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Gold nanoparticle-conjugated fluorescent hydroxyapatite (AuFHAp) was developed as a smart nanoprobe for measuring alkaline phosphatase (ALP) activity. AuFHAp showed NIR fluorescence due to the hydrolysis of its phosphate groups by ALP. In addition, gold nanoparticles help reduce the nonspecific signal by absorbing nonspecific fluorescence. Through in vitro tests, we confirmed that the AuFHAp probe was capable of detecting ALP levels related to osteoblast activity in living cells with high fluorescence intensity.

We developed a colorimetric method to specifically detect single-strand DNA breaks using gold nanoparticles. In our assay, broken DNA cannot stabilize gold nanoparticles to prevent salt-induced aggregation as good as intact DNA can, and this effect can be easily observed with the naked eye as a red-to-purple color change.

This paper demonstrates the development of a novel nanoparticle-enhanced surface plasmon resonance (SPR) sensing platform for the selective and sensitive in situ detection of nickel(II) ions at concentrations as low as 50 parts per trillion (211 pM). An enhancement in selectivity was achieved by designing a surface sandwich assay involving two different ligands each selective toward nickel(II) ions, namely, N-[5-(3'-maleimidopropylamido)-1-carboxypentyl]iminodiacetic acid (NTA) and polyhistidine. Maleimido-modified NTA was first immobilized on an alkanedithiol-modified gold thin film, followed by the sequential adsorption of Ni(II) ions. Next, polyhistidine-functionalized quasispherical gold nanoparticles, designed to enhance the SPR sensitivity, were specifically adsorbed onto surface Ni(II)-NTA complexes. This process was monitored by real-time SPR. The ability to detect Ni(II) ions as low as 50 parts per trillion (ppt) is a remarkable improvement compared to other optical and colorimetric techniques utilizing nanoparticles and is comparable to what can be achieved by state-of-the-art inductively coupled plasma mass spectrometry (ICP-MS). The improved selectivity for Ni(II) ions by the sandwich assay approach was confirmed by comparing measurements involving other divalent cations such as Zn(II), Pb(II), and Cu(II), some of which individually possess binding affinities toward either the NTA or histidine moieties.

A new strategy for highly sensitive and rapid protease assay is developed by mediating proteolytic formation of oligonucleotide duplexes and using the duplexes for signal amplification. In the presence of matrix metalloprotease-2 (MMP-2), fragmentation of the intact DNA-peptide on gold nanoparticles (GNP) by hydrolytic cleavage of a peptide bond within the substrate allows diffusion of DNA away from the GNP and the formation of a DNA/RNA heteroduplex, leading to digestion of RNA by RNase H. Because of the high quenching efficacy of GNP to the fluorophore in RNA and multiple digestions of the RNA, the fluorescence signal recovery is amplified. This method permits the assessment of the activity of MMP-2 at concentrations as low as 10 pM within 4 h. Compared with the reported protease nanosensors using quantum dots, GNP, and magnetic nanoparticles with the same peptide sequence, the assay time of this method is sixfold faster and the limit of detection is 100-fold more sensitive. The formulations for proteolytic formations of oligonucleotides duplexes for signal amplification on GNP could lead to the development of more sensitive and rapid protease assay techniques, thus extending the role of proteases as therapeutic targets and disease indicators.

In general, gold nanoparticles are recognized as being as nontoxic. Still, there have been some reports on their toxicity, which has been shown to depend on the physical dimension, surface chemistry, and shape of the nanoparticles. In this study, we carry out an in vivo toxicity study using 13 nm-sized gold nanoparticles coated with PEG (MW 5000). In our findings the 13 nm sized PEG-coated gold nanoparticles were seen to induce acute inflammation and apoptosis in the liver. These nanoparticles were found to accumulate in the liver and spleen for up to 7 days after injection and to have long blood circulation times. In addition, transmission electron microscopy showed that numerous cytoplasmic vesicles and lysosomes of liver Kupffer cells and spleen macrophages contained the PEG-coated gold nanoparticles. These findings of toxicity and kinetics of PEG-coated gold nanoparticles may have important clinical implications regarding the safety issue as PEG-coated gold nanoparticles are widely used in biomedical applications.

Periodic arrays of pseudotetrahedal-shaped gold nanoparticles were fabricated using nanosphere lithography (NSL) and examined for localized surface plasmon resonance (LSPR). The dependence of the LSPR on particle size of the periodic gold nanostructures was explored for potential application as a new biosensor. With increasing size and height of the Au nanoparticles, the absorption peak of the LSPR shifts to the longer wavelength and becomes relatively sharper. With thinner metal deposition or finer Au nanostructure, the absorption signal varies more sensitively for the changes in the Au particle size. The binding affinity study for biotin-streptavidine system on the Au nanopatterns resulted in blue-shifted absorption signal, opening up the possibility of the nanostructured Au pattern as a new LSPR biosensor.

This paper describes the effect of halide ions during the seed-mediated growth of gold nanoparticles employing cetyltrimethylammonium bromide (CTAB) as a cationic surfactant system. With the addition of a small amount of iodide ion (∼20 μM) in a growth solution, the major product of the gold nanostructures formed were notably changed into triangular nanoprisms in the presence of excessive bromide ion (∼0.1 M); otherwise, in its absence, nanorods with an aspect ratio of ∼11 were the main products. The major role of the iodide ion was in retarding the overall rate of crystal growth, and the iodide adsorption appeared to repress the crystal growth along Au(111) direction, resulting in Au(111)-faced triangular nanoprisms. When the counteranions of the surfactant were replaced with chloride ions, a novel nanostructure (i.e., nanorice) was manufactured, which demonstrates the effectiveness of the adsorption of halide ions. However, this finding is quite contrasted with the work of the Sastry group (J. Nanosci. ...

An efficient strategy for immobilizing proteins on a gold surface was developed by employing the gold binding polypeptide (GBP) as a fusion partner. Using the enhanced green fluorescent protein (EGFP), severe acute respiratory syndrome coronavirus (SARS-CoV) envelope protein (SCVme), and core streptavidin (cSA) of Streptomyces avidinii as model proteins, specific immobilization of the GBP-fusion proteins onto the gold nanoparticles and generation of protein nanopatterns on the bare gold surface were demonstrated. The GBP-fused SCVme bound to gold nanoparticles successfully interacted with its antibody and showed changes in absorbance and color, allowing efficient diagnosis of SARS-CoV. The fusion proteins could be successfully immobilized on the gold surface by nanopatterning and microcontact printing as examined by atomic force microscopy and surface plasmon resonance analysis. The poly(dimethylsiloxane) microfluidic channels were created on the gold surface and were used for antigen-antibody and DNA-DNA interaction studies. Specific immobilization of GBP-EGFP fusion protein and its interaction with the antibody in the microchannels could be demonstrated. By immobilizing the DNA probe through the use of GBP-fused cSA, specific hybridization of the target DNA prepared from Salmonella could also be achieved. The GBP-fusion method allows immobilization of proteins onto the gold surface without surface modification and in bioactive forms suitable for studying protein-protein, DNA-DNA, and other biomolecular interaction studies. Furthermore, these studies can be carried out in a microfluidic system, which allows high-throughput analysis of biomolecular interactions.

The optical properties of polymer nanospheres were tuned by in situ transformation of metal structures on their surfaces. Silver nanoparticles (NPs) deposited on the polystyrene nanospheres were transformed into metal hollows made of gold/silver alloy by a galvanic replacement reaction. The metal hollows made of gold/silver alloy were finally changed into solid gold nanoparticles by the additional treatment of chloroauric acid. Through the transformation process, the optical resonance peak of metal-coated polystyrene (PS) nanospheres was tuned in the 410 to 820 nm region. The transformation of metal nanostructures on the surface of PS nanospheres was monitored and characterized by UV–visible–near infrared (NIR) spectroscopy and transmission electron microscopy. The described protocols should be applied to prepare the metal-coated polymer nanospheres with tunable surface plasmon resonance (from 450 to 820 nm) which would be very useful for biological assays.

We developed a new detection method for L-Dopa decarboxylase (DDC) activity using gold nanoparticles (AuNPs). When L-3,4-dihydroxyphenylalanine (L-Dopa) is decarboxylated to dopamine (DA) by DDC, DA induces the aggregation of AuNPs, and the color of the AuNPs changes from red to blue.

There has been great progress in the development of functional DNA-based sensors for the detection of metal ions. However, many functional DNAs are vulnerable to hydrolysis by nucleases in human blood. In addition, the detection methods that are based on DNA often exhibit interference due to the high blood concentrations of other ions, such as K(+) and Na(+). Therefore, we selected highly Pb(2+)-specific DNA-aptamer sequences based on CD spectroscopy of 4 G-rich DNA sequences and Hg(2+)-specific T-rich DNA sequences and immobilized them on gold nanoparticles for the simultaneous detection of Pb(2+) and Hg(2+) in human serum. We used gold nanoparticles because these have a superior fluorescence-quenching efficiency over a broad range of wavelengths compared with other organic quenchers. In addition, gold nanoparticles have a stabilizing effect on the immobilized DNA, which makes it more resistant to degradation by nucleases than free DNA. As a result, even in the presence of DNase, we were able to simultaneously detect Pb(2+) and Hg(2+) in serum at concentrations as low as 128 pM and 121 pM, respectively, within 10 min. These detection limits for Pb(2+) and Hg(2+) were 39-fold and 26.4-fold lower, respectively, than the detection limits that were obtained using free DNAs. Given the multi-color-fluorescence quenching capability of the gold nanoparticles and the possibility of developing functional nucleic acids for the detection of other metal ions, this study extends the application of oligonucleotides to a point-of-care detection system for the detection of multiple harmful metal ions in body fluids.

We introduce a scanometric detection method for the analysis of DNA microarrays using DNA intercalator-conjugated gold nanoparticles that can be analyzed with the naked eye or with an optical scanner after the enhancement of the AuNPs. Moreover, we successfully detected a hemagglutinin-subtyping DNA array using this method.

For the electrical detection of target DNA (partial avian influenza virus/H1N1/HA sequence) prepared via asymmetric PCR, we fabricated DNA-templated conducting gold nanowire bridges on planar nanogap electrodes using positively charged gold nanoparticles.

This paper describes a novel approach to label-free electrochemical detection of human α-thrombin in human blood serum that utilizes ferrocene-coated gold nanoparticles (Fc-AuNPs). Human α-thrombin was specifically bound by the thiolated aptamers immobilized on the electrode. Positively charged Fc-AuNPs were electrostatically bound to the negatively charged aptamers. In principle, a high current peak should be observed in the absence of interactions between the aptamers and the human α-thrombin. This behavior indicates maximum adsorption of Fc-AuNPs by the negatively charged aptamers on the electrode surface. In contrast, when the thrombin–aptamer complex is formed, a low signal is expected because of the blocking capacities of the protein, which hinders the electrostatic binding of the Fc-AuNPs. The electrochemical signal, recorded by cyclic voltammetry and differential pulse voltammetry, indicates whether interactions between aptamers and proteins have occurred. There is a good correlation between the ferrocene oxidation peak intensity readings from our thrombin sensing system and the thrombin concentration, within the range of 1.2 μM–12 pM.

We report an enzymatic method to control the plasmon resonance absorbance of gold nanoparticle (AuNP) arrays assembled on hyaluronic acids. While multiple electrostatic interactions between cysteamine on the AuNPs and the carboxylic acid residues in the whole intact hyaluronic acid induced the formation of large aggregates, precise control of the plasmon absorbance was possible by tailoring the size of the bio-polymeric templates with hyaluronidase, almost over the entire range of the resonant coupling wavelengths. It was possible to precisely tune the position of the second plasmon absorbance by manipulating the amount of the template and the enzymatic hydrolysis time. Finally, we were able to produce a chain-like array of AuNPs, which was nearly one dimensional, with a maximum shift of up to 189 nm in the plasmon absorbance at the optimal hydrolysis time of the templates. This enzymatic method can be used as a useful tool to tailor the plasmonic properties of the nanostructures required for specific applications.

We developed a method to detect mutagenic DNA photodimers by the naked eye using gold nanoparticles. The stability of gold nanoparticles in a high ionic strength solution is maintained by straight ssDNA adsorbed physically on the AuNPs. However, we found that UV-irradiated DNA was less adsorptive onto gold nanoparticles because of a conformational change of UV-irradiated DNA. The accumulated deformation of the DNA structure by multiple-dimer formation triggered aggregation of the gold nanoparticles mixed with the UV-irradiated DNA and thus red to purple color changes of the mixture, which allowed colorimetric detection of the DNA photodimers by the naked eye. No fragmented mass and reactive oxygen species production under the UVB irradiation confirmed that the aggregation of gold nanoparticles was solely attributed to the accumulated deformation of the UV irradiated DNA. The degree of gold nanoparticles-aggregation was dependent on the UVB irradiated time and base compositions of the UV-irradiated oligonucleotides. In addition, we successfully demonstrated how to visually qualify the photosensitizing effect of chemical compounds in parallel within only 10 min by applying this new method. Since our method does not require any chemical or biochemical treatments or special instruments for purifying and qualifying the DNA photolesions, it should provide a feasible tool for the studies of the UV-induced mutagenic or carcinogenic DNA dimers and accelerate screening of a large number of drug candidates.

For previously reported fluorescence Pb 2+ sensors, DNAzymes have lead to a significant increase in Pb 2+ detecting sensitivity and specificity. However, these sensors suffer from incomplete fluorescence quenching and require additional steps for annealing DNAzymes and substrates as well as for removing the uncoupled substrates. In this study, we successfully overcome these issues by immobilizing the substrate nucleic acids on gold nanoparticles through thiol linkages. The immobilization of the substrate molecules to the gold nanoparticles lead to almost-complete fluorescence quenching and fast Pb 2+ detection, without altering the Pb 2+ specificity of the DNAzymes. After optimizing the concentration of DNAzymes, reaction time and pH, we could detect Pb 2+ as low as 5 nM within 20 min without the preliminary and the post treatments. Considering the multi-color-fluorescence quenching capability of gold nanoparticles and the to-be-developed functional nucleic acids for other metal ions, this study could extend the application of DNAzymes to the detection of multiple heavy metal ions.

Gold nanoparticles (AuNPs) can be used in various biomedical applications, however, very little is known about their size-dependent in vivo kinetics. Here, we performed a kinetic study in mice with different sizes of PEG-coated AuNPs. Small AuNPs (4 or 13 nm) showed high levels in blood for 24 h and were cleared by 7 days, whereas large (100 nm) AuNPs were completely cleared by 24 h. All AuNPs in blood re-increased at 3 months, which correlated with organ levels. Levels of small AuNPs were peaked at 7 days in the liver and spleen and at 1 month in the mesenteric lymph node, and remained high until 6 months, with slow elimination. In contrast, large AuNPs were taken up rapidly (∼ 30 min) into the liver, spleen, and mesenteric lymph nodes with less elimination phase. TEM showed that AuNPs were entrapped in cytoplasmic vesicles and lysosomes of Kupffer cells and macrophages of spleen and mesenteric lymph node. Small AuNPs transiently activated CYP1A1 and 2B, phase I metabolic enzymes, in liver tissues from 24 h to 7 days, which mirrored with elevated gold levels in the liver. Large AuNPs did not affect the metabolic enzymes. Thus, propensity to accumulate in the reticuloendothelial organs and activation of phase I metabolic enzymes, suggest that extensive further studies are needed for practical in vivo applications.

Mixed self-assembled monolayers (MSAMs) composed of diverse ligands offer a mechanism for the specific binding of biomolecules onto solid surfaces. In this study, we examined the formation of MSAMs on gold nanoparticles (AuNPs) and the immobilization of hexa-arginine-tagged esterase (Arg(6)-esterase) on the surfaces of the resulting particles. The functionalization of AuNPs with MSAMs was achieved by introducing a mixture of tethering and shielding ligands into an AuNP solution. The formation of self-assembled monolayers (SAMs) on the AuNP surface was characterized by UV/visible spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. Arg(6)-esterase was immobilized in a highly specific manner onto AuNPs treated with mixed SAMs (MSAM-AuNPs) by providing a shielding ligand which reduce the non-specific adsorption of enzymes caused by hydrophobic interaction compared to AuNPs treated with single-component SAMs (SSAM-AuNPs). Moreover, Arg(6)-esterase immobilized on MSAM-AuNPs showed substantially enhanced catalytic activity up to an original activity compared to that on SSAM-AuNPs (58%).

Paramagnetic gold nanostructures were synthesized by combining the paramagnetism of gadolinium with the plasmonic properties of gold nanoparticles and used for dual modal (MRI and optical) imaging and phototherapy of breast cancer cells.

The real-time monitoring of the caspase cascade in cancer cells during apoptosis was performed using various caspase substrate-linked fluorescent proteins-conjugated gold nanoparticles as a new imaging probe.

Utilizing a gold enhancement process after inducing electrostatic interaction between positively charged gold nanoparticles and negatively charged target DNA hybridized to neutral PNA capture probes, a new method for label-free detection of DNA was developed and successfully applied to detect H5-type DNA.

An operationally simple colorimetric way for measuring hyaluronidase activity was developed using cysteamine-bound gold nanoparticles. The addition of gold nanoparticles into hyaluronidase-containing solutions resulted in color changes, which could easily be observed with the naked eye or a UV/Vis spectrophotometer.

We describe the development of hollow-type gold nanoparticles (NPs) for the photonic-based imaging and therapy of macrophage cells. The strong light-absorption and light-scattering properties of gold NPs render them to be useful as molecular imaging agents as well as therapeutic moieties. By controlling the geometry of the gold NPs, the optical resonance peak was shifted to around the near-infrared (NIR) region, where light transmission through biological tissue is known to be fairly high. Hollow-type gold NPs modified with dextran were phagocytosed by macrophage cells. Using dark-field microscopy, it was possible to image macrophage cells targeted with NPs. After NIR irradiation, macrophages labeled with NPs were selectively destroyed by the photothermal effect. FACS analysis revealed that the photothermal effect caused principally late apoptosis-related cell death or secondary necrosis. The experimental results showed that hollow-type gold NPs conjugated with dextran could be used not only as optical imaging contrast agents but also as a component of a novel anti-macrophage therapeutic strategy.