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  • Sciforum conference paper
  • 10 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05636

The control electronics for low field pulsed NMR systems, commonly referred to as the console, are designed to be wide band and highly programmable. The process of making spin lattice relaxation time (T1) measurements with such a pulsed system usually use recovery sequences that will typically take many minutes to give a single T1 value. A simple transient effect method for the determination of the spin-lattice relaxation time using continuous wave NMR with a marginal oscillator, known as TEDSpiL, was recently reported (doi:10.1002/mrc.4594). Such a system measures a parameter, called Tx, that is related to T1 and allows T1 to be determined with the aid of calibration samples. For such a system, the process of making the Tx measurement only takes a few seconds and does not require variable parameters so is ideal for implementing in microcontroller code. In this presentation, we demonstrate that TEDSpiL may be automated using two microcontrollers from the Teensy family. One microcontroller is used to generate a magnetic field sweep voltage and a trigger pulse for the second microcontroller that is used to record the data and calculate the value of Tx. Whilst the Tx value is not a direct equivalent for T1, there are applications where such a method may provide a suitable cost effective, low power and portable measurement technique.

  • Sciforum conference paper
  • 10 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05637

The use of accelerometers to obtain information on the state of honeybee colonies has several advantages over sound recorded by microphones, in that (i) accelerometers can reside in a honeybee hive for several years with a negligible effect of propolis coating (ii) they are particularly good at monitoring the low frequency signals which form a large part of the honeybee communication processes, and (iii) they sense a physical property, the vibration, that is probably far more relevant to them than sounds. One example of accelerometers allowing the observation of specific vibrational communication signals has been reported for the ‘whooping signal’ (doi: 10.1371/journal.pone.0171162). The vibrational amplitude is also dependent on the local environment/substrate and this has been demonstrated to be a strong indicator of an active queen (doi:10.1371/journal.pone.0141926). These previous reports have used ultra-high performance accelerometers (Brüel and Kjær, 4507) which also require separate signal conditioning electronics before the vibrational data can be logged; this represents a very expensive arrangement that precludes wide deployment. In this work we demonstrate that the 805M1 single axis analogue output accelerometer, that incorporates a piezo-ceramic crystal with low power electronics in a shielded housing, can be used to monitor honey bee activity and requires only a low cost microcontroller with an audio shield to log the data. We present high quality accelerometer output signals for both individual bee pulses and long term amplitude monitoring using this affordable measurement system. The signals appear of similar quality to those acquired with ten fold more expensive equipment.

  • Sciforum conference paper
  • 10 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05714

Optical integrated sensors, such as Mach-Zehnder Interferometers (MZI), offer remarkable advantages in terms of sensitivity and compactness for label-free bio-sensing applications [1-2], although they need from additional structures and long arms to perform the sensing. In this work, we report a new interferometric sensing method encompassing the benefits of MZIs while reducing the footprint of the integrated device. This new approach is based on the interference between two Bloch modes propagating through a single-channel and one-dimensional photonic crystal, where the slow-wave effect takes place.

The principle of operation is the following: a single-mode waveguide working in TE polarization excites two modes, which interfere with each other by an abrupt discontinuity into the second single-mode waveguide at the output. For a given variation of the cladding refractive index unit (RIU), the propagation constant of the guided modes changes, producing an increase in the phase shift. Due to the slow-wave phenomenon whereby light travels slower than in other structures, good values of sensitivity are obtained for short device lengths in comparison to other interferometers and without the necessity of long modal sections to achieve enough phase shift (dimensions around 35 microns) . In summary, this approach could result in novel interferometric sensing structures for lab-on-a-chip integrated devices and other bio-sensing applications.

[1] Q. Liu, X. Tu, K. W. Kim, J. S. Kee, Y. Shin, K. Han, Y. J. Yoon, G. Q. Lo, and M. K. Park, Sensors Actuators, B Chem. 188, 681 (2013).

[2] Q. Kun, H. Shuren, and S. T., Opt. Lett. 1 (2016).

[3] K. E. Zinoviev, A. B. González-Guerrero, C. Domínguez, and L. M. Lechuga, J. Light. Technol. 29, 1926 (2011).

  • Sciforum conference paper
  • 6 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05715

Porous silicon (PS) is a nanostructured material generated by electrochemically etching silicon in electrolytes containing hydrofluoric acid (HF) with many potential application areas such as optoelectronics and biosensing. PS retains the advantages of silicon technology while adding the ability of controlling optical properties. Fabry-Pérot interferometers, Fabry-Pérot filters or distributed Bragg reflectors are some of the 1D structures that have been fabricated in PS under different etching conditions, e.g. changing anodization current and concentration of HF.

Tuning pore diameter is essential for some applications in which substances must be flown through the pores, so that a size-based filtering of the molecules can be done. However, macropore (>50nm) formation on p-type silicon is still poorly known due to the strong dependence with resistivity [1]. Electrochemically etching heavily doped p-type silicon usually forms micropores (<10nm) but it has been found that bigger sizes can be achieved by adding a solvent to the electrolyte (aqueous or organic).

In this work we present the results of using dimethylformamide (DMF), dimethylsulfoxide (DMSO), potasium hydroxide (KOH) and sodium hydroxide (NaOH) for macropore formation in p-type silicon with resistivities between 0.001 and 9 Ω∙cm, achieving pore size range from 5 to 100nm.

[1] G.X. Zhang, Porous silicon: morphology and formation mechanisms, Modern Aspects of Electrochemistry, number 39, edited by C. Vayenas et al., Springer, New York, 2005.

  • Sciforum conference paper
  • 10 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05716

Track-etched polycarbonate membranes (TEPM) are commercially available membranes typically used in particle filtration due to the pores present in their surfaces. This porous structure reminds of that of a Fabry-Pérot interferometer made on porous silicon, an optical structure long employed in optical chemical sensing. Because of this morphological similarity, we hypothesized that TEPM could exhibit a similar optical response and thus being useful for creating simpler to fabricate, easily available and low cost chemical sensors. To asses this hypothesis, we investigated the optical response of TEPM in the infrared range, improved it by chemically attaching the membranes to a silicon flat surface and then, performed reflectivity measurements in presence of different concentrations of ethanol.

When exposing a TEPM to a change of the refractive index of the medium it is surrounded by (air) by placing a drop of ethanol, with a higher refractive index, we can observe a shift of its spectrum towards higher wavelengths. This indicates the presence of the solvent, and we could check that the bigger the concentration, the bigger the magnitude of that shift. Furthermore, when the solvent is evaporated the spectrum returns to its initial position, which allowed us to perform different concentration sensing steps using the same sample. These promising results, although early, could indicate the utility of these membranes to easily fabricate cheap chemical sensors and, probably, optical biosensors as their surface can be chemically modified.

  • Sciforum conference paper
  • 5 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05717

Porous silicon (PS) is a good host for fabricating high sensitivity sensors due to the high aspect ratio between surface and volume that can be achieved. The anodization in hydrofluoric acid solutions forms nano-size pores with a few microns of thickness that can be functionalized for the detection of analytes. However, closed-ended porous silicon films have some drawbacks, like air entrapment and bad flow diffusion that can lower the sensitivity.

Porous silicon membranes appeared as a solution to those effects by flowing the substances through open-ended films. This reduces the time of detection, optimises the sensitivity and avoid mixture of different substances [1].

Lift-off of a porous silicon film is the easiest method for obtaining self-standing porous silicon membranes. The layer is detached from the substrate in a single step by electrochemically etching with a current close to electropolishing.

In this work, we present the experimental results of sensing with a PS sensor based on the lift-off method. We have measured the reflectance spectrum each 30 seconds and followed the shift while flowing through the pores. Experimental sensitivity values are in good agreement with the theoretical simulations performed.

[1] Y. Zhao, G. Gaur, R.L. Mernaugh, P.E. Laibinis, S.M, Weiss, Comparative kinetics analysis of closed-ended and open-ended porous silicon, Nanoscale Research Letters, 11:395, 2016.

  • Sciforum conference paper
  • 6 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05718

The development and demand of label-free biosensors devices for a direct, rapid and cost effective analysis has rapidly increased during the last years. In this context, we report here our work towards the development of an integrated label-free biosensor based on an innovative nanophotonic technology for the detection of low protein concentrations. Photonic bandgap (PBG) sensing structures based on a silicon on insulator (SOI) substrate were used, as they demonstrates high sensitivities with an extremely small footprint due to the slow-wave effect [1].

Regarding the biofunctionalization, the thiol-ene coupling (TEC) reaction was used to covalently immobilize the bioreceptors onto the surface. TEC reaction was selected because it provides more compact functionalized surface, what is translated into a higher interaction with the photonic evanescent wave, and a spatially-specific immobilization of the bioreceptors upon UV light photo-catalysis, what can be used to biofunctionalize each sensing area with a different bioreceptor in order to perform a multiplexed sensing device [2]. Half antibodies (hIgGs), which were immobilized using the SH groups from their hinge region, were used as bioreceptors for the specific recognition of the target protein.

To implement this biofunctionalization strategy, first the SOI surface silanization was carried out using triethoxyvinylsilane at 1% in water. The use of water as carrier for the organosilane provides several advantages such as vertical polymerization prevention, compactness and sustainability. Once the sensing surface was silanized, the TEC-based immobilization of the hIgGs onto the photonic sensors was monitored for the ``live´´ hIgG immobilization performance. BSA hIgGs obtained by the TCEP protocol were used in these experiments [2]. The real-time monitoring of the sensing structures allowed demonstrating that the immobilization of the hIgGs only took place when the system was photo-catalysed with UV light. Finally, the recognition of the target protein (BSA) at 1 µg/mL by the PBG sensors was successfully measured.

References
[1] X. Fan, I. M. White, S. I. Shopova, H. Zhu, J. D. Suter, and Y. Sun. Anal. Chim. Acta. 2008, 620, 8-26.
[2] R. Alonso, P. Jiménez-Meneses, J. García-Rupérez, M.J Bañuls, Á. Maquieira. Chem.Comm. 2018, , 54, 6144--6147.

  • Sciforum conference paper
  • 9 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05719

Cardiac troponin I (cTnI) is currently the gold-standard biomarker for the fast and early detection of a myocardial failure. Within this context, in this work we report a computational study of the interactions of the cTnI antibody (αcTnI) capture probe with cTnI and its principal interferon, skeletal troponin I (sTnI). This study allows having a better understanding of those biochemical interactions and to computationally predict the binding performance and the selectivity of the αcTnI to cTnI versus sTnI. This information is very relevant for the development of analysis systems for myocardial failure diagnosis based on cTnI detection.

The computational study was performed using different simulation platforms. FTSite and FTMap were used for the determination and mapping of the binding sites sequences [1]. Then, FTDock and pyDock were used to study the molecular dockings [2]. Thus, several energies parameters were generated and represented as well.

This study can also be applied to a wide range of different scenarios were other targets (e.g., lipids, oligonucleotides, etc.) or other applications (e.g., pharmacological drug design) are considered.

References:

[1] Y. Yuan, J. Pei, L. Lai. Curr. Pharm. Des. 2016, 19 (12), 2326-2333.

[2] M. Cheng, L. Blundell, J. Fernandez-Recio. Proteins. 2007, 68, 503-515.

  • Sciforum conference paper
  • 7 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05720

The improvement of the quality of life in the framework of the smartcity paradigm cannot be limited to a set of objective measures carried out over several critical parameters (e.g. noise, air pollution). The citizen's perception of the problem to be solved, as well as the perception of the improvement achieved with the policies defined for this purpose, is more important than the objectivity and the measurement of the change achieved. A first auralization approach for the evaluation of the acoustic perception of street noise is presented in this work. The wireless acoustic sensor network can pick up street noise, and can even record specific sounds that reach a higher equivalent level for study, but the most important thing for administration is whether the neighbour has noticed an improvement in the quality of life. This work is a first approximation to an estimation of the real perception of citizens of the street urban noises collected by a low-cost wireless acoustic sensor network.

  • Sciforum conference paper
  • 10 Reads
In Proceedings of the 5th Int. Electron. Conf. Sens. Appl. 15-30 November 2018; MDPI AG , 2018,
doi: 10.3390/ecsa-5-05721

Rogowski coils are inductive sensors based on Faraday’s Law to measure currents through conductors without galvanic contact. The main advantage of Rogowski coils when compared with current transformers is the fact that the core is air so they never saturate and there is no limit in the frequency of the primary current. These characteristics makes Rogowski coils ideal candidates to measure high amplitude pulsed currents. On the contrary, there are two main drawbacks. On the one hand, the output voltage is the derivative of the primary current so it has to be integrated; and, on the other hand, the transfer function is resonant due to the turn-to-turn capacitance and the self-inductance of the coil. The solution is the use of a passive integration with a terminating resistor at the output of the sensor that splits the two complex poles and gives a constant transfer function for a determined bandwidth. The downside is a loss of sensitivity. Since it is possible to calculate the electrical parameters of the coil based on its geometrical dimensions, the geometry can be adapted to design sensors for different applications depending on the time characteristics of the input current. This paper proposes the design of Rogowski coils based on their geometric characteristics maximizing the gain-bandwidth product using particle swarm optimization and adapting the coil to the specific requirements of the application.

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