Highly luminescent carbon nanodots by microwave-assisted pyrolysis

Carbon nanodots (CDs) with a low cytotoxicity have been synthesized by one-step microwave-assisted pyrolysis of citric acid in the presence of various amine molecules. The primary amine molecules have been confirmed to serve dual roles as N-doping precursors and surface passivation agents, both of which considerably enhanced the fluorescence of the CDs.     

Development of a zinc ion-selective luminescent lanthanide chemosensor for biological applications

Detection of chelatable zinc (Zn(2+)) in biological studies has attracted much attention recently, because chelatable Zn(2+) plays important roles in many biological systems. Lanthanide complexes (Eu(3+), Tb(3+), etc.) have excellent spectroscopic properties for biological applications, such as long luminescence lifetimes of the order of milliseconds, a large Stoke's shift of >200 nm, and high water solubility. Herein, we present the design and synthesis of a novel lanthanide sensor molecule, [Eu-7], for detecting Zn(2+). This europium (Eu(3+)) complex employs a quinolyl ligand as both a chromophore and an acceptor for Zn(2+). Upon addition of Zn(2+) to a solution of [Eu-7], the luminescence of Eu(3+) is strongly enhanced, with high selectivity for Zn(2+) over other biologically relevant metal cations. One of the important advantages of [Eu-7] is that this complex can be excited with longer excitation wavelengths (around 340 nm) as compared with previously reported Zn(2+)-sensitive luminescent lamthanide sensors, whose excitation wavelength is at too high an energy level for biological applications. The usefulness of [Eu-7] for monitoring Zn(2+) changes in living HeLa cells was confirmed. This novel Zn(2+)-selective luminescent lanthanide chemosensor [Eu-7]should be an excellent lead compound for the development of a range of novel luminescent lanthanide chemosensors for biological applications.     

Polyacrylic acid coating of highly luminescent CdS nanocrystals for biological labeling applications

Surface coating of highly luminescent CdS nanocrystals by polyacrylic acid was demonstrated. The method proceeded in 2 steps, (i) modification of the CdS surface by alkyl molecules and (ii) polyacrylic acid coating of the surface modified CdS. Attachment of alkyl ammonium on the CdS surface induced a phase transfer reaction from an aqueous to a non-polar phase with a yield of approximately 100%. Investigating alkyl molecules with various functional groups revealed that the alkyl molecules, possessing the cation moiety, such as amine or ammonium salt, can electrostatically interact with the CdS surface. The PL of the uncoated nanocrystals was almost entirely quenched in the pH range of approximately 7, while the polyacrylic acid coated nanocrystals exhibited moderate PL intensity. This PL intensity was preserved for at least several days, facilitating biological labeling application under a neutral condition.     

Development of responsive lanthanide-based magnetic resonance imaging and luminescent probes for biological applications

Lanthanide complexes have unique chemical characteristics compared with typical organic complexes, and have recently attracted much interest because of the expanding need for new bioanalytical sensors. For example, magnetic resonance imaging (MRI) permits noninvasive three-dimensional imaging inside opaque organisms, and gadolinium ion (Gd(3+)) complexes have become important tools as MRI contrast agents. However, most of them are nonspecific, and report solely on anatomy. Therefore, responsive MRI contrast agents, so-called "smart" MRI contrast agents whose ability to relax water protons is greatly enhanced by recognition of a particular biomolecule, have great potential for elucidating biological phenomena. On the other hand, lanthanide complexes such as europium (Eu(3+)) and terbium (Tb(3+)) complexes have excellent luminescence properties for biological applications, i.e., long luminescence lifetime of the order of milliseconds and a large Stoke's shift of >200 nm. Their long-lived luminescence is especially suitable for time-resolved measurements, because the interference from short-lived background fluorescence and scattered light rapidly decays to a negligible level after a pulse of excitation light is applied, and the emitted light can be collected after an appropriate delay time. These luminescent lanthanide complexes have already found commercial use as highly sensitive luminescent probes in heterogeneous and homogeneous assays. This paper reviews our research on the design and synthesis of responsive lanthanide-based MRI and luminescent probes for advanced bioimaging.     

Protein A-conjugated luminescent gold nanodots as a label-free assay for immunoglobulin G in plasma

We have employed protein A-modified gold nanodots (PA-Au NDs) as a luminescence sensor for the detection of human immunoglobulin G (hIgG) in homogeneous solutions. The luminescent PA-Au NDs were prepared simply by mixing protein A with the luminescent Au NDs (average diameter: ca. 1.8 nm). The specific interactions that occur between protein A and hIgG allowed us to use the PA-Au NDs to detect hIgG selectively. Under optimal conditions [10 nM PA-Au NDs (two protein A molecules per Au ND), 5.0 mM phosphate buffer solution, pH 7.4], the PA-Au ND probe detected hIgG with high sensitivity (limit of detection = 10 nM) and remarkable selectivity (>50-fold) over other proteins. In an assay that took advantage of the competition between protein G and the PA-Au NDs for IgG, we detected protein G at concentrations as low as 85 nM. This PA-Au ND probe allowed determination of the hIgG concentration in plasma samples without any need for sample pretreatment. Our results exhibited a good linear correlation (R(2)=0.97) with those obtained using an enzyme-linked immunosorbent assay. Our simple, sensitive, and selective approach appears to hold practical potential for use in the clinical diagnosis of immune diseases associated with changes in hIgG levels.     

Size control for two-dimensional iron oxide nanodots derived from biological molecules

We demonstrated the fabrication of size-controlled two-dimensional iron oxide nanodots derived from the heat treatment of ferritin molecules self-immobilized on modified silicon surfaces. Ferritin molecules were immobilized onto 3-aminopropyltrimethoxysilane (3-APMS)-modified silicon surfaces by electrostatic interactions between negatively charged amino acids of ferritin molecules and amino terminal functional groups of 3-APMS. Heat treatments were performed at 400 degrees C for 60 min to fabricate two-dimensional nanodots based on ferritin cores. XPS and FT-IR results clearly indicate that ferritin shells were composed of amino acids and 3-APMS modifiers on silicon surfaces were eliminated by heat treatment. Nanodots on substrate surfaces corresponded to iron oxides. The size of nanodots was tunable in the range of 0-5 (+/-0.75) nm by in situ reactions of iron ion chelators with ferritin molecules immobilized on substrates before heat treatment.     

Application of luminescent nanocrystals as labels for biological molecules

Luminescent semiconductor nanocrystals, so called quantum dots (QD), have attracted increasing interest for bioanalytical labeling applications in recent years. This review describes the major optical and (bio)chemical features of this class of label, compared with organic dyes. Different conjugation methods are also discussed and the most important recent applications are presented. An overview over the current state-of-the-art is given, as also is an outlook on possibilities and limitations.     

Zeolite micropattern for biological applications

A facile method was established using composition-gradient pattern on zeolite surface to guide the deposition and formation of chemical and biomolecular patterns with features as small as five microns.     

Carbon nanodots as peroxidase mimetics and their applications to glucose detection

Carbon nanodots (C-Dots) were found to possess intrinsic peroxidase-like activity, and could catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) by H(2)O(2) to produce a colour reaction. This offers a simple, sensitive and selective colorimetric method for glucose determination in serum.     

Small-sized silver nanoparticles for studies of biological effects

The influence of the hydration extent, AOT and silver ion concentration on average particle size and size distribution in micellar solution of silver nanoparticles obtained by biochemical synthesis was investigated. Formation and stability of nanoparticles were controlled by measurements of optical absorption spectra. Particle sizes were determined by transmission electron microscopy. Combinations of varied parameters have been found, making it possible to prepare three micellar solutions of spherical silver nanoparticles with a different average size in the range 4.6–10.5 nm and narrow size distribution (the standard deviation does not exceed 2.5 nm). For the water dispersions prepared from such solutions by the specially developed procedure, possible applications for studies of size effects in the biological action of nanoparticles are also discussed.     

A photopatternable silicone for biological applications

We show the application of a commercially available photopatternable silicone (PPS) that combines the advantageous features of both PDMS and SU-8 to address a critical bioMEMS materials deficiency. Using PPS, we demonstrate the ability to pattern free-standing mechanically isolated elastomeric structures on a silicon substrate: a feat that is challenging to accomplish using soft lithography-based fabrication. PPS readily integrates with many cell-based bioMEMS since it exhibits low autofluorescence and cells easily attach and proliferate on PPS-coated substrates. Because of its inherent photopatternable properties, PPS is compatible with standard microfabrication processes and easily aligns to complex featured substrates on a wafer scale. By leveraging PPS' unique properties, we demonstrate the design of a simple dielectrophoresis-based bioMEMS device for patterning mammalian cells. The key material properties and integration capabilities explored in this work should present new avenues for exploring silicone microstructures for the design and implementation of increasingly complex bioMEMS architectures.     

Polymeric actuators for biological applications.

To shed light on the role of cell rheology and mechanotransduction in various physiological and disease states, different techniques of force application, such as optical tweezers and deformable substrates, are employed. In this present paper we describe a new approach for the deformation of cells based on the temperature-sensitive polymer poly(N-isopropylacrylamide), PNIPAM. In response to temperature changes, PNIPAM gels undergo extensive and reversible changes in volume that allow them to be used as actuators for stretching and compressing cells and tissues. Herein we focus mainly on our experience with the deformation of red blood cells as proof of principle, and demonstrate the wealth of possibilities such stimuli-responsive materials may offer as actuators.     

Biocompatible quantum dots for biological applications

Semiconductor quantum dots are quickly becoming a critical diagnostic tool for discerning cellular function at the molecular level. Their high brightness, long-lasting, size-tunable, and narrow luminescence set them apart from conventional fluorescence dyes. Quantum dots are being developed for a variety of biologically oriented applications, including fluorescent assays for drug discovery, disease detection, single protein tracking, and intracellular reporting. This review introduces the science behind quantum dots and describes how they are made biologically compatible. Several applications are also included, illustrating strategies toward target specificity, and are followed by a discussion on the limitations of quantum dot approaches. The article is concluded with a look at the future direction of quantum dots.     

Synthesis of luminescent bioapatite nanoparticles for utilization as a biological probe

A europium-doped apatitic calcium phosphate was synthesized at low temperature (37°C) in water–ethanol medium. This apatite was calcium-deficient, rich in hydrogen phosphate ions, and poorly crystallized with nanometric sized crystallites. It is similar to the mineral part of calcified tissues of living beings and is thus a biomimetic material. The substitution limit of Eu³⁺ for Ca²⁺ ions in this type of bioapatite ranged about 2–3%. The substitution at this temperature was facilitated by vacancies in the calcium-deficient apatite structure. As the luminescence of europium is photostable, the doped apatite could be employed as a biological probe. Internalization of these nanoparticles by human pancreatic cells in culture was observed by luminescence confocal microscopy.     

Anion dependent structures of luminescent silver(i) complexes

The reaction of AgX, where X = trifluoroacetate (CF(3)CO(2)(-), tfa), nitrate (NO(3)(-)), trifluoromethanesulfonate (triflate, CF(3)SO(3)(-), OTf), hexafluorophosphate (PF(6)(-)), or perchlorate (ClO(4)(-)), with 2,2',3' '-tripyridylamine (tpa) yields five novel silver(I) complexes, which have been structurally characterized. The five complexes have the same 1:1 stoichiometry of Ag/tpa but exhibit different modes of coordination, depending upon the counterion present in the compound. Compound 1, [Ag(tpa)(tfa)](n)(), forms a 1D coordination polymer of [Ag(tpa)(tfa)](2) dimer units linked through bridging tfa counterions. Compound 2, [Ag(tpa)(CH(3)CN)(NO(3))](n), forms a zigzag chain 1D coordination polymer exclusively through Ag-N bonds. In compounds 1 and 2, each tpa ligand is bound to two Ag(I) ions via a 2-py and a 3-py group. Compound 3, [Ag(tpa)(OTf)](n), forms a ribbonlike 1D coordination polymer, in which each tpa ligand binds to three different silver centers via all three pyridyl groups, and the counterion remains coordinated to the Ag(I) center. Compounds 4, [Ag(tpa)(CH(3)CN)](n)(PF(6))(n), and 5, [Ag(tpa)(CH(3)CN)](n)() (ClO(4))(n), display ribbonlike structures resembling that of 3, except that the counterions are not coordinated. All complexes are luminescent in acetonitrile solution, with emission maxima in the near-UV region (lambda(max) = 366, 368, 367, 367, and 368 nm for 1-5, respectively). At 77 K, the emission maxima are red-shifted to lambda(max) = 452, 453, 450, 450, and 454 nm for 1-5, respectively.     

Ethylene sensing by silver(I) salt-impregnated luminescent films

Luminescent oligomers and polymers doped with silver(I) salts were used as optical sensors for ethylene and other gaseous small molecules. Films of poly(vinylphenylketone) (PVPK) or 1,4-bis(methylstyryl)benzene (BMSB) impregnated with AgBF(4), AgSbF(6), or AgB(C(6)F(5))(4) respond to ethylene exposures with a reversible emission quenching that is proportional to the pressure of the gas. Experiments with various analytes revealed that only gases capable of forming coordinate bonds with Ag(I) ions (i.e., ethylene, propylene, and ammonia) produced a sensing response. Comparison of the effects of ethylene and tetradeuterioethylene revealed that the emission quenching was due to enhanced vibrational relaxation. The Ag(I) ions are essential to the observed optical response. The oligomer/polymer support enhances the response characteristics of the impregnated salt by promoting separation of Ag(I) from its anion, a separation that improves accessibility of the Ag(I) ion to the gaseous analytes. Salts with large lattice energies, where the anion is not dissociated from Ag(I) in the matrix, fail to sensitize film responses. Photoluminescence experiments with Ag(I)-impregnated BMSB films established that the Ag(I) ions serve to communicate the analyte-binding signal to the support by altering the support-based emission. These experiments demonstrate a sensing paradigm where simultaneous coordination of Ag(I) ions to the support matrix and to a gaseous analyte enables the optical response.     

Nonmacrocyclic luminescent lanthanide complexes stable in biological media

The synthesis of ligand L(P)H(8), based on a 2,6-bispyrazolyl-pyridine scaffold functionalized by iminobismethylenephosphonate functions, is described and its pK values were determined by a combination of pH-spectrophotometric titrations and potentiometry. The interaction of L(P) with Tb(3+) was investigated in water (0.01 M TRIS/HCl pH = 7.0) by means of UV-vis and fluorescence titration experiments and evidenced the formation of at least three species with 1:1; 1:2, and 2:1 M-L ratios, the 1:1 complex appearing as particularly stable under these conditions (log K(cond) > 8). Na(4)[LnL(P)H] complexes (Ln = Eu and Tb) were prepared and characterized by elemental analysis, IR spectroscopy, and electrospray mass spectrometry. Their photophysical properties were investigated in aqueous solutions, revealing an excellent shielding of the Ln cations from the solvent environment (no water molecules in the first coordination sphere), very long luminescence lifetimes (τ(H(2)(O)) = 1.50 and 3.28 ms, respectively, for Eu and Tb) and reasonable luminescent quantum yields (?(H(2)(O)) = 2.4 and 37%, respectively, for Eu and Tb). Using fetal bovine serum as a model for biological media showed the Tb complex to remain luminescent in these conditions. The structure of the europium complex was studied by means of density functional theory (DFT) modeling, confirming the wrapping of the ligand around the cation, and the very good shielding of the coordinated Ln cation. The conditional stability constant for the formation of the Tb complex with L(P) was determined by competition experiments with EDTA and monitored by fluorescence spectroscopy (log K(TbL(P)cond) = 14.1 ± 0.3, 0.01 M TRIS/HCl, pH = 7.4) and was used to determine the thermodynamic constant (log K(TbL(P)) = 20.4 ± 0.4). A systematic comparison with ligand L(C), in which phosphonate functions are replaced by carboxylate ones, is made throughout the study, highlighting the large interest of the introduction of phosphonate moieties to obtain biologically stable luminescent lanthanide complexes.