Detection of arsenic(III) through pulsed laser-induced desorption/ionization of gold nanoparticles on cellulose membranes.

We have developed an assay based on gold nanoparticle-modified mixed cellulose ester membrane (Au NPs-MCEM) coupled with laser-induced desorption/ionization mass spectrometry (LDI-MS)-for the detection of arsenic(III) ions (arsenite, AsO2(-)) in aqueous solution. When the Au NPs reacted with lead ions (Pb(2+)) in alkaline solution (5 mM glycine-NaOH, pH 12), Au-Pb complexes, PbO, and Pb(OH) were formed immediately on the Au NP surfaces. The Pb species reacted rapidly with subsequently added AsO2(-) to form PbOAs2O3, (PbO)2As2O3, and/or (PbO)3As2O3 shells (2-5 nm) on the Au NPs' surfaces. As a result, significant observable aggregation of the Au NPs occurred in the solution. This Pb(2+)/Au NP probe allowed the detection of AsO2(-) at concentrations as low as 0.6 µM with high selectivity (at least 100-fold over other anions and metal ions). To further improve the sensitivity, we prepared Au NPs-MCEM for the LDI-MS-based detection of AsO2(-) ions. The intensity of the signal for the [Pb](+) ions in the mass spectra increased when the Au NPs-MCEM reacted with AsO2(-); in contrast, the intensity of the signal for [Au](+) ions decreased. Accordingly, the [Pb](+)/[Au](+) peak ratio increased upon increasing the AsO2(-) concentration over the range from 10 nM to 10 µM. The limit of detection at a signal-to-noise ratio of 3 was 2.5 nM, far below the action level of As (133 nM, ca. 10 ppb) permitted by the US EPA for drinking water. Relative to other nanoparticle-based arsenic sensors, this approach is rapid, specific, and sensitive; in addition, it can be applied to the detection of AsO2(-) in natural water samples (in this case, streamwater, lake water, tap water, groundwater, and mineral water).

Using rhodamine 6G-modified gold nanoparticles to detect organic mercury species in highly saline solutions.

We developed a gold nanoparticle (Au NP)-based fluorescence sensor for the detection of mercury ions in aqueous solutions. After introducing bovine serum albumin (BSA) to a solution of rhodamine 6G (R6G) and 3-mercaptopropionic acid (MPA)-modified Au NPs, the as-prepared BSA@R6G/MPA-Au NP probe could sense mercury ions under high salt conditions. This probe operated through a mechanism involving mercury species depositing onto the surfaces of the Au NPs and releasing R6G molecules into the solution, causing the fluorescence intensity of the BSA@R6G/MPA-AuNP solution to increase. We improved the selectivity of the nanosensor by adding masking agents (ethylenediamine tetraacetic acid (EDTA) and Na2S) or tellurium nanowires (Te NWs) to the sample solutions. In the presence of 1.0 mM EDTA and 10 µM Na2S, the selectivities of this system toward phenylmercury (PhHg(I)) over other metal ions and mercury species were greater than 200- and 10-fold, respectively. The limit of detection (LOD), at a signal-to-noise ratio of 3, for PhHg(I) was 20 nM. Selective detection of the total organic mercury (methylmercury (MeHg(I)), ethylmercury (EtHg(I)), and PhHg(I)) was possible when using the BSA@R6G/MPA-Au NPs in conjunction with Te NWs (3.0 nM). The selectivity of this nanosensor system for the total organic mercury over Hg(II) was remarkably high (100-fold) with an LOD for organic mercury of 10 nM. We also demonstrated the feasibility of using the developed nanosensor for rapid determination of mercury species in river, sea, and tap water as well as in fish samples.

Quantitation of toxic arsenic species and arsenobetaine in Pacific oysters using an off-line process with hydride generation-atomic absorption spectroscopy.

An off-line process-based speciation technique was devised here to quantitatively determine toxic inorganic arsenic (iAs), methylarsonic acid (MA), dimethylarsinic acid (DMA), and the dominant, albeit virtually nontoxic, arsenobetaine (AB) in Pacific oysters (Crassostrea gigas). Oysters were extracted with fresh methanol-water (8+2), and this was replicated three times. They were then evaporated to near dryness and subsequently redissolved in pure water; defatting was then performed with a C18 cartridge. The trace hydride active arsenic species, that is, iAs, MA, and DMA, in the defatted solutions were determined with a sensitive hydride generation-packed coldfinger trap-atomic absorption spectrometric (HG-PCFT-AAS) coupled system. The arsenicals that were desorbed from the cation-exchange resin (Dowex 50W-X8) in the washings of 4 M NH3 were categorized on the basis of AB + DMA. The total quantity of arsenic in the recovered AB + DMA was determined with a commercial hydride generation-atomic absorption spectrometric (HG-AAS) system, and finally, AB was calculated from (AB + DMA) - DMA. The average concentrations of iAs, MA, DMA, AB, and total arsenic (TAs) in the oysters collected from six aquacultural sites along the west coast of Taiwan were, respectively, 0.15, 0.06, 0.64, 6.93, and 13.74 mg kg(-1) of dry weight. AB was the major species, whereas iAs (arsenite + arsenate) were the most toxic species, although the iAs made up only approximately 1% of the TAs in the oysters. The lifetime target cancer risk, as determined by the concentration of iAs on a fresh weight basis in the oysters, was well below the ordinary health protection criteria (10(-6)).

Identification of Microalgae by Laser Desorption/Ionization Mass Spectrometry Coupled with Multiple Nanomatrices.

In this study, we demonstrate a simple method to identify microalgae by surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using three different substrates: HgSe, HgTe, and HgTeSe nanostructures. The fragmentation/ionization processes of complex molecules in algae varied according to the heat absorption and transfer efficiency of the nanostructured matrices (NMs). Therefore, the mass spectra obtained for microalgae showed different patterns of m/z values for different NMs. The spectra contained both significant and nonsignificant peaks. Constructing a Venn diagram with the significant peaks obtained for algae when using HgSe, HgTe, and HgTeSe NMs in m/z ratio range 100-1000, a unique relationship among the three sets of values was obtained. This unique relationship of sets is different for each species of microalgae. Therefore, by observing the particular relationship of sets, we successfully identified different algae such as Isochrysis galbana, Emiliania huxleyi, Thalassiosira weissflogii, Nannochloris sp., Skeletonema cf. costatum, and Tetraselmis chui. This simple and cost-effective SALDI-MS analysis method coupled with multi-nanomaterials as substrates may be extended to identify other microalgae and microorganisms in real samples. Graphical Abstract Identification of microalgae by surface-assisted laser desorption/ionization mass spectrometry coupled with three different mercury-based nanosubstrates.

Characterization of Fe/Mn-superoxide dismutase from diatom Thallassiosira weissflogii: cloning, expression, and property.

A cDNA clone of 1114 bp encoding a putative Mn-superoxide dismutase (Mn-SOD) from diatom Thallassiosira weissflogii was cloned by the PCR technique. Nucleotide sequence analysis of this cDNA clone revealed that it was translated into 201 amino acid residues. When the sequence was compared with Mn-SODs from Vibrio mimicus and Escherichia coli, as well as two Fe-SODs from E. coli and Photobacterium leiognathi, this SOD showed higher homology to Mn-SOD. The amino acid residues required to coordinate the single manganese ion were conserved in all reported Mn-SOD sequences. This cDNA was introduced in an expression vector, pET-20b(+), and transformed into E. coli BL21(DE3)pLysS. The expressed SOD protein was then purified by a His-tag column. The recombinant enzyme was heated at 55 degrees C with a time-dependent assay; the time interval for 50% inactivation was 23 min, and its thermal inactivation rate constant K(d) was 3.03 x 10(-)(2) min(-)(1). The enzyme was inactivated either in acidic pH (below 4.0) or in the presence of imidazole (above 1.6 M) and had only a moderate effect under SDS (above 4%), whereas it was not affected under an alkaline pH (above 9.0). The atomic absorption spectrometric assay showed that 0.6 atom of iron/manganese (3:1) was present in each subunit of SOD. Reconstitution study was suggested that diatom SOD was cambialistic (Fe/Mn)-SOD. The finding of this SOD cDNA could be used for a reference in comparing the differences among marine phytoplankton species and as a probe to detect the transcription level of this enzyme, which can be applied in cosmetics for skin protection or defending unesthetic effects caused by oxygen-containing free radicals.

A label-free colorimetric detection of lead ions by controlling the ligand shells of gold nanoparticles.

We have developed a simple, colorimetric and label-free gold nanoparticle (Au NP)-based probe for the detection of Pb(2+) ions in aqueous solution, operating on the principle that Pb(2+) ions change the ligand shell of thiosulfate (S(2)O(3)(2-))-passivated Au NPs. Au NPs reacted with S(2)O(3)(2-) ions in solution to form Au(+).S(2)O(3)(2-) ligand shells on the Au NP surfaces, thereby inhibiting the access of 4-mercaptobutanol (4-MB). Surface-assisted laser desorption/ionization time-of-flight ionization mass spectrometry (SALDI-TOF MS) and inductively coupled plasma mass spectrometry (ICP-MS) measurements revealed that PbAu alloys formed on the surfaces of the Au NPs in the presence of Pb(2+) ions; these alloys weakened the stability of the Au(+).S(2)O(3)(2-) ligand shells, enhancing the access of 4-MB to the Au NP surfaces and, therefore, inducing their aggregation. As a result, the surface plasmon resonance (SPR) absorption of the Au NPs red-shifted and broadened, allowing quantitation of the Pb(2+) ions in the aqueous solution. This 4-MB/S(2)O(3)(2-)-Au NP probe is highly sensitive (linear detection range: 0.5-10 nM) and selective (by at least 100-fold over other metal ions) toward Pb(2+) ions. This cost-effective sensing system allows the rapid and simple determination of the concentrations of Pb(2+) ions in real samples (in this case, river water, Montana soil and urine samples).