Detection of Arsenic(III) through Pulsed Laser-Induced Desorption/Ionization of Gold Nanoparticles on Cellulose Membranes

Colorimetric chemosensors for the selective detection of arsenite over arsenate anions in aqueous medium: Application in environmental water samples and DFT studies

Novel organic receptors N3R1- N3R3 were developed for the selective colorimetric recognition of arsenite ions in the organo-aqueous media. In the 50% aq. acetonitrile media and 70% aq. DMSO media, receptors N3R2 and N3R3 showed specific sensitivity and selectivity towards arsenite anions over arsenate anions. Receptor N3R1 showed discriminating recognition of arsenite in the 40% aq. DMSO medium. All three receptors formed a 1:1 complex with arsenite and stable for a pH range of 6-12. The receptors N3R2 and N3R3 achieved a detection limit of 0.008 ppm (8 ppb) and 0.0246 ppm, respectively, for arsenite. Initial hydrogen bonding on binding with the arsenite followed by the deprotonation mechanism was well supported by the UV-Vis titration, ¹H- NMR titration, electrochemical studies, and the DFT studies. Colorimetric test strips were fabricated using N3R1- N3R3 for the on-site detection of arsenite anion. The receptors are also employed for sensing arsenite ions in various environmental water samples with high accuracy.

Picomolar detection of As(III) ions by using hydrothermal synthesis of functionalized polymer dots as a highly selective fluorescence sensor

Arsenic is a toxic and ubiquitous metalloid that leads to a widespread health risk to human beings and other living organisms. In this paper, a novel water-soluble fluorescent probe based on functionalized polypyrrole dots (FPPyDots) was designed and applied to determine As(III) selectively and sensitively in aqueous media. FPPyDots probe was synthesized by using a hydrothermal method, via the facile chemical polymerization of pyrrole (Py) and cysteamine (Cys) and then functionalized with ditheritheritol (DTT). To investigate the chemical composition, morphology, and optical properties of the resultant fluorescence probe various characterization techniques including FTIR, EDC, TEM, Zeta potential, UV-vis, and fluorescence spectroscopies were used. The Stern-Volmer equation was used for calibration curves and show a negative deviation with the two linear concentration ranges of 270-2200 pM and 2.5-22.5 nM with an excellent limit of detection (LOD) of 110 pM. FPPyDots exhibit high selectivity to As(III) ions over various transition and heavy metal ions interferences. The performance of the probe has also been perused concerning the pH effect. Finally, to illustrate the applicability and reliability of the FPPyDots probe, the As(III) traces were identified in water real samples and compared with ICP-OES analysis.

Engineering of nanomaterials for mass spectrometry analysis of biomolecules

Mass spectrometry (MS) based analysis has received intense attention in diverse biological fields. However, direct MS interrogation of target biomolecules in complex biological samples is still challenging, due to the extremely low abundance and poor ionization potency of target biological species. Innovations in nanomaterials create new auxiliary tools for deep and comprehensive MS characterization of biomolecules. More recently, growing research interest has been directed to the compositional and structural engineering of nanomaterials for enriching target biomolecules prior to MS analysis, enhancing the ionization efficiency in MS detection and designing biosensing nanoprobes in sensitive MS readout. In this review, we mainly focus on the recent advances in the engineering of nanomaterials towards their applications in sample pre-treatment, desorption/ionization matrices and ion signal amplification for MS profiling of biomolecules. This review will provide a toolbox of nanomaterials for researchers devoted to developing analytical methods and practical applications in the biological MS field.

Portable smartphone-integrated paper sensors for fluorescence detection of As(III) in groundwater

Arsenic contamination in groundwater is a supreme environmental problem, and levels of this toxic metalloid must be strictly monitored by a portable, sensitive and selective analytical device. Herein, a new system of smartphone-integrated paper sensors with Cu nanoclusters was established for the effective detection of As(III) in groundwater. For the integration system, the fluorescence emissive peak of Cu nanoclusters at 600 nm decreased gradually with increasing As(III) addition. Meanwhile, the fluorescence colour also changed from orange to colourless, and the detection limit was determined as 2.93 nM (0.22 ppb) in a wide detection range. The interfering ions also cannot influence the detection selectivity of As(III). Furthermore, the portable paper sensors based on Cu nanoclusters were fabricated for visual detection of As(III) in groundwater. The quantitative determination of As(III) in natural groundwater has also been accomplished with the aid of a common smartphone. Our work has provided a portable and on-site detection technique toward As(III) in groundwater with high sensitivity and selectivity.

3D paper-based microfluidic device: a novel dual-detection platform of bisphenol A

A novel platform of 3D paper-based microfluidic device (μPADs) was fabricated by a digital plotter for high precision analysis of bisphenol A using electrochemistry along with LDI-MS detection.

Gold Nanoparticles (AuNPs) as Reactive Matrix for Detection of Trace Levels of HCN in Air by Laser Desorption/Ionization Mass Spectrometry (LDI-MS)

Under direct laser desorption/ionization mass spectrometric conditions, the irradiation of target spots made of gold nanoparticle residues generates a series of peaks at m/z 197, 394, 591… representing Au_n^- ions (n = 1-3). In contrast, spectra recorded from gold nanoparticles directly mixed with an alkali cyanide exhibited an additional peak at m/z 249, indicating an abundant generation of gaseous [Au(CN)₂]^- ions upon irradiation. The relative intensity of the m/z 249 peak surged when the amount of cyanide in the mixture was increased. Most remarkably, a peak at m/z 249 was observed even from neat AuNPs upon irradiation, if a nearby spot, which was not irradiated, happened to bear a cyanide sample. We postulated that traces of HCN emanating from the headspace of aqueous cyanide solution during the sample-plate preparation is sufficient to convert gold to AuCN, which is subsequently detected as [Au(CN)₂]^-. Further experiments demonstrated that the relative intensity of the m/z 249 peak diminishes exponentially as the AuNP spot becomes more distant from the putative HCN source. Eventually, the method was developed as an efficient procedure to detect HCN or alkali cyanides. Using KCN, the detection limits were determined to be below 10 pg of CN^- per spot. The method also demonstrated that, upon crushing, the seeds or roots of certain fruits and vegetables such as apple, peach, radish, and cassava, but not carrot, release HCN in amounts detectable by this method. Graphical Abstract.

Novel chitosan-Nafion composite for fabrication of highly sensitive impedimetric and colorimetric As(III) aptasensor

In the present work, for the first time we takes the advantages of chitosan-Nafion (Chit-Naf) composite as a highly conductive surface platform and a novel CNT-based signal amplification strategy to develop a lable-free impedimetricaptamer-based sensor for highly sensitive detection of As(III). The electrochemical impedance spectroscopy (EIS) investigations surprisingly revealed that the glassy carbon electrode (GC) electrode modified with Chit-Naf composite had higher electron transfer kinetics compared the bare GC, GC/Naf and GC/Chit electrodes, which promises a great potential as an efficient platform in construction of biosensing assays. In this work, we employed a signal amplification strategy based on carbon nanotube-bovine serum albumin (CNT-BSA) hybrid system, by which sensitivity and detection limit of the aptasensor for the detection of As(III) were obtained to be 100.82 Ω nM^-1 and a of 74 pM, respectively. This protocol provided one of the lowest limits of detection for As(III) on aptamer-based electrodes recently described in the literature. Moreover, the change of the optical absorptive properties of CNTs upon biorecognition interactions provides a way to detect the biorecognition process and thus allowed us to design an optical As(III) aptasensor using the UV-Vis spectroscopic method. The discrimination capability of the fabricated aptasensor for recognizing As(III) in the presence of other metal ions and a complex matrix of waste water samples was successfully investigated. This protocol provided a new method for sensitive detection of As(III) with considerable advantages in terms of reproducibility, selectivity, being mediator free and regenerability of the sensing interface.

An ultratrace assay of arsenite based on the synergistic quenching effect of Ru(bpy)32+ and arsenite on the electrochemiluminescence of Au–g-C3N4 nanosheets

An arsenite assay based on the synergistic quenching effect of As(iii) and Ru(bpy)₃²⁺ on the ECL of Au–g-C₃N₄ coupled with the generation of a new ECL signal of Ru(bpy)₃²⁺.

π-Conjugated thiolate amplified spectrophotometry nitrite assay with improved sensitivity and accuracy

π-Conjugated thiolate amplified sensitive nitrite detection based on the π-conjugation enhanced molar absorption coefficient and the corresponding absorbance is presented.

Cellulose-gold nanoparticle hybrid materials

Cellulose and gold nanoparticles have exciting characteristics and new combinations of both materials may lead to promising functional nanocomposites with unique properties. We have reviewed current research on cellulose-gold nanoparticle composite materials, and we present an overview of the preparation methods of cellulose-gold composite materials and discuss their applications. We start with the nanocomposite fabrication methods, covering in situ gold reduction, blending, and dip-coating methods to prepare gold-cellulose nanocomposite hybrids. We then move on to a discussion of the ensuing properties where the combination of gold nanoparticles with cellulose results in functional materials with specific catalytic, antimicrobial, sensing, antioxidant and Surface Enhanced Raman Scattering (SERS) performance. Studies have also been carried out on orientationally ordered composite materials and on the chiral nematic phase behaviour of these nanocomposites. To exert even more control over the structure formation and the resultant properties of these functional materials, fundamental studies on the physico-chemical interactions of cellulose and gold are necessary to understand better the driving forces and limitations towards structuring of gold-cellulose hybrid materials.

A biomolecular recognition approach for the functionalization of cellulose with gold nanoparticles

Materials with new and improved functionalities can be obtained by modifying cellulose with gold nanoparticles (AuNPs) via the in situ reduction of a gold precursor or the deposition or covalent immobilization of pre-synthesized AuNPs. Here, we present an alternative biomolecular recognition approach to functionalize cellulose with biotin-AuNPs that relies on a complex of 2 recognition elements: a ZZ-CBM3 fusion that combines a carbohydrate-binding module (CBM) with the ZZ fragment of the staphylococcal protein A and an anti-biotin antibody. Paper and cellulose microparticles with AuNPs immobilized via the ZZ-CBM3:anti-biotin IgG supramolecular complex displayed an intense red color, whereas essentially no color was detected when AuNPs were deposited over the unmodified materials. Scanning electron microscopy analysis revealed a homogeneous distribution of AuNPs when immobilized via ZZ-CBM3:anti-biotin IgG complexes and aggregation of AuNPs when deposited over paper, suggesting that color differences are due to interparticle plasmon coupling effects. The approach could be used to functionalize paper substrates and cellulose nanocrystals with AuNPs. More important, however, is the fact that the occurrence of a biomolecular recognition event between the CBM-immobilized antibody and its specific, AuNP-conjugated antigen is signaled by red color. This opens up the way for the development of simple and straightforward paper/cellulose-based tests where detection of a target analyte can be made by direct use of color signaling.

Hexagonal boron nitride nanosheets as a multifunctional background-free matrix to detect small molecules and complicated samples by MALDI mass spectrometry

h-BN nanosheets were applied as a background-free matrix for the analysis and imaging of small molecules and as an adsorbent to enrich samples.

Fluorometric sensing of ultralow As(III) concentrations using Ag doped hollow CdS/ZnS bi-layer nanoparticles

Arsenic poisoning from drinking water has been an important global issue in recent years. Because of the high level toxicity of arsenic to human health, an easy, inexpensive, low level and highly selective detection technique is of great importance to take any early precautions. This study reports the synthesis of Ag doped hollow CdS/ZnS bi-layer (Ag-h-CdS/ZnS) nanoparticles for the easy fluorometric determination of As(iii) ions in the aqueous phase. The hollow bi-layer structures were synthesized by a sacrificial core method using AgBr as the sacrificial core and the core was removed by dissolution in an ammonium hydroxide solution. The synthesized nanoparticles were characterized using different instrumental techniques. A good linear relationship was obtained between fluorescence quenching intensity and As(iii) concentration in the range of 0.75-22.5 μg L(-1) at neutral pH with a limit of detection as low as 0.226 μg L(-1).

Optically tunable chiral nematic mesoporous cellulose films

Demand for sustainable functional materials has never been larger. The introduction of functionality into pure cellulose might be one step forward in this field as it is one of the most abundant natural biopolymers. In this paper, we demonstrate a straightforward and scalable way to produce iridescent, mesoporous cellulose membranes with tunable colors and porosity. Concomitant assembly of cellulose nanocrystals (CNCs) and condensation of silica precursors results in CNC-silica composites with chiral nematic structures and tunable optical properties. Removal of the stabilizing silica matrix by alkaline or acid treatment gives access to novel chiral nematic mesoporous cellulose (CNMC) films. Importantly, the optical properties and the mesoporosity can be controlled by either varying the silica-to-CNC ratio, or by varying the substrate used during the evaporation-induced self-assembly process. In order to introduce additional functionality, CNMC has been used to stabilize gold nanoparticles with three different concentrations by wet impregnation. These materials are stable in water and can potentially function in sensors, tissue engineering or functional membranes.

Multivalent aptamer/gold nanoparticle-modified graphene oxide for mass spectrometry-based tumor tissue imaging

The protein mucin1 (MUC1) is an attractive target for cancer biomarkers because it is overexpressed in most adenocarcinomas. In this study, we exploited a MUC1-binding aptamer (Apt_MUC1) as a targeting agent for nanoparticle-based imaging systems coupled with laser desorption/ionization mass spectrometry (LDI-MS). We found that Apt_MUC1-conjugated gold nanoparticles immobilized, through hydrophobic and π–π interactions, on graphene oxide (Apt_MUC1–Au NPs/GO) bound effectively to MUC1 units on tumor cell membranes. The ultrahigh density and high flexibility of Apt_MUC1 on the GO surface enhanced the platform’s cooperative and multivalent binding affinity for MUC1 on cell membranes. After we had labeled MUC1-overexpressing MCF-7 cells (human breast adenocarcinoma cell line) with Apt_MUC1–Au NPs/GO, we used LDI-MS to monitor Au cluster ions ([Au_n]⁺; n = 1–3), resulting in the detection of as few as 100 MCF-7 cells. We also employed this Apt_MUC1–Au NPs/GO–LDI-MS system to analyze four different MUC1 expression cell lines. In addition, the Apt_MUC1–Au NPs/GO platform could be used further as a labeling agent for tumor tissue imaging when coupled with LDI-MS. Thus, Apt–Au NPs/GO can function as a highly amplified signal transducer through the formation of large Au clusters ions during LDI-MS analysis.