Wen-Tsen Chen

Enzyme mimics of Au/Ag nanoparticles for fluorescent detection of acetylcholine.

We have developed a highly sensitive and selective fluorescent assay for the detection of acetylcholine (ACh) based on enzyme mimics of Au/Ag nanoparticles (NPs). These NPs were prepared via a one-step solution phase reaction between 13 nm Au NPs and Ag(+) ions in the presence of stabilizing agents such as adenosine triphosphate (ATP) and polyethylene glycol (PEG). Our sensing strategy involves reacting ACh with acetylcholinesterase (AChE) to form choline that is in turn oxidized by choline oxidase (ChOx) to produce betaine and H(2)O(2), which reacts with Amplex UltraRed (AUR) in the presence of bimetallic NPs catalyst to form a fluorescent product. The fluorescence intensity (excitation/emission wavelengths of 540/592 nm) is proportional to the concentration of ACh over a range of 1-100 nM (R(2) = 0.998), with a limit of detection of 0.21 nM (signal/noise = 3). When compared with Au NPs and horseradish peroxidase, the Au/Ag NPs provide 150- and 115-fold higher catalytic activity toward the H(2)O(2)-mediated AUR reaction. The practicality of the assay has been validated by determining the concentrations of ACh in plasma and blood samples, with results of 2.69 ± 0.84 nM (n = 5) and 6.75 ± 1.42 nM (n = 5), respectively. Thus, the present assay holds great potential for the analysis of ACh in biological samples.

Catalytic gold nanoparticles for fluorescent detection of mercury(II) and lead(II) ions

In this study, we developed a fluorescence assay for the highly sensitive and selective detection of Hg(2+) and Pb(2+) ions using a gold nanoparticle (Au NP)-based probe. The Hg-Au and Pb-Au alloys that formed on the Au NP surfaces allowed the Au NPs to exhibit peroxidase-mimicking catalytic activity in the H(2)O(2)-mediated oxidation of Amplex UltraRed (AUR). The fluorescence of the AUR oxidation product increased upon increasing the concentration of either Hg(2+) or Pb(2+) ions. By controlling the pH values of 5mM tris-acetate buffers at 7.0 and 9.0, this H(2)O(2)-AUR-Au NP probe detected Hg(2+) and Pb(2+) ions, respectively, both with limits of detection (signal-to-noise ratio: 3) of 4.0 nM. The fluorescence intensity of the AUR oxidation product was proportional to the concentrations of Hg(2+) and Pb(2+) ions over ranges 0.05-1 μM (R(2)=0.993) and 0.05-5 μM (R(2)=0.996), respectively. The H(2)O(2)-AUR-Au NP probe was highly selective for Hg(2+) (>100-fold) and Pb(2+) (>300-fold) ions in the presence of other tested metal ions. We validated the practicality of this simple, selective, and sensitive H(2)O(2)-AUR-Au NP probe through determination of the concentrations of Hg(2+) and Pb(2+) ions in a lake water sample and of Pb(2+) ions in a blood sample. To the best of our knowledge, this system is the first example of Au NPs being used as enzyme-mimics for the fluorescence detection of Hg(2+) and Pb(2+) ions.

Detection of proteins and protein-ligand complexes using HgTe nanostructure matrixes in surface-assisted laser desorption/ionization mass spectrometry.

We have analyzed peptides, proteins, and protein-drug complexes through surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using HgTe nanostructures as matrixes. We investigated the effects of several parameters, including the concentration of the HgTe nanostructures, the pH of the buffer, and the concentration of salt, on the performance of this system. When HgTe nanostructures are used as matrixes, [M + H](+) ions were the dominant signals. Relative to other commonly used nanomaterials, HgTe nanostructures provided lower background signals from metal clusters, fewer fragment ions, less interference from alkali-adducted analyte ions, and a higher mass range (up to 150,000 Da). The present approach provides limits of detection for angiotensin I and bovine serum albumin of 200 pM and 14 nM, respectively, with great reproducibility (RSD: <25%). We validated the applicability of this method through the detections of (i) the recombinant proteins that were transformed in E. coli, (ii) the specific complex between bovine serum albumin and l-tryptophan, and (iii) a carbonic anhydrase-acetazolamide complex. Our results suggest that this novel and simple SALDI-MS approach using HgTe nanostructures as matrixes might open several new ways for proteomics and the analysis of drug-protein complexes.

Accurate quantitation of glutathione in cell lysates through surface-assisted laser desorption/ionization mass spectrometry using gold nanoparticles

We developed a method for the determination of three aminothiols--cysteine, glutathione (GSH), and homocysteine--using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The analytes were first captured using the unmodified 14-nm gold nanoparticles; N-2-mercaptopropionylglycine-modified gold nanoparticles serving as internal standard were sequentially added, and then the sample was analyzed using SALDI-MS. This approach provided good quantitative linearity of the three analytes (R(2) = approximately 0.99), with good reproducibility (relative standard deviations: <10%), in the analyses of GSH in the lysates of human red blood cells and MCF-7 cancer breast cells in the presence and absence of the anti-inflammatory drug sulfasalazine. The internal-standard SALDI-MS approach provides simplicity, accuracy, and precision to the determination of GSH in cells under drug invasion, to open an avenue for SALDI-MS to be used for the precise quantitative determination of a variety of analytes. From the clinical editor: This paper reports the development of a surface assisted laser desorption/ionization mass spectrometry method to precisely determine aminothiols-cysteine (Cys), glutathione (GSH), and homocysteine (HCys).

Quantification of captopril in urine through surface-assisted laser desorption/ionization mass spectrometry using 4-mercaptobenzoic acid-capped gold nanoparticles as an internal standard

We have developed a new internal standard method for the determination of the concentration of captopril (CAP) through surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using gold nanoparticles (Au NPs). This approach provided linearity for CAP over the concentration range 2. 5–25 µM (R2 = 0. 987), with a limit of detection (signal-to-noise ratio = 3) of 1. 0 µM. The spot-to-spot variations in the concentration of CAP through SALDI-MS analyses performed in the absence and presence of the internal standard were 26% and 9%, respectively (15 measurements). This approach provides simplicity, accuracy, precision, and great reproducibility to the determination of the levels of CAP in human urine samples.

Using Surface-Assisted Laser Desorption/Ionization Mass Spectrometry to Detect Proteins and Protein–Protein Complexes

In this study, we combined surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) with HgTe nanostructures as matrix for the detection of several proteins (α1-antitrypsin, trypsin, IgG, protein G) and their complexes. We investigated the effects of several parameters (the concentration and nature of surfactants and metal ions, the pH, and concentration of the analytes in the sample matrixes) on the sensitivity of the detection of these proteins and their complexes. The presence of stabilizing Brij 76 surfactant and Zn(II) ions allowed the detection of weak protein complexes, such as α1-antitrypsin-trypsin and IgG-protein G complexes, at the picomole level. We observed multiply charged states at m/z 72,160 ([α1-antitrypsin + trypsin + H](+)) and 86,585 ([IgG + protein G + 2H](2+)) for the α1-antitrypsin-trypsin and IgG-protein G complexes, respectively. To the best of our knowledge, detection of weak protein complexes and determination of their stoichiometry have not been demonstrated previously when a combination of SALDI-MS and nanostructures were used. This simple and reproducible SALDI-MS approach using HgTe nanostructures holds great potential for the detection of other proteins and their complexes.

Exploring the interactions between gold nanoparticles and analytes through surface‐assisted laser desorption/ionization mass spectrometry

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is applied to provide strong evidence for the chemical reactions of functionalized gold nanoparticles (Au NPs) with analytes--Hg(2+) ions induced MPA-Au NPs aggregation in the presence of 2,6-pyridinedicarboxylic acid (PDCA) and H(2)O(2) induced fluorescence quenching of 11-MUA-Au NDs. PDCA-Hg(2+)-MPA coordination is responsible for Au NPs aggregation, while the formation of 11-MUA disulfide compounds that release into the bulk solution is responsible for H(2)O(2)-induced fluorescence quenching. In addition to providing information about the chemical structures, SALDI-MS is also selective and sensitive for the detection of Hg(2+) ions and H(2)O(2). The limits of detection (LODs) for Hg(2+) ions and H(2)O(2) by SALDI-MS were 300 nM and 250 microM, respectively. The spot-to-spot variations in the two studies were both less than 18% (50 sample spots). Our results reveal that SALDI-MS can be used to study analyte-induced changes in the surface properties of nanoparticles.

Detection of melamine in infant formula and grain powder by surface-assisted laser desorption/ionization mass spectrometry

We have developed a method for the determination of melamine (MEL), ammeline (AMN), and ammelide (AMD) by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using gold nanoparticles (Au NPs). The major peaks for MEL, AMN, and AMD at m/z 127.07, 128.05, and 129.04 are assigned to the [MEL + H](+), [AMN + H](+), and [AMD + H](+) ions. Because the three tested compounds adsorb weakly onto the surfaces of the Au NPs through Au-N bonding, they can be easily concentrated from complex samples by applying a simple trapping/centrifugation process. The SALDI-MS method provides limits of detection of 5, 10, and 300 nM for MEL, AMN, and AMD, respectively, at a signal-to-noise ratio of 3. The signal variation for 150-shot average spectra of the three analytes within the same spot was 15%, and the batch-to-batch variation was 20%. We have validated the practicality of this approach by the analysis of these three analytes in infant formula and grain powder. This simple and rapid SALDI-MS approach holds great potential for screening of MEL in foods.

Analysis of the Formation Process of Gold Nanoparticles by Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

AbstractChemical reactions of reducing agents in the gold nanoparticle (AuNP) formation process were characterized using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). As the reaction of the AuNPs progresses, the produced AuNPs can serve as an efficient SALDI substrate. SALDI-MS revealed that the reducing agents and their oxidation products can be determined in the mass spectra. With respect to the transmission electron microscopic and UV-Vis spectroscopic examination of AuNPs, SALDI-MS results confirm not only the tendency toward AuNPs formation, but also reflect the information of the redox reaction process. Our results provide useful information for developing SALDI-MS methods to explore the chemical information regarding the surface behavior between adsorbates and nanomaterials.

Nanomaterial based mass spectrometry of oligodeoxynucleotide–drug complexes

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using HgTe nanostructures as the matrix has been employed for the detection of four 15-base oligodeoxynucleotides (ODNs) that are genes found in acute myeloid leukemia (AML) patients and their complexes with mitoxantrone (MTX), which is a common drug for the treatment of AML patients. The major peaks for the four tested ODNs are at m/z values of 4571, 4586, 4610, and 4635, while they are at m/z values of 5017, 5031, 5055, and 5079 for their corresponding complexes with MTX. The ODN with a m/z value of 4610 is assigned to a normal gene of AML, while the other three are single-base mutant ODNs. This approach allows detection of the tested ODNs at concentrations down to 2 nM, showing their potential for the diagnosis of AML. The dissociation constant values of the four tested ODN–MTX complexes determined by the SALDI-MS approach are similar and at the μM level, which agree with that determined by applying a conventional absorption approach. Relative to the conventional approach, the SALDI-MS approach has advantages of simplicity, rapidity, reproducibility, and use of smaller amounts of ODNs and MTX.