Huan-Tsung Chang

Detection of mercury(II) based on Hg2+–DNA complexes inducing the aggregation of gold nanoparticles

A DNA-Au NP probe for sensing Hg2+ using the formation of DNA-Hg2+ complexes through thymidine (T)-Hg2+ -T coordination to control the negative charge density of the DNA strands-thereby varying their structures-adsorbed onto Au NPs.

Fluorescent Gold Nanoclusters: Recent Advances in Sensing and Imaging

F gold nanoclusters (Au NCs) or nanodots (NDs) with sizes smaller than 3 nm are a specific type of gold nanomaterials. In this review, Au NCs are used to represent fluorescent Au nanomaterials with sizes smaller than 3 nm. Unlike the most popular and well-known spherical, large gold nanoparticles, Au NCs do not exhibit surface plasmon resonance (SPR) absorption in the visible region but have fluorescence in the visible to near-infrared (NIR) region. With advantages of long lifetime, large Stokes shift, and biocompatibility, Au NCs have become interesting sensing and imaging materials. Although Au NCs prepared from Au in the presence of small thiol compounds such as 2-phenylethanethiol (PhCH2CH2SH) have been reported over the past decade, 5 their use for bioapplications have not been well recognized, mainly because of their low quantum yield (usually less than 1%), poor water dispersibility, photo and chemical instability, and difficulty for conjugation. In the past decade, many strategies for the preparation of stable, water dispersible, highly fluorescent, and biocompatible Au NCs have been reported. There are two major categories elucidating the recent advanced techniques for the preparation of Au NCs. The first category is through etching of larger sizes of nonfluorescent gold nanoparticles (Au NPs) by thiol compounds such as mercaptopropionic acid. The second category is from reduction of Au in the presence of a ligand or template (protein) such as bovine serum albumin (BSA). The optical properties of biocompatible Au NCs are dependent on their size, surface ligand or template, and the surrounding medium, and thus they can be studied to develop sensitive and selective sensing and imaging systems for the detection of various analytes. The growing popularity of Au NCs in analytical applications has been realized in these few years. Several excellent review papers dealing with Au NCs from the viewpoint of analytical chemistry have been reported to highlight their potential for the analysis of environmental and biological samples. This review focuses on recent advances in Au NCs based sensing and imaging systems between 2012 and 2014. Current challenges and future prospects of Au NCs for fundamental studies and analytical applications will be provided.

Oligonucleotide-Based Fluorescence Probe for Sensitive and Selective Detection of Mercury(II) in Aqueous Solution

In this paper we unveil a new homogeneous assayusing TOTO-3 and the polythymine oligonucleotide T 33for the highly selective and sensitive detection of Hg (2+) in aqueous solution. The fluorescence of TOTO-3 is weak in the absence or presence of randomly coiled T 33. After T 33 interacts specifically with Hg (2+) ions through T-Hg (2+)-T bonding, however, its conformation changes to form a folded structure that preferably binds to TOTO-3. As a result, the fluorescence of a mixture of T 33 and TOTO-3 increases in the presence of Hg (2+). Our data from fluorescence polarization spectroscopy, capillary electrophoresis with laser-induced fluorescence detection, circular dichroism spectroscopy, and melting temperature measurements confirm the formation of folded T 33-Hg (2+) complexes. Under optimum conditions, the TOTO-3/T 33 probe exhibited a high selectivity (>or=265-fold) toward Hg (2+) over other metal ions, with a limit of detection of 0.6 ppb. We demonstrate the practicality of this TOTO-3/T 33 probe for the rapid determination of Hg (2+) levels in pond water and in batteries. This approach offers several advantages, including rapidity (<15 min), simplicity (label-free), and low cost.

Parameters for selective colorimetric sensing of mercury(II) in aqueous solutions using mercaptopropionic acid-modified gold nanoparticles

We unveil a new homogeneous assay-using mercaptopropionic acid-modified Au nanoparticles in the presence of 2,6-pyridinedicarboxylic acid for the highly selective and sensitive detection of Hg(2+) ions.

Cancer Cell Targeting Using Multiple Aptamers Conjugated on Nanorods

Molecular recognition toward specific cells is a key issue for effective disease, such as cancer, diagnosis and therapy. Although many molecular probes such as aptamers and antibodies can recognize the unique molecular signatures of cancer cells, some of these probes only have relatively weak binding affinities. This results in poor signaling and hinders cell targeting. Here, we use Au-Ag nanorods (NRs) as a nanoplatform for multivalent binding by multiple aptamers on the rod to increase both the signal and binding strengths of these aptamers in cancer cell recognition. Up to 80 fluorophore-labeled aptamers can be attached on a 12 nm x 56 nm NR, resulting in a much stronger fluorescence signal than that of an individual dye-labeled aptamer probe. The molecular assembly of aptamers on the NR surfaces also significantly improves the binding affinity with cancer cells through simultaneous multivalent interactions with the cell membrane receptors. This leads to an affinity at least 26-fold higher than the intrinsic affinity of the original aptamer probes. As determined by flow cytometric measurements, an enhancement in fluorescence signal in excess of 300-fold is obtained for the NR-aptamer-labeled cells compared with those labeled by individual aptamer probes. Therefore, the molecular assembly of aptamers clearly shows potential applications for the elucidation of cells with low density of binding sites, or with relatively weak binding probes, and can thus greatly improve our ability to perform cellular imaging and targeting. This is an excellent example of using nanomaterials to develop advanced molecular binders with greatly improved properties for cellular studies.

Quantum dot-sensitized solar cells incorporating nanomaterials

Quantum dot-sensitized solar cells (QDSSCs) are interesting energy devices because of their (i) impressive ability to harvest sunlight and generate multiple electron/hole pairs, (ii) ease of fabrication, and (iii) low cost. The power conversion efficiencies (η) of most QDSSCs (typically <4%) are, however, less than those (up to 12%) of dye-sensitized solar cells, mainly because of narrow absorption ranges and charge recombination occurring at the QD-electrolyte and TiO(2)-electrolyte interfaces. To further increase the values of η of QDSSCs, it will be necessary to develop new types of working electrodes, sensitizers, counter electrodes and electrolytes. This Feature Article describes the nanomaterials that have been used recently as electronic conductors, sensitizers and counter electrodes in QDSSCs. The nature, size, morphology and quantity of these nanomaterials all play important roles affecting the efficiencies of electron injection and light harvesting. We discuss the behavior of several important types of semiconductor nanomaterials (sensitizers, including CdS, Ag(2)S, CdSe, CdTe, CdHgTe, InAs and PbS) and nanomaterials (notably TiO(2), ZnO and carbon-based species) that have been developed to improve the electron transport efficiency of QDSSCs. We point out the preparation of new generations of nanomaterials for QDSSCs and the types of electrolytes, particularly iodide/triiodide electrolytes (I(-)/I(3)(-)), polysulfide electrolytes (S(2-)/S(x)(2-)), and cobalt redox couples ([Co(o-phen)(3)(2+)/(3+)]), that improve their lifetimes. With advances in nanotechnology, we foresee significant improvements in the efficiency (η > 6%) and durability (>3000 h) of QDSSCs.

Detection of Mercury(II) Ions Using Colorimetric Gold Nanoparticles on Paper-Based Analytical Devices

An on-field colorimetric sensing strategy employing gold nanoparticles (AuNPs) and a paper-based analytical platform was investigated for mercury ion (Hg(2+)) detection at water sources. By utilizing thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination chemistry, label-free detection oligonucleotide sequences were attached to unmodified gold nanoparticles to provide rapid mercury ion sensing without complicated and time-consuming thiolated or other costly labeled probe preparation processes. Not only is this strategys sensing mechanism specific toward Hg(2+), rather than other metal ions, but also the conformational change in the detection oligonucleotide sequences introduces different degrees of AuNP aggregation that causes the color of AuNPs to exhibit a mixture variance. To eliminate the use of sophisticated equipment and minimize the power requirement for data analysis and transmission, the color variance of multiple detection results were transferred and concentrated on cellulose-based paper analytical devices, and the data were subsequently transmitted for the readout and storage of results using cloud computing via a smartphone. As a result, a detection limit of 50 nM for Hg(2+) spiked pond and river water could be achieved. Furthermore, multiple tests could be performed simultaneously with a 40 min turnaround time. These results suggest that the proposed platform possesses the capability for sensitive and high-throughput on-site mercury pollution monitoring in resource-constrained settings.

Synthesis of Fluorescent Carbohydrate-Protected Au Nanodots for Detection of Concanavalin A and Escherichia coli

This study describes a novel, simple, and convenient method for the preparation of water-soluble biofunctional Au nanodots (Au NDs) for the detection of Concanavalin A (Con A) and Escherichia coli (E. coli). First, 2.9 nm Au nanoparticles (Au NPs) were prepared through reduction of HAuCl(4).3H(2)O with tetrakis(hydroxymethyl)phosphonium chloride (THPC), which acts as both a reducing and capping agent. Addition of 11-mercapto-3,6,9-trioxaundecyl-alpha-D-mannopyranoside (Man-SH) onto the surfaces of the as-prepared Au NPs yielded the fluorescent mannose-protected Au nanodots (Man-Au NDs) with the size and quantum yield (QY) of 1.8 (+/-0.3) nm and 8.6%, respectively. This QY is higher than those of the best currently available water-soluble, alkanethiol-protected Au nanoclusters. Our fluorescent Man-Au NDs are easily purified and by multivalent interactions are capable of sensing, under optimal conditions, Con A with high sensitivity (LOD = 75 pM) and remarkable selectivity over other proteins and lectins. To the best of our knowledge, this approach provided the lowest LOD value for Con A when compared to the other nanomaterials-based detecting method. Furthermore, we have also developed a new method for fluorescence detection of E. coli using these water-soluble Man-Au NDs. Incubation with E. coli revealed that the Man-Au NDs bind to the bacteria, yielding brightly fluorescent cell clusters. The relationship between the fluorescence signal and the E. coli concentration was linear from 1.00 x 10(6) to 5.00 x 10(7) cells/mL (R(2) = 0.96), with the LOD of E. coli being 7.20 x 10(5) cells/mL.

Detection of Copper Ions Through Recovery of the Fluorescence of DNA-Templated Copper/Silver Nanoclusters in the Presence of Mercaptopropionic Acid

We have developed a simple and homogeneous fluorescence assay, comprised of 3-mercaptopropionic acid (MPA) and DNA-Cu/Ag nanoclusters (NCs) in aqueous solution, for the detection of Cu(2+) ions. The fluorescence of the DNA-Cu/Ag NCs was quenched by MPA, which was recovered in the presence of Cu(2+) ions. This MPA-induced fluorescence quenching arises through changes in the DNA conformation that occur after interactions between MPA and the Cu/Ag clusters. The MPA-induced fluorescence quenching displayed typical characteristics in Stern-Volmer plots; it followed a static quenching mechanism. The presence of Cu(2+) ions resulted in the oxidation of MPA to form a disulfide compound, leading to recovery of the fluorescence of the DNA-Cu/Ag NCs. The fluorescence of the DNA-Cu/Ag NCs in the presence of MPA increased upon increasing the concentration of Cu(2+) ions over the range from 5 to 200 nM. The DNA-Cu/Ag NC probe provided the limit of detection (at a signal-to-noise ratio of 3) for Cu(2+) ions of 2.7 nM, with high selectivity (by at least 2300-fold over other tested metal ions). We validated the practicality of using this probe for the detection of Cu(2+) ions in environmental samples through analyses of Montana soil and pond water samples.

Selective photothermal therapy for mixed cancer cells using aptamer-conjugated nanorods.

Safe and effective photothermal therapy depends on efficient delivery of heat for killing cells and molecular specificity for targeting cells. To address these requirements, we have designed an aptamer-based nanostructure which combines the high absorption efficiency of Au-Ag nanorods with the target specificity of molecular aptamers, a combination resulting in the development of an efficient and selective therapeutic agent for targeted cancer cell photothermal destruction. Most nanomaterials, such as gold nanoshells or nanorods (NRs), require a relatively high power of laser irradiation (1 x 10 (5)-1 x 10 (10) W/m (2)). In contrast, the high absorption characteristic of our Au-Ag NRs requires only 8.5 x 10 (4) W/m (2) laser exposure to induce 93 (+/-11)% cell death of NR-aptamer-labeled cells. Aptamers, the second component of the nanostructure, are generated from a cell-SELEX (systematic evolution of ligands by exponential enrichment) process and can be easily selected for specific recognition of individual tumor cell types without prior knowledge of the biomarkers for the cell. When tested with both cell suspensions and artificial solid tumor samples, these aptamer conjugates were shown to have excellent hyperthermia efficiency and selectivity. Under a specific laser intensity and duration of laser exposure, about 50 (+/-1)% of target (CEM) cells were severely damaged, while more than 87 (+/-1)% of control (NB-4) cells remained intact in a suspension cell mixture. These results indicate that the Au-Ag nanorod combination offers selective and efficient photothermal killing of targeted tumor cells, thus satisfying the two key challenges noted above. Consequently, for future in vivo application, it is fully anticipated that the tumor tissue will be selectively destroyed at laser energies which will not harm the surrounding normal tissue.