Sensitivity comparison of a self-standing porous silicon membrane under flow-through and flow-over conditionshttps://aplicat.upv.es/senia-app/edicion/mantArticuloBib.faces?p_idioma=v

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertisíng or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] An optical sensor based on a self-standing porous silicon (PS) membrane is presented. The sensor was created by electrochemically etching a heavily doped p-type silicon wafer with an organic electrolyte that contained dimethylformamide. After fabrication, a high-current density close to electropolishing was applied in order to allow the detachment from the substrate using a lift-off method. The PS membrane was integrated ina microfluidic cell for sensing purposes, and reflectance spectra were continuously obtained while the target substance was flowed. A comparison of the bulk sensitivity is achieved when flowing through and over the pores is reported. During the experiments,a maximum sensitivity of 770 nm/RIU measured at 1700 nm was achieved. Experimental sensitivity values are in good agreement with the theoretical calculations performed when flowing through the PS membrane, it means that the highest possible sensitivity of that sensor was achieved. In contrast, a drop in the sensi-tivity of around 25% was observed when flowing over the PS membrane.This work was supported by the Ministry of Economy and Competitiveness. The associate editor coordinating the review of this paper and approving it for publication was Prof. Aime Lay-Ekuakille.Martín-Sánchez, D.; Ponce-Alcántara, S.; García-Rupérez, J. (2019). Sensitivity comparison of a self-standing porous silicon membrane under flow-through and flow-over conditionshttps://aplicat.upv.es/senia-app/edicion/mantArticuloBib.faces?p_idioma=v. IEEE Sensors Journal. 19(9):3279-3281. https://doi.org/10.1109/JSEN.2019.2893885S3279328119

Stabilization of Polymeric Nanofibers Layers for Use as Real-Time and In-Flow Photonic Sensors

In order to increase the sensitivity of a sensor, the relationship between its volume and the surface available to be functionalized is of great importance. Accordingly, porous materials are becoming very relevant, because they have a notable surface-to-volume ratio. Moreover, they offer the possibility to infiltrate the target substances on them. Among other porous structures, polymeric nanofibers (NFs) layers fabricated by electrospinning have emerged as a very promising alternative to low-cost and easy-to-produce high-performance photonic sensors. However, experimental results show a spectrum drift when performing sensing measurements in real-time. That drift is responsible for a significant error when trying to determine the refractive index variation for a target solution, and, because of that, for the detection of the presence of certain analytes. In order to avoid that problem, different chemical and thermal treatments were studied. The best results were obtained for thermal steps at 190 °C during times between 3 and 5 h. As a result, spectrum drifts lower than 5 pm/min and sensitivities of 518 nm/refractive index unit (RIU) in the visible range of the spectrum were achieved in different electrospun NFs sensors.This work was supported by the Spanish government through the project TEC2015-63838-C3-1-ROPTONANOSENS and from the Basque government through the project KK-2019/00101 -µ4INDUSTR

Thermo-optic coefficient of porous silicon in the infrared region and oxidation process at low temperatures

[EN] In this work, a porous silicon nanostructure has been fabricated by electrochemical means and used as a thermal sensor. The thermo-optic effect in the near infrared region has been experimentally studied based on spectroscopy measurements. Values of the thermo-optic coefficient between 3.2 and 7.9·10¿5 K¿1 have been obtained, depending on the porosity, reaching a maximum thermal sensitivity of 91 ± 3 pm/°C during the experiments carried out with the fabricated samples. Additionally, the oxidation process of the sensor at temperatures below 500 K has been studied, showing that the growth of the silicon oxide was dependent on the characteristics of the porous layers. Based on the experimental results, a mathematical model was developed to estimate the evolution of the oxidation process as a function of porosity and thickness.The authors acknowledge the funding from the Spanish government through the project TEC2015-63838-C3-1-R-OPTONANOSENS.Martín-Sánchez, D.; Kovylina, M.; Ponce-Alcántara, S.; García-Rupérez, J. (2019). Thermo-optic coefficient of porous silicon in the infrared region and oxidation process at low temperatures. Journal of The Electrochemical Society. 166(6):B355-B359. https://doi.org/10.1149/2.0341906jesSB355B359166

Macropore Formation and Pore Morphology Characterization of Heavily Doped p-Type Porous Silicon

[EN] Tuning the pore diameter of porous silicon films is essential for some applications such as biosensing, where the pore size can be used for filtering analytes or to control the biofunctionalization of its walls. However, macropore (>50nm) formation on p-type silicon is not yet fully controlled due to its strong dependence on resistivity. Electrochemical etching of heavily doped p-type silicon usually forms micropores (<5nm), but it has been found that bigger sizes can be achieved by adding an organic solvent to the electrolyte. In this work, we compare the results obtained when adding dimethylformamide (DMF) and dimethylsulfoxide (DMSO) to the electrolyte as well as the effect of a post-treatment of the sample with potasium hydroxide (KOH) and sodium hydroxide (NaOH) for macropore formation in p-type silicon with resistivities between 0.001 and 10ohm· cm, achieving pore sizes from 5 to 100nm.The authors acknowledge the funding from the Spanish government through the project TEC2015-63838-C3-1-R-OPTONANOSENS.Martín-Sánchez, D.; Ponce-Alcántara, S.; Martinez-Perez, P.; García-Rupérez, J. (2019). Macropore Formation and Pore Morphology Characterization of Heavily Doped p-Type Porous Silicon. Journal of The Electrochemical Society. 166(2):B9-B12. https://doi.org/10.1149/2.0051902jesB9B121662Canham, L. T. (1990). Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers. Applied Physics Letters, 57(10), 1046-1048. doi:10.1063/1.103561Dhanekar, S., & Jain, S. (2013). Porous silicon biosensor: Current status. Biosensors and Bioelectronics, 41, 54-64. doi:10.1016/j.bios.2012.09.045Pacholski, C. (2013). Photonic Crystal Sensors Based on Porous Silicon. Sensors, 13(4), 4694-4713. doi:10.3390/s130404694Hutter, T., Horesh, M., & Ruschin, S. (2011). Method for increasing reliability in gas detection based on indicator gradient in a sensor array. Sensors and Actuators B: Chemical, 152(1), 29-36. doi:10.1016/j.snb.2010.09.058Mariani, S., Strambini, L. M., & Barillaro, G. (2016). Femtomole Detection of Proteins Using a Label-Free Nanostructured Porous Silicon Interferometer for Perspective Ultrasensitive Biosensing. Analytical Chemistry, 88(17), 8502-8509. doi:10.1021/acs.analchem.6b01228Caroselli, R., Ponce-Alcántara, S., Quilez, F. P., Sánchez, D. M., Morán, L. T., Barres, A. G., … García-Rupérez, J. (2017). Experimental study of the sensitivity of a porous silicon ring resonator sensor using continuous in-flow measurements. Optics Express, 25(25), 31651. doi:10.1364/oe.25.031651Ashuri, M., He, Q., & Shaw, L. L. (2016). Silicon as a potential anode material for Li-ion batteries: where size, geometry and structure matter. Nanoscale, 8(1), 74-103. doi:10.1039/c5nr05116aAshuri, M., He, Q., Liu, Y., Zhang, K., Emani, S., Sawicki, M. S., … Shaw, L. L. (2016). Hollow Silicon Nanospheres Encapsulated with a Thin Carbon Shell: An Electrochemical Study. Electrochimica Acta, 215, 126-141. doi:10.1016/j.electacta.2016.08.059Ashuri, M., He, Q., Liu, Y., Emani, S., & Shaw, L. L. (2017). Synthesis and performance of nanostructured silicon/graphite composites with a thin carbon shell and engineered voids. Electrochimica Acta, 258, 274-283. doi:10.1016/j.electacta.2017.10.198Ashuri, M., He, Q., Zhang, K., Emani, S., & Shaw, L. L. (2016). Synthesis of hollow silicon nanospheres encapsulated with a carbon shell through sol–gel coating of polystyrene nanoparticles. Journal of Sol-Gel Science and Technology, 82(1), 201-213. doi:10.1007/s10971-016-4265-zLiu, N., Huo, K., McDowell, M. T., Zhao, J., & Cui, Y. (2013). Rice husks as a sustainable source of nanostructured silicon for high performance Li-ion battery anodes. Scientific Reports, 3(1). doi:10.1038/srep01919Yi, R., Dai, F., Gordin, M. L., Chen, S., & Wang, D. (2012). Micro-sized Si-C Composite with Interconnected Nanoscale Building Blocks as High-Performance Anodes for Practical Application in Lithium-Ion Batteries. Advanced Energy Materials, 3(3), 295-300. doi:10.1002/aenm.201200857Föll, H., Christophersen, M., Carstensen, J., & Hasse, G. (2002). Formation and application of porous silicon. Materials Science and Engineering: R: Reports, 39(4), 93-141. doi:10.1016/s0927-796x(02)00090-6Zhang G. X. , in Modern Aspects of Electrochemistry, Vayenas C. Gamboa-Adelco M. E. , Springer, Boston, USA, (2006).Canham L. T. , in Handbook of porous silicon, Canham L. T. , Springer International Publishing, Switzerland (2014).Lehmann, V., & Föll, H. (1990). Formation Mechanism and Properties of Electrochemically Etched Trenches in n‐Type Silicon. Journal of The Electrochemical Society, 137(2), 653-659. doi:10.1149/1.2086525Lehmann, V., & Ronnebeck, S. (1999). The Physics of Macropore Formation in Low‐Doped p‐Type Silicon. Journal of The Electrochemical Society, 146(8), 2968-2975. doi:10.1149/1.1392037Lehmann, V., Stengl, R., & Luigart, A. (2000). On the morphology and the electrochemical formation mechanism of mesoporous silicon. Materials Science and Engineering: B, 69-70, 11-22. doi:10.1016/s0921-5107(99)00286-xMariani, S., Pino, L., Strambini, L. M., Tedeschi, L., & Barillaro, G. (2016). 10 000-Fold Improvement in Protein Detection Using Nanostructured Porous Silicon Interferometric Aptasensors. ACS Sensors, 1(12), 1471-1479. doi:10.1021/acssensors.6b00634Lau, H. ., Parker, G. ., & Greef, R. (1996). High aspect ratio silicon pillars fabricated by electrochemical etching and oxidation of macroporous silicon. Thin Solid Films, 276(1-2), 29-31. doi:10.1016/0040-6090(95)08042-2Chernienko, A. V., Astrova, E. V., & Zharova, Y. A. (2013). Zigzag structures obtained by anisotropic etching of macroporous silicon. Technical Physics Letters, 39(11), 990-993. doi:10.1134/s1063785013110175Ponomarev, E. A., & Lévy-Clément, C. (2000). Journal of Porous Materials, 7(1/3), 51-56. doi:10.1023/a:1009690521403Haldar, S., De, A., Chakraborty, S., Ghosh, S., & Ghanta, U. (2014). Effect of Dimethylformamide, Current Density and Resistivity on Pore Geometry in P-type Macroporous Silicon. Procedia Materials Science, 5, 764-771. doi:10.1016/j.mspro.2014.07.326Rasband W. S. , U. S. National Institutes of Health, Bethesda, Maryland, USA, 1997.Mawhinney, D. B., Glass, J. A., & Yates, J. T. (1997). FTIR Study of the Oxidation of Porous Silicon. The Journal of Physical Chemistry B, 101(7), 1202-1206. doi:10.1021/jp963322

Evaluation of Mesoporous TiO2 Layers as Glucose Optical Sensors

[EN] Porous materials are currently the basis of many optical sensors because of their ability to provide a higher interaction between the light and the analyte, directly within the optical structure. In this study, mesoporous TiO2 layers were fabricated using a bottom-up synthesis approach in order to develop optical sensing structures. In comparison with more typical top-down fabrication strategies where the bulk constitutive material is etched in order to obtain the required porous medium, the use of a bottom-up fabrication approach potentially allows increasing the interconnectivity of the pore network, hence improving the surface and depth homogeneity of the fabricated layer and reducing production costs by synthesizing the layers on a larger scale. The sensing performance of the fabricated mesoporous TiO2 layers was assessed by means of the measurement of several glucose dilutions in water, estimating a limit of detection even below 0.15 mg/mL (15 mg/dL). All of these advantages make this platform a very promising candidate for the development of low-cost and high-performance optical sensors.This research was supported by the Spanish Ministerio de Ciencia e Innovacion (MCIN/AEI/10.13039/501100011033) through the PID2019-106965RB-C21 project, and by the European Union through the operational program of the European Regional Development Fund (FEDER) of the Valencia Regional Government 2014-2020 and of the Ministerio de Ciencia e InnovacionAgencia Estatal de Investigacion (Ref.ICTS-2017-28-UPV-9).Ortiz De Zárate-Díaz, D.; Serna, S.; Ponce-Alcántara, S.; García-Rupérez, J. (2022). Evaluation of Mesoporous TiO2 Layers as Glucose Optical Sensors. Sensors. 22(14):1-12. https://doi.org/10.3390/s22145398112221

Bottom-Up Synthesis of Mesoporous TiO2 Films for the Development of Optical Sensing Layers

[EN] Many optical sensors exploit the interesting properties of porous materials, as they ensure a stronger interaction between the light and the analyte directly within the optical structure. Most porous optical sensors are mainly based on porous silicon and anodized aluminum oxide, showing high sensitivities. However, the top-down strategies usually employed to produce those materials might offer a limited control over the properties of the porous layer, which could affect the homogeneity, reducing the sensor reproducibility. In this work, we present the bottom-up synthesis of mesoporous TiO2 Fabry-Perot optical sensors displaying high sensitivity, high homogeneity, and low production cost, making this platform a very promising candidate for the development of high-performance optical sensors.This work was supported by the Spanish Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033) through the PID2019-106965RB-C21 project, by the Generalitat Valenciana through grant PPC/2021/036, and by the European Union through the operational program of the European Regional Development Fund (FEDER) of the Valencia Regional Government 2014-2020 and of the Ministerio de Ciencia e Innovación-Agencia Estatal de Investigación (Ref.ICTS-2017-28-UPV-9)Ortiz De Zárate-Díaz, D.; Serna, S.; Ponce-Alcántara, S.; Kovylina, M.; García-Rupérez, J. (2021). Bottom-Up Synthesis of Mesoporous TiO2 Films for the Development of Optical Sensing Layers. Chemosensors. 9(12):329.1-329.14. https://doi.org/10.3390/chemosensors9120329S329.1329.1491

High performance photonic biosensors based on periodic configurations

[EN] Periodic photonic configurations as photonic crystals (PhCs) and subwavelength grating (SWG) waveguides are gaining a renewed interest for the development of biosensing structures. By performing a proper design, these periodic configurations allow a significant sensitivity increase while keeping a compact footprint, what is achieved by exploiting concepts such as the slow-wave effect, the increase of the light-matter overlap or the interference of dispersion engineered modes.These results were achieved thanks to the funding received from the European Union (ICT-644242-SAPHELY, PHC634013-PHOCNOSIS and the operational program of the European Regional Development Fund (FEDER) of the Valencia Regional Government 2014¿2020), the Spanish Government (TEC2015-63838-C3-1-R-OPTONANOSENS and PID2019-106965RB-C21-PHOLOW), the Generalitat Valenciana (AVANTI/2019/123, ACIF/2019/009 and PPC/2020/037), the Universitat Politècnica de València (PAID-01-17, PAID-01-18 and OCUSENSOR).García-Rupérez, J.; Torrijos-Morán, L.; Gómez-Gómez, MI.; Martinez-Perez, P.; Ponce-Alcántara, S. (2021). High performance photonic biosensors based on periodic configurations. SPIE. 1-6. https://doi.org/10.1117/12.2576401S1

Real-Time and In-Flow Sensing Using a High Sensitivity Porous Silicon Microcavity-Based Sensor

[EN] Porous silicon seems to be an appropriate material platform for the development of high-sensitivity and low-cost optical sensors, as their porous nature increases the interaction with the target substances, and their fabrication process is very simple and inexpensive. In this paper, we present the experimental development of a porous silicon microcavity sensor and its use for real-time in-flow sensing application. A high-sensitivity configuration was designed and then fabricated, by electrochemically etching a silicon wafer. Refractive index sensing experiments were realized by flowing several dilutions with decreasing refractive indices, and measuring the spectral shift in real-time. The porous silicon microcavity sensor showed a very linear response over a wide refractive index range, with a sensitivity around 1000 nm/refractive index unit (RIU), which allowed us to directly detect refractive index variations in the 10(-7) RIU range.Funding from Spanish government through grants TEC2015-63838-C3-1-R (MINECO/FEDER, UE) and TEC2013-49987-EXP BIOGATE, from the European Commission through the project H2020-644242 SAPHELY is acknowledged. Raffaele Caroselli also acknowledges the Generalitat Valenciana for funding his grant through the Doctoral Scholarship GRISOLIAP/2014/109.Caroselli, R.; Martín-Sánchez, D.; Ponce-Alcántara, S.; Prats-Quílez, F.; Torrijos-Morán, L.; García-Rupérez, J. (2017). Real-Time and In-Flow Sensing Using a High Sensitivity Porous Silicon Microcavity-Based Sensor. Sensors. 17(12):1-12. https://doi.org/10.3390/s17122813S112171

Label-Free Optical Biosensing Using Low-Cost Electrospun Polymeric Nanofibers

Polymeric nanofiber matrices are promising structures to develop biosensing devices due to their easy and affordable large-scale fabrication and their high surface-to-volume ratio. In this work, the suitability of a polyamide 6 nanofiber matrix for the development of a label-free and real-time Fabry–Pérot cavity-based optical biosensor was studied. For such aim, in-flow biofunctionalization of nanofibers with antibodies, bound through a protein A/G layer, and specific biodetection of 10 µg/mL bovine serum albumin (BSA) were carried out. Both processes were successfully monitored via reflectivity measurements in real-time without labels and their reproducibility was demonstrated when different polymeric nanofiber matrices from the same electrospinning batch were employed as transducers. These results demonstrate not only the suitability of correctly biofunctionalized polyamide 6 nanofiber matrices to be employed for real-time and label-free specific biodetection purposes, but also the potential of electrospinning technique to create affordable and easy-to-fabricate at large scale optical transducers with a reproducible performance.This research was supported by a co-financed action by the European Union through the operational program of the European Regional Development Fund (FEDER) of the Valencian Community 2014–2020, the Generalitat Valenciana through the PROMETEO project AVANTI/2019/123 and the grant PPC/2020/037, the Spanish government through the project TEC2015-63838-C3-OPTONANOSENS, Universitat Politècnica de València through grant PAID-01-17, and by the Basque government through the project µ4Industry, KK-2019/00101, from the ELKARTEK Program