This review (with 85 refs.) summarizes the recent literature on the adsorption of common aromatic pollutants by using modified metal-organic frameworks (MOFs). Four kinds of aromatic pollutants are discussed, namely benzene homologues, polycyclic aromatic hydrocarbons (PAHs), organic dyes and their intermediates, and pharmaceuticals and personal care products (PPCPs). MOFs are shown to be excellent adsorbents that can be employed to both the elimination of pollutants and to their extraction and quantitation. Adsorption mechanisms and interactions between aromatic pollutants and MOFs are discussed. Finally, the actual challenges of existence and the perspective routes towards future improvements in the field are addressed.
Graphical abstract Recent advance on adsorption of common aromatic pollutants including benzene series, polycyclic aromatic hydrocarbons, organic dyes and their intermediates, pharmaceuticals and personal care products by metal-organic frameworks.
A fluorometric ATP assay is described that makes use of carbon dots and graphene oxide along with toehold-mediated strand displacement reaction. In the absence of target, the fluorescence of carbon dots (with excitation/emission maxima at 360/447 nm) is strong and in the “on” state, because the signal probe hybridizes with the aptamer strand and cannot combine with graphene oxide. In the presence of ATP, it will bind to the aptamer and induce a strand displacement reaction. Consequently, the signal probe is released, the sensing strategy will change into the “off” state with the addition of graphene oxide. This aptasensor exhibits selective and sensitive response to ATP and has a 3.3 nM detection limit.
Graphical abstract Schematic of signal amplification by strand displacement in a carbon dot based fluorometric assay for ATP. This strategy exhibits high sensitivity and selectivity with a detection limit as low as 3.3 nM.
The authors report on a novel sorbent (thermally treated natural zeolite; clinoptilolite) for use in dispersive micro-solid phase extraction (D-μ-SPE) of polycyclic aromatic hydrocarbons (PAHs) from water samples. The method was applied to the D-μ-SPE of 16 priority PAHs which then were quantified by gas chromatography with mass spectrometric detection (GC-MS). The method was validated in terms of specificity and selectivity, linearity and linear range, accuracy, precision, uncertainty, limits of detection and quantification. Figures of merit include (a) linear analytical ranges between 2.08 and 208 ppb, and (b) detection limits in the range from 0.01 to 0.92 ppb. The method was successfully applied to the determination of PAHs in river waters.
Graphical abstract Schematic representation of dispersive micro-solid phase extraction (D-μ-SPE) of trace levels of PAHs in water samples by using thermally treated clinoptilolite as sorbent prior to gas chromatography-mass spectrometry analysis (GC-MS).
Amorphous titania was modified with boric acid, and the resulting material was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction and X-ray photoelectron spectrometry. The new material, in contrast to conventional boronate affinity materials containing boronic acid ligands, bears boric acid groups. It is shown to exhibit high specificity for glycoproteins, and this was applied to design a method for solid phase extraction of glycoproteins as shown for ribonuclease B, horse radish peroxidase and ovalbumin. Glycoproteins were captured under slightly alkaline environment and released in acidic solutions. The glycoproteins extracted were detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The binding capacities for ribonuclease B, horse radish peroxidase and ovalbumin typically are 9.3, 26.0 and 53.0 mg ? g?1, respectively. The method was successfully applied to the selective enrichment of ovalbumin from egg white.
A highly selective electrochemical sensor was fabricated based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe2O4 NPs). The nanocomposite has attractive properties such as high surface-to-volume ratio and good electrocatalytic activity towards the drugs acetaminophen (AC), epinephrine (EP), and melatonin (MT), best at working voltages of 0.35, 0.09 and 0.55 V (vs. Ag/AgCl), respectively. The linear ranges (and detection limits) are 6.5–135 (0.4) μmol L?1 for AC, 5–100 (0.7) μmol L?1 for EP, and 6.5–145 (3) μmol L?1 for MT.
Graphical abstract A novel electrochemical sensor based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe2O4) for the simultaneous detection of the acetaminophen, epinephrine and melatonin was fabricated
An electrochemical nanoaptasensor is described that is based on the use of a glassy carbon electrode (GCE) modified with electrodeposited silver nanoparticles (AgNPs). An aptamer (Apt) against trinitrotoluene (TNT) was then immobilized on the AgNPs. The addition of TNT to the modified GCE leads to decrease in peak current (typically measured at a potential of ?0.45 V vs. Ag/AgCl) of riboflavin which acts as an electrochemical probe. Even small changes in the surface (as induced by binding of Apt to TNT) alter the interfacial properties. As a result, the LOD is lowered to 33 aM, and the dynamic range extends from 0.1 fM to 10 μM without sacrificing specificity.
Graphical abstract Schematic presentation of a nanoaptasensor which is based on a glassy carbon electrode (GCE) modified with electrodeposited silver nanoparticles (AgNPs) and aptamer (Apt). It was applied to the detection of 2,4,6-trinitrotoluene (TNT) with the help of riboflavin (RF) as a redox probe.
A binary nanocomposite of type copper tungstate and polyaniline (CuWO4@PANI) is described that was obtained by single step polymerization on the surface of a glassy carbon electrode (GCE). The resulting electrode is shown to be a viable tool for voltammetric sensing of quercetin (Qn) in blood, urine and certain food samples. The nanocomposite was characterized by UV-visible absorption spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and high-resolution transmission electron microscopy. Differential pulse voltammetry was applied to quantify Qn, typically at the relatively low working potential of 0.15 V (vs. Ag/AgCl). The modified GCE has a wide analytical range (0.001–0.500 μM) and a low detection limit (1.2 nM). The sensor is reproducible, selective and stable. This makes it suitable for determination of Qn in real samples without complicated sample pretreatment.
Graphical abstract Schematic of a copper tungstate and polyaniline nanocomposite modified glassy carbon electrode for voltammetric determination of quercetin in real samples.
A highly selective and sensitive aptasensor is described for voltammetric determination of the pesticide chlorpyrifos (CPS). The sensor was constructed by modifying a glassy carbon electrode (GCE) with gold nanorods and a polymer that was molecularly imprinted with an aptamer against CPS. This results in double specific recognition. Under optimal conditions and a working potential as low as 0.22 V (vs. Ag/AgCl), the nanotools has a dynamic range that covers the 1.0 fM - 0.4 pM CPS concentration range, and the detection limit is 0.35 fM. This is lower than any of the previously reported methods. This MIP-aptasensor is selective over structural analogs, stable, and adequately reproducible. It was successfully applied to the determination of CPS in spiked food samples.
Graphical abstract Impedimetric detection of Chlorpyrifos by using a Fe(CN)63?/4- probe based on double recognition of aptamer-molecular imprinted polymer onto a glassy carbon electrode modified with gold nanorod nanocomposite. The incubation with Chlorpyrifos lead to an increase of electron transfer resistance.
Hydroxyapatite nanoparticles (HAP-NPs) were rendered fluorescence by doping with Eu(III) ion. The resulting fluorescent NPs are shown to be viable probes for sensitive and selective determination of dipicolinic acid (DPA), a major constituent of bacterial spores as used in bioterrorism. It is found that the addition of DPA to solutions of such HAP-NPs result in an enhancement of fluorescence due to the coordination of DPA with the Eu(III) dopant. The assay allows DPA to be detected in the 0.1 to 40 μM concentration range and with a 77 nM detection limit. The assay was applied to the detection of spores of Bacillus subtilis. The attractive properties of the probe make it a promising candidate for used in rapid detection of pathogenic bacterial spores.
Graphical abstract Fluorescent hydroxyapatite nanoparticles (HAP-NPs) are shown to be a viable probe for detection of dipicolinic acid, a major constituent of bacterial spores. The red asterisks represent the fluorescence intensity of the HAP-NPs.
Two-dimensional (2D) nanomaterials are promising building blocks for sensors due to their unique physical, chemical, electronic, and optical properties. This review (with 253 references) first summarizes the historical developments of 2D nanomaterials and discusses the advantages of 2D nanomaterials when applied for constructing sensors. Next, their properties are discussed, with subsections on electronic, optical, mechanical and chemical properties. This is followed by an overview on methods for syntheses and the effects of positive and/or negative charges on the properties and in sensing applications. Then, recent advances in 2D nanomaterial-based electrochemical, fluorometric, colorimetric, electrochemiluminescent, photoelectrochemical, and field-effect transistor sensors are discussed. The discussion also includes the preparation of sensing elements, the roles of such nanomaterials, and assay strategies. Finally, on the basis of the current achievements in the field of 2D nanomaterials, the perspectives on the challenges and opportunities for the exploration of 2D nanomaterial-based sensors are put forward.
A voltammetric sensor is described for the quantitation of propyl gallate (PG). A screen-printed carbon electrode (SPCE) was modified with reduced graphene sheets that were decorated with cobalt diselenide nanoparticles (CoSe2@rGO). The material was hydrothermally prepared and characterized by several spectroscopic techniques. The modified SPCE displays excellent electrocatalytic ability towards PG. Differential pulse voltammetry, with a peak voltage at 0.34 V (vs. Ag/AgCl) has a sensitivity of 12.84 μA·μM?1·cm?2 and a detection limit as low as 16 nM. The method is reproducible, selective, and practical. This method was applied to the determination of PG in spiked meat samples, and the result showed an adequate recovery.
The paper describes a voltammetric method for the quantitation of the activity of telomerase extracted from cancer cells. A thiolated single-stranded telomerase substrate primer was firstly immobilized on a gold electrode. In the presence of a mixture of telomerase and deoxynucleotide triphosphates, the primer becomes elongated and contains repetitive nucleotide sequences (TTAGGG)n. After hybridization with blocker DNA, gold nanoparticles are added and captured by the elongated single-stranded DNA. This reduces the charge transfer resistance of the gold electrode. The telomerase activity is then quantified via differential pulse voltammetry, typically at 0.12 V (vs. SCE). The method is PCR-free, rapid, and convenient. It was applied to the detection of HeLa cells via the telomerase activity of lysed cells. The detection range was from 500 to 50,000 cells/mL and the detection limit was as low as 500 cells/mL.
Graphical abstract A telomerase substrate (TS) primer is immobilized on a gold electrode as the sensing interface to detect the activity of telomerase extracted from cancer cells. Unmodified gold nanoparticles (AuNPs) are utilized which change the electrochemical responses.
A modified Kendrick Mass Defect (KMD) analysis was applied to the analysis of polycyclic aromatic hydrocarbons (PAHs) and fullerenes in the diffusion flame from a handheld butane torch.
A three-dimensional magnetic hollow porous raspberry-like hierarchical Co/Ni@carbon microspheres (3D Co/Ni@carbon) were synthesized by using a bimetal-organic framework (Co/Ni-MOF) as a precursor and subsequent calcination under nitrogen. The 3D Co/Ni@carbon is a novel solid phase extractant that displays outstanding extraction capability and separation efficiency for the pyrethroid pesticides ethofenprox and bifenthrin. This is ascribed to the beneficial effects of facile analyte transport (due to the presence of free pores), the abundant number of adsorption sites (which warrant efficient extraction), and the excellent structural stability of the material. The 3D Co/Ni@carbon was applied to dispersive magnetic solid-phase extraction (d-MSPE), and the two pyrethroids were quantified by HPLC (UV detection wavelength: 220 nm). The method has a high preconcentration factor (937–1012) and give recoveries that range between 85.6–106.9%, with RSDs (for n?=?5) of <6% in case of real samples.
Graphical abstract The hierarchical porous Co/Ni@carbon microsphere as adsorbent was fabricated, and it showed high extraction efficiency for two pyrethroids.
A method is described for the determination of the activity of alkaline phosphatase (ALP). It is based on the reversible modulation of the fluorescence of WS2 quantum dots (QDs). The fluorescence of the QDs is quenched by Cr(VI) but restored by free ascorbic acid (AA). The detection scheme relies on the fact that ALP hydrolyzes the substrate ascorbic acid 2-phosphate to produce AA, and that enzymatically generated AA can restore the fluorescence of the QDs. The signal (best measured at excitation/emission peak wavelengths of 365/440 nm) increases linearly in the 0.5 to 10 U·L?1 ALP activity range, with a detection limit of 0.2 U·L?1. The method was applied to the determination of ALP activity in human serum samples and demonstrated satisfactory results.
Graphical abstract The fluorescence of chromate-loaded tungsten disulfide quantum dots (QDs) is quenched but restored after reaction with ascorbic acid that is formed by the catalytic action of alkaline phosphatase (ALP) on ascorbic acid 2-phosphate (AAP). The increase in fluorescence can be related to the activity of ALP.
A sorbent for selective extraction of phosphoproteins was obtained by immobilization of a Ce(IV)-substituted polyoxometalate on ethylenediamine-functionalized graphene oxide (CeEGO). The resulting composites exhibit an adsorption capacity of 981 mg g?1 for β-casein due to the synergistic effect of metal-affinity interaction between Ce(IV) and phosphate groups and π-stacking interaction between the polyoxometalate framework and the phosphate groups. The results of LC-MS and SDS-PAGE analysis show that the CeEGO composites can be applied to the extraction of phosphoproteins from protein mixture, and as little as 50 μg mL?1 of the phosphoprotein β-casein can be detected by SDS-PAGE. It was also applied to the extraction of β-casein from spiked biological samples such as drinking milk, whole blood and swine heart tissue extract.
Graphical abstract An efficient sorbent is obtained by immobilization of a Ce(IV)-substituted polyoxometalate on ethylenediamine-functionalized graphene oxide (CeEGO). The resulting composites exhibit highly selective capture capacity towards phosphoproteins due to the synergistic effect of metal-affinity interaction between Ce(IV) and phosphate groups and π-stacking interaction between the polyoxometalate framework and the phosphate groups.
Stable copper nanoclusters (CuNCs) were prepared by utilizing D-penicillamine as both the stabilizer and reductant. The emission of the CuNCs (with excitation/emission peaks at 390/645 nm) is largely stabilized by coating with poly(sodium-p-styrenesulfonate) (PSS). Cytochrome c (Cyt c) quenches the fluorescence of the PSS-coated CuNCs, and this effect was exploited to design a quenchometric fluorometric assay for Cyt c. If trypsin is added to the loaded CuNCs, it will hydrolyze Cyt c to form peptide fragments, and fluorescence is gradually restored. A highly sensitive and fluorometric turn-off-on assay was constructed for sequential detection of Cyt c and trypsin. The linear ranges for Cyt c and trypsin are from 8.0 nM to 680 nM, and from 0.1 to 6.0 μg mL?1, and the lower detection limits are 0.83 nM and 20 ng mL?1 for Cyt c and trypsin, respectively.
Graphical abstract Schematic illustration of the fluorometric assay for trypsin based on the electron transfer between poly(p-styrenesulfonate)-protected copper nanoclusters (PSS-CuNCs) and cytochrome c (Cyt c).
The authors describe a method for functionalization of gold nanoparticles (AuNPs) with the supramolecular host molecule, curcubit[7]uril (CB[7]) which can bind rhodamine B (RhB). The fluorescence of RhB is quenched by the AuNPs via surface energy transfer. On addition of ATP, a dimeric RhB-ATP complex is formed and RhB is pushed out of CB[7]. Hence, fluorescence increases by a factor of 8. This fluorescence recovery effect has been utilized to develop a new detection scheme for ATP. The assay, measured at fluorescence excitation and emission wavelengths of 500 nm and 574 nm respectively, works in the 0.5–10 μM concentration range and has a 100 nM detection limit. The method is not interfered by UTP, GTP, CTP, TTP, ascorbic acid and glutathione.
Graphical abstract Schematic of a method for determination of ATP in the 500 nM to 10 μM concentration range by using fluorescence recovery after surface energy transfer (SET) between rhodamine B (RhB) and gold nanoparticles capped with curcubit[7]uril (CB[7]).
Under visible-light irradiation, a cathodic photoelectrochemical (PEC) sensor is presented for highly sensitive determination of Cr(VI) at a potential of ?0.25 V (vs SCE). PbS quantum dots (QDs) were capped with mercaptoacetic acid and assembled on the surface of an indium tin oxide (ITO) electrode via the linker poly(diallyl dimethyl ammonium chloride) providing a photoactive sensor. Cr(VI) accepts the photoelectrons generated by the PbS QDs. This promotes the separation of electron holes and enhances the cathodic photocurrent generated by a 470-nm LED. The sensor has 10 pM detection limit and a linear working range from 0.02 nM to 2 μM of chromate. The method was successfully applied to the determination of Cr(VI) and total chromium in spiked environmental water samples.
Graphical abstract Schematic illustration of the photocurrent enhancement response of ITO/PbS toward chromium(VI). In the presence of Cr(VI) (red line), Cr(VI) accepts the photoelectrons generated by the PbS QDs under 470-nm LED irradiation, resulting in improved photocurrent of ITO/PbS.
An efficient approach is demonstrated for preparing particles consisting of a silver core and a shell of molecularly imprinted polymer (Ag@MIP). The MIP is prepared by using bisphenol A (BPA) as the template and 4-vinylpyridine as the functional monomer. The Ag@MIP fulfills a dual function in that the silver core acts as a SERS substrate, while the MIP allows for selective recognition of BPA. The Ag@MIP is characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, thermogravimetric analysis and Raman spectroscopy. The Raman intensity of Ag@MIP is higher than that of bare silver microspheres. The detection limit for BPA is as low as 10?9 mol·L?1.
Graphical abstract Schematic illustration of the preparation of silver microspheres coated with a molecularly imprinted polymer (Ag@MIPs) for detecting bisphenol A (BPA) by surface enhanced Raman scattering (SERS).
