TY - JOUR A1 - Polley, Nabarun A1 - Werner, Peter A1 - Balderas-Valadez, Ruth Fabiola A1 - Pacholski, Claudia T1 - Bottom, top, or in between BT - combining plasmonic nanohole arrays and hydrogel microgels for optical fiber snsor applications JF - Advanced materials interfaces N2 - Attractive label-free plasmonic optical fiber sensors can be developed by cleverly choosing the arrangement of plasmonic nanostructures and other building blocks. Here, the final response depends very much on the alignment and position (stacking) of the individual elements. In this work, three different types of fiber optic sensing geometries fabricated by simple layer-by-layer stacking are presented, consisting of stimulus-sensitive poly-N-isopropylacrylamide (polyNIPAM) microgel arrays and plasmonic nanohole arrays (NHAs), namely NHA/polyNIPAM, polyNIPAM/NHA, polyNIPAM/NHA/polyNIPAM. Their optical response to a representative stimulus, namely temperature, is investigated. NHA/polyNIPAM monitors the volume phase transition of polyNIPAM microgels through changes in the spectral position and the amplitude of the reflection minimum of plasmonic NHA. In contrast, polyNIPAM/NHA shows a more complex response to the swelling and collapse of polyNIPAM microgels in their reflectance spectra. The most pronounced changes in optical response are observed by monitoring the amplitude of the reflectance minimum of this sensor during heating/cooling cycles. Finally, the triple stack of polyNIPAM/NHA/polyNIPAM at the end of a optical fiber tip combines the advantages of the NHA/polyNIPAM, polyNIPAM/NHA double stacks for optical sensing. The unique layer-by-layer stacking of microgel and nanostructure is customizable and can be easily adopted for other applications. KW - bottom-up fabrication KW - layer-by-layer stacking KW - microgel arrays KW - optical KW - fiber sensors KW - plasmonic nanohole arrays Y1 - 2022 U6 - https://doi.org/10.1002/admi.202102312 SN - 2196-7350 VL - 9 IS - 15 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Polley, Nabarun A1 - Basak, Supratim A1 - Hass, Roland A1 - Pacholski, Claudia T1 - Fiber optic plasmonic sensors BT - Providing sensitive biosensor platforms with minimal lab equipment JF - Biosensors and bioelectronics : the principal international journal devoted to research, design development and application of biosensors and bioelectronics N2 - A simple, convenient, and inexpensive method to fabricate optical fiber based biosensors which utilize periodic hole arrays in gold films for signal transduction is reported. The process of hole array formation mainly relies on self-assembly of hydrogel microgels in combination with chemical gold film deposition and subsequent transfer of the perforated film onto an optical fiber tip. In the fabrication process solely chemical wet lab techniques are used, avoiding cost-intensive instrumentation or clean room facilities. The presented method for preparing fiber optic plasmonic sensors provides high throughput and is perfectly suited for commercialization using batch processing. The transfer of the perforated gold film onto an optical fiber tip does not affect the sensitivity of the biosensor ((420 +/- 83) nm/refractive index unit (RIU)), which is comparable to sensitivities of sensor platforms based on periodic hole arrays in gold films prepared by significantly more complex methods. Furthermore, real-time and in-line immunoassay studies with a specially designed 3D printed flow cell are presented exploiting the presented optical fiber based biosensors. KW - Surface plasmon resonance KW - Optical fiber KW - Bottom-up fabrication KW - Biosensor KW - 3D printed flow-cell Y1 - 2019 U6 - https://doi.org/10.1016/j.bios.2019.03.020 SN - 0956-5663 SN - 1873-4235 VL - 132 SP - 368 EP - 374 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Zude-Sasse, Manuela A1 - Hashim, Norhashila A1 - Hass, Roland A1 - Polley, Nabarun A1 - Regen, Christian T1 - Validation study for measuring absorption and reduced scattering coefficients by means of laser-induced backscattering imaging JF - Postharvest Biology and Technology N2 - Decoupling of optical properties appears challenging, but vital to get better insight of the relationship between light and fruit attributes. In this study, nine solid phantoms capturing the ranges of absorption (μa) and reduced scattering (μs’) coefficients in fruit were analysed non-destructively using laser-induced backscattering imaging (LLBI) at 1060 nm. Data analysis of LLBI was carried out on the diffuse reflectance, attenuation profile obtained by means of Farrell’s diffusion theory either calculating μa [cm−1] and μs’ [cm−1] in one fitting step or fitting only one optical variable and providing the other one from a destructive analysis. The nondestructive approach was approved when calculating one unknown coefficient non-destructively, while no ability of the method was found to analysis both, μa and μs’, non-destructively. Setting μs’ according to destructive photon density wave (PDW) spectroscopy and fitting μa resulted in root mean square error (rmse) of 18.7% in comparison to fitting μs’ resulting in rmse of 2.6%, pointing to decreased measuring uncertainty, when the highly variable μa was known. The approach was tested on European pear, utilizing destructive PDW spectroscopy for setting one variable, while LLBI was applied for calculating the remaining coefficient. Results indicated that the optical properties of pear obtained from PDW spectroscopy as well as LLBI changed concurrently in correspondence to water content mainly. A destructive batch-wise analysis of μs’ and online analysis of μa may be considered in future developments for improved fruit sorting results, when considering fruit with high variability of μs’. KW - Absorption KW - European pear KW - Fruit quality KW - Phantoms KW - Reduced scattering coefficient KW - Scattering KW - Spatially resolved spectroscopy Y1 - 2019 U6 - https://doi.org/10.1016/j.postharvbio.2019.04.002 SN - 0925-5214 SN - 1873-2356 VL - 153 SP - 161 EP - 168 PB - Elsevier CY - Amsterdam ER -