Nanostructured titanium nitride for highly sensitive localized surface plasmon resonance biosensing

Titanium nitride (TiN) as an alternative plasmonic ceramic material with superb properties including high hardness, outstanding corrosion resistance and excellent biocompatibility, has exhibited great potential for optical biochemical sensing applications. By sputtering about 35 nm–50 nm TiN on glass (f-TiN), the surface was found to provide sensing capability toward NaCl solution through the phenomenon of surface plasmon resonance. When the TiN film of about 27 nm–50 nm in thickness was sputtered onto a roughened glass surface (R–TiN), the sensing capability was improved. This was further improved when holes at nanoscale were created in the TiN film of about 19 nm–27 nm in thickness (NH–TiN). The roughened surface and nanohole patterns provided confinement of surface plasmons and significantly improved the sensitivity toward the local refractive index changes. In detail, the calculated refractive index resolution (RIR) of the optimal NH–TiN sensors for NaCl was found to be 9.5 × 10⁻⁸ refractive index unit (RIU), which had outperformed the f-TiN and R–TiN sensors. For biosensing, the optimized NH–TiN sensor was found to be capable to detect both small and large biomolecules, i.e. biotin (molecular weight of 244.3 g/mol) and human IgG (160,000 g/mol), in a label-free manner. Especially, the NH–TiN sensor significantly improved sensitivity in detecting small molecules due to the localized plasmonic confinement of electromagnetic field. Combining with the excellent mechanical and durability properties of TiN, the proposed NH–TiN can be a strong candidate for plasmonic biosensing applications.     

Electrochemical synthesis of a novel poly(2,5-dimethoxy aniline) nanorod for ultrasensitive glucose biosensor application

We report for the first time a rapid electrochemical synthesis of one-dimensional poly(2,5-dimethoxyaniline) nanorods (PDMA-NR) in the presence of surfactant. FE-SEM and TEM images confirm the PDMA-NR formation and the average diameter of single rod sizes in the range of ∼200–300 nm. An enzymatic glucose biosensor was fabricated through immobilizing glucose oxidase (GOx) into PDMA-NR matrix. The amperometric current response of PDMA-NR/GOx to glucose is linear in the concentration range between 1 and 10 μM with a detection limit of 0.5 μM (S/N = 3). The PDMA-NR/GOx electrode possesses high sensitivity (5.03 μA/μM), selectivity, stability, and reproducibility toward glucose.     

Functionalized polythiophenes: Recognition materials for chemosensors and biosensors of superior sensitivity,selectivity, and detectability

Recent progress in derivatized polythiophenes (PTs) and polymerized thiophene derivatives is reviewed, with emphasis on applications that involve devising and fabricating selective and sensitive chemo- and biosensors. The literature results summarized show that appreciable selectivity is attained if derivatized polythiophene films are used as recognition units. Illustrative examples include determination of polyatomic anions and metal cations, volatile organic compounds, and biocompounds including glucose and nucleic acids. Moreover, progress is presented in the use of derivatized thiophenes as functional monomers for preparation of molecularly imprinted polymers (MIPs) for chemosensing. Thanks to the range of synthetic procedures developed for preparation of derivatized PTs, these electronically conducting polymers have served as excellent recognition units for fabricating highly sensitive and selective chemosensors for target analytes.     

DNA-directed immobilization of horseradish peroxidase onto porous SiO2optical transducers

ABSTRACT: Multifunctional porous Si nanostructure is designed to optically monitor enzymatic activity of Horseradish Peroxidase. First, an oxidized PSi optical nanostructure, a Fabry-Perot thin film, is synthesized and is used as the optical transducer element. Immobilization of the enzyme onto the nanostructure is performed through DNA-Directed Immobilization. Preliminary studies demonstrate high enzymatic activity levels of the immobilized Horseradish Peroxidase, while maintaining its specificity. The catalytic activity of the enzymes immobilized within the porous nanostructure is monitored in real time by reflective interferometric Fourier transform spectroscopy. We show that we can easily regenerate the surface for consecutive biosensing analysis by mild de-hybridization conditions.     

Rapid and simultaneous determination of tetracycline and cefixime antibiotics by mean of gold nanoparticles-screen printed gold electrode and chemometrics tools

The screen-printed gold electrode (SPGE) modified with the formation of self-assembly monolayer (SAM) of cysteine (Cys) on gold-nanoparticles (Au_nano) was utilized for rapid and simultaneous determination of tetracycline and cefixime antibiotics by square wave voltammetry (SWV). Electrochemical investigation and characterization of the modified electrode was achieved using cyclic voltammetry (CV) and scanning electron microscopy (SEM). A principal component artificial neural network (PCANN) with three layer back-propagation network was utilized for the analysis of the voltammogram data. It is possible to simultaneously determine the tetracycline and cefixime concentrations in the ranges of 10⁻⁵ and 10⁻³ mol L⁻¹, under the optimum conditions. Moreover the SPGE-Au_nano-Cys biosensor together with chemometrics tools was successfully applied to the determination of tetracycline and cefixime in biological fluids, which may provide a promising alternative in routine biosensing applications.     

Dietary supplement for energy and reduced appetite containing the β-agonist isopropyloctopamine leads to heart problems and hospitalisations

In 2013 the Dutch authorities issued a warning against a dietary supplement that was linked to 11 reported adverse reactions, including heart problems and in one case even a cardiac arrest. In the UK a 20-year-old woman, said to have overdosed on this supplement, died. Since according to the label the product was a herbal mixture, initial LC-MS/MS analysis focused on the detection of plant toxins. Yohimbe alkaloids, which are not allowed to be present in herbal preparations according to Dutch legislation, were found at relatively high levels (400–900 mg kg^–1). However, their presence did not explain the adverse health effects reported. Based on these effects the supplement was screened for the presence of a β-agonist, using three different biosensor assays, i.e. the validated competitive radioligand β2-adrenergic receptor binding assay, a validated β-agonists ELISA and a newly developed multiplex microsphere (bead)-based β-agonist assay with imaging detection (MAGPIX^®). The high responses obtained in these three biosensors suggested strongly the presence of a β-agonist. Inspection of the label indicated the presence of N-isopropyloctopamine. A pure standard of this compound was bought and shown to have a strong activity in the three biosensor assays. Analysis by LC-full-scan high-resolution MS confirmed the presence of this ‘unknown known’ β3-agonist N-isopropyloctopamine, reported to lead to heart problems at high doses. A confirmatory quantitative analysis revealed that one dose of the preparation resulted in an intake of 40–60 mg, which is within the therapeutic range of this compound. The case shows the strength of combining bioassays with chemical analytical techniques for identification of illegal pharmacologically active substances in food supplements.     

Study of the biosensor based on platinum nanoparticles supported on carbon nanotubes and sugar–lectin biospecific interactions for the determination of glucose

Highly sensitive electrochemical platform based on Pt nanoparticles supported on carbon nanotubes (Pt_nano-CNTs) and sugar–lectin biospecific interactions is developed for the direct electrochemistry of glucose oxidase (GOD). Firstly, Pt_nano-CNTs nanocomposites were prepared in the presence of carbon nanotubes (CNTs), and then the mixture was cast on a glassy carbon electrode (GCE) using chitosan as a binder. Thereafter, concanavalin A (Con A) was adsorbed onto the precursor film by the electrostatic force between positively charged chitosan and the negatively charged Con A. Finally, the multilayers of Con A/GOD films were prepared based on biospecific affinity of Con A and GOD via layer-by-layer (LBL) self-assembly technique. The electrochemical behavior of the sensor was studied using cyclic voltammetry and chronoamperometry. The electrochemical parameters of GOD in the film were calculated with the results of the electron transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (k_s) as 0.5 and 5.093 s⁻¹, respectively. Experimental results show that the biosensor responded linearly to glucose in the range from 1.2 × 10⁻⁶ to 2.0 × 10⁻³ M, with a detection limit of 4.0 × 10⁻⁷ M under optimized conditions.     

A highly selective electrochemical biosensor for Hg using hemin as a redox indicator

A highly selective electrochemical biosensor for the detection of Hg²⁺ in aqueous solution has been developed. This sensor is based on the strong and specific binding of Hg²⁺ by two DNA thymine bases (T–Hg²⁺–T). The hemin worked as a redox indicator to generate a readable electrochemical signal. Short oligonucleotide strands containing 5 thymine (T₅) were used as probe. Thiolated T₅ strands were self-assembled through Au–S bonding on gold electrode. In the presence of Hg²⁺, the specific coordination between Hg²⁺ and thymine bases resulted in more stable and porous arrangement of oligonucleotide strands, so hemin could be adsorbed on the surface of gold electrode and produced an electrochemical signal, which was monitored by differential pulse voltammetry (DPV). The DPV showed a linear correlation between the signal and the concentration of Hg²⁺ over the range 0–2 μM (R² = 0.9983) with a detection limit of 50 nM. The length of probe DNA had no significant impact on the sensor performance. This electrochemical biosensor could be widely used for selective detection of Hg²⁺.     

Layer by layer assembly of glucose oxidase and thiourea onto glassy carbon electrode: Fabrication of glucose biosensor

For the first time a novel, simple and facile approach is described to construct highly stable glucose oxidase (GOx) multilayer onto glassy carbon (GC) electrode using thiourea (TU) as a covalent attachment cross-linker. The layer by layer (LBL) attachment process was confirmed by cyclic voltammetry, electrochemical impedance spectroscopy and Fourier transform infrared reflection spectroscopy (FT-IR-RS) techniques. Immobilized GOx shows excellent electrocatalytic activity toward glucose oxidation using ferrocenemethanol as artificial electron transfer mediator and biosensor response was directly correlated to the number of bilayers. The surface coverage of active GOx per bilayer, heterogeneous electron transfer rate constant (k_s) and Michaelis–Menten constant (K_M), of immobilized GOx were 1.50 × 10⁻¹² mol cm⁻², 9.2 ± 0.5 s⁻¹ and 3.42(±0.2) mM, respectively. The biosensor constructed with four-bilayers of TU/GOx showed good stability, high reproducibility, long life-time, fast amperometric response (5 s) with the high sensitivity of 5.73 μA mM⁻¹ cm⁻² and low detection limit of 6 μM at concentration range up to 5.5 mM.     

Rapid and direct determination of fructose in food: A new osmium-polymer mediated biosensor

This paper describes the development and performance of a new rapid amperometric biosensor for fructose monitoring in food analysis. The biosensor is based on the activity of fructose dehydrogenase (FDH) immobilised into a carbon nanotube paste electrode according to two different procedures. The direct wiring of the FDH in a highly original osmium-polymer hydrogel was found to offer a better enzyme entrapment compared to the immobilisation of the enzyme in an albumin hydrogel. The optimised biosensor required only 5 U of FDH and kept the 80% of its initial sensitivity after 4 months. During this time, the biosensor showed a detection limit for fructose of 1 μM, a large linear range between 0.1 and 5 mM, a high sensitivity (1.95 μA cm⁻² mM), good reproducibility (RSD = 2.1%) and a fast response time (4 s).