Chronocoulometric determination of urea in human serum using an inkjet printed biosensor

A biosensor for the determination of urea in human serum was fabricated using a combination of inkjet printed polyaniline nanoparticles and inkjet printed urease enzyme deposited sequentially onto screen-printed carbon paste electrodes. Chronocoulometry was used to measure the decomposition of urea via the doping of ammonium at the polyaniline-modified electrode surface at -0.3 V vs. Ag/AgCl. Ammonium could be measured in the range from 0.1 to 100 mM. Urea could be measured by the sensor in the range of 2-12 mM (r(2)=0.98). The enzyme biosensor was correlated against a spectrophotometric assay for urea in 15 normal human serum samples which yielded a correlation coefficient of 0.85. Bland-Altman plots showed that in the range of 5.8-6.6 mM urea, the developed sensor had an average positive experimental bias of 0.12 mM (<2% RSD) over the reference method.     

Electrochemical preparation of distinct polyaniline nanostructures by surface charge control of polystyrene nanoparticle templates

A family of nanostructured polyaniline (PANI) materials including polystyrene (PS)/PANI core/shell particles, PANI hollow spheres, PANI/PS nanocomposite and nanoporous PANI, were conveniently prepared by surface charge control of PS nanoparticle templates which resulted in different polymer growth mechanisms when PANI was electropolymerized around the templates.     

Microwave digestion of sediment, soils and urban particulate matter for trace metal analysis

A microwave digestion technique was developed to determine the content of nine heavy metals in sediments and soils. The digests were subsequently analysed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The metals determined were Ca, Mg, Fe, Mn, Zn, Cr, Cd, Cu, Pb and V. The digestion was achieved by using an acid mixture of HNO₃, HF and distilled H₂O. The experimental study was conducted using four standard reference materials (SRMs): sewage sludge (LGC6136), marine sediment (PACS-1), urban particulate matter (NIST 1648) and coal carbonisation site soil (LGC6138). Two different programs were examined to determine which was optimal for the digestion of real environmental samples. The accuracy and precision of the two digestion programs for the analysis of the SRMs were compared. From the results obtained, the microwave program providing a maximum of power of 650 W and a cycle time of 51 min resulted in the best analytical performance. The experimental results obtained were in good agreement with the certified values and demonstrated that the proposed method is precise and accurate.     

Printing polyaniline for sensor applications

In recent years, much research has focused on the development of low-cost, printed electrochemical sensor platforms for environmental monitoring and clinical diagnostics. Much effort in this area has been based on utilising the redox properties of conducting polymers, particularly polyaniline (PANI). In tackling the inherent lack of processability exhibited by these materials, several groups have examined various mass-amenable fabrication approaches to obtain suitable thin films of PANI for sensing applications. Specifically, the approaches investigated over the years include the in situ chemical synthesis of PANI, the use of sulphonated derivatives of PANI and the synthesis of aqueousbased nano-dispersions of PANI. Nano-dispersions have shown a great deal of promise for sensing applications, given that they are inkjet-printable, facilitating the patterning of conducting polymer directly to the substrate. We have shown that inkjet-printed films of PANI can be finely controlled in terms of their two-dimensional pattern, thickness, and conductivity, highlighting the level of precision achievable by inkjet printing. Utilising these nanomaterials as inkjet-printable inks opens novel, facile, and economical possibilities for conducting polymer-printed electronic applications in areas of sensing, but also many other application areas such as energy storage, displays, organic light-emitting diodes. Given that inkjet-printing is a scalable manufacturing technique, it renders possible the large-scale production of devices such as sensors for a range of applications. Several successes have emerged from our work and from the work of others in the area of applying PANI in low-cost sensor applications, which is the focus of this review.     

Algebraic properties of Riordan subgroups

Journal of Algebraic Combinatorics - We present properties of the group structure of Riordan arrays. We examine similar properties among known Riordan subgroups, and from this, we define...     

Self-assembly of the 3-aminopropyltrimethoxysilane multilayers on Si and hysteretic current–voltage characteristics

We report the deposition of 3-aminopropyltrimethoxysilane (APTMS) multilayers on SiO_x/Si(p⁺⁺) substrates by a layer-by-layer self-assembly process. The multilayers were grafted in a glove box having nitrogen ambient with both humidity and oxygen contents <1 ppm using APTMS solutions prepared in an anhydrous toluene. Deposition of the multilayers has been carried out as a function of solution concentration and grafting time. Characterization of the multilayers using static de-ionized water contact angle, ellipsometry, X-rayphotoelectron spectroscopy and atomic force microscope measurements revealed that self-assembling of the multilayers takes place in two distinct stages: (i) the first APTMS monolayer chemisorbs on a hydroxylated oxide surface by a silanization process and, (ii) the surface amino group of the first monolayer chemisorbs the hydrolyzed silane group of other APTMS molecules present in the solution, leading to the formation of a bilayer. The second stage is a self-replicating process that results in the layer-by-layer self-assembly of the multilayers with trapped NH₃ ⁺ ions. The current–voltage characteristics of the multilayers exhibit a hysteresis effect along with a negative differential resistance, suggesting their potential application in the molecular memory devices. A possible mechanism for the observed hysteresis effect based on filling and de-filling of the NH₃ ⁺ acting as traps is presented. PACS 73.30.+y     

A review of recent trends in polymer characterization using non-destructive vibrational spectroscopic modalities and chemical imaging

This review focuses on the recent developments in vibrational spectroscopy and chemical imaging (i.e. Raman, Near Infrared, Mid Infrared) to characterize polymers in diverse forms, their behaviour and transient phenomenon. First, important polymeric properties and traditional methods of their characterization are outlined. Then relative advantages & disadvantages have been presented of different characterization methods are presented. This is followed by a detailed review of applications of chemical imaging and spectroscopic techniques in polymer characterization, including the limitations encountered. The article ends with a discussion on the future of chemical imaging with regards to polymer characterization.     

Extraction of lifetime distributions from fluorescence decays with application to DNA-base analogues

Several important aspects of fluorescence decay analysis are addressed and tested against new experimental measurements. A simulated-annealing method is described for deconvoluting the instrument response function from a measured fluorescence decay to yield the true decay, which is more convenient for subsequent fitting. The method is shown to perform well against the conventional approach, which is to fit a convoluted fitting function to the experimentally measured decay. The simulated annealing approach is also successfully applied to the determination of an instrument response function using a known true fluorescence decay (for rhodamine 6G). The analysis of true fluorescence decays is considered critically, focusing specifically on how a distribution of decay constants can be incorporated in to a fit. Various fitting functions are applied to the true fluorescence decays of 2-aminopurine in water-dioxane mixtures, in a dinucleotide, and in DNA duplexes. It is shown how a suitable combination of exponential decays and non-exponential decays (based on a Γ distribution of decay constants) can provide fits of equal quality to the conventional multi-exponential fits used in the majority of previous studies, but with fewer fitting parameters. Crucially, the new approach yields decay-constant distributions that are physically more meaningful than those corresponding to the conventional multi-exponential fit. The methods presented here should find wider application, for example to the analysis of transient-current or optical decays and in F?rster resonance energy transfer (FRET).