Electrochemical sensor for naphthols based on gold nanoparticles/hollow nitrogen-doped carbon microsphere hybrids functionalized with SH-β-cyclodextrin

Electrochemical aptasensor for 17β-estradiol using disposable laser scribed graphene electrodes

17β-Estradiol (E2), the strongest of the three major physiological estrogens in females, is an important factor in the female reproductive system. The abnormal level of E2 causes health issues, such as weak bones, urinary tract infections and even depression. Here, we present a novel, sensitive and selective, electrochemical aptasensor for detection of 17β-estradiol (E2). The E2 recognition aptamer was split into two fragments: the first fragment, functionalised with adamantane, is attached to poly(β-cyclodextrin) (poly(β-CD))-modified electrode surface through host-guest interactions between the adamantane and poly(β-CD). The second fragment, labelled with gold nanoparticles, forms the stem-loop structure with the first fragment only in the presence of E2. That specific recognition process triggers the change in the electrochemical signal (a change in the peak current from reduction of AuNPs), recorded by means of differential pulse voltammetry (DPV). The feasibility of the sensing design was firstly investigated on the commercially available glass carbon electrodes (GCE), with achieved a linear detection range of 1.0 × 10^-13 to 1.0 × 10^-8 M and a limit of detection (LoD) 0.7 fM. The sensing methodology was then translated onto single-use, disposable, laser-scribed graphene electrodes (LSGE) on a plastic substrate. The dynamic sensing range of E2 on LSGE was found to be 1.0 × 10^-13 to 1.0 × 10^-9 M, with a LoD of 63.1 fM, comparable to these of GCE. The successful translation of the developed E2 aptasensor from GCE to low-cost, disposable LSGE highlights a potential of this sensing platform in commercial, portable sensing detection systems for E2 and similar targets of biological interest.

A nitrogen doped carbon dots-enhanced peroxynitrous acid chemiluminescence method for 2-naphthol detection

A weak CL emission was initiated by peroxynitrous acid (PA) produced by the interaction of nitrite with hydrogen peroxide in sulphuric acid solution. In the presence of nitrogen doped carbon dots (NCDs), the CL intensity was enhanced significantly. The CL mechanism of the NCDs-PA system was studied using the CL spectrum, FL spectrum and the effect of radical scavengers. The NCDs-PA CL system was developed for the determination of 2-naphthol (2-NAP) based on its inhibition effect. The reduced CL intensity was proportional to the concentration of 2-NAP in the range from 0.3 to 20.0 μM and the detection limit was 48.0 nM. This method had been successfully applied to determine 2-NAP in environmental water samples with recoveries of 99.5-102.8%.

N-doped mesoporous carbon as a new sorbent for ultrasonic-assisted dispersive micro-solid-phase extraction of 1-naphthol and 2-naphthol, the biomarkers of exposure to naphthalene, from urine samples

This study aimed to optimize a new sample preparation method using N-doped mesoporous carbon sorbent for simultaneous measurement of 1-naphthol and 2-naphthol, the biomarkers of exposure to naphthalene. The samples were analyzed using high-performance liquid chromatography supplied with ultraviolet detector (HPLC-UV). N-doped mesoporous carbon sorbent was obtained via the hard template procedure. The synthesized nanosorbent was then characterized by transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and elemental analysis (CHN). The effective factors in the extraction of the studied biomarkers were examined by the Box-Behnken (BBD) methodology. Regarding the optimum conditions, the sketched calibration curve for naphthols was linear in the concentration levels of 1-600 µg L^-1 for human urine samples. The accuracy and reproducibility of the introduced method were determined using the relative recovery (RR %) and relative standard deviation (RSD %) tests on the fortified urine samples. RR% and RSD% were found to be 97.0-101.2% and 3.1-9.0%, respectively. The calculated method detection limit of the optimized procedure was 0.3 µg L^-1 and 0.5 µg L^-1 for 1-naphthol and 2-naphthol, respectively.

Homogeneous detection of 5-hydroxymethylcytosine based on electrochemiluminescence quenching of g-C3N4/MoS2 nanosheets by ferrocenedicarboxylic acid polymer

A sensitively homogeneous electrochemiluminescence (ECL) method was developed for 5-hydroxymethylcytosine (5hmC) detection using TiO₂/MoS₂/g-C₃N₄/GCE as substrate electrode, where g-C₃N₄ was employed as the ECL active material, the MoS₂ nanosheets were used as co-catalyst, and TiO₂ was adopted as phosphate group capture reagent. To achieve the specific recognition and capture of 5hmC, the covalent reaction between -CH₂OH and -SH was employed under the catalysis of HhaI methyltransferase, in which, -SH functionalized ferrocenedicarboxylic acid polymer (PFc-SH) was prepared as 5hmC capture reagent and ECL signal quencher. Then, based on the interaction between TiO₂ and phosphate group of 5hmC, the target was recognized and captured on electrode, resulting in a decreased ECL response due to the quenching effect of PFc-SH. Under optimal conditions, the biosensor presented the linear range from 0.01 to 500 nM with the detection limit of 3.21 pM (S/N = 3). The steric effect on electrode surface is a bottle-neck issue restricting devised biosensors advancement. In this work, the reaction between 5hmC and PFc was carried out in the solution, which can avoid steric effect on electrode surface to keep the high activity of enzyme. In addition, the biosensor was successfully applied to detect 5hmC in genomic DNA of chicken embryo fibroblast cells and different tissues of rice seedlings.

Ratiometric electrochemical sensor for sensitive detection of sunset yellow based on three-dimensional polyethyleneimine functionalized reduced graphene oxide aerogels@Au nanoparticles/SH-β-cyclodextrin

Electrochemical methods have been deemed effective strategies for the detection of dye additive sunset yellow (SY) owing to their low cost, good stability, and high sensitivity. However, the application of the existing sensors with single electrical signal response is limited by their inadequate sensitivity and large background interference. Herein, a ratiometric electrochemical strategy with a dual signal was developed to detect SY. The strategy had an intrinsic built-in correction to the effects from the system, and thus reduced the influence of environmental change. 3D polyethyleneimine functionalized reduced graphene oxide aerogels@Au nanoparticles/SH-β-cyclodextrin (PEI-rGAs@AuNPs/SH-β-CD) was used as the sensing material due to its 3D macroporous microstructure with high specific surface area and excellent electronic conductivity. Guest molecule methylene blue (MB) was chosen as a probe molecule, which formed an inclusion host-guest complex with a SH-β-CD host in advance. The target molecule SY displaced MB from the CD cavities, resulting in the decrease of MB current and the increase of SY current. With the logarithmic value of I_SY/I_MB as the readout signal, the detection limit of the developed ratiometric electrochemical sensor reached as low as 0.3 nM, confirming the excellent sensitivity. Furthermore, this strategy exhibited good selectivity and repeatability, and could be used for the detection of SY in a real sample.

Voltammetric chiral discrimination of tryptophan using a multilayer nanocomposite with implemented amino-modified β-cyclodextrin as recognition element

An electrochemical chiral multilayer nanocomposite was prepared by modifying a glassy carbon electrode (GCE) via opposite-charge adsorption of amino-modified β-cyclodextrin (NH₂-β-CD), gold-platinum core-shell microspheres (Au@Pts), polyethyleneimine (PEI), and multi-walled carbon nanotubes (MWCNTs). The modified GCE was applied to the enantioselective voltammetric determination of tryprophan (Trp). The Au@Pts enable an effective immobilization of the chiral selector (NH₂-β-CD) and enhance the electrochemical performance. Scanning electron microscopy, transmission electron microscopy, UV-vis spectroscopy, FTIR and electrochemical methods were used to characterize the nanocomposite. Trp enantiomers were then determined by differential pulse voltammetry (DPV) (with a peak potential of +0.7 V vs. Ag/AgCl). The recognition efficiency was expressed by an increase in peak height by about 32% for DPV determinations of L-Trp compared to D-Trp in case of a 5 mM Trp solution of pH 7.0. Response was linear in the 10 μM to 5.0 mM concentration range, and the limits of detection were 4.3 μM and 5.6 μM with electrochemical sensitivity of 43.5 μA·μM^-1·cm^-2 and 34.6 μA·μM^-1·cm^-2 for L-Trp and D-Trp, respectively (at S/N = 3). Graphical Abstract Schematic of an electrochemical chiral multilayer nanocomposite composed of multi-walled carbon nanotubes (MWCNTs), polyethyleneimine (PEI), gold-platinum core-shell microspheres (Au@Pt) and amino-modified β-cyclodextrin (NH₂-β-CD). It was prepared by modifying a glassy carbon electrode (GCE) for enantioselective voltammetric determination of tryptophan (Trp) enantiomers.

A new nanomatrix based on functionalized fullerene and porous bimetallic nanoparticles for electrochemical chiral sensing

A simple, functionalized fullerene and porous Au@Pd nanoparticle-based chiral sensor for tyrosine enantiomer recognition.

A new electrochemical immunosensor for sensitive detection of prion based on Prussian blue analogue

Based on Co-Co Prussian blue analogue (Co-Co PBA), a novel immunosensor has been developed for sensitive detection of prion protein (PrP^C). Gold nanoparticles (AuNPs)-modified Co-Co PBA nanocubes (PBA-AuNPs) worked as a support of the antibody (Ab2) of PrP^C to obtain Ab2-PBA-AuNPs composite and also as the signal source for PrP^C assay. When PrP^C existed, Ab2-PBA-AuNPs could be introduced to the surface of another antibody of PrP^C (Ab1) modified AuNPs/GC electrode (the gold nanoparticles-modified glassy carbon electrode) through specific antigen-antibody interaction between PrP^C and its antibodies to form the Ab1-PrP^C-Ab2 sandwich structure. With the help of KOH aqueous solution, PBA generated a large DPV response. The response peak currents were linear with the logarithmic values of the concentration of PrP^C in the range from 0.075pgmL^-1 to 100pgmL^-1 with the detection limit of 0.014pgmL^-1. Also, the immunosensor showed good selectivity and reproducibility. Based on the simple sensing structure and good analytical performance, the developed immunosensor may have promising applications in practical assay of infectious isoform of prion (PrP^Sc) and other proteins by simply changing the related antibody.

Zeolitic imidazolate framework 8 (ZIF-8) reinforced macroporous resin D101 for selective solid-phase extraction of 1-naphthol and 2-naphthol from phenol compounds

Macroporous resin has been attracting intensive attention due to its critical role in separation and purification of natural products. Herein, a zeolitic imidazolate framework 8 reinforced macroporous resin D101 was prepared via a room temperature growth method and used for dispersive SPE of 1-naphthol and 2-naphthol. The parameters affecting the adsorption and desorption efficiency such as the sample pH, adsorbent amount, extraction time, desorption solvent, and desorption time were investigated. The as-prepared adsorbent showed selectivity for 1-naphthol and 2-naphthol compared to other phenols. Under the optimum dispersive SPE conditions, the detection of 1-naphthol and 2-naphthol coupled with a CZE method was conducted and the LODs for 1-naphthol and 2-naphthol were 1.37 and 1.43 ng/mL, respectively. Moreover, the results of urine sample analysis showed the spiked recoveries to be in the range of 96.2-106.9%. This study indicated that D101@ZIF-8 (where ZIF is zeolitic imidazolate framework) is a promising selective adsorbent for the analysis of 1-naphthol and 2-naphthol in urine samples.

Enantioselective recognition of ascorbic acid and isoascorbic acid on HS-β-cyclodextrin/gold nanoparticles/hollow carbon microspheres hybrid modified electrodes

The HS-β-cyclodextrin/gold nanoparticles/hollow carbon microspheres hybrids were prepared to develop a simple strategy for electrochemical chiral analysis.

The self-assembled Ru(bpy)3(PF6)2 nanoparticle on polystyrene microfibers and its application for ECL sensing

Ruthenium nanoparticle tris(2,2'-bipyridyl)ruthenium(II) bis(hexafluorophosphate) (Ru(bpy)3(PF6)2, RuNP) was self-assembled on polystyrene (PS) electrospun microfibers. The formation of RuNP is attributed to the sulfonated PS (SPS) microfibers' high adsorptive capability of 94% for Ru(bpy)3(2+), as well as the strong interaction between the Ru(bpy)3(2+) and ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6). The RuNP/SPS microfibers exhibited an enhanced electrochemiluminescence (ECL) emission, 2.3 times higher than that from Ru(bpy)3(2+)/SPS microfibers and 6.6 times higher than that from Ru(bpy)3(2+)/SPS continuous thin films. It is worthy of note that, as a result of the hydrophobic nature of the RuNP, the transfer of water-insoluble α-naphthol is accelerated, and thus the α-naphthol ECL quenching efficiency is enhanced. An ECL sensor based on the RuNP/SPS microfibers was fabricated and used to detect low concentrations of α-naphthol. The detection limit was of 1.0 nM (S/N > 3), and the linear response ranged from 0 to 18 μM. This sensor has been successfully applied to measure the α-naphthol content in pesticide carbaryl samples. Our work provides a very simple and cost-effective method to fabricate RuNP on polymer microfibers with great potential in the field of chemo/biosensors.

Selective electrochemical recognition of the α-naphthol isomer and in situ immobilization of naphthoquinones for tunable electrocatalysis

Fits like a glove: Separationless and selective electrochemical oxidation of the α-naphthol (α-NAP) isomer yields naphthoquinone species on the surface of multiwalled carbon nanotubes, which can further catalyze the electro-oxidation of NADH and hydrazine at different potentials. The β-NAP isomer failed to show any such electro-oxidation.

Synthesis of monodisperse hollow carbon nanocapsules by using protective silica shells

Monodisperse hollow carbon nanocapsules (<200 nm) with mesoporous shells were synthesized by coating their outer shells with silica to prevent aggregation during their high-temperature annealing. Monodispersed silica nanoparticles were used as starting materials and octadecyltrimethoxysilane (C18TMS) was used as a carbon source to create core-shell nanostructures. These core-shell nanoparticles were coated with silica on their outer shell to form a second shell layer. This outer silica shell prevented aggregation during calcination. The samples were characterized by TEM, SEM, dynamic light scattering (DLS), UV/Vis spectroscopy, and by using the Brunauer-Emmett-Teller (BET) method. The as-synthesized hollow carbon nanoparticles exhibited a high surface area (1123 m(2) g(-1)) and formed stable dispersions in water after the pegylation process. The drug-loading and drug-release properties of these hollow carbon nanocapsules were also investigated.

β-Cyclodextrin non-covalently functionalized single-walled carbon nanotubes bridged by 3,4,9,10-perylene tetracarboxylic acid for ultrasensitive electrochemical sensing of 9-anthracenecarboxylic acid

We report a simple and facile approach for the synthesis of β-cyclodextrin non-covalently functionalized single-walled carbon nanotubes bridged by 3,4,9,10-perylene tetracarboxylic acid (β-CD-PTCA-SWCNTs). Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy and electrochemical methods were used to characterize the as-prepared functionalized SWCNTs. Furthermore, the β-CD-PTCA-SWCNTs were applied successfully to detect 9-anthracenecarboxylic acid (9-ACA, one derivative of polycyclic aromatic hydrocarbons) by electrochemical methods. The results show that the oxidation peak current of 9-ACA on β-CD-PTCA-SWCNTs modified glassy carbon (GC) electrode is 4.0 and 31.2 times higher than that at the SWCNTs/GC and bare GC electrodes, respectively. The proposed modified electrode has a linear response range of 2.00 to 140.00 nM with a detection limit of 0.65 nM (S/N = 3) towards 9-ACA, which is due to the synergic effects of the SWCNTs (e.g. their good electrochemical properties and large surface area) and β-CD (e.g. a hydrophilic external surface and a high supramolecular recognition and enrichment capability).