Raquel B. Queirós

Evanescent wave DNA-aptamer biosensor based on long period gratings for the specific recognition of E. coli outer membrane proteins

An evanescent wave fiber optic sensor for detection of Escherichia coli (E. coli) outer membranes proteins (EcOMPs) using long period gratings (LPGs) as a refractometric platform is presented. The sensing probes were attained by the functionalization of LPGs inscribed in single mode fiber using two different methods of immobilization; electrostatic assembly and covalent binding. The resulting label-free configuration enabled the specific recognition of EcOMPs in water by monitoring the resonance wavelength shift due to refractive index changes induced by binding events. The sensors displayed linear responses in the range of 0.1 nM to 10 nM EcOMPs with sensitivities of -0.1563±0.005 nm decade(-1) [EcOMP, M] (electrostatic method) and -0.1597±0.004 nm decade(-1) [EcOMP, M] (covalent method). The devices could be regenerated (under low pH conditions) with a deviation less than 0.1% for at least three subsequent detection events. The sensors were also applied to spiked environmental water samples.

Microcystin-LR detection in water by the Fabry–Pérot interferometer using an optical fibre coated with a sol–gel imprinted sensing membrane

Cyanobacteria deteriorate the water quality and are responsible for emerging outbreaks and epidemics causing harmful diseases in Humans and animals because of their toxins. Microcystin-LR (MCT) is one of the most relevant cyanotoxin, being the most widely studied hepatotoxin. For safety purposes, the World Health Organization recommends a maximum value of 1 μg L(-1) of MCT in drinking water. Therefore, there is a great demand for remote and real-time sensing techniques to detect and quantify MCT. In this work a Fabry-Pérot sensing probe based on an optical fibre tip coated with a MCT selective thin film is presented. The membranes were developed by imprinting MCT in a sol-gel matrix that was applied over the tip of the fibre by dip coating. The imprinting effect was obtained by curing the sol-gel membrane, prepared with (3-aminopropyl) trimethoxysilane (APTMS), diphenyl-dimethoxysilane (DPDMS), tetraethoxysilane (TEOS), in the presence of MCT. The imprinting effect was tested by preparing a similar membrane without template. In general, the fibre Fabry-Pérot with a Molecular Imprinted Polymer (MIP) sensor showed low thermal effect, thus avoiding the need of temperature control in field applications. It presented a linear response to MCT concentration within 0.3-1.4 μg L(-1) with a sensitivity of -12.4±0.7 nm L μg(-1). The corresponding Non-Imprinted Polymer (NIP) displayed linear behaviour for the same MCT concentration range, but with much less sensitivity, of -5.9±0.2 nm L μg(-1). The method shows excellent selectivity for MCT against other species co-existing with the analyte in environmental waters. It was successfully applied to the determination of MCT in contaminated samples. The main advantages of the proposed optical sensor include high sensitivity and specificity, low-cost, robustness, easy preparation and preservation.

Assessing and comparing the total antioxidant capacity of commercial beverages: application to beers, wines, waters and soft drinks using TRAP, TEAC and FRAP methods.

This work measures and tries to compare the Antioxidant Capacity (AC) of 50 commercial beverages of different kinds: 6 wines, 12 beers, 18 soft drinks and 14 flavoured waters. Because there is no reference procedure established for this purpose, three different optical methods were used to analyse these samples: Total Radical trapping Antioxidant Parameter (TRAP), Trolox Equivalent Antioxidant Capacity (TEAC) and Ferric ion Reducing Antioxidant Parameter (FRAP). These methods differ on the chemical background and nature of redox system. The TRAP method involves the transfer of hydrogen atoms while TEAC and FRAP involves electron transfer reactions. The AC was also assessed against three antioxidants of reference, Ascorbic acid (AA), Gallic acid (GA) and 6-hydroxy-2,5,7,8-tetramethyl- 2-carboxylic acid (Trolox). The results obtained were analyzed statistically. Anova one-way tests were applied to all results and suggested that methods and standards exhibited significant statistical differences. The possible effect of sample features in the AC, such as gas, flavours, food colouring, sweeteners, acidity regulators, preservatives, stabilizers, vitamins, juice percentage, alcohol percentage, antioxidants and the colour was also investigated. The AC levels seemed to change with brand, kind of antioxidants added, and kind of flavour, depending on the sample. In general, higher ACs were obtained for FRAP as method, and beer for kind of sample, and the standard expressing the smaller AC values was GA.

Aptamer-based fiber sensor for thrombin detection

Abstract. The detection of thrombin based on aptamer binding is studied using two different optical fiber-based configurations: long period gratings coated with a thin layer of titanium dioxide and surface plasmon resonance devices in optical fibers coated with a multilayer of gold and titanium dioxide. These structures are functionalized and the performance to detect thrombin in the range 10 to 100 nM is compared in transmission mode. The sensitivity to the surrounding refractive index (RI) of the plasmonic device is higher than 3100  nm RIU−1 in the RI range 1.335 to 1.355, a factor of 20 greater than the sensitivity of the coated grating. The detection of 10 nM of thrombin was accomplished with a wavelength shift of 3.5 nm and a resolution of 0.54 nM.

Fiber optical beam shaping using polymeric structures

A method to control the output intensity profile of optical fibers is presented. Using guided wave photopolymerization in multimode structures the fabrication with modal assisted shaping of polymeric micro lenses is demonstrated. Results showing that a given linear polarized mode can be selectively excited controlling the intensity distribution at the fiber tip are presented. This pattern is then reproduced in the polymeric micro structure fabricated at the fiber tip thus modulating its output intensity distribution. Such structures can therefore be used to obtain at the fiber tip predetermined intensity patterns for attaining optical trapping or patterned illumination.

Optical cavity fibre sensor for detection of microcystin-LR in water

The deterioration of water quality by Cyanobacteria causes outbreaks and epidemics associated with harmful diseases in Humans and animals because of the released toxins. Microcystin-LR (mcyst) is one of the most widely studied hepatotoxin and World Health Organization recommends a maximum value of 1 μg L-1 of mcyst in drinking-water. Therefore, there is a great demand for remote, real-time sensing techniques to detect and quantify the presence of mcyst. In this work a Fabry-Perot sensing probe based on a fibre tip coated with a mcyst sensitive thin film is presented. Highly specific recognition membranes, using sol-gel based Molecular Imprinted Polymers (MIPs), were developed to quantify microcystins in water, showing great potential in the analysis of this kind of samples. The fibre Fabry-Perot MIP sensor shows a linear response to mcyst concentration with a sensitivity of -13.2 ±} 0.4 nm L μg-1.

DNA-Aptamer optical biosensors based on a LPG-SPR optical fiber platform for point-of-care diagnostic

Surface Plasmon Resonance (SPR) is the base for some of the most sensitive label free optical fiber biosensors. However, most solutions presented to date require the use of fragile fiber optic structure such as adiabatic tapers or side polished fibers. On the other hand, long-period fiber gratings (LPG) present themselves as an interesting solution to attain an evanescent wave refractive index sensor platform while preserving the optical fiber integrity. The combination of these two approaches constitute a powerful platform that can potentially reach the highest sensitivities as it was recently demonstrated by detailed theoretical study [1, 2]. In this work, a LPG-SPR platform is explored in different configurations (metal coating between two LPG – symmetric and asymmetric) operating in the telecom band (around 1550 nm). For this purpose LPGs with period of 396 μm are combined with tailor made metallic thin films. In particular, the sensing regions were coated with 2 nm of chromium to improve the adhesion to the fiber and 16 nm of gold followed by a 100 nm thick layer of TiO2 dielectric material strategically chosen to attain plasmon resonance in the desired wavelength range. The obtained refractometric platforms were then validated as a biosensor. For this purpose the detection of thrombin using an aptamer based probe was used as a model system for protein detection. The surface of the sensing fibers were cleaned with isopropanol and dried with N2 and then the aminated thrombin aptamer (5’-[NH2]- GGTTGGTGTGGTTGG-3’) was immobilized by physisorption using Poly-L-Lysine (PLL) as cationic polymer. Preliminary results indicate the viability of the LPFG-SPR-APTAMER as a flexible platforms point of care diagnostic biosensors.

Emerging (Bio)Sensing Technology for Assessing and Monitoring Freshwater Contamination - Methods and Applications

Water is life and its preservation is not only a moral obligation but also a legal requirement. By 2030, global demands will exceed more than 40 % the existing resources and more than a third of the worlds population will have to deal with water shortages (European Environmental Agency [EEA], 2010). Climate change effects on water resources will not help. Efforts are being made throughout Europe towards a reduced and efficient water use and prevention of any further deterioration of the quality of water (Eurostat, European Comission [EC], 2010). The Water Framework Directive (EC, 2000) lays down provisions for monitoring, assessing and classifying water quality. Supporting this, the Drinking Water sets standards for 48 microbiological and chemical parameters that must be monitored and tested regularly (EC, 1998). The Bathing Water Directive also sets concentration limits for microbiological pollutants in inland and coastal bathing waters (EC, 2006), addressing risks from algae and cyanobacteria contamination and faecal contamination, requiring immediate action, including the provision of information to the public, to prevent exposure. With these directives, among others, the European Union [EU] expects to offer its citizens, by 2015, fresh and coastal waters of good quality.

Rapid fabrication of polymeric micro lenses for optical fiber trapping and beam shaping

This work reports a new type of optical fiber tweezers based on polymeric micro-lenses. The lenses are achieved by means of an economical and fast fabrication process, using an in-fiber photo-polymerization technique. The polymerization radiation is guided towards the fiber tip creating a polymeric waveguide. The method allows tailoring the geometry of the tip by adjusting the fabrication parameters. Furthermore, more complex shapes can be fabricated by exploring modal effects at the polymerization/trapping wavelengths, which can be used for different applications such as trapping, beam shaping and patterned illumination.

Rapid Determination of Tartaric Acid in Wines

A flow-spectrophotometric method is proposed for the routine determination of tartaric acid in wines. The reaction between tartaric acid and vanadate in acetic media is carried out in flowing conditions and the subsequent colored complex is monitored at 475 nm. The stability of the complex and the corresponding formation constant are presented. The effect of wavelength and pH was evaluated by batch experiments. The selected conditions were transposed to a flow-injection analytical system. Optimization of several flow parameters such as reactor lengths, flow-rate and injection volume was carried out. Using optimized conditions, a linear behavior was observed up to 1000 microg mL(-1) tartaric acid, with a molar extinction coefficient of 450 L mg(-1) cm(-1) and +/- 1 % repeatability. Sample throughput was 25 samples per hour. The flow-spectrophotometric method was satisfactorily applied to the quantification of TA in wines from different sources. Its accuracy was confirmed by statistical comparison to the conventional Rebelein procedure and to a certified analytical method carried out in a routine laboratory.