Detection of polycyclic aromatic hydrocarbons using quartz crystal microbalances

MoS2 Defect Healing for High-Performance Chemical Sensing of Polycyclic Aromatic Hydrocarbons

The increasing population and industrial development are responsible for environmental pollution. Among toxic chemicals, polycyclic aromatic hydrocarbons (PAHs) are highly carcinogenic contaminants resulting from the incomplete combustion of organic materials. Two-dimensional materials, such as transition metal dichalcogenides (TMDCs), are ideal sensory scaffolds, combining high surface-to-volume ratio with physical and chemical properties that are strongly susceptible to environmental changes. TMDCs can be integrated in field-effect transistors (FETs), which can operate as high-performance chemical detectors of (non)covalent interaction with small molecules. Here, we have developed MoS₂-based FETs as platforms for PAHs sensing, relying on the affinity of the planar polyaromatic molecules for the basal plane of MoS₂ and the structural defects in its lattice. X-ray photoelectron spectroscopy analysis, photoluminescence measurements, and transfer characteristics showed a notable reduction in the defectiveness of MoS₂ and a p-type doping upon exposure to PAHs solutions, with a magnitude determined by the correlation between the ionization energies (E_I) of the PAH and that of MoS₂. Naphthalene, endowed with the higher E_I among the studied PAHs, exhibited the highest output. We observed a log-log correlation between MoS₂ doping and naphthalene concentration in water in a wide range (10^-9-10^-6 M), as well as a reversible response to the analyte. Naphthalene concentrations as low as 0.128 ppb were detected, being below the limits imposed by health regulations for drinking water. Furthermore, our MoS₂ devices can reversibly detect vapors of naphthalene with both an electrical and optical readout, confirming that our architecture could operate as a dual sensing platform.

Probing the interactions of organic molecules, nanomaterials, and microbes with solid surfaces using quartz crystal microbalances: methodology, advantages, and limitations

Quartz crystal microbalances (QCMs) provide a new analytical opportunity and prospect to characterize many environmental processes at solid/liquid interfaces, thanks to their almost real-time measurement of physicochemical changes on their quartz sensor. This work reviews the applications of QCMs in probing the interactions of organic molecules, nanomaterials (NMs) and microbes with solid surfaces. These interfacial interactions are relevant to critical environmental processes such as biofilm formation, fate and transport of NMs, fouling in engineering systems and antifouling practices. The high sensitivity, real-time monitoring, and simultaneous frequency and dissipation measurements make QCM-D a unique technique that helps reveal the interaction mechanisms for the abovementioned processes (e.g., driving forces, affinity, kinetics, and the interplay between surface chemistry and solution chemistry). On the other hand, QCM measurement is nonselective and spatially-dependent. Thus, caution should be taken during data analysis and interpretation, and it is necessary to cross-validate the results using complementary information from other techniques for more quantitative and accurate interpretation. This review summarizes the general methodologies for collecting and analyzing raw QCM data, as well as for evaluating the associated uncertainties. It serves to help researchers gain deeper insights into the fundamentals and applications of QCMs, and provides new perspectives on future research directions.

Nanoporous Gold Films Prepared by a Combination of Sputtering and Dealloying for Trace Detection of Benzo[a]pyrene Based on Surface Plasmon Resonance Spectroscopy

A wavelength-interrogated surface plasmon resonance (SPR) sensor based on a nanoporous gold (NPG) film has been fabricated for the sensitive detection of trace quantities of benzo[a]pyrene (BaP) in water. The large-area uniform NPG film was prepared by a two-step process that includes sputtering deposition of a 60-nm-thick AuAg alloy film on a glass substrate and chemical dealloying of the alloy film in nitric acid. For SPR sensor applications, the NPG film plays the dual roles of analyte enrichment and supporting surface plasmon waves, which leads to sensitivity enhancement. In this work, the as-prepared NPG film was first modified with 1-dodecanethiol molecules to make the film hydrophobic so as to improve BaP enrichment from water via hydrophobic interactions. The SPR sensor with the hydrophobic NPG film enables one to detect BaP at concentrations as low as 1 nmol·L^-1. In response to this concentration of BaP the sensor produced a resonance-wavelength shift of Δλ_R = 2.22 nm. After the NPG film was functionalized with mouse monoclonal IgG1 that is the antibody against BaP, the sensor's sensitivity was further improved and the BaP detection limit decreased further down to 5 pmol·L^-1 (the corresponding Δλ_R = 1.77 nm). In contrast, the conventional SPR sensor with an antibody-functionalized dense gold film can give a response of merely Δλ_R = 0.9 nm for 100 pmol·L^-1 BaP.

BODIPY based hyperbranched conjugated polymers for detecting organic vapors

BODIPY-based hyperbranched polymer showed improved selectivity and sensitivity for toluene as originated from the strong π–π interaction and high porosity within polymer matrix.

Electrochemical detection of benzo(a)pyrene in acetonitrile-water binary medium

Electrochemical oxidation of adsorbed benzo(a)pyrene (BaP) on the glassy carbon electrode (GCE) was explored in acetonitrile-water. When the GCE was incubated in 100 nM BaP acetonitrile-water (V(water):V(acetonitrile)=1:1) for 10 min at open circuit, and then transferred into blank acetonitrile-water (V(water):V(acetonitrile)=1:1, pH= 0.70) for differential pulse voltammetry measurement, a distinct oxidation peak at 0.98 V (vs. Ag/AgCl) was observed. The peak potential was about 180 mV lower than that in acetonitrile. Importantly, the peak current was more than 22 times greater. The effects of water on BaP preconcentration on the electrode and electrochemical oxidation were revealed, respectively. Based on the results, an electrochemical assay for BaP detection was developed. The GCE was respectively incubated in acetonitrile-water (V(water):V(acetonitrile)=1:1)with BaP concentration ranged from 0 nM to 1000 nM, and then transferred into the corresponding blank acetonitrile-water (pH= 0.70) for DPV measurements. When the BaP concentration was increased, an increased oxidative current at 0.98 V (vs. Ag/AgCl) was observed, and a detection limit of 0.67 nM was achieved. Because all other priority polycyclic aromatic hydrocarbons could not be electrochemically oxidized at 0.98 V, the electrochemical assay showed very high selectivity to BaP. Finally, the developed electrochemical assay was successfully applied to determination of BaP in a series of real world samples, such as drinking water, tap water, lake water and river water.

A gold nanoparticle-based colorimetric probe for rapid detection of 1-hydroxypyrene in urine

Direct and rapid detection of 1-hydroxypyrene (1-OHP) is of great importance owing to its high carcinogenicity, teratogenicity and toxicity.

Preparation of MIP-based QCM nanosensor for detection of caffeic acid

In the present work, a new caffeic acid imprinted quartz crystal microbalance (QCM) nanosensor has been designed for selective assignation of caffeic acid in plant materials. Methacrylamidoantipyrine-iron(III) [MAAP-Fe(III)] as metal-chelating monomer has been used to prepare selective molecular imprinted polymer (MIP). MIP film for detection of caffeic acid has been developed on QCM electrode and selectivity experiments and analytical performance of caffeic acid imprinted QCM nanosensor has been studied. The caffeic acid imprinted QCM nanosensor has been characterized by AFM. After the characterization studies, imprinted and non-imprinted nanosensors was connected to QCM system for studies of connection of the target molecule, selectivity and the detection of amount of target molecule in real samples. The detection limit was found to be 7.8 nM. The value of Langmuir constant (b) (4.06 × 10(6)) that was acquired using Langmuir graph demonstrated that the affinity of binding sites was strong. Also, selectivity of prepared caffeic acid imprinted nanosensor was found as being high compared to chlorogenic acid. Finally, the caffeic acid levels in plant materials was determined by the prepared QCM nanosensor.

Cyclodextrin-enhanced extraction and energy transfer of carcinogens in complex oil environments

Reported herein is the use of γ-cyclodextrin for two tandem functions: (a) the extraction of carcinogenic polycyclic aromatic hydrocarbons (PAHs) from oil samples into aqueous solution and (b) the promotion of highly efficient energy transfer from the newly extracted PAHs to a high-quantum-yield fluorophore. The extraction proceeded in moderate to good efficiencies, and the resulting cyclodextrin-promoted energy transfer led to a new, brightly fluorescent signal in aqueous solution. The resulting dual-function system (extraction followed by energy transfer) has significant relevance in the environmental detection and cleanup of oil-spill-related carcinogens.

Fine particulate phase PAHs in ambient atmosphere of Chennai metropolitan city, India

BACKGROUND

Airborne fine particulates (PM 2.5) and its associated polycyclic aromatic hydrocarbons (PAHs) are reportedly hazardous in urban environment due to the presence of multiple emission sources.

METHODS

In this study, fine particulates collected from fourth largest metropolitan city of India, Chennai, were extracted and analyzed for 11 PAHs by high-performance liquid chromatography equipped with a fluorescence detector.

RESULTS

PM 2.5 values varied between 27.2 and 190.2 μg/m(3), while average concentration of particle-associated PAHs determined was in the range from 325.7 to 790.8 ng/m(3), which signaled an alarming pollution level in Chennai.

CONCLUSIONS

Factor analysis suggested vehicular emissions inclusive of petrol- and diesel-driven engines as probable sources.

Sensitive detection of polycyclic aromatic hydrocarbons using CdTe quantum dot-modified TiO₂ nanotube array through fluorescence resonance energy transfer

CdTe quantum dots (QDs) are prepared on TiO(2) nanotubes (TiO(2) NTs), for the first time, with pulse electrodeposition. A novel single-drop optical sensor is prepared with the CdTe QDs-modified TiO(2) NTs, and applied for the detection of polycyclic aromatic hydrocarbons (PAHs) based on fluorescence resonance energy transfer (FRET). Excited at 270 nm, the sensor shows fluorescence emission at around 370 nm. As PAHs are with absorption/fluorescence emission at around 364/410 nm, FRET happens between the CdTe QDs and PAHs with the CdTe QDs as donors and PAHs as receptors. The sensitivity is dependent on the number of rings of the PAHs, with the highest sensitivity observed in the response to benzo(a)pyrene (BaP). Using FRET, the sensitivity to BaP is enhanced by about 2 orders with respect to the direct fluorescent spectrometry. The proposed sensor shows a linear response to the logarithm of BaP concentration in the range of 400 nM to 40 pM, with a detection limit of 15 pM, which is much close to the quality criteria (15.1 pM) in drinking water set by U.S. Environment Protection, suggesting that the proposed sensor can be used for quick scanning of PAHs. The achieved sensitivity is much higher than that of the published sensor-based methods. As PAHs are quantified based on the relative fluorescence intensity at 410-370 nm, the sensor need no calibration with a standard sensor, avoiding the influence from the sensor-to-sensor difference. The practicability of the sensor is tested by analyzing PAHs in Xiangjiang River water, the PAHs contents ranges from 0.045 to 2.847 ng/L based on the sampling spots.

Mechanism and kinetics of Pb(II) adsorption on ultrathin nanocrystalline titania coatings

Pb(II) is a highly toxic substance, exposure to which can cause various diseases. To better understand the application of titania as an adsorbent for removing Pb(II) from wastewater, quartz crystal microbalance (QCM) technique was employed to investigate the adsorption behavior of Pb(II) on ultrathin nanocrystalline titania coatings. The present study focused on the mechanism and kinetics of Pb(II) adsorption. The obtained results show that the driving force of Pb(II) adsorption on titania coatings is electrostatic interaction, and that Pb(II) is adsorbed onto titania coatings by Pb(II) ions coordinating with hydroxyl groups of titania surface. In terms of the in situ frequency measurements of QCM, the adsorption kinetic parameter is estimated to be 4.12x10(5)L/mol. QCM measurement provides a useful method for monitoring the adsorption process of Pb(II) on titania coatings.

On-line monitoring imidacloprid and thiacloprid in celery juice using quartz crystal microbalance

In this article, we report a quartz crystal microbalance (QCM)-based detection method which allows the identification and quantification of two neonicotinoid pesticides, imidacloprid and thiacloprid, in aqueous solutions and celery juice. To achieve high selectivity, molecular imprinted monolayers (MIMs), which can either recognize 1 muM of imidacloprid or 1 muM of thiacloprid, are prepared from alkanethiols self-assembled on QCM sensor chips with preadsorbed templates (either imidacloprid or thiacloprid). Our experimental results show that the detection limit can be improved by using alkanethiols having longer hydrocarbon chains. For example, MIMs prepared from hexadecanethiol have dissociation constants 2-5 times smaller than those prepared from octanethiol. To detect two neonicotinoids in vegetable samples simultaneously, we also develop a new type of MIM with two different templates. A single QCM decorated with this MIM can respond to 10 muM of imidacloprid and 10 muM thiacloprid in celery juice in a real-time manner.

Mechanism and kinetics of apatite formation on nanocrystalline TiO2 coatings: a quartz crystal microbalance study

Apatite (Ca5(PO4)3OH) has long been considered as an excellent biomaterial to promote bone repairs and implant. Apatite formation induced by negatively charged nanocrystalline TiO2 coatings soaked in simulated body fluid (SBF) was investigated using in situ quartz crystal microbalance (QCM), scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) techniques, and factors affecting its formation such as pH, size of TiO2 particles and thickness of TiO2 coatings, were discussed in detail. Two different stages were clearly observed in the process of apatite precipitation, indicating two different kinetic processes. At the first stage, the calcium ions in SBF were initially attracted to the negatively charged TiO2 surface, and then the calcium titanate formed at the interface combined with phosphate ions, consequently forming apatite nuclei. After the nucleation, the calcium ions, phosphate ions and other minor ions (i.e. CO3(2-) and Mg2+) in supersaturated SBF deposited spontaneously on the original apatite coatings to form apatite precipitates. In terms of the in situ frequency shifts, the growth-rate constants of apatite (K1 and K2) were estimated, respectively, at two different stages, and the results were (1.96+/-0.14)x10(-3)s(-1) and (1.28+/-0.10)x10(-4)s(-1), respectively, in 1.5 SBF solution. It was found that the reaction rate at the first stage is obviously higher than that at the second stage.

Environmental monitoring of hydrocarbons: a chemical sensor perspective

Assessing the environmental impact of organic pollutants requires reliable analytical tools that can rapidly screen them with minimal sample handling. Chemical sensors are expected to play an increasing role in environmental monitoring, and recent technological advances are certain to facilitate the application of chemical sensing devices. The search for highly selective, sensitive, low cost, stable, and robust sensors for hydrocarbons is an area of interest that is reflected by many publications on this topic. This report surveys some of the work that has been undertaken using sensors to detect hydrocarbons in the gas and liquid phase. The analytical capabilities of various sensors are compared and discussed in terms of their selectivity, sensitivity, and detection limit. It was found that the sensitivity is highly dependent on the experimental conditions used in the preparation of the sensing surface. Many sensors display acceptable sensitivity under controlled laboratory conditions; however, very few are selective enough to distinguish among several hydrocarbons in complex mixtures. Selectivity is still a challenge that is hindering the widespread application of chemical sensors for environmental monitoring of hydrocarbons and a number of strategies have been proposed to help overcome some of these problems.

Sensor technology and its application in environmental analysis

Environmental analysis is one of the fundamental applications of chemical sensors. In this review we describe different sensor systems for the gas and liquid phases that have been tested either with real-life samples or in the field during the last five years. Most field sensors rely either on electrochemical or optical transducers. In the gas phase, systems have been proposed for analysis of oxides of nitrogen, carbon, and sulfur in air, and volatile organic compounds. In the liquid phase, most detection systems used for real-life samples detect heavy-metal ions or organic contamination, for example pesticides, organic solvents and polycyclic aromatic hydrocarbons.

Interaction analysis of chimeric metal-binding green fluorescent protein and artificial solid-supported lipid membrane by quartz crystal microbalance and atomic force microscopy

Non-specific adsorption and specific interaction between a chimeric green fluorescent protein (GFP) carrying metal-binding region and the immobilized zinc ions on artificial solid-supported lipid membranes was investigated using the quartz crystal microbalance technique and the atomic force microscopy (AFM). Supported lipid bilayer, composed of octanethiol and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycero-3-[N-(5-amino-1-carboxypentyl iminodiacetic acid)succinyl] (NTA-DOGS)-Zn2+, was formed on the gold electrode of quartz resonator (5 MHz). Binding of the chimeric GFP to zinc ions resulted in a rapid decrease of resonance frequency. Reversibility of the process was demonstrated via the removal of metal ions by EDTA. Nanoscale structural orientation of the chimeric GFP on the membrane was imaged by AFM. Association constant of the specific binding to metal ions was 2- to 3-fold higher than that of the non-specific adsorption, which was caused by the fluidization effect of the metal-chelating lipid molecules as well as the steric hindrance effect. This infers a possibility for a further development of biofunctionalized membrane. However, maximization is needed in order to attain closer advancement to a membrane-based sensor device.

Molecular imprinting: a dynamic technique for diverse applications in analytical chemistry

Continuous advances in analyzing complex matrices, improving reliability and simplicity, and performing multiple simultaneous assays with extreme sensitivity are increasing. Several techniques have been developed for the quantitative assays of analytes at low concentrations (e.g., high-pressure liquid chromatography, gas chromatography, immunoassay and the polymerase chain reaction technique). To achieve highly specific and sensitive analysis, high affinity, stable, and specific recognition agents are needed. Although biological recognition agents are very specific and sensitive they are labile and/or have a low density of binding sites. During the past decade molecular imprinting has emerged as an attractive and highly accepted tool for the development of artificial recognition agents. Molecular imprinting is achieved by the interaction, either noncovalent or covalent, between complementary groups in a template molecule and functional monomer units through polymerization or polycondensation. These molecularly imprinted polymers have been widely employed for diverse applications (e.g., in chromatographic separation, drug screening, chemosensors, catalysis, immunoassays etc.) owing to their specificity towards the target molecules and high stability against physicochemical perturbations. In this review the advantages, applications, and recent developments in molecular imprinting technology are highlighted.