Wei-Yu Chen

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.

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.

Fluorescent gold and silver nanoclusters for the analysis of biopolymers and cell imaging

Fluorescent gold and silver nanoclusters are interesting sensing materials because of their molecule-like optical properties, easy preparation, and biocompatibility. In this review, we highlight the chemical and optical properties of fluorescent gold and silver nanoclusters, as well as their preparation and applications in biomolecular analysis and cell imaging.

Control of synthesis and optical properties of DNA templated silver nanoclusters by varying DNA length and sequence

We have used a simple method to prepare five fluorescent Ag nanoclusters (NCs) through the NaBH4-mediated reduction of Ag+ ions in the presence of various DNA scaffolds. The emission intensities and wavelengths (536–644 nm) of the as-prepared DNA–Ag NCs were dependent on the sequence and length of the DNA scaffold. Electrospray ionization mass spectrometry of the DNA–Ag NCs revealed that different numbers of Ag atoms (2–6 atoms) were present per DNA scaffold, depending on the number and position of the cytosine bases. Using the oligonucleotide 5′-CCC(TTCC)2TT(CCAA)2CCC-3′ (DNATAr2) as the scaffold, we obtained DNATAr2–Ag NCs exhibiting a quantum yield (Φf) of 61% at 608 nm; these NCs were stable in the presence of the tested thiols, Cl− ions and DNase I. Because of their strong fluorescence and stability, the DNATAr2–Ag NCs were highly selective and sensitive for the detection of Hg2+ ions [linear range: 2.5–50 nM; limit of detection (signal-to-noise ratio = 3): 0.9 nM]. We validated the practicality of this probe through analyses of several water samples spiked with Hg2+ ions (10 nM); the recoveries were 98–118%.

Synthesis of Photoluminescent Au ND–PNIPAM Hybrid Microgel for the Detection of Hg2+

Poly(N-isopropylacrylamide) microgels (PNIPAM MGs) incorporated with photoluminescent gold nanodots (Au NDs) have been prepared and employed for the detection of mercury ions (Hg(2+)). Each of the PNIPAM MGs (hydrodynamic diameter 615 ± 15 nm) contains several Au NDs (diameter 1.8 ± 0.2 nm) in the Au ND-PNIPAM MGs. Like Au NDs, Au ND-PNIPAM MGs exhibit an absorption band at 375 nm that is assigned for ligand to metal charge transfer mixed with metal centered (ds/dp) states and photoluminescence at 520 nm originated from Au ND/polynuclear gold(I)-thiolate (core/shell) complexes. Purification of Au ND-PNIPAM MGs relative to Au NDs is much easier through a simple centrifugation/wash process. On the basis of Hg(2+)-induced photoluminescence quenching due to the formation of Au-Hg amalgam and formation of Au ND-PNIPAM MGs aggregates, the signal response of Au ND-PNIPAM MGs against Hg(2+) concentration is linear over a range from 2 to 20 nM (r = 0.9945). This selective approach provides limits of detection for Hg(2+) (at a signal-to-noise ratio of 3) of 1.9 and 1.7 nM in phosphate buffer solutions (5 mM, pH 7.0) with and without containing 500 mM NaCl, respectively. This selective and sensitive Au ND-PNIPAM MG probe has been applied to the determination of the concentration of Hg in a representative fish sample, showing its practical potential for monitoring of Hg levels in complicated biological and environmental samples.

Using photoluminescent gold nanodots to detect hemoglobin in diluted blood samples.

In this study we used photoluminescent 11-mercaptoundecanoic acid-bound gold nanodots (11-MUA-Au NDs) to detect hemoglobin through photoluminescence (PL) quenching. The mechanism of quenching, which occurred through redox reactions between the 11-MUA-Au NDs and the Fe(II) atoms of hemin units, was supported by an increase in the signals (G 2.0 and 5.9) of high-spin state Fe(III) ions. The Stern-Volmer quenching constants (Ksv) for hemin, cytochrome c, hemoglobin, and myoglobin were 5.6×10(7), 1.7×10(7), 1.6×10(7), and 6.2×10(6)M(-1), respectively, in good agreement with the order of their reduction potentials. When excited at 375nm, the PL intensity of the 11-MUA-Au NDs at 520nm decreased upon increasing the concentration of hemoglobin from 1.0 to 10nM (R(2)=0.9913). This approach using bovine serum albumin blocked 11-MUA-Au NDs provided a limit of detection for hemoglobin (at a signal-to-noise ratio of 3) of 0.5nM in biological buffer, with great selectivity over other non-heme-containing proteins, including human serum albumin, β-casein, and carbonic anhydrase. We validated the practicality of this approach through the determination of the concentrations (1.85-2.46mM) of hemoglobin in diluted (10(6)-fold) human blood samples based on PL quenching of Au NDs. This simple, sensitive, and selective approach holds great potential for the diagnosis of several diseases, including anemia, erythrocytosis, and thalassemias.

Synthesis of Fluorescent Gold Nanodot–Liposome Hybrids for Detection of Phospholipase C and Its Inhibitor

We report the synthesis of fluorescent 11-mercaptoundecanoic acid-gold nanodot-liposome (11-MUA-Au ND/Lip) hybrids by incorporation of gold nanoparticles (∼3 nm) and 11-MUA molecules in hydrophobic phospholipid membranes that self-assemble to form small unilamellar vesicles. A simple and homogeneous fluorescence assay for phospholipase C (PLC) was developed on the basis of the fluorescence quenching of 11-MUA-Au ND/Lip hybrids in aqueous solution. The fluorescence of the 11-MUA-Au ND/Lip hybrids is quenched by oxygen (O2) molecules in solution, and quenching is reduced in the presence of PLC. PLC catalyzes the hydrolysis of phosphatidylcholine units from Lip to yield diacylglycerol (DAG) and phosphocholine (PC) products, leading to the decomposition of Lip. The diacylglycerol further interacts with 11-MUA-Au NDs via hydrophobic interactions, leading to inhibition of O2 quenching. The 11-MUA-Au ND/Lip probe provides a limit of detection (at a signal-to-noise ratio of 3) of 0.21 nM for PLC, with high selectivity over other proteins, enzymes, and phospholipases. We have validated the practicality of using this probe for the determination of PLC concentrations in breast cancer cells (MCF-7 and MDA-MB-231 cell lines) and nontumor cells (MCF-10A cell line), revealing that the PLC activity in the first two is at least 1.5-fold higher than that in the third. An inhibitor assay using 11-MUA-Au ND/Lip hybrids demonstrated that tricyclodecan-9-yl potassium xanthate (D609) inhibits PLC (10 nM) with an IC50 value of 3.81 ± 0.22 μM. This simple, sensitive, and selective approach holds great potential for detection of PLC in cancer cells and for the screening of anti-PLC drugs.