equivalent to a molecular positioning system within a single cell, raises many challenges, coming from optics, physical and biological chemistry, as well as image processing.

Multifunctional nanoparticles, quantum dots (QDs) are being developed as uniquely sensitive tools for elucidating the (bio)chemical and (bio)physical molecular mechanisms underlying functional states, i.e. the molecular physiology, of biological cells and organisms. Here we present a group of strategies and examples for (i) controlling the spectroscopic properties of QDs via Fluorescence Resonance Energy Transfer (FRET); (ii) determining the emission spectra of individual QDs in a population with an imaging spectrograph (ASI SpectraCube); and (iii) employing such liganded QDs as nano-probes in cellular studies of signal transduction.

Quantum dots (QDs) could offer significant advantages in clinical settings due to their high photostability and quantum yield. We are investigating the uptake and compartmentalization of QDs by cells because these processes are not fully characterized and there is potential for heavy metal toxicity when semiconductor nanocrystals are sequestered. Here we demonstrate the intracellular accumulation of QDs in human embryonic kidney cells (HEK-293; ATCC) exposed to nontargeted (Qtracker 565nm; QDot Corp.) or targeted (Qtracker 565 Cell Labeling Kit; QDot Corp.) QDs. As expected, 10 nM targeted QDs (Lagerholm et al., 2004, Nano Letters, 4:2019-2022) accumulated in HEK-293 cells and normal human astrocytes (NHA; Cambrex Biosciences) after 1 hr, while nontargeted QDs (200 nM) could be detected after 24 hr in HEK-293 but not NHA. The uptake of 10 nM targeted QDs was greater than the uptake of 200 nM nontargeted QDs as confirmed by the number and intensity of puncta visible in HEK-293 cells imaged with confocal microscopy. QD uptake was not detected in two Xenopus kidney cell lines (XLK-WG and A6; ATCC) exposed to nontargeted QDs (10-500 nM) for 18 hours. Co-labeling of HEK-293 cultures with CellTracker Red CMTPX (Invitrogen) following QD uptake verified that QD accumulation does not affect cell viability. Differences in QD uptake between cell lines could be species-specific or due to different growth conditions. The unexpected accumulation of nontargeted QDs raises questions about the uptake mechanism and the intracellular location that are being investigated with TEM. Supported by NIH-NIDCD (DC003292) and NMSU-ADVANCE (NSF0123690) to EES.

Scanning Fluorescence Microscope (SFM) is a new technique for automated motorized microscopes to measure multiple fluorochrome labeled cells (Bocsi et al. Cytometry 2004, 61A:1). The ratio of CD4+/CD8+ cells is an important in immune diagnostics in immunodeficiency and HIV. Therefor a four-color staining protocol (DNA, CD3, CD4 and CD8) for automated SFM analysis of lymphocytes was developed. EDTA uncoagulated blood was stained with organic and inorganic (Quantum dots) fluorochromes in different combinations. Aliquots of samples were measured by Flow Cytometry (FCM) and SFM. By SFM specimens were scanned and digitized using four fluorescence filter sets. Automated cell detection (based on Hoechst 33342 fluorescence), CD3, CD4 and CD8 detection were performed, CD4/CD8 ratio was calculated. Fluorescence signals were well separable on SFM and FCM. Passing and Bablok regression of all CD4/CD8 ratios obtained by FCM and SFM (F(X)=0.0577+0.9378x) are in the 95% confidence interval. Cusum test did not show significant deviation from linearity (P>0.10). This comparison indicates that there is no systemic bias between the two different methods. In SFM analyses the inorganic Quantum dot staining was very stable in PBS in contrast to the organic fluorescent dyes, but bleached shortly after mounting with antioxidant and free radical scavenger mounting media. This shows the difficulty of combinations of organic dyes and Quantum dots. Slide based multi-fluorescence labeling system and automated SFM are applicable tools for the CD4/CD8 ratio determination in peripheral blood samples. Quantum Dots are stable inorganic fluorescence labels that may be used as reliable high resolution dyes for cell labeling.

The possibilities of designing and mastering the new physical and chemical properties of nano-structured materials have been at the center of the large interest they have received in the academic and industrial domains. Confinement effects and the enhanced role of the interface are key parameters. Designing composite materials with controlled nanometric interfacing of different materials is offering new possibilities for developing new structures. Proper design allows to create new properties to meet biological requirements. The purpose of this work is to illustrate the synthesis of various types of nanocrystalline materials that can be used to tackle biological problems inside or outside of living specimens, such as targeted drug delivery, ultra-sensitive disease detection and cell labelling. Two main classes of nanomaterials uses will be discussed. The nanocrystalline materials developed are highly dispersable in water and coated providing biocompatibility. They are elaborated either by precipitation or radiolysis. First, magnetic particles, often called (U)SPIO for (Ultrasmall) SuperParamagnetic Iron Oxide, used as contrast agent for Magnetic Resonance Imaging (MRI) will be presented. Their use for magnetic hyperthermia is now envisaged for cancer treatment. Second, a new generation of inorganic luminophors based on metal colloidal particles will be shown. The coupling of plasmon in nearby particles (semiconductor or metal clusters) is used to enhance their oscillator strength and to target the incident energy. The resulting composite nano-objects can be used for making the smallest possible labels with large oscillator strengths. Those objects will greatly expand the accessibility of single molecule methods.

Fluorescence is a tool widely employed in biological assays. Fluorescent semiconducting nanocrystals, quantum dots (QDs), are beginning to find their way into the tool box of many biologist, chemist and biochemist. These quantum dots are an attractive alternative to the traditional organic dyes due to their broad excitation spectra, narrow emission spectra and photostability. Quantum dots were used to detect and monitor the progession of viral glycoproteins, F (fusion) and G (attachment), from Respiratory Syncytial Virus (RSV) in HEp-2 cells. Additionally, oligo-Qdot RNA probes have been developed for identification and detection of mRNA of the N(nucleocapsid) protein for RSV. The use of quantum dot-FISH probes provides another confirmatory route to diagnostics as well as a new class of probes for monitoring the flux and fate of viral RNA RSV is the most common cause of lower respiratory tract infection in children worldwide and the most common cause of hospitalization of infants in the US. Antiviral therapy is available for treatment of RSV but is only effective if given within the first 48 hours of infection. Existing test methods require a virus level of at least 1000-fold of the amount needed for infection of most children and require several days to weeks to obtain results. The use of quantum dots may provide an early, rapid method for detection and provide insight into the trafficking of viral proteins during the course of infection.

It is assumed that activated neutrophils contribute to the development of anti-neutrophil cytoplasmic auto-antibody (ANCA)-associated vasculitis due to the association of myelopeoxidase(MPO)-ANCA with MPO expressed on the surface of activated neutrophils. FITC-labeled antibody (Ab) used widely are not suitable for neutrophil examination because of the labile fluorescence emission of FITC. Therefore, it is necessary to develop specific fluorescent probes for MPO detection in neutrophils in vivo. Recently, fluorescent nanocrystal quantum dots (QDs) have been used for biotechnological and medical applications because of their greater and far longer fluorescence in. QDs have several advantages over organic fluorophores: high luminescence, far longer stability against photobleaching, and a range of fluorescence wavelengths from blue to infrared, depending on particle size. Thus, we examined the role of MPO and the Ab to MPO in the pathogenesis of glomerulonephritis associated with MPO-ANCA in experimental glomerulonephritis mice using QDs. We demonstrated the QD-conjugated anti-MPO Ab visualized the expression of MPO on the neutrophil surface after stimulation with proinflammatory cytokines. In addition, QD immuno-conjugates with anti-recombinant murine MPO (rmMPO) Ab revealed the trafficking of MPO-ANCA in vivo. Deceleration of blood flow in kidney vessels occurred in model mice, in which serum proteins including anti-rmMPO Ab were leaked out from collapsed glomeruli into the proximal tubule. Thus, sustained MPO expression on the neutrophil surface was significantly related to glomerulonephritis. These results indicate that the expressed MPO on the activated neutrophils with anti-MPO Ab may coordinately play essential roles in the initial steps for the development of glomerulonephritis.

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. Here we report an example of labeling immune cells by QDs. We collected splenic CD4⁺ T-lymphocyte and peritoneal macrophages from mice. Then cells were labeled with QDs. QDs are incorporated into the T-lymphocyte and macrophages immediately after addition and located in the cytoplasm via endocytosis pathway. The fluorescence of QDs held in the endosomes was easily detected for more than a week. In addition, T-lymphocytes labeled with QDs were stable and cell proliferation or cytokine production including IL-2 and IFN-γ was not affected. When QD-labeled T-lymphocytes were adoptively transferred intravenously to mice, they remained in the peripheral blood and spleen up to a week. Using QD-labeled peritoneal macrophages, we studied cell traffic during inflammation on viscera in peritoneum cavity. QD-labeled macrophages were transplanted into the peritoneum of the mouse, and colitis was induced by intracolonic injection of a hapten, trinitrobenzensulfonic acid. With the aid of stong signals of QDs, we found that macrophage accumuled on the inflammation site of the colon. These results suggested that fluorescent probes of QDs might be useful as bioimaging tools for tracing target cells in vivo.

The number of different subtypes of neurons, which form the basic component of the mammalian brain, has not been determined. Histological study is typically limited to the simultaneous detection of very few markers, in part because of the spectral overlap and quenching properties of organic fluorophores. The photostability and narrow emission spectra of non-organic colloidal quantum-dot fluorophores (QDs) make them desirable candidates for multiplex immunohistochemistry (IHC) and for fluorescent in situ hybridization (FISH). IHC is used to study specific protein epitopes and FISH to study the expression of specific mRNA transcripts. In order to investigate the patterns of coexpression of multiple specific protein and nucleic acid targets within cells in complex tissues, such as brain, we have developed protocols for the multiplex use of different QDs and organic fluorophores for combined IHC and FISH. We developed a method for direct QD labeling of modified oligonucleotide probes through streptavidin and biotin interactions and validated this technique in mouse brainstem sections. The reproducible histological results obtained with this protocol allow the use of high throughput computer image analysis to quantify the cellular and subcellular spatial pattern of expression of all markers studied. This approach is being utilized to generate a multiplex co-expression map of neuronal subtypes in mouse brain regions.

We applied single-molecule fluorescence microscopy (using organic dyes or semiconductor quantum dots) to study the lateral diffusion of glutamate receptors (AMPA and NMDA) in live synapses. We directly imaged glutamate receptors movements inside and outside synapses of live cultured hippocampal neurons. We could record exchanges of receptors through lateral diffusion between these different membrane compartments. In addition, our data suggest that this lateral diffusion might be regulated by neuronal activity. To overcome the photobleaching problem inherent to fluorescence techniques we recently developed new optical methods for the detection of individual metallic nanoparticles. We can now detect signatures of diffusing AMPA receptors labeled with 10 nm gold nanoparticles on live neurons.

In this work we present the preparation, characterization and conjugation of colloidal core shell CdS-Cd(OH)₂ quantum dots to health and cancer glial rats living cells in culture media. The particles were obtained via colloidal synthesis in aqueous medium, with final pH=7.3-7.4. Laser Scan Confocal Microscopy (LSCM) and Fluorescence Microscopy were used to evaluate fluorescence intensities and patterns of health and cancer (glioblastoma) glial cells labeled with the quantum dots in different time intervals. Health and cancer glial cells clearly differ in their fluorescence intensities and patterns. These different fluorescence intensities and patterns may be associated to differences concerning cellular membrane and metabolic features of health and cancer cells. The results obtained indicate the potential of the methodology for fast and precise cancer diagnostics.

When conjugated with targeting molecules, quantum dots (QD) can be used as powerful cancer diagnostic tools providing the molecular profiles of cancer cases based on common clinical biopsies. Such personalized analyses will enable doctors to treat and manage the patients' diseases more effectively. The unique optical properties (e.g., size-tunable emission, simultaneous excitation, high brightness and photostability) of these nanoparticles make them superior to conventionally popular organic fluorophores^1-2. Polymer-encapsulated, antibody-tagged QDs were prepared and used to successfully stain both fixed and live cells as well as clinical formalin-fixed paraffin-embedded (FFPE) tissue sections. In the tissue staining study, QD bioconjugates targeting mutated p53 and early growth response protein (egr-1) were used to examine prostate cancer tissues. The tissue slides were then analyzed with a wavelength-resolved spectrometer to accurately quantify the protein expression levels. In comparison to traditional qualitatively based diagnostic procedures, quantum dot nanotechnology allows for a more quantitative, rigorous and objective analysis of tissue specimens in question. In addition, new developments in imaging instrumentation could automate spectroscopy measurements and data analysis.

Inorganic semiconductor nanocrystals, also known as quantum dots (QDs), are interesting as as fluorescent labels in biological studies. We have found that introduction of CdSe QDs to the vicinity of black lipid membranes (BLMs) results in current bursts through the membranes with bias voltage. These current bursts resemble those of the peptaibol class of antibiotics such as alamethicin and trichorzins, and are dependent both on voltage level and on concentration of the QDs applied to the membrane. Our data suggest that QDs with dipole moments similar to alamethicin are influenced by an external electric field, which creates a torque promoting insertion into the BLM, and a simple model predicts that at least three QDs can aggregate to form a pore leading to a macroscopic conductance.

We developed the smaller sized quantum dots covered with sodium 2-mercaptoethanesulfonate which has a sulfonyl group (QDs-SO₃-), 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 NH₂ group (QDs-NH₂). We found that the QD-SO₃- 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-SO₃- did not show noticeable cell damage in the 0.2mg/mL by the comet assay as well as QD-MUA and QD-NH₂ in the same concentration. All these results could suggest that SO₃- might be useful for the biomedical engineering.

Semiconductor nanocrystal quantum dots (QDs) have a great potential for use in biological assays and imaging, due to their unique optical properties. These inorganic nanocrystals are coated with ligands (bifunctional ligands, amphiphilic polymers, phospholipids) that provide them with both hydrophilicity and functionalization. The nanoparticle hydrodynamic radius and electric charge are particularly important parameters as they influence properties such as their diffusion inside live cells or tissues. Techniques such as transmission electron microscopy probe only the nanocrystal core size and don't take into account the size of the ligand coating. We use dynamic light scattering (DLS) to characterize the hydrodynamic diameter (DH) and polydispersity of CdSe/ZnS core-shell QDs capped with various types of hydrophilic surface coatings (dihydrolipoic acid (DHLA), poly(ethylene glycols)-terminated dihydrolipoic acid (DHLA-PEG), amphiphilic polymers, and the native trioctylphosphine/trioctylphosphine oxide (TOP/TOPO) used for solubilization in organic solvents), and of QDs/proteins conjugates. We observe a consistent increase in the hydrodynamic radius with the increasing size of the inorganic core and with the lateral extension of the hydrophilic coating materials. We complement our studies with a derivation of the zeta potential and effective charge of nanoparticles capped with purely charged ligands (DHLA) or encapsulated in a charged polymer using agarose gel electrophoresis. These properties are extremely relevant for designing assay and sensing schemes based on fluorescence resonance energy transfer (FRET) as well as diffusion in live cells, for instance.

In this study we use CdS/Cd(OH)₂ quantum dots functionalized with concanavalin-A (Con-A) lectin, specific to glucose/mannose residues, to investigate cell alterations regarding carbohydrate profile in human mammary tissues diagnosed as fibroadenoma (benign tumor). These particles were functionalized with glutaraldehyde and Con-A and incubated with tissue sections of normal and to Fibroadenoma, a benign type of mammary tumor. The tissue sections were deparafinized, hydrated in graded alcohol and treated with a solution of Evans Blue in order to avoid autofluorescence. The fluorescence intensity of QD-Con-A stained tissues showed different patterns, which reflect the carbohydrate expression of glucose/mannose in fibroadenoma when compared to the detection of the normal carbohydrate expression. The pattern of unspecific labeling of the tissues with glutaraldehyde functionalized CdS/Cd(OH)₂ quantum dots is compared to the targeting driven by the Con-A lectin. The preliminary findings reported here support the use of CdS/Cd(OH)₂ quantum dots as specific probes of cellular alterations and their use in diagnostics.