Evaluation of two sterically directed attachments of biomolecules on a coaxial nanofibre membrane to improve the development of optical biosensors.

In this study, we have optimised the sterically directed attachment of biomolecules on the surface of coaxial membranes prepared by co-electrospinning which have been proved to be a material with very high performance for the development of biosensors with optical oxygen transduction. Uricase has been used as model enzyme. Two sterically directed strategies: a) covalent attachment via maleimide, and b) affinity bonding via biotin-streptavidin interaction, have been tested in order to preserve the enzymatic activity of uricase and to improve the analytical figures of merits on the determination of uric acid. The best results were obtained with biotin-streptavidin affinity interaction and using a biotinylation reagent containing a polyethylene glycol chain. The developed biosensor showed high sensitivity towards uric acid with a detection limit of 0.5 µM, a quantification limit of 1.8 µM and linear range from 1.8 to 250 µM. The applicability of the membrane as biosensor with optical oxygen transduction was proved by determining uric acid in serum samples. The obtained results showed a good correlation (0.999) with those obtained by an external reference laboratory.

A multifunctional material based on co-electrospinning for developing biosensors with optical oxygen transduction.

A multifunctional material based on co-electrospinning has been developed as a basic material for the development of biosensors with optical oxygen transduction. It is based on coaxial nanofibres: inner fibres containing an oxygen sensitive dye and outer fibres containing aldehyde groups to allow the formation of Schiff bases with the amino groups of the enzyme. The resulting material preserves the oxygen sensing properties of the inner optical transducer as well as exhibits a high capacity for immobilizing molecules on its surface. Uricase has been selected as model enzyme and several parameters (temperature, pH, reaction time, buffer, and enzyme concentration) have been optimised to demonstrate the versatility of this novel multifunctional material in the development of biosensors with optical oxygen transduction for determining uric acid in serum samples. It suggests that the proposed multifunctional material can provide a promising multifunctional platform for biosensing applications.

A novel optical biosensor for direct and selective determination of serotonin in serum by Solid Surface-Room Temperature Phosphorescence.

This paper describes a novel biosensor which combines the use of nanotechnology (non-woven nanofibre mat) with Solid Surface-Room Temperature Phosphorescence (SS-RTP) measurement for the determination of serotonin in human serum. The developed biosensor is simple and can be directly applied in serum; only requires a simple clean-up protocol. Therefore it is the first time that serotonin is analysed directly in serum with a non-enzymatic technique. This new approach is based on the covalent immobilization of serotonin directly from serum on a functional nanofibre material (Tiss®-Link) with a preactivated surface for direct covalent immobilization of primary and secondary amines, and the subsequent measurement of serotonin phosphorescent emission from the solid surface. The phosphorescent detection allows avoiding the interference from any fluorescence emission or scattering light from any molecule present in the serum sample which can be also immobilised on the nanofibre material. The determination of serotonin with this SS-RTP sensor overcomes some limitations, such as large interference from the matrix and high cost and complexity of many of the methods widely used for serotonin analysis. The potential applicability of the sensor in the clinical diagnosis was demonstrated by analysing serum samples from seven healthy volunteers. The method was validated with an external reference laboratory, obtaining a correlation coefficient of 0.997 which indicates excellent correlation between the two methods.

Novel optical sensing film based on a functional nonwoven nanofibre mat for an easy, fast and highly selective and sensitive detection of tryptamine in beer.

In this paper, the combination of Solid Surface-Room Temperature Phosphorescence (SS-RTP) and nanotechnology has led to a new approach in the detection of biogenic amines in complex matrices. This novel approach allows, for the first time, the direct determination of the concentration of tryptamine in beers. The novelty of the proposed optical sensor resides in its simplicity, rapidity, absence of complex chromatographic separation, sample clean-up, preconcentration, and derivatization protocols. Therefore, this novel methodology simplifies and reduces considerably the time and cost of the analysis, resolving the two major problems of the determination of tryptamine in beer up to now: low sensitivity and matrix effects. The proposed sensor is based on a novel white, uncharged, and non-luminescent functional nonwoven nanofibre mat (Tiss®-Link) formed by hydrophilic nanofibres of 300 nm of diameter functionalized with a high concentration of active vinyl groups (330 µmol g(-1)). It is used to carry out a kinetically controlled covalent immobilisation of tryptamine via Michael type-reaction. The transduction of the sensor is phosphorescence; the covalently immobilized tryptamine is quantified by SS-RTP, obtaining a detection limit of 6 ng mL(-1) with short response times (15 min). The applicability of the sensor was demonstrated by analysing tryptamine in 10 different varieties of beers, obtaining recovery percentages close to 100%.