FO-SPR Model for Full-Spectrum Signal Analysis of Back-reflecting FO-SPR Sensors to Monitor MOF Deposition.

In this study, we explore the full-spectrum capabilities of fiber-optic surface plasmon resonance (FO-SPR) for analyzing heterogeneous samples with increased comprehensiveness. Our approach involves refining a literature-derived FO-SPR model to more precisely reflect experimental data obtained using a back-reflecting sensor configuration. Key enhancements in our model include adjustments to the thickness and permittivity of the gold SPR-active layer on the FO-SPR sensor as well as improvements to the angular distribution of light within the system. We apply this optimized model to the investigation of the deposition process of a metal-organic framework (MOF), specifically ZIF-8, using FO-SPR. By closely examining the temporal variations in the FO-SPR signal during MOF layer formation, we simultaneously determine the evolving thickness and refractive index (RI) of the MOF layer, offering a dual-parameter analysis. Our results demonstrate that a full-spectrum analysis of the FO-SPR signal can extract critical information from samples exhibiting radial heterogeneity. This advancement significantly enhances the quantitative assessment of various phenomena that alter the refractive index in the sensor's domain, such as adsorption and binding processes. This work thus represents a significant step forward in the field of FO-SPR sensor technology, promising broad applications in areas requiring the precise detection and analysis of complex samples.

Design and Implementation of a Dual-Region Self-Referencing Fiber-Optic Surface Plasmon Resonance Biosensor.

The need for self-referencing is extremely important in the field of biosensing. In this manuscript, we report on the study, design, and validation of a dual-region self-referencing fiber-optic surface plasmon resonance biosensor. One region is intended to measure and monitor the binding events of the biological sample under test, while the other one is designed to be used as a reference channel to compensate for external factors, such as bulk refractive index modifications and temperature oscillations, that can negatively affect the biomolecular interaction measurement. Two different configurations for the biosensor probe are presented and investigated here, both theoretically and experimentally. First, the theoretical performance of the proposed biosensor probes, in terms of surface plasmon resonance wavelength shift, was simulated using a numerical model. Afterward, they were experimentally validated in sucrose-water solutions and showed a response to refractive index and temperature changes with sensitivities up to 2000 nm/RIU and 1.559 nm/°C, respectively. Finally, an aptamer-based bioassay and a high-resolution melting assay were successfully implemented on the two proposed configurations, demonstrating the feasibility of analyzing the binding events and measuring other external signal modifications simultaneously using the same biosensor probe.

Unraveling the effect of the aptamer complementary element on the performance of duplexed aptamers: a thermodynamic study.

Duplexed aptamers (DAs) are widespread aptasensor formats that simultaneously recognize and signal the concentration of target molecules. They are composed of an aptamer and aptamer complementary element (ACE) which consists of a short oligonucleotide that partially inhibits the aptamer sequence. Although the design principles to engineer DAs are straightforward, the tailored development of DAs for a particular target is currently based on trial and error due to limited knowledge of how the ACE sequence affects the final performance of DA biosensors. Therefore, we have established a thermodynamic model describing the influence of the ACE on the performance of DAs applied in equilibrium assays and demonstrated that this relationship can be described by the binding strength between the aptamer and ACE. To validate our theoretical findings, the model was applied to the 29-mer anti-thrombin aptamer as a case study, and an experimental relation between the aptamer-ACE binding strength and performance of DAs was established. The obtained results indicated that our proposed model could accurately describe the effect of the ACE sequence on the performance of the established DAs for thrombin detection, applied for equilibrium assays. Furthermore, to characterize the binding strength between the aptamer and ACEs evaluated in this work, a set of fitting equations was derived which enables thermodynamic characterization of DNA-based interactions through thermal denaturation experiments, thereby overcoming the limitations of current predictive software and chemical denaturation experiments. Altogether, this work encourages the development, characterization, and use of DAs in the field of biosensing.

Thermal unequilibrium of strained black CsPbI3 thin films.

The high-temperature, all-inorganic CsPbI3 perovskite black phase is metastable relative to its yellow, nonperovskite phase at room temperature. Because only the black phase is optically active, this represents an impediment for the use of CsPbI3 in optoelectronic devices. We report the use of substrate clamping and biaxial strain to render black-phase CsPbI3 thin films stable at room temperature. We used synchrotron-based, grazing incidence, wide-angle x-ray scattering to track the introduction of crystal distortions and strain-driven texture formation within black CsPbI3 thin films when they were cooled after annealing at 330°C. The thermal stability of black CsPbI3 thin films is vastly improved by the strained interface, a response verified by ab initio thermodynamic modeling.

Parts per Million Detection of Alcohol Vapors via Metal Organic Framework Functionalized Surface Plasmon Resonance Sensors.

The development of novel molecular sieves opens opportunities in the development of more sensitive analytical devices. In this paper, metal organic frameworks (MOFs), specifically ZIF-8 and ZIF-93, are grown on fiber optic based surface plasmon resonance (FO-SPR) sensors. FO-SPR has enabled sensitive sensing capabilities in biomedical settings and the addition of an MOF coating opens the way for the sensing of volatile organic compounds (VOCs) in gaseous media. FO-SPR probes were homogeneously functionalized with ZIF-8 and ZIF-93 in each case using two different precursor solutions to obtain a sequential nucleation and growth phase. The difference in MOF nucleation and growth kinetics of the two solutions was directly monitored by the FO-SPR system. The two established MOF-FO-SPR sensors were then subjected to sensing experiments with several alcohol vapors to establish their sensing capabilities. Vapors with mPa partial pressures, ppm concentrations, could successfully be detected, e.g., an LOD of 2.5 ppm for methanol detection was acquired. The difference in recognition behavior of the hydrophobic ZIF-8 and more hydrophilic ZIF-93 recognition layers can be exploited to yield qualitative information regarding the vapor composition.