Ming-Li Chen

Cyanobacterium metallothionein decorated graphene oxide nanosheets for highly selective adsorption of ultra-trace cadmium

Graphene oxide (GO) nanosheets were decorated with a cysteine-rich metal-binding protein, cyanobacterium metallothionein (SmtA). The SmtA–GO composites were characterized by means of FT-IR, AFM and TGA, giving rise to a SmtA binding amount of 867 mg g−1. The SmtA–GO composites exhibit ultra-high selectivity toward the adsorption of cadmium, i.e., the tolerant concentrations for the coexisting metal and anionic species were 1–800 000 fold improved after SmtA decoration with respect to bare GO. The SmtA–GO composites were then assembled onto the surface of cytopore microbeads and used for highly selective adsorption and preconcentration of ultra-trace cadmium. In comparison with bare GO (carboxyl-rich GO) loaded cytopore (GO@cytopore), SmtA–GO loaded cytopore (SmtA–GO@cytopore) shows a 3.3-fold improvement over the binding capacity of cadmium, i.e. 7.70 mg g−1 for SmtA–GO@cytopore compared to 2.34 mg g−1 for that by GO@cytopore. A novel procedure for selective cadmium preconcentration was developed using SmtA–GO@cytopore beads as a renewable sorption medium incorporated into a sequential injection lab-on-valve system, with detection by graphite furnace atomic absorption spectrometry (GFAAS). The cadmium retained on the SmtA–GO surface was eluted with a small amount of nitric acid. An enrichment factor of 14.6 and a detection limit of 1.2 ng L−1 were achieved within a linear range of 5–100 ng L−1 by using a sample volume of 1 mL. The procedure was validated by analyzing cadmium in certified reference materials and a series of environmental water samples.

A FRET ratiometric fluorescence sensing system for mercury detection and intracellular colorimetric imaging in live Hela cells

The detection of mercury in biological systems and its imaging is of highly importance. In this work, a ratiometric fluorescence sensor is developed based on fluorescence resonance energy transfer (FRET) with N-acetyl-L-cysteine functionalized quantum dots (NAC-QDs) as donor and Rhodamine 6G derivative-mercury conjugate (R6G-D-Hg) as acceptor. Mercury annihilates the fluorescence of NAC-QDs at 508 nm and meanwhile interacts with R6G derivative to form a fluorescent conjugate giving rise to emission at 554 nm. Resonance energy transfer from NAC-QDs to R6G-D-Hg is triggered by mercury resulting in concentration-dependent variation of fluorescence ratio F508/F554. A linear calibration of F508/F554 versus mercury concentration is obtained within 5-250 μg L(-1), along with a detection limit of 0.75 μg L(-1) and a RSD of 3.2% (175 μg L(-1)). The sensor generates colorimetric images for mercury within 0-250 μg L(-1), facilitating visual detection of mercury with a distinguishing ability of 50 μg L(-1). This feature is further demonstrated by colorimetric imaging of intracellular mercury. On the other hand, the NAC-QDs/R6G-D FRET sensing system is characterized by a combination of high sensitivity and selectivity. The present study provides an approach for further development of ratiometric sensors dedicated to selective in vitro or in vivo sensing some species of biologically interest.

Green preparation of carbon dots with papaya as carbon source for effective fluorescent sensing of Iron (III) and Escherichia coli.

A simple one-step hydrothermal green approach was reported for the preparation of carbon dots (CDs) without any further decoration or modification with papaya powder as natural carbon source. In this economical and eco-friendly system, deionized water or 90% ethanol was used as solvent to produce water-soluble or ethanol-soluble CDs, respectively, termed as W-CDs and E-CDs. The quantum yield (QY) for W-CDs was 18.98%, while that for E-CDs was 18.39%. The potentials of the prepared carbon dots toward diverse applications were thoroughly investigated. W-CDs and E-CDs provide promising probes for fluorescence detection of Fe(3+), offering limits of detection of 0.48μmolL(-1) and 0.29μmolL(-1), respectively. W-CDs was further demonstrated to be a promising probe for fluorescence sensing of Escherichia coli O157: H7, along with a limit of detection of 9.5×10(4)cfumL(-1). Meanwhile, both W-CDs and E-CDs exhibit favorable biocompatibility, and demonstrated to be efficient for Hela cell imaging.

Sequential/bead injection lab-on-valve incorporating a renewable microcolumn for co-precipitate preconcentration of cadmium coupled to hydride generation atomic fluorescence spectrometry

A sequential/bead injection lab-on-valve apparatus incorporating a renewable microcolumn packed with co-polymeric immobilized C18 microbeads was applied to the on-line co-precipitate separation/preconcentration of ultra-trace cadmium by hyphenating with hydride generation atomic fluorescence spectrometry. Cadmium was co-precipitated with lanthanum hydroxide and collected on a microcolumn in the lab-on-valve. The co-precipitate was eluted with hydrochloric acid and directed to meet tetrahydroborate and facilitate hydride generation. The hydride was separated from the reaction mixture and was swept into the atomizer. With a sampling volume of 500 μl, quantitative retention of cadmium was achieved, along with an enrichment factor of 9.8 and a sampling frequency of 11 h−1. A detection limit of 3.5 ng l−1 was derived, along with a RSD of 1.6% (0.1 μg l−1). The procedure was validated analyzing cadmium in certified reference materials.

Sequential injection reductive bio-sorption of Cr(VI) on the surface of egg-shell membrane and chromium speciation with detection by electrothermal atomic absorption spectrometry

Egg-shell membrane (ESM) is a unique cell surface with various functional groups, providing the potential for bio-sorption of metal species. We have demonstrated the selective retention of chromium(VI)via a reductive sorption process, while Cr(III) is virtually not retained. This includes adsorption of Cr(VI) onto the ESM surface while charge transfer on the ESM results in the reduction of Cr(VI) to Cr(III) through transient, unstable species of Cr(V) and Cr(IV). A novel procedure for chromium speciation was thus developed in a sequential injection system with detection by electrothermal atomic absorption spectrometry. The procedure includes the separation and preconcentration of Cr(VI) on ESM at pH 2 and its subsequent detection after elution, followed by conversion of Cr(III) to Cr(VI) and total chromium analysis, Cr(III) finally being obtained by subtraction. With a sampling volume of 1000 µl, an enrichment factor of 13.3 was achieved. A linear range of 0.05–1.25 µg l−1 for Cr(VI), along with a detection limit of 0.01 µg l−1 and a precision of 3.2% at the level of 0.5 µg l−1, were obtained. Chromium speciation was performed by using a certified reference material of riverine water (GBW08608) and cave water.

Biological cell-sorption for separation/preconcentration of ultra-trace cadmium in a sequential injection system with detection by electrothermal atomic absorption spectrometry

The potential of biological cell-sorption for separation/pre-concentration of ultra-trace heavy metals was exploited by immobilizing Chlorella vulgaris and Saccharomyces cerevisiae cells onto silica beads and using them for cadmium sorption. FT-IR investigations showed that when C. vulgaris was used, the functional groups on the cell wall, i.e., hydroxyl and ether, were both involved in the sorption, while for S. cerevisiae, hydroxyl, amide and acetyl served as binding sites, but ether was not active. Because both cells contribute to the sorption, a significant improvement in retention efficiency was observed by immobilizing a mixture of C. vulgaris and S. cerevisiae cells onto silica used for sorption, with respect to those obtained by a single type of cell. A novel procedure for cadmium pre-concentration was developed based on this observation with detection by electrothermal atomic absorption spectrometry (ETAAS), employing cell immobilized silica beads for packing a micro-column in a sequential injection system. The cadmium retained on the column was eluted with a small amount of nitric acid and quantified with ETAAS. Within a range of 0.005–0.2 μg l−1 and a sample volume of 1000 μl, the retention efficiencies achieved by using mixed cells, individual cells of C. vulgaris and individual cells of S. cerevisiae were 97%, 74% and 65%, respectively, with respect to 32% with pure silica. When a cell mixture was employed, an enrichment factor of 38.6, a limit of detection of 1.0 ng l−1, along with a sampling frequency of 20 h−1, was attained, leading to a precision of 2.3% RSD (0.05 μg l−1). The procedure was validated by analyzing cadmium in a certified reference material of riverine water and spike recovery in a lake water sample.

New procedures for arsenic speciation: A review

Considerable analytical methods have been developed for arsenic speciation in the last 5 years, the details of these new arsenic speciation procedures are thus summarized in present mini review. The performances of various sample pretreatment techniques including solid phase extraction, liquid-liquid extraction, hydride generation, liquid chromatography and capillary electrophoresis, which offer effective preconcentration/separation and eventually contribute greatly to excellent sensitivity and selectivity in arsenic speciation when coupling with suitable detection mode, are discussed and compared thoroughly. High-performance liquid chromatography coupling with inductively coupled plasma mass spectrometry and hydride generation atomic spectrometry are proved to be the most powerful hyphenated methodologies for arsenic speciation in environmental and biological matrices.

New Developments in Flow Injection/Sequential Injection On‐line Separation and Preconcentration Coupled with Electrothermal Atomic Absorption Spectrometry for Trace Metal Analysis

Abstract During the last 30 years, flow injection analysis has gone through three generations, that is, the first generation in 1970s, supplemented by sequential injection in the 1990s as the second generation, and the recently emerged lab‐on‐valve system as the third generation, which holds clear advantages for instrumental miniaturization. The three generations have revolutionized the concept of sample pretreatment by facilitating on‐line operation and coupling with various detection techniques, among which its hyphenation with electrothermal atomic absorption spectrometry (ETAAS) has been one of the most attractive research field offering vast potentials and versatilities in the quantification of ultra‐trace metal species in complex matrices. In the present mini‐review, the state‐of‐the‐art developments for flow injection on‐line sample pretreatment coupled to ETAAS for trace metal analysis since 2003 were summarized, with special emphasis on the exploitations of the lab‐on‐valve system.

Polyhedral Oligomeric Silsesquioxane Functionalized Carbon Dots for Cell Imaging.

In the present study, octa-aminopropyl polyhedral oligomeric silsesquioxane hydrochloride salt (OA-POSS) functionalized carbon dots (CDs/POSS) are prepared by a one-pot approach with glycerol as carbon source and solvent medium. OA-POSS serves as a passivation agent, and it is obtained via hydrolytic condensation of 3-aminopropyltriethoxysilane (APTES). During the functionalization process, the amino groups on OA-POSS combine with carboxylic groups on the bare CDs via formation of amide bond to construct organic-inorganic hybrid carbon dots. The obtained CDs/POSS are well dispersed in aqueous medium with a diameter of ca. 3.6 nm. It is demonstrated that CDs/POSS provide favorable photoluminescent property with a quantum yield of 24.0%. They also exhibit resistance to photobleaching and excellent photoluminescence stability in the presence of biological sample matrix (characterized by heavy metals and organic molecules), which facilitate cell imaging in biological systems. Both the photoluminescent emission wavelength and the fluorescence intensity depend closely on the excitation wavelength, and thus, it provides a potential for multicolor imaging as demonstrated with HeLa cells and MCF-7 cells.

Arsenic sorption and speciation with branch-polyethyleneimine modified carbon nanotubes with detection by atomic fluorescence spectrometry

Multi-wall carbon nanotubes (MWNTs) are modified with branched cationic polyethyleneimine (BPEI). The MWNTs-BPEI nanocomposites serve as a novel adsorbent and exhibit favorable selectivity toward adsorption of As(V). Appropriate amount of MWNTs-BPEI suspension containing ca. 5 mg of the composites is used to pack a mini-column for on-line solid phase extraction preconcentration of inorganic arsenic in a sequential injection system, following detection by hydride generation atomic fluorescence spectrometry. At pH 5.8, an sorption efficiency of 80% is achieved for As(V) at 10 μg L(-1), resulting in a sorption capacity of 26.18 mg g(-1). Meanwhile, the sorption efficiency for As(III) is <5%. The retained As(V) is readily recovered by 100 μL NH4HCO3 (0.6%, m/v). With a sample volume of 2.0 mL, an enrichment factor of 16.3 for As(V) is obtained along with a detection limit of 14 ng L(-1) within a linear range of 0.05-1.50 μg L(-1). A RSD of 3.6% is derived at 0.5 μg L(-1). Total amount of arsenic is obtained by converting As(III) to As(V) and following the same procedure. The speciation of inorganic arsenic is realized by difference. This procedure is validated by analyzing a certified reference material of human hair (GBW09101), achieving satisfactory agreements between the certified and the obtained values. Speciation of As(V) and As(III) is also performed in snow water and rain water samples.