Jordi Vila-Planas

Hybrid electronic tongue based on optical and electrochemical microsensors for quality control of wine.

A multiparametric system able to classify red and white wines according to the grape varieties and for analysing some specific parameters is presented. The system, known as hybrid electronic tongue, consists of an array of electrochemical microsensors and a colorimetric optofluidic system. The array of electrochemical sensors is composed of six ISFETs based sensors, a conductivity sensor, a redox potential sensor and two amperometric electrodes, an Au microelectrode and a microelectrode for sensing electrochemical oxygen demand. The optofluidic system is entirely fabricated in polymer technology and comprises a hollow structure, air mirrors, microlenses and self-alignment structures. The data obtained from these sensors has been treated with multivariate advanced tools; Principal Component Analysis (PCA), for the patterning recognition and classification of wine samples, and Partial-Least Squares (PLS) regression, for quantification of several chemical and optical parameters of interest in wine quality. The results have demonstrated the utility of this system for distinguishing the samples according to the grape variety and year vintage and for quantifying several sample parameters of interest in wine quality control.

Monolithic PDMS passband filters for fluorescence detection

We present the fabrication and characteristics of monolithically integrated ink dyed poly(dimethylsiloxane) (PDMS) filters for optical sensing in disposable lab-on-a-chip. This represents a migration of auxillary functions onto the disposable chip with the goal of producing truly portable systems. Filters made from commercially available ink (Pelikan) directly mixed into PDMS oligomer without the use of any additional solvents were patterned with standard soft lithography technologies. Furthermore, a fabrication process based on capillary forces is presented allowing PDMS coloration of arbitrary shapes. Different filters of varying thickness fabricated using red, green and blue ink in four different concentrations were characterized. The optimal performance was found with filter thicknesses of 250 microm and ink to PDMS ratios of 0.1 (mL ink : mL PDMS oligomer) resulting in a transmittance ranging from -15.1 dB to -12.3 dB in the stopband and from -4.0 dB to -2.5 dB in the passband. Additionally, we demonstrate the robustness of this approach as the ink dyed PDMS filters do not exhibit temporal ageing due to diffusion or autofluorescence. We also show that such filters can easily be integrated in fluorescence systems, with stopbands efficient enough to allow fluorescence measurements under non-optimal conditions (broadband excitation, 180 degrees configuration). Integrated ink dyed PDMS filters add robust optical functionalities to disposable microdevices at a low cost and will enable the use of these devices for a wide range of fluorescence and absorbance based biological and chemical analysis.

Cell analysis using a multiple internal reflection photonic lab-on-a-chip

Here we present a protocol for analyzing cell cultures using a photonic lab-on-a-chip (PhLoC). By using a broadband light source and a spectrometer, the spectrum of a given cell culture with an arbitrary population is acquired. The PhLoC can work in three different regimes: light scattering (using label-free cells), light scattering plus absorption (using stained cells) and, by subtraction of the two former regimes, absorption (without the scattering band). The acquisition time of the PhLoC is ∼30 ms. Hence, it can be used for rapid cell counting, dead/live ratio estimation or multiparametric measurements through the use of different dyes. The PhLoC, including microlenses, micromirrors and microfluidics, is simply fabricated in a single-mask process (by soft lithographic methods) using low-cost materials. Because of its low cost it can easily be implemented for point-of-care applications. From raw substrates to final results, this protocol can be completed in 29 h.

Application of an E-Tongue to the Analysis of Monovarietal and Blends of White Wines

This work presents a multiparametric system capable of characterizing and classifying white wines according to the grape variety and geographical origin. Besides, it quantifies specific parameters of interest for quality control in wine. The system, known as a hybrid electronic tongue, consists of an array of electrochemical microsensors—six ISFET based sensors, a conductivity sensor, a redox potential sensor and two amperometric electrodes, a gold microelectrode and a microelectrode for sensing electrochemical oxygen demand—and a miniaturized optofluidic system. The test sample set comprised eighteen Catalan monovarietal white wines from four different grape varieties, two Croatian monovarietal white wines and seven bi- and trivarietal mixtures prepared from the Catalan varieties. Different chemometric tools were used to characterize (i.e., Principal Component Analysis), classify (i.e., Soft Independent Modeling Class Analogy) and quantify (i.e., Partial-Least Squares) some parameters of interest. The results demonstrate the usefulness of the multisensor system for analysis of wine.

Cell Screening Using Disposable Photonic Lab on a Chip Systems

A low-cost photonic lab on a chip with three different working regimes for cell screening is presented. The proposed system is able to perform scattering, scattering + absorption, and absorption measurements without any modification. Opposite to the standard flow cytometers, in this proposed configuration, a single 30 ms scan allows to obtain information regarding the cell optical properties. An additional novelty is that the whole spectrum is obtained and analyzed, being then possible to determine for each regime which is the optimal working wavelength that would provide the best performance in terms of sensitivity and limit of detection (LOD). Experimental results have provided with an LOD of 54.9 +/- 0.7 cells (in the scattering regime using unlabeled cells), 53 +/- 1 cells (in the scattering + absorption regime using labeled cells), and 105 +/- 4 cells (in the absorption regime using labeled cells). Finally, the system has also been used for measuring the dead/live cell ratio, obtaining LODs between 7.6 +/- 0.4% and 6.7 +/- 0.3%, depending on the working regime used.

Classification and characterization of different white grape juices by using a hybrid electronic tongue

A multisensor system combined with multivariate analysis is applied for the characterization and classification of white grape juices. The proposed system, known as hybrid electronic tongue, consists of an array of electrochemical microsensors and a colorimetric optofluidic system. A total of 25 white grape juices representing the large variability of vines grown in the Northwest Iberian Peninsula were studied. The data obtained were treated with Principal Component Analysis (PCA) and Soft Independent Modeling Class Analogy (SIMCA). The first tool was used to train the system with the reference genotypes -Albariño, Muscat à Petit Grains Blanc and Palomino- and the second to study the feasibility of the hybrid electronic tongue to distinguish between different grape juice varieties. The results show that the three reference genotypes are well differentiated in the PCA model and this can be used to interpolate the rest of varieties and predict their basic characteristics. Besides, using the SIMCA, the system demonstrates high potential for classifying and discriminating grape varieties.

Analysis of the Structural Integrity of SU-8-Based Optofluidic Systems for Small-Molecule Crystallization Studies

The use of SU-8-based optofluidic systems (OFS) is validated as an affordable and easy alternative to expensive glass device manufacturing for small-molecule crystallization studies and, in comparison with other polymers, able to withstand most organic solvents. A comparison between two identical OFS (using SU-8 and poly(dimethylsiloxane), PDMS) against the 36 most commonly used organic solvents for small-molecule crystallization studies have confirmed both the structural and optical stability of the SU-8, whereas PDMS suffered from unsealing or tearing in most cases. In order to test its compatibility, measurements before and after 24 h of continued exposure against solvents have been pursued. Here, three aspects have been considered: in the macroscale, swelling has been determined by analyzing the variations in the optical path in the OFS. For determining compatibility at microscale, fabricated SU-8 micropatterns were solvent-etched and subsequently characterized by scanning electron microscopy (SEM). Roughness of the polymer has also been studied through atomic force microscopy (AFM) measurements at the nanoscale. Experimental measurements of PDMS swelling were in accordance with previously reported observations, while SU-8 displayed a great stability against all the tested solvents. Through this experimental procedure we also show that the OFS are suitable for real-time, on-chip, UV-vis spectroscopy. Micro- and nanoscale observations did not show apparent corrosion on SU-8 surface. Also, two commonly used carrier fluids for microdroplet generation (FC-70 Fluorinert oil and silicone oil) were also tested against the different solvents with the aim of providing useful information for later microbatch experiments.

Hybrid Electronic Tongues Applied to the Quality Control of Wines

The legislation of food industry is becoming increasingly strict with regard to the quality of food products. Therefore, the market is demanding for automatic systems of analysis that allow fast and accurate monitoring of the evolution of quality parameters in agrofood products or permit obtaining information to optimize production processes. In this context, sensors and more specifically microsensors play an important role since they allow fast and reproducible measurement of a large number of quality parameters with good reliability and can be implemented in portable systems. This paper presents a review of the results obtained with an electronic tongue based on different kinds of microsensors applied to wine analysis by the team of IMB-CNM. This multisensor system allows on one hand classifying the wine according to its features like grape variety, geographic origin, year, and organoleptic characteristics and on the other hand quantifying some parameters of interest in quality control, such as alcoholic degree, pH, ions, total acidity, glycerol, and color.

Poly(dimethylsiloxane) photonic microbioreactors based on segmented waveguides for local absorbance measurement

We present the development of microbioreactors (MBRs) based on poly(dimethylsiloxane) (PDMS) segmented waveguides (SWG) for local absorbance measurements. Two different MBRs were studied, either using symmetric or asymmetric SWG (being defined as MBR‐S and MBR‐A, respectively). Their optical and fluidic performances were numerically analyzed, showing robustness from an optical point of view and distinct fluid flow profile. The optical characterization was done in two steps. Initially, the experimental limit of detection (LOD) and the sensitivity were determined for two different analytes (fluorescein and methylorange). With both systems, a similar limit of detection for both analytes was obtained, being in the micromolar level. Their sensitivities were 20.2±0.3 (×10−3) A.U./μM and 5.5±0.2 (×10−3) A.U./μM for fluorescein and methylorange, respectively. Once validated its applicability for local absorbance measurements, a continuous cultivation of Saccharomyces cerevisiae was done to test the viability of the proposed systems for photonic MBRs. Concretely, the cell growth was locally monitored inside the MBR during 33 h. Spectral analysis showed that the determination of the culture parameters were wavelength dependant, with a growth rate of 0.39±0.02 h−1 and a doubling time of 1.65±0.09 h at an optimal wavelength of 469.9±0.3 nm. Besides the easy and monolithic integration of the SWG into poly(dimethylsiloxane) microfluidic systems, the results presented here are very promising for the application in any disposable photonic lab‐on‐a‐chip systems used for online analysis or photonic MBRs.

Hybrid electronic tongues based on microsensors applied to wine quality control

In this work an hybrid electronic tongue for the analysis of wine is presented. Its main novelty is the joint use of different kind of sensors- potentiometric ISFETs, thin film metal microelectrodes as amperometric and conductivity sensors and an optofluidic system- thus allowing an unprecedented measurement of information of a specific sample. Moreover, this electronic tongue is completed with the use of data processing tools like Principal Component Analysis (PCA) Partial Least Square (PLS) and Soft Independent Modeling Class Analogy (SIMCA). The so-called hybrid electronic tongue, here developed, has been applied to classify the wine according to its distinct features like grape variety, geographic origin, year and organoleptic characteristics. This approach has also allowed performing quantitative measurements of parameters of interest in quality control, such as alcoholic degree, pH, ions, total acidity, glycerol and color.