Electrochemically fabricated molecule–electrode contacts for molecular electronics

Connecting molecules to electrodes is key for a range of applications. Conventional methods typically involve a spontaneous reaction of thiol/disulfide-terminated molecules with metal surfaces. Although modifying metal surfaces with thiol chemistry is simple, it is limited to forming a specific S–metal bonding, which is labile and hence there are concerns regarding its mechanical instability. In addition, spontaneous grafting requires long processing times to achieve high molecular coverages on the surface, which adds challenges for manufacturing devices comprising molecular films. Electrochemical methods for forming molecular films on surfaces offer powerful advantages over traditional methods, including reaction acceleration, molecular coverage control, and guiding the chemical bonding at the molecule?electrode interface. Electrochemical grafting enables connecting molecules to various types of electrodes including those that cannot be functionalized by other methods. More recently, electrochemical approaches were expanded to enable connecting 2D materials to electrodes, opening a realm of possibilities for hybrid technologies. In this opinion, we survey the recent progress in electrochemical methods for connecting (bio) molecules to electrodes for advancing molecular and bioelectronics.     

Electrochemically modified piezoelectric crystal biosensor for detection of Staphylococcus aureus

Electropolymerized o-phenylenediamine film is used as a functional coating for the immobilization of anti-S. aureus antibody on the surface of a gold-plated piezoelectric crystal, and this piezoelectric immunosensor is applied to detect S. aureus. The frequency shift (F = F20s - F380s, Hz) between the frequency at the 20th second (after the addition of sample, F20s) and that at 380 seconds later (F380s) was introduced to construct a calibration graph, and shortening of assay time was achieved. The S. aureus concentrations in the range of 105-109 cells/mL can be detected by this system.     

Synthesis of a new β-naphthothiazole monomethine cyanine dye for the detection of DNA in aqueous solution

Novel monomethine cyanine dye (MC) derived from β-naphthothiazole and benzothiazole has been prepared and characterized by ¹H and ¹³C NMR, FTIR, ESIMS, elemental analyses, absorption and fluorescence spectroscopy. The dye was conveniently synthesized by the condensation of two sulfate heterocyclic quaternary salts. The interaction between calf thymus DNA (ct-DNA) in tris(hydroxymethyl)aminomethane–HCl (Tris–HCl) aqueous buffer solution and MC has been studied with spectral fluorescence method. The binding constant value has been determined by fluorescence titration of MC with ct-DNA concentrations. The result obtained is consistent with an intercalative binding interaction between MC and ct-DNA. Compared with ethidium bromide (EB), MC showed a huge fluorescence enhancement upon mixing with ct-DNA.     

Capillary electrophoresis with direct chemiluminescence detection for the analysis of catecholamines in human urine

A rapid and sensitive method for the analysis of three catecholamines by capillary electrophoresis(CE)with directchemiluminescence(CL)detection is described.The detection limits(S/N=3)were 1.3*10-8g/mL for isoprenaline,1.0*10-8g/mL for epinephrine and 2.8*10-8g/mL for dopamine.The proposed method was successfully applied to theanalysis of catecholamines in urine samples of cigarette smokers and nonsmokers.The results showed that there is a close relationbetween the release of dopamine in human body fluids and cigarette smoking/nonsmoking.     

Electrogeneration of ferrate (Ⅵ) in low concentration NaOH solution for flow-injection-chemiluminescence detection

<正>The possibility of direct analytical applications of ferrate(Ⅵ) solution,which was freshly electrogenerated in low-concentration NaOH electrolyte,was studied by a flow-injection-chemiluminescence(FI-CL) system.It was found that some inorganic ions, organic molecule and biomolecule could enhance the chemiluminescence emission caused by ferrate(Ⅵ)-luminol reaction.V(Ⅴ), Ca(Ⅱ),Mg(Ⅱ),phloroglucinol,and bovine hemoglobin(Hb) chosen as samples were successfully detected by this developed method.The analytical characteristics of the system for the analytes determination including linear ranges,correlation coefficients, limits of detection combined with FI analysis were studied.     

Electrochemical detection of miRNA-21 based on molecular beacon formed by thymine-mercury(II)-thymine base pairing

We present a molecular beacon-based electrochemical biosensor with high sensitivity and specificity for the detection of microRNA-21. A special oligonucleotide probe was prepared containing a nucleotide sequence complementary to miR-21 and consecutively linking eight and six thymines to the 3′ and 5′ ends, respectively, to allow the formation of a T-Hg²⁺-T complex-based molecular beacon on the electrode surface by the selective binding of Hg²⁺ ions. The introduction of multiple thymines at the end of the probe avoids base overlapping between the miRNA sequence and the molecular beacon formation sequence, enabling a universal probe design that can detect all types of miRNAs. A ferrocene moiety was attached to the 5′-end of the specially designed probe as an electrochemical signal indicator. The molecular beacons are formed by six consecutive T-Hg²⁺-T pairs by Hg²⁺ addition, and the molecular beacons are destroyed by perfect hybridization between 22 bases as a result of miR-21 addition. Based on this detection mechanism, we were able to detect miR-21 with LODs of 0.64 pM and 1.08 pM in buffer solution and human serum, respectively. In addition, the specifically designed oligonucleotide probe showed perfect specificity in detecting only miR-21 without binding to other miRNAs. Finally, the sensor showed excellent miR-21 recovery ability from samples spiked into serum, indicating that the method described in this study worked perfectly, even in a turbid complex matrix such as human serum.     

G-quadruplex − based homogenous fluorescence platform for ultrasensitive DNA detection through isothermal cycling and cascade signal amplification

We describe a simple and homogenous fluorimetric method for sensitive determination of DNA. It is based on target-triggered isothermal cycling and a cascade exponential amplification reaction that generates a large amount of a G-quadruplex. This results in strong fluorescence signal when using thioflavin T as a G-quadruplex-specific light-up fluorescent probe. Tedious handling after amplification is widely eliminated by the addition of thioflavin T. No other exogenous reagent is required. This detection platform is inexpensive and rapid, and displays high sensitivity for target DNA, with a detection limit as low as 91 pM.

The addition of target DNA can trigger the isothermal exponential amplification reaction to generate a large amount of G-quadruplex sequence oligonucleotides and then employ thioflavin T (Th T) (a G-quadruplex-specific light-up dye) as signal output for sensitive DNA detection.

     

Microarray of DNA–protein complexes on poly-3-hydroxybutyrate surface for pathogen detection

A novel strategy was developed for the specific immobilization of DNA probes on poly-3-hydroxybutyrate (PHB) surface by using the substrate-binding domain (SBD) of PHB depolymerase as an active binding motif. To demonstrate whether this method can be used for the detection of clinical pathogens, the pathogen-specific biotin-labeled DNA probes were immobilized via core streptavidin (cSA) fused to the SBD. The pathogen-specific 15-mer oligonucleotide probes were designed for four model pathogens, while the target DNAs were prepared by PCR using universal primers. The complex of pathogen-specific probes and cSA-SBD fusion protein was immobilized on the PHB-coated slide by microspotting. This DNA–protein complex microarray was able to successfully diagnose Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Furthermore, the specific pathogens could be diagnosed in the presence of other microorganisms. Thus, the DNA–protein complex microarray platform technology employing PHB and the SBD reported here can be widely used for the detection of DNA–DNA and DNA–biomolecule interactions without synthetic or chemical modification of biomolecules or solid surface.     

Ascorbic acid for homogenous redox buffering in electrospray ionization–mass spectrometry

Electrospray ionization (ESI) involves the dispersion of a liquid containing analytes of interest into a fine aerosol by applying a high potential difference to the sample solution with respect to a counter electrode. Thus, from the electrochemical point of view, the ESI source represents a two-electrode controlled-current electrochemical flow cell. The electroactive compounds part of the solvent sprayed may be altered by occurring electrolysis (oxidation in positive ion mode and reduction in negative ion mode). These reactions can be troublesome in the context of unknown identification and quantification. In the search for a simple, inexpensive, and efficient way to suppress electrochemical oxidation in positive ESI, the usability of ascorbic acid, hydroquinone, and glutathione for homogenous redox buffering was tested. Performance of the antioxidants was assessed by analyzing pharmaceutical compounds covering a broad range of functional groups prone to oxidation. Different emitter setups were applied for continuous infusion, flow injection, and liquid chromatography/mass spectrometry experiments. Best performance was obtained with ascorbic acid. In comparison to hydroquinone and glutathione, ascorbic acid offered superior antioxidant activity, a relatively inert oxidation product, and hardly any negative effect on the ionization efficiency of analytes. Furthermore, ascorbic acid suppressed the formation of sodiated forms and was able to induce charge state reduction. Only in the very special case of analyzing a compound isobaric to ascorbic acid, interference with the low-abundant [ascorbic acid+H](+) signal may become a point of attention.     

Glycol modified titanosiloxane as molecular precursor for homogenous titania–silica material: synthesis and characterization

Ti(OPrⁱ)₄ reacts with HOSi(O^tBu)₃ in anhydrous benzene in 1:1 and 1:2 molar ratios to afford alkoxy titanosiloxane precursors, [Ti(OPrⁱ)₃{OSi(O^tBu)₃}] (A) and [Ti(OPrⁱ)₂{OSi(O^tBu)₃}₂] (B), respectively. Further reactions of (A) or (B) with glycols in 1:1 molar ratio afforded six complexes of the types [Ti(OPrⁱ)(O–G–O){OSi(O^tBu)₃}] (1A–3A) and [Ti(O–G–O){OSi(O^tBu)₃}₂] (1B–3B), respectively [where G = (CH₂)₂ (1A, 1B); (CH₂)₃ (2A, 2B) and {CH₂CH₂CH(CH₃)} (3A, 3B)]. Both (A) and (B) are liquids while all the other products are viscous liquids which get solidified on ageing. Cryoscopic molecular weight measurements of the fresh products indicate their monomeric nature. FAB mass studies of (A) and (B) also indicate monomeric nature. However, FAB mass spectra of the two representative solids (1A) and (2B) suggest dimeric behavior of the glycolato derivatives. (A) distills at 85 °C/5 mm while other products get decomposed even under reduced pressure. TG analyses of (A), (B), (1A), and (1B) suggest formation of titania–silica materials at 200 °C for (A) and (B) and 350 °C for (1A) and (1B). The products have been characterized by elemental analyses, FTIR and ¹H, ¹³C & ²⁹Si-NMR techniques. All these products are soluble in common organic solvents indicating a homogenous distribution of the components on the molecular scale. The Si/Ti ratio of the oxide may be controlled easily by the composition of the starting precursors. Hydrolysis of the glycol modified derivative, (1A) by the Sol–Gel technique affords the desired homogenous titania–silica material, TiO₂·SiO₂ in nano-size while, the precursor (A) yields a non-stiochiometric silica doped titania material. However, pyrolysis of (A) yields nano-sized crystallites of TiO₂·SiO₂. All these materials were characterized by FTIR, powder XRD patterns, SEM images, and EDX analyses.     

Dichlorosilylene–hydrogen chloride complex: direct IR spectroscopic detection in argon matrix

A 1: 1 donor–acceptor complex between SiCl₂ and HCl was detected by matrix IR spectroscopy. The existence of the complex was previously predicted theoretically in the course of analysis of mechanisms of chemical vapor deposition (CVD) processes involving chlorosilanes. The quantum chemical calculations at the G4(MP₂) level confirmed the possibility of formation of only one stable complex upon the reaction of SiCl₂ with HCl. In addition to the complex of the simplest composition, complexes of SiCl₂ with HCl associates were observed upon matrix annealing. The only product formed upon the photolysis of the complexes of all types was trichlorosilane, a product of silylene insertion into the H–Cl bond.

     

Liquid chromatography–fluorescence detection for simultaneous analysis of sulfonamide residues in honey

A rapid, accurate LC analytical method has been developed for determination of eight sulfonamides (sulfacetamide, sulfapyridine, sulfamerazine, sulfamethoxypyridazine, sulfameter, sulfachloropyridazine, sulfamethoxazole and sulfadimethoxine) in honey. The sample was dissolved in phosphoric acid solution (pH 2). After filtration, the sample solution was cleaned by use of two solid-phase extraction (SPE) cartridges-an aromatic sulfonic cation-exchange cartridge and an Oasis HLB cartridge. The eight sulfonamides were then derivatized with fluorescamine and the derivatives were determined by LC with fluorescence detection at excitation and emission wavelengths of 405 and 495 nm, respectively. Average recoveries at three fortification levels in the range 0.02-0.50 mg kg(-1) in twelve different kinds of honey were 73.5-94.1% with coefficients of variation of 4.35-16.60%. The limit of detection (LOD) was 0.002 mg kg(-1) for sulfacetamide, sulfapyridine, sulfamerazine, and sulfamethoxypyridazine; that for sulfameter, sulfachloropyridazine, sulfamethoxazole and sulfadimethoxine was 0.005 mg kg(-1). The limit of quantitation (LOQ) was 0.005 mg kg(-1) for sulfacetamide, sulfapyridine, sulfamerazine, and sulfamethoxypyridazine; that for sulfameter, sulfachloropyridazine, sulfamethoxazole, and sulfadimethoxine was 0.010 mg kg(-1). The method is suitable for determination of multiresidue sulfonamides in the various kinds of honey.     

Techniques for direct experimental evaluation of structure–transport relationships in disordered porous solids

Determining structure–transport relationships is critical to optimising the activity and selectivity performance of porous pellets acting as heterogeneous catalysts for diffusion-limited reactions. For amorphous porous systems determining the impact of particular aspects of the void space on mass transport often requires complex characterization and modelling steps to deconvolve the specific influence of the feature in question. These characterization and modelling steps often have limited accuracy and precision. It is the purpose of this work to present a case-study demonstrating the use of a more direct experimental evaluation of the impact of pore network features on mass transport. The case study evaluated the efficacy of the macropores of a bidisperse porous foam structure on improving mass transport over a purely mesoporous system. The method presented involved extending the novel integrated gas sorption and mercury porosimetry method to include uptake kinetics. Results for the new method were compared with those obtained by the alternative NMR cryodiffusometry technique, and found to lead to similar conclusions. It was found that the experimentally-determined degree of influence of the foam macropores was in line with expectations from a simple resistance model for a disconnected macropore network.     

Development of a direct ELISA based on carboxy-terminal of penicillin-binding protein BlaR for the detection of β-lactam antibiotics in foods

β-Lactam antibiotics, including penicillins and cephalosporins, are commonly used in veterinary medicine. Illegal use and abuse of β-lactams could cause allergy and selected bacterial resistance. BlaR-CTD, the carboxy-terminal of penicillin-recognizing protein BlaR from Bacillus licheniformis ATCC 14580, was utilized in this study to develop a receptor-based ELISA for detection and determination of β-lactam antibiotics in milk, beef, and chicken. This assay was based on directly competitive inhibition of binding of horseradish peroxidase-labeled ampicillin to the immobilized BlaR-CTD by β-lactams. The assay was developed as screening test with the option as semiquantitative assay, when the identity of a single type of residual β-lactam was known. The IC₅₀ values of 15 β-lactam antibiotics, including benzylpenicillin, ampicillin, amoxicillin, dicloxacillin, oxacillin, nafcillin, cefapirin, cefoperazone, cefalotin, cefazolin, cefquinome, ceftriaxone, cefotaxime, cefalexin, ceftiofur and its metabolite desfuroylceftiofur were evaluated and ranged from 0.18 to 170.81 μg L^?1. Simple sample extraction method was carried out with only phosphate-buffered saline, and the recoveries of selected β-lactam antibiotics in milk, beef, and chicken were in the range of 53.27 to 128.29 %, most ranging from 60 to 120 %. The inter-assay variability was below 30 %. Limits of detection in milk, beef, and chicken muscles with cefquinome matrix calibration were 2.10, 30.68, and 31.13 μg kg^?1, respectively. This study firstly established a rapid, simple, and accurate method for simultaneous detection of 15 β-lactams in edible tissues, among which 11 β-lactams controlled by European Union could be detected below maximum residue limits.

Cerium oxide nanofiber–based electrochemical immunosensor for detection of sepsis in biological fluid

Sepsis causes life-threatening complications with the highest burden of death and medical expenses in hospitals worldwide. Despite the progression of targeted therapies for sepsis, the challenge of early diagnosis of sepsis-related biomarkers remains. The analysis of the TNF-α and sTREM-1 in biological fluids provides essential information for effective treatments. In this work, we report developing an electrochemical immunosensor for the rapid detection of TNF-α and sTREM-1 proteins in human plasma samples. First, using the electrospinning process, cerium oxide nanofibers were synthesized. Subsequently, the antibodies corresponding to the targeted proteins are immobilized onto the surface-functionalized working electrodes using NHS/EDC chemistry. The proposed immunosensor’s performance in a biological fluid was assessed using an analytical electrochemistry approach. The limit of detection for the electrochemical immunosensors was 0.51 and 0.41 pg/mL for TNF-α and sTREM-1, respectively, with high selectivity and sensitivity for the use as a point of care device.

     

Reflection–absorption infrared sensing device for detection of semivolatile aromatic compounds in soils

In this article, a new IR-sensing device is described for the examination of chlorinated aromatic compounds in soils. To prepare this sensing device, a 20-mL glass vial was modified for use in the analysis of soil samples by conventional Fourier-transform infrared (FT-IR) spectroscopy. In this sampling device, an aluminium plate coated with a hydrophobic film was placed on top of the cap of the sample vial to absorb the analytes that evaporated from the soil matrix. After this absorption process was complete, the cap was placed in an FT-IR spectrometer, and the absorbed analytes were detected in the reflection–absorption (RA) mode. To accelerate the rate of evaporation of the analytes, the soil samples were heated to various temperatures. Meanwhile, other factors, such as the moisture content, sampling time, thickness of the hydrophobic film, and the volatilities and concentrations of the analytes, were also examined to optimize the analytical conditions. The results indicated that the time required to reach equilibrium conditions was short, and evaporation/absorption could be achieved within 10?min. With a water content of 10% (v/w) or less, the intensities of the analytical signals were increased greatly when compared with those of dry samples; when the water content was above 10% (v/w), these intensities decreased, partially as a result of the heating efficiency. After examining the compounds that had different vapour pressures, the analytical results indicated that this method was applicable to the examination of compounds that had vapour pressures below 1.0?Torr. Using the optimal conditions determined in this study, the detection limits for semivolatile aromatic compounds were lower than 100?ng/g, and the regression coefficients of the standard curves for compounds that had a vapour pressure lower than 1.0?Torr were larger than 0.99 in the concentration range of 1–100?µg/g.     

First-principles determination of molecular conformations of indolizidine (−)-235B′ in solution

Indolizidine (?)-235B′ is a particularly interesting natural product, as it is the currently known, most potent and subtype-selective open-channel blocker of the α4β2 nicotinic acetylcholine receptor (nAChR). In the current study, extensive first-principles electronic structure calculations have been carried out in order to determine the stable molecular conformations and their relative free energies of the protonated and deprotonated states of (?)-235B′ in the gas phase, in chloroform, and in aqueous solution. The ¹H and ¹³C NMR chemical shifts calculated using the computationally determined dominant molecular conformation of the deprotonated state are all consistent with available experimental NMR spectra of (?)-235B′ in chloroform, which suggests that the computationally determined molecular conformations are reasonable. Our computational results reveal for the first time that two geminal H atoms on carbon-3 (C3) of (?)-235B′ have remarkably different chemical shifts (i.e., 3.24 and 2.03 ppm). The computational results help one to better understand and analyze the experimental ¹H NMR spectra of (?)-235B′. The finding of remarkably different chemical shifts of two C3 geminal H atoms in a certain molecular conformation of (?)-235B′ may also be valuable in analysis of NMR spectra of other related ring-containing compounds. In addition, the pK _a of (?)-235B′ in aqueous solution is predicted to be ~9.7. All of the computational results provide a solid basis for future studies of the microscopic and phenomenological binding of various receptor proteins with the protonated and deprotonated structures of this unique open-channel blocker of α4β2 nAChRs. This computational study also demonstrates how one can appropriately use computational modeling and spectroscopic analysis to address the structural and spectroscopic problems that cannot be addressed by experiments alone.     

Manifestation of side-chain interactions in solution properties of “loose” PI-graft-PMMA molecular brushes

The molecular properties of polymer brushes composed of polyimide with polymerization degree 50 and loosely grafted poly(methyl methacrylate) chains of variable length (PI-graft-PMMA) were studied by viscometry, dynamic light scattering, and equilibrium electro-optical Kerr effect methods in a diluted solution. It was established that the intrinsic viscosity and hydrodynamic dimension of PI-graft-PMMA copolymers increase when the electro-optical Kerr constant decreases with the elongation of PMMA side chains in the range of 40–110 monomer units. The observed difference in the solution properties of the copolymers was explained by their side-chain interactions in spite of a large distance between the neighboring grafting points typical of “loose brushes.” A strong effect of the chain rigidity and dipole structure on solution properties of the studied samples was demonstrated. The Kuhn segment lengths for PI-graft-PMMA copolymers were estimated to vary in the range 3.8–12.1?nm.     

Bimetallic gold–silver nanoplate array as a highly active SERS substrate for detection of streptavidin/biotin assemblies

The silver-modified gold nanoplate arrays as bimetallic surface-enhanced Raman scattering (SERS) substrates were optimized for the surface-enhanced Raman detection of streptavidin/biotin monolayer assemblies. The bimetallic gold–silver nanoplate arrays were fabricated by coating silver nanoparticles uniformly on the gold nanoplate arrays. Depending on silver nanoparticle coating, the localized surface plasmon resonance (LSPR) peak of the bimetallic gold–silver nanoplate arrays blue-shifted and broadened significantly. The common probe molecule, Niel Blue A sulfate (NBA) was used for testing the SERS activity of the bimetallic gold–silver nanoplate arrays. The SERS intensity increased with the silver nanoparticle coating, due to a large number of hot spots and nanoparticle interfaces. The platforms were tested against a monolayer of streptavidin functionalized over the bimetallic gold–silver nanoplate arrays showing that good quality spectra could be acquired with a short acquisition time. The supramolecular interaction between streptavidin (strep) and biotin showed subsequent modification of Raman spectra that implied a change of the secondary structure of the host biomolecule. And the detection concentration for biotin by this method was as low as 1.0 nM. The enhanced SERS performance of such bimetallic gold–silver nanoplate arrays could spur further interest in the integration of highly sensitive biosensors for rapid, nondestructive, and quantitative bioanalysis, particularly in microfluidics.