@article{BalderasValadezPacholski2021,
  author    = {Balderas-Valadez, Ruth Fabiola and Pacholski, Claudia},
  title     = {Plasmonic Nanohole Arrays on Top of Porous Silicon Sensors},
  series = {ACS applied materials \& interfaces},
  volume    = {13},
  journal   = {ACS applied materials \& interfaces},
  number    = {30},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1944-8244},
  doi       = {10.1021/acsami.1c07034},
  pages     = {36436 -- 36444},
  year      = {2021},
  abstract  = {Label-free optical sensors are attractive candidates, for example, for detecting toxic substances and monitoring biomolecular interactions. Their performance can be pushed by the design of the sensor through clever material choices and integration of components. In this work, two porous materials, namely, porous silicon and plasmonic nanohole arrays, are combined in order to obtain increased sensitivity and dual-mode sensing capabilities. For this purpose, porous silicon monolayers are prepared by electrochemical etching and plasmonic nanohole arrays are obtained using a bottom-up strategy. Hybrid sensors of these two materials are realized by transferring the plasmonic nanohole array on top of the porous silicon. Reflectance spectra of the hybrid sensors are characterized by a fringe pattern resulting from the Fabry-P{\´e}rot interference at the porous silicon borders, which is overlaid with a broad dip based on surface plasmon resonance in the plasmonic nanohole array. In addition, the hybrid sensor shows a significant higher reflectance in comparison to the porous silicon monolayer. The sensitivities of the hybrid sensor to refractive index changes are separately determined for both components. A significant increase in sensitivity from 213 ± 12 to 386 ± 5 nm/RIU is determined for the transfer of the plasmonic nanohole array sensors from solid glass substrates to porous silicon monolayers. In contrast, the spectral position of the interference pattern of porous silicon monolayers in different media is not affected by the presence of the plasmonic nanohole array. However, the changes in fringe pattern reflectance of the hybrid sensor are increased 3.7-fold after being covered with plasmonic nanohole arrays and could be used for high-sensitivity sensing. Finally, the capability of the hybrid sensor for simultaneous and independent dual-mode sensing is demonstrated.},
  language  = {en}
}
@article{BalderasValadezSchuermannPacholski2019,
  author    = {Balderas-Valadez, Ruth Fabiola and Sch{\"u}rmann, Robin Mathis and Pacholski, Claudia},
  title     = {One Spot-Two Sensors: Porous Silicon Interferometers in Combination With Gold Nanostructures Showing Localized Surface Plasmon Resonance},
  series = {Frontiers in chemistry},
  volume    = {7},
  journal   = {Frontiers in chemistry},
  publisher = {Frontiers Research Foundation},
  address   = {Lausanne},
  issn      = {2296-2646},
  doi       = {10.3389/fchem.2019.00593},
  pages     = {12},
  year      = {2019},
  abstract  = {Sensors composed of a porous silicon monolayer covered with a film of nanostructured gold layer, which provide two optical signal transduction methods, are fabricated and thoroughly characterized concerning their sensing performance. For this purpose, silicon substrates were electrochemically etched in order to obtain porous silicon monolayers, which were subsequently immersed in gold salt solution facilitating the formation of a porous gold nanoparticle layer on top of the porous silicon. The deposition process was monitored by reflectance spectroscopy, and the appearance of a dip in the interference pattern of the porous silicon layer was observed. This dip can be assigned to the absorption of light by the deposited gold nanostructures leading to localized surface plasmon resonance. The bulk sensitivity of these sensors was determined by recording reflectance spectra in media having different refractive indices and compared to sensors exclusively based on porous silicon or gold nanostructures. A thorough analysis of resulting shifts of the different optical signals in the reflectance spectra on the wavelength scale indicated that the optical response of the porous silicon sensor is not influenced by the presence of a gold nanostructure on top. Moreover, the adsorption of thiol-terminated polystyrene to the sensor surface was solely detected by changes in the position of the dip in the reflectance spectrum, which is assigned to localized surface plasmon resonance in the gold nanostructures. The interference pattern resulting from the porous silicon layer is not shifted to longer wavelengths by the adsorption indicating the independence of the optical response of the two nanostructures, namely porous silicon and nanostructured gold layer, to refractive index changes and pointing to the successful realization of two sensors in one spot.},
  language  = {en}
}
@article{WeilerMenzelPertschetal.2016,
  author    = {Weiler, Markus and Menzel, Christoph and Pertsch, Thomas and Alaee, Rasoul and Rockstuhl, Carsten and Pacholski, Claudia},
  title     = {Bottom-Up Fabrication of Hybrid Plasmonic Sensors: Gold-Capped Hydrogel Microspheres Embedded in Periodic Metal Hole Arrays},
  series = {Polymer : the international journal for the science and technology of polymers},
  volume    = {8},
  journal   = {Polymer : the international journal for the science and technology of polymers},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1944-8244},
  doi       = {10.1021/acsami.6b08636},
  pages     = {26392 -- 26399},
  year      = {2016},
  abstract  = {The high potential of bottom-up fabrication strategies for realizing sophisticated optical sensors combining the high sensitivity of a surface plasmon resonance with the exceptional properties of stimuli-responsive hydrogel is demonstrated. The sensor is composed of a periodic hole array in a gold film whose holes are filled with gold-capped poly(N-isoproyl-acrylamide) (polyNIPAM) microspheres. The production of this sensor relies on a pure chemical approach enabling simple, time-efficient, and cost-efficient preparation of sensor platforms covering areas of cm(2). The transmission spectrum of this plasmonic sensor shows a strong interaction between propagating surface plasmon polaritons at the metal film surface and localized surface plasmon resonance of the gold cap on top of the polyNIPAM microspheres. Computer simulations support this experimental observation. These interactions lead to distinct changes in the transmission spectrum, which allow for the simultaneous, sensitive optical detection of refractive index changes in the surrounding medium and the swelling state of the embedded polyNIPAM microsphere under the gold cap. The volume of the polyNIPAM microsphere located underneath the gold cap can be changed by certain stimuli such as temperature, pH, ionic strength, and distinct molecules bound to the hydrogel matrix facilitating the detection of analytes which do not change the refractive index of the surrounding medium significantly.},
  language  = {en}
}