Optical and Electrochemical Combination Sensor with Poly‐Aniline Film Modified Gold Surface and Its Application for Dissolved Oxygen Detection

Poly‐aniline (PAn) film can be oxidized by contacting oxygen in an electron‐transfer reaction and its redox state, for instance the open circuit potential and the dielectric constant, is quantitatively related to oxygen concentration. This feature may contribute to an improved application of dissolved oxygen (DO) detection with the combined optical and electrochemical sensor. In this paper, PAn is used as a sensing surface to detect DO by the combination sensor composed of electrochemistry and total internal reflection imaging ellipsometry (EC‐TIRIE). Results demonstrate that both optical and electrical signals show a logarithmic correlation with DO concentration (0–20 ppm). Compared with the results obtained only with the gold surface, both the optical and electrical signals of the EC‐TIRIE sensor for DO detection are amplified with the PAn modified gold surface.     

Electrocatalytic Reduction and Determination of Dissolved Oxygen at a Preanodized Screen‐Printed Carbon Electrode Modified with Palladium Nanoparticles

Efficient and stable electrocatalytic activity for the reduction of O₂ at activated screen‐printed carbon electrodes modified with palladium nanoparticles (SPE*‐Pd) was demonstrated in this study. X‐ray photoelectron spectroscopy confirmed the formation of >C?O functional group on electrode surface during the preanodization procedure at 2.0 V (vs. Ag/AgCl). The existence of chloride moieties was also identified possibly from the organic binder of carbon ink used in SPE fabrication. Both >C?O and chloride functional groups were essential for the excellent stability of the SPE*‐Pd. Electrochemical impedance spectroscopy verified the enhanced kinetic rate of oxygen reduction reaction at the as‐prepared Pd nanoparticles. The SPE*‐Pd showed ca. 250 mV positive shift in peak potential together with twice increase in peak current compared to those observed at a SPE‐Pt. The calibration plot was linear up to 8 ppm of DO with sensitivity and regression coefficient of 4.49 μA/ppm and 0.9936, respectively. The variation coefficient of i_pc for 7 DO determinations with O₂‐saturated pH 7.4 PBS was 2.1%. Real sample assays for ground and tap waters gave consistent values to those measured by a commercial dissolved oxygen meter.     

Improved Potentiometric and Optic Sensitivity of Polyaniline Film to Dissolved Oxygen by Incorporating Iron‐Porphyrin

Polyaniline (PAn) films can be used in an electrochemical and optical combination system to amplify the optical signal for dissolved oxygen (DO) detection. To further improve the sensitivity of PAn film to DO, an oxygen‐sensitive molecule, Fe(III) meso‐tetera (4‐sulfonatophenyl) porphyrin (FeTSPP) is incorporated into PAn during the film generation. Results show that, after incorporating FeTSPP into the PAn matrix, both optical and potentiometric responses to DO are improved. The optimal optical signal is obtained under the application of ?2.5 μA to the modified electrode. Under this applied current, both optical and potentiometric signals show linear relations with the DO concentration within the range of 0.00–4.63 mg L^?1, and the sensitivities for optical and potentiometric signals are 4.18 grayscale units mg^?1 L and 13.39 mV mg^?1 L, respectively.     

Self‐Powered and Sensitive DNA Detection in a Three‐Dimensional Origami‐Based Biofuel Cell Based on a Porous Pt‐Paper Cathode

In this work, a mediator‐less and compartment‐less glucose/air enzymatic biofuel cell (BFC) was introduced into microfluidic paper‐based analytical devices (μ‐PADs) with gold nanoparticles (AuNPs) and platinum nanoparticles (PtNPs)‐modified paper electrode as the anodic and cathodic substrate, respectively, to implement self‐powered, sensitive, low‐cost and simple DNA detection. As a further development of the analytical equipment, an all‐solid‐state paper supercapacitor (PS) was designed and integrated into the BFC for current amplification, and a terminal digital multi‐meter detector (DMM) was introduced for the current detection. A highly sensitive DNA sensor was fabricated by covalently immobilizing the capture DNA in the AuNPs‐modified anode. The nanoporous gold conjugated with bienzymes, glucose oxidase and horseradish peroxidase, which were used as electrochemical labels. The electrons generated at the anode flow through an external circuit to the PtNPs‐modified cathode that catalyzed the reduction of oxygen with the participation of protons. In addition, the generated current could be collected and stored by the PS. After that, the PS was automatically shorted under the control of a switch to output an instantaneously amplified current, which could be sensitively detected by the terminal DMM. At the optimal conditions, the paper‐based analytical platform can detect DNA at the femtomole level. This approach also shows excellent specificity toward single nucleotide mismatches.     

Immunosensor for Detection of the Textile Dye Disperse Orange 1 Based on Non‐conventional Competitive Assay

Textile dyes appear as an important class of compounds that has become a matter of public concern and a serious challenge for scientists and environmentalists due to their large‐scale production and extensive application. In this work, a non‐conventional competitive‐type amperometric immunosensor was successfully developed for detection of the textile dye Disperse Orange 1 (DO1). The DO1 was magnetically captured and separated from the sample solution using magnetic particles (MP) functionalized with the antibody anti‐DO1 and with HRP and gold electrodes were modified with the conjugate DO1‐BSA. Molecules of DO1 immobilized on the electrode surface and DO1 captured by MP compete for antibody binding sites. As a result, the amperometric signal decreases with increasing target DO1 concentration at the capture step, because this decreases, the attachment between the HRP coated MP and the electrode. This strategy allowed us to determine DO1 at the low detection limit of 0.87 ng mL^?1 with great specificity. Also, there were good recoveries for detection of the textile dye in river water samples without the need of sample pre‐treatment. The competitive amperometric immunosensor shows applicability for the determination of small molecules that cannot be determined by conventional competitive or sandwich immunosensors.     

GOx@ZIF‐8(NiPd) Nanoflower: An Artificial Enzyme System for Tandem Catalysis

We report a facile approach to prepare an artificial enzyme system for tandem catalysis. NiPd hollow nanoparticles and glucose oxidase (GOx) were simultaneously immobilized on the zeolitic imidazolate framework 8 (ZIF‐8) via a co‐precipitation method. The as‐prepared GOx@ZIF‐8(NiPd) nanoflower not only exhibited the peroxidase‐like activity of NiPd hollow nanoparticles but also maintained the enzymatic activity of GOx. A colorimetric sensor for rapid detection of glucose was realized through the GOx@ZIF‐8(NiPd) based multi‐enzyme system. Moreover, the GOx@ZIF‐8(NiPd) modified electrode showed good bioactivity of GOx and high electrocatalytic activity for the oxygen reduction reaction (ORR), which could also be used for electrochemical detection of glucose.     

Highly Efficient,Conjugated‐Polymer‐Based Nano‐Photosensitizers for Selectively Targeted Two‐Photon Photodynamic Therapy and Imaging of Cancer Cells

Two‐photon photodynamic therapy (2P‐PDT) is a promising noninvasive treatment of cancers and other diseases with three‐dimensional selectivity and deep penetration. However, clinical applications of 2P‐PDT are limited by small two‐photon absorption (TPA) cross sections of traditional photosensitizers. The development of folate receptor targeted nano‐photosensitizers based on conjugated polymers is described. In these nano‐photosensitizers, poly{9,9‐bis[6′′‐(bromohexyl)fluorene‐2,7‐ylenevinylene]‐co‐alt‐1,4‐(2,5‐dicyanophenylene)}, which is a conjugated polymer with a large TPA cross section, acts as a two‐photon light‐harvesting material to significantly enhance the two‐photon properties of the doped photosensitizer tetraphenylporphyrin (TPP) through energy transfer. These nanoparticles displayed up to 1020‐fold enhancement in two‐photon excitation emission and about 870‐fold enhancement in the two‐photon‐induced singlet oxygen generation capability of TPP. Surface‐functionalized folic acid groups make these nanoparticles highly selective in targeting and killing KB cancer cells over NIH/3T3 normal cells. The 2P‐PDT activity of these nanoparticles was significantly improved, potentially up to about 1000 times, as implied by the enhancement factors of two‐photon excitation emission and singlet oxygen generation. These nanoparticles could act as novel two‐photon nano‐photosensitizers with combined advantages of low dark cytotoxicity, targeted 2P‐PDT with high selectivity, and simultaneous two‐photon fluorescence imaging capability; these are all required for ideal two‐photon photosensitizers.     

Controlled Anisotropic Growth of Co‐Fe‐P from Co‐Fe‐O Nanoparticles

A facile approach to bimetallic phosphides, Co‐Fe‐P, by a high‐temperature (300 °C) reaction between Co‐Fe‐O nanoparticles and trioctylphosphine is presented. The growth of Co‐Fe‐P from the Co‐Fe‐O is anisotropic. As a result, Co‐Fe‐P nanorods (from the polyhedral Co‐Fe‐O nanoparticles) and sea‐urchin‐like Co‐Fe‐P (from the cubic Co‐Fe‐O nanoparticles) are synthesized with both the nanorod and the sea‐urchin‐arm dimensions controlled by Co/Fe ratios. The Co‐Fe‐P structure, especially the sea‐urchin‐like (Co_0.54Fe_0.46)₂P, shows enhanced catalysis for the oxygen evolution reaction in KOH with its catalytic efficiency surpassing the commercial Ir catalyst. Our synthesis is simple and may be readily extended to the preparation of other multimetallic phosphides for important catalysis and energy storage applications.     

Gold Nanoparticles‐β‐Cyclodextrin‐Chitosan‐Graphene Modified Glassy Carbon Electrode for Ultrasensitive Detection of Dopamine and Uric Acid

The nanocomposite (denoted as GR‐AuNPs‐CD‐CS) of graphene (GR), gold nanoparticles (AuNPs), chitosan (CS) and β‐cyclodextrin (β‐CD) was prepared to modify a glassy carbon electrode. The as‐modified electrode was explored for the ultrasensitive detection of dopamine (DA) and uric acid (UA). The modified electrode demonstrated linearly increased current response in the concentration range of 0.1–120 µm for DA and 0.05–70 µm for UA, with so far the best detection limit for DA and UA. Good stability and repeatability were further demonstrated for the as‐made sensor.     

Luminescent,Oxygen‐Supplying,Hemoglobin‐Linked Conjugated Polymer Nanoparticles for Photodynamic Therapy

Photodynamic therapy (PDT) is a promising method for cancer treatment. Two parameters that influence the efficacy of PDT are the light source and oxygen supply. Herein, we prepared a system for PDT using hemoglobin (Hb)‐linked conjugated polymer nanoparticles (CPNs), which can luminesce and supply oxygen. Hb catalyzes the activation of luminol, the conjugated polymer poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH–PPV) nanoparticles can absorb the chemiluminescence of luminol through chemiluminescence resonance energy transfer (CRET) and then sensitize the oxygen supplied by Hb to produce reactive oxygen species that kill cancer cells. This system could be used for the controlled release of an anticancer prodrug. The system does not need an external light source and circumvents the insufficient level molecular oxygen under hypoxia. This work provides a proof‐of‐concept to explore smart and multifunctional nanoplatforms for phototherapy.     

Luminescent,Oxygen‐Supplying,Hemoglobin‐Linked Conjugated Polymer Nanoparticles for Photodynamic Therapy

Photodynamic therapy (PDT) is a promising method for cancer treatment. Two parameters that influence the efficacy of PDT are the light source and oxygen supply. Herein, we prepared a system for PDT using hemoglobin (Hb)‐linked conjugated polymer nanoparticles (CPNs), which can luminesce and supply oxygen. Hb catalyzes the activation of luminol, the conjugated polymer poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH–PPV) nanoparticles can absorb the chemiluminescence of luminol through chemiluminescence resonance energy transfer (CRET) and then sensitize the oxygen supplied by Hb to produce reactive oxygen species that kill cancer cells. This system could be used for the controlled release of an anticancer prodrug. The system does not need an external light source and circumvents the insufficient level molecular oxygen under hypoxia. This work provides a proof‐of‐concept to explore smart and multifunctional nanoplatforms for phototherapy.     

Imprinted silica nanoparticles coated with N‐propylsilylmorpholine‐4‐carboxamide for the determination of m‐cresol in synthetic and real samples

m‐Cresol‐imprinted silica nanoparticles coated with N‐propylsilylmorpholine‐4‐carboxamide have been developed that contain specific pockets for the selective uptake of m‐cresol. Silica nanoparticles were synthesized by a sol–gel process followed by functionalization of their surface with N‐propylsilylmorpholine‐4‐carboxamide. The formation of m‐cresol‐imprinted silica nanoparticles was confirmed by UV‐Vis spectrophotometry, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. Electron microscopic studies revealed the formation of monodispersed imprinted silica nanoparticles with spherical shape and an average size of 83 nm. The developed nanoparticles were filled in a syringe and used for the extraction of m‐cresol from aqueous samples followed by quantification using high‐performance liquid chromatography with diode array detection. Various adsorption experiments showed that developed m‐cresol‐imprinted silica nanoparticles exhibited a high adsorption capacity and selectivity and offered a fast kinetics for rebinding m‐cresol. The chromatographic quantification was achieved using mobile phase consisting of acetonitrile/water (70:30 v/v) at an isocratic flow rate of 1.0 mL/min using a reversed‐phase C₁₈ column and detection at λ_max = 275 nm. The limits of detection and quantification were 1.86 and 22.32 ng/mL, respectively, for the developed method. The percent recoveries ranged from 96.66–103.33% in the spiked samples. This combination of this nanotechnique with molecular imprinting was proved as a reliable, sensitive and selective method for determining the target from synthetic and real samples.     

“Metal‐Free” Catalytic Oxygen Reduction Reaction on Heteroatom‐Doped Graphene is Caused by Trace Metal Impurities

The oxygen reduction reaction (ORR) is of high industrial importance. There is a large body of literature showing that metal‐based catalytic nanoparticles (e.g. Co, Mn, Fe or hybrid Mn/Co‐based nanoparticles) supported on graphene act as efficient catalysts for the ORR. A significant research effort is also directed to the so‐called “metal‐free” oxygen reduction reaction on heteroatom‐doped graphene surfaces. While such studies of the ORR on nonmetallic heteroatom‐doped graphene are advertised as “metal‐free” there is typically no sufficient effort to characterize the doped materials to verify that they are indeed free of any trace metal. Here we argue that the claimed “metal‐free” electrocatalysis of the oxygen reduction reaction on heteroatom‐doped graphene is caused by metallic impurities present within the graphene materials.     

Normal‐phase high‐performance counter‐current chromatography for the fractionation of dissolved organic matter from a freshwater source

Normal‐phase high‐performance counter‐current chromatography (HPCCC) is used to obtain a preliminary fractionation of components in dissolved organic matter (DOM) from a freshwater source. The HPCCC solvent system involved a normal‐phase approach with water/methanol (1:1) as the lower stationary phase and hexane/ethyl acetate (1:1) as the upper mobile phase. The critical experiment parameters were optimised: revolution speed 1800 rpm and flow rate 0.15 mL/min. Under these conditions 50 μL of a 0.50 mg/mL DOM solution was loaded. The detection wavelength was monitored at 330 nm in order to isolate the main portion of DOM, which includes substances such as carboxyl‐rich alicyclic molecules. By optimising this system it was possible to isolate materials that, according to GC–MS, can be related to molecules with an analogous structural background. Where fraction analysis was not suitable for GC–MS, RP‐HPLC with UV absorbance detection was used, showing unique chromatograms for each fraction at both 210 and 330 nm.     

Comprehensive Evaluation of the Physicochemical Properties of LnIII Complexes of Aminoethyl‐DO3A as pH‐Responsive T1‐MRI Contrast Agents

N‐Substituted aminoethyl groups were attached to 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid (DO3A) with the aim to design pH‐responsive Ln^III complexes based on the pH‐dependent on/off ligation of the amine nitrogen to the metal ion. The following ligands were synthesized: AE ‐ DO3A (aminoethyl‐DO3A), MAE ‐ DO3A (N‐methylaminoethyl‐DO3A), DMAE ‐ DO3A (N,N‐dimethylaminoethyl‐DO3A) and MEM ‐ AE ‐ DO3A (N‐methoxyethyl‐N‐methylaminoethyl‐DO3A). The physicochemical properties of the Ln^III complexes were investigated for the evaluation of their potential applicability as magnetic resonance imaging (MRI) contrast agents. In particular, a ¹H and ¹⁷O NMR relaxometric study was carried out for these Gd^III complexes at two different pH values: at basic pH (pendant amino group coordinated to the metal centre) and at acidic pH (protonated amine, not interacting with the metal ion). Eu^III complexes allow one to estimate the number of inner‐sphere water molecules through luminescence lifetime measurements and obtain some structural information through variable‐temperature (VT) high‐resolution ¹H NMR studies. Equilibria between differently hydrated species were found for most of the complexes at both acidic and basic pH. The thermodynamic stability of Ca^II, Zn^II, Cu^II and Ln^III complexes and kinetics of formation and dissociation reactions of Ln^III complexes of AE ‐ DO3A and DMAE ‐ DO3A were investigated showing stabilities comparable to currently approved Gd^III‐based CAs. In detail, higher total basicity (Σlog K_i^H) and higher stability constants of Ln^III complexes were found for AE ‐ DO3A with respect to DMAE ‐ DO3A (i.e., log K_{Gd‐ AE‐DO3A} =22.40 and log K_{Gd‐ DMAE‐DO3A} =20.56). The transmetallation reactions of Gd^III complexes are very slow (Gd‐ AE ‐ DO3A : t_1/2=2.7×10⁴ h; Gd‐ DMAE ‐ DO3A : 1.1×10⁵ h at pH 7.4 and 298 K) and occur through proton‐assisted dissociation.     

Flow‐Enabled Self‐Assembly of Large‐Scale Aligned Nanowires

One‐dimensional nanowires enable the realization of optical and electronic nanodevices that may find applications in energy conversion and storage systems. Herein, large‐scale aligned DNA nanowires were crafted by flow‐enabled self‐assembly (FESA). The highly oriented and continuous DNA nanowires were then capitalized on either as a template to form metallic nanowires by exposing DNA nanowires that had been preloaded with metal salts to an oxygen plasma or as a scaffold to direct the positioning and alignment of metal nanoparticles and nanorods. The FESA strategy is simple and easy to implement and thus a promising new method for the low‐cost synthesis of large‐scale one‐dimensional nanostructures for nanodevices.     

Synthesis of a Gold–Metal Oxide Core–Satellite Nanostructure for In Situ SERS Study of CuO‐Catalyzed Photooxidation

This work reports on an assembling–calcining method for preparing gold–metal oxide core–satellite nanostructures, which enable surface‐enhanced Raman spectroscopic detection of chemical reactions on metal oxide nanoparticles. By using the nanostructure, we study the photooxidation of Si?H catalyzed by CuO nanoparticles. As evidenced by the in situ spectroscopic results, oxygen vacancies of CuO are found to be very active sites for oxygen activation, and hydroxide radicals (*OH) adsorbed at the catalytic sites are likely to be the reactive intermediates that trigger the conversion from silanes into the corresponding silanols. According to our finding, oxygen vacancy‐rich CuO catalysts are confirmed to be of both high activity and selectivity in photooxidation of various silanes.     

Photo‐ and pH‐Tunable Multicolor Fluorescent Nanoparticle‐Based Spiropyran‐ and BODIPY‐Conjugated Polymer with Graphene Oxide

We report a stimuli‐responsive fluorescent nanomaterial, based on graphene oxide coupled with a polymer conjugated with photochromic spiropyran (SP) dye and hydrophobic boron dipyrromethane (BODIPY) dye, for application in triggered target multicolor bioimaging. Graphene oxide (GO) was reduced by catechol‐conjugated polymers under mildly alkaline conditions, which enabled to formation of functionalized multicolor graphene nanoparticles that can be induced by irradiation with UV light and by changing the pH from acidic to neutral. Investigation of these nanoparticles by using AFM, fluorescence emission, and in vitro cell and in vivo imaging revealed that they show different tunable colors in bioimaging applications and, more specifically, in cancer‐cell detection. The stability, biocompatibility, and quenching efficacy of this nanocomposite open a different perspective for cell imaging in different independent colors, sequentially and simultaneously.     

Influence of the preparation conditions of Pd‐ZrO2 and AuPd‐ZrO2 nanoparticle–decorated functionalised MWCNTs: Electron spectroscopy study aided with the QUASES

The Pd, AuPd, and ZrO₂ nanoparticle–decorated functionalised multiwalled carbon nanotubes (f‐MWCNTs) were reported as efficient catalysts of formic acid (FA) electro‐oxidation. Different preparation conditions influence their chemical and structural properties analysed by X‐ray photoelectron spectroscopy aided with the quantitative analysis of surfaces by electron spectroscopy. Different reduction procedures such as NaBH₄, a polyol microwave‐assisted method (PMWA), and a high pressure microwave reactor (HPMWR) were applied for decorating ZrO₂/f‐MWCNTs with Pd and AuPd nanoparticles. The ZrO₂ nanoparticles are attached through oxygen groups to the surface of f‐MWCNTs. In NaBH₄ and HPMWR procedures, Pd nanoparticles precipitate predominantly on ZrO₂ of nearly nominal stoichiometry, whereas in PMWA procedure, Pd and AuPd nanoparticles precipitate predominantly on the surface of f‐MWCNTs, bridging with oxygen groups and ZrO_x (x < 2) and leading to Pd‐O‐Zr phase formation. Strong reducing procedures (NaBH₄ and FA) led to smaller Pd nanoparticle size, Pd oxide content, and PdO_x overlayer thickness in contrary to weak reduction procedures (HPMWR and PMWA). The highest content of Pd‐O‐Zr phase appeared for Pd predominant precipitation on ZrO₂ nanoparticles (HPMWR) in contrary to Pd and AuPd predominant precipitation on surface of f‐MWCNTs (NaBH₄ ~ FA > PMWA). Larger content of Pd‐O‐Zr phase in AuPd‐decorated ZrO₂/f‐MWCNTs in contrary to Pd‐decorated sample (PMWA) could be justified by different electronic properties of nanoparticles. The FA treatment of Pd and AuPd‐ZrO₂/f‐MWCNTs samples provided decreasing Pd oxide content, overlayer thickness, nanoparticle size, increasing nanoparticle surface coverage and density, amount of Pd‐O‐Zr, what results from reduction of oxygen groups bridging with Pd and ZrO_x nanoparticles, also through Pd‐O‐Zr phase.