Bulk Water Solution Research Articles

Steady State and Time-Resolved Fluorescence Spectroscopy of Cinchonine Dication in Sodium Dodecylsulphate Micellar System.

This paper reports the influence of surface charge of the micelles on to the photophysical properties of a cinchonine dication (C2+) fluorophore in anionic, sodium dodecylsulphate (SDS), surfactant at premicellar, micellar and post-micellar concentrations in aqueous phase at room temperature. The magnitude of edge excitation red shift (EERS) in the fluorescence maximum of C2+ in bulk water solution is 1897cm- 1 whereas, in the case of SDS it is observed to be 1984cm- 1. The fluorescence decay curve of C2+ fits with multi exponential functions in the micellar system. The increase in lifetime of C2+ in SDS has been attributed to the increase in radiative rate due to the incorporation of C2+ at the micelle -water interface. The value of dynamic quenching constant determined is 16.9 M- 1. The location of the probe molecule in micellar systems has been justified by a variety of spectral parameters such as dielectric constant, ET (30), viscosity, EERS, average fluorescence decay time, radiative and non-radiative rate constants. All experimental results suggest that the C2+ molecule binds strongly with the SDS micelles and resides at micellar-water interface. The binding constant (Kb) calculated (3.85 × 105 M- 1) for C2+ in SDS revealed that the electrostatic forces mediate charge probe-micelle association.

The Structure of Carbon Dioxide at the Air-Water Interface and its Chemical Implications.

The efficient reduction of CO2 into valuable products is a challenging task in an international context marked by the climate change crisis and the need to move away from fossil fuels. Recently, the use of water microdroplets has emerged as an interesting reaction media where many redox processes which do not occur in conventional solutions take place spontaneously. Indeed, several experimental studies in microdroplets have already been devoted to study the reduction of CO2 with promising results. The increased reactivity in microdroplets is thought to be linked to unique electrostatic solvation effects at the air-water interface. In the present work, we report a theoretical investigation on this issue for CO2 using first-principles molecular dynamics simulations. We show that CO2 is stabilized at the interface, where it can accumulate, and that compared to bulk water solution, its electron capture ability is larger. Our results suggest that reduction of CO2 might be easier in interface-rich systems such as water microdroplets, which is in line with early experimental data and indicate directions for future laboratory studies. The effect of other relevant factors which could play a role in CO2 reduction potential is discussed.

Distinguishing homogeneous advanced oxidation processes in bulk water from heterogeneous surface reactions in organic oxidation

Clarifying the reaction pathways at the solid-water interface and in bulk water solution is of great significance for the design of heterogeneous catalysts for selective oxidation of organic pollutants. However, achieving this goal is daunting because of the intricate interfacial reactions at the catalyst surface. Herein, we unravel the origin of the organic oxidation reactions with metal oxide catalysts, revealing that the radical-based advanced oxidation processes (AOPs) prevail in bulk water but not on the solid catalyst surfaces. We show that such differing reaction pathways widely exist in various chemical oxidation (e.g., high-valent Mn3+ and MnOX) and Fenton and Fenton-like catalytic oxidation (e.g., Fe2+ and FeOCl catalyzing H2O2, Co2+ and Co3O4 catalyzing persulfate) systems. Compared with the radical-based degradation and polymerization pathways of one-electron indirect AOP in homogeneous reactions, the heterogeneous catalysts provide unique surface properties to trigger surface-dependent coupling and polymerization pathways of a two-electron direct oxidative transfer process. These findings provide a fundamental understanding of catalytic organic oxidation processes at the solid-water interface, which could guide the design of heterogeneous nanocatalysts.

(Invited) In Situ spectroscopy of Electrochemical and Photoelectrochemical Interfaces

We explore various aspects of electrochemistry and photoelectrochemistry using in situ spectroscopy of electrode (metal) and photoelectrode (semiconductor) interfaces under electrochemical working conditions. Using sum frequency generation (SFG) spectroscopy, we measure the voltage dependence of the orientation of D2O molecules at a graphene electrode surface, which enables us to extract the free energy orienting potential of interfacial water.1 In particular, we measure the “free OD” feature in the spectra, which corresponds to the topmost water molecule that is rotated up out of the bulk water solution and is, therefore, not hydrogen bonded. Using transient absorption spectroscopy (TAS), we measure the lifetime of hot electrons photoexcited in plasmon resonant nanostructures.5 In a similar study, we use transient reflectance spectroscopy (TRS) to measure the photoexcited carrier dynamics in a GaP/TiO2 photoelectrode, as well as the electrostatic field dynamics at this semiconductor-liquid interface in situ under various electrochemical potentials.2 Here, the electrostatic fields at the surface of the semiconductor are measured via Franz−Keldysh oscillations (FKO). These spectra reveal that the nanoscale TiO2 protection layer enhances the built-in field and charge separation performance of GaP photoelectrodes. Using surface enhanced Raman scattering (SERS) spectroscopy, we monitor local electric fields via Stark-shifts of nitrile-functionalized silicon photoelectrodes.6 By monitoring Stark shifts in graphene-enhanced Raman spectroscopy (GERS), we measure local electric fields and local charge densities at monolayer graphene electrode surfaces.3 Lastly, we measure the stacking dependence of monolayer WSe2/MoSe2 heterostructures and observe resonant excitation of interlayer excitons for photocatalytic energy conversion.4 Montenegro, A., C. Dutta, M. Mammetkuliev, H.T. Shi, B.Y. Hou, D. Bhattacharyya, B.F. Zhao, S.B. Cronin and A.V. Benderskii, Asymmetric response of interfacial water to applied electric fields. Nature, 594, 62 (2021).Xu, Z.H., B.Y. Hou, F.Y. Zhao, Z. Cai, H.T. Shi, Y.W. Liu, C.L. Hill, D.G. Musaev, M. Mecklenburg, S.B. Cronin and T.Q. Lian, Nanoscale TiO2 Protection Layer Enhances the Built-In Field and Charge Separation Performance of GaP Photoelectrodes. Nano Letters, 21, 8017-8024 (2021).Shi, H.T., B.F. Zhao, J. Ma, M.J. Bronson, Z. Cai, J.H. Chen, Y. Wang, M. Cronin, L. Jensen and S.B. Cronin, Measuring Local Electric Fields and Local Charge Densities at Electrode Surfaces Using Graphene-Enhanced Raman Spectroscopy (GERS)-Based Stark-Shifts. ACS Applied Materials & Interfaces, 11, 36252-36258 (2019).Chen, J., C.S. Bailey, D. Cui, Y. Wang, B. Wang, H. Shi, Z. Cai, E. Pop, C. Zhou and S.B. Cronin, Stacking Independence and Resonant Interlayer Excitation of Monolayer WSe2/MoSe2 Heterostructures for Photocatalytic Energy Conversion. ACS Applied Nano Materials, DOI:10.1021/acsanm.9b01898 (2020).Yu Wang, Yi Wang, Indu Aravind, Zhi Cai, Lang Shen, Boxin Zhang, Bo Wang, Jihan Chen, Bofan Zhao, Haotian Shi, Jahan M. Dawlaty, and Stephen B. Cronin. In Situ Investigation of Ultrafast Dynamics of Hot Electron-Driven Photocatalysis in Plasmon-Resonant Grating Structures. Journal of the American Chemical Society. DOI: 10.1021/jacs.1c12069 (2022).Haotian Shi, Ryan T. Pekarek, Ran Chen, Boxin Zhang, Yu Wang, Indu Aravind, Zhi Cai, Lasse Jensen, Nathan R. Neale, and Stephen B. Cronin. Monitoring Local Electric Fields using Stark Shifts on Napthyl Nitrile-Functionalized Silicon Photoelectrodes. The Journal of Physical Chemistry C, 124, 17000-17005 (2020).

Water Dynamics and Structure of Highly Concentrated LiCl Solutions Investigated Using Ultrafast Infrared Spectroscopy.

In highly concentrated salt solutions, the water hydrogen bond (H-bond) network is completely disrupted by the presence of ions. Water is forced to restructure as dictated by the water-ion and ion-ion interactions. Using ultrafast polarization-selective pump-probe (PSPP) spectroscopy measurements of the OD stretch of dilute HOD, we demonstrate that the limited water-water H-bonding present in concentrated lithium chloride solutions (up to four waters per ion pair) is, on average, stronger than that occurring in bulk water. Furthermore, information on the orientational dynamics and the angular restriction of water H-bonded to both water oxygens and chloride anions was obtained through analysis of the frequency-dependent anisotropy decays. It was found that, when the salt concentration increased, the water showed increasing restriction and slowing at frequencies correlated with strong H-bonding. The angular restriction of the water molecules and strengthening of water-water H-bonds are due to the formation of a water-ion network not present in bulk water and dilute salt solutions. The structural evolution of the ionic medium was also observed through spectral diffusion of the OD stretch using 2D IR spectroscopy. Compared to bulk water, there is significant slowing of the biexponential spectral diffusion dynamics. The slowest component of the spectral diffusion (13 ps) is virtually identical to the time for complete reorientation of HOD measured with the PSPP experiments. This result suggests that the slowest component of the spectral diffusion reflects rearrangement of water molecules in the water-ion network.

Hygroscopicity of Microplastic and Mixed Microplastic Aqueous Ammonium Sulfate Systems.

A growing body of research suggests the presence and long-range transport of microplastics in the atmosphere. However, the interactions between these microplastics and atmospheric aerosol are poorly understood. Environmental microplastics vary in color, morphology, and chemical composition and become oxidized over time by UV, mechanical, and biological action. Once introduced to the atmosphere, these microplastics will likely become mixed with atmospheric aerosol. Determining how microplastics interact with aerosol particles and how they may alter aerosol physical properties, including water uptake and loss, is necessary to understand the impact of these microplastics on our environment. Herein, we investigate the effect of microplastics on the water activity of bulk water and ammonium sulfate solutions. We compare a variety of plastic compositions and microplastic morphologies including plastics that have been aged by UV irradiation and mechanical forces in the lab. In addition, we investigate the water uptake and loss in microplastic samples through dynamic vapor sorption. We find an increase in total water sorption for UV-aged plastics compared to pristine plastics. Finally, we investigate the effect of fractional surface coverage on the equilibration time scale.

Molecular Properties and Chemical Transformations Near Interfaces.

The properties of bulk water and aqueous solutions are known to change in the vicinity of an interface and/or in a confined environment, including the thermodynamics of ion selectivity at interfaces, transition states and pathways of chemical reactions, and nucleation events and phase growth. Here we describe joint progress in identifying unifying concepts about how air, liquid, and solid interfaces can alter molecular properties and chemical reactivity compared to bulk water and multicomponent solutions. We also discuss progress made in interfacial chemistry through advancements in new theory, molecular simulation, and experiments.

Tight electrostatic regulation of the OH production rate from the photolysis of hydrogen peroxide adsorbed on surfaces

Recently, experimental and theoretical works have reported evidence indicating that photochemical processes may significantly be accelerated at heterogeneous interfaces, although a complete understanding of the phenomenon is still lacking. We have carried out a theoretical study of interface and surface effects on the photochemistry of hydrogen peroxide (H2O2) using high-level ab initio methods and a variety of models. Hydrogen peroxide is an important oxidant that decomposes in the presence of light, forming two OH radicals. This elementary photochemical process has broad interest and is used in many practical applications. Our calculations show that it can drastically be affected by heterogeneous interfaces. Thus, compared to gas phase, the photochemistry of H2O2 appears to be slowed on the surface of apolar or low-polar surfaces and, in contrast, hugely accelerated on ionic surfaces or the surface of aqueous electrolytes. We give particular attention to the case of the neat air-water interface. The calculated photolysis rate is similar to the gas phase, which stems from the compensation of two opposite effects, the blue shift of the n→σ* absorption band and the increase of the absorption intensity. Nevertheless, due to the high affinity of H2O2 for the air-water interface, the predicted OH production rate is up to five to six orders of magnitude larger. Overall, our results show that the photochemistry of H2O2 in heterogeneous environments is greatly modulated by the nature of the surface, and this finding opens interesting new perspectives for technological and biomedical applications, and possibly in various atmospheres.

Confining a Protein-Containing Water Nanodroplet inside Silica Nanochannels.

Incorporation of biological systems in water nanodroplets has recently emerged as a new frontier to investigate structural changes of biomolecules, with perspective applications in ultra-fast drug delivery. We report on the molecular dynamics of the digestive protein Pepsin subjected to a double confinement. The double confinement stemmed from embedding the protein inside a water nanodroplet, which in turn was caged in a nanochannel mimicking the mesoporous silica SBA-15. The nano-bio-droplet, whose size fits with the pore diameter, behaved differently depending on the protonation state of the pore surface silanols. Neutral channel sections allowed for the droplet to flow, while deprotonated sections acted as anchoring piers for the droplet. Inside the droplet, the protein, not directly bonded to the surface, showed a behavior similar to that reported for bulk water solutions, indicating that double confinement should not alter its catalytic activity. Our results suggest that nanobiodroplets, recently fabricated in volatile environments, can be encapsulated and stored in mesoporous silicas.

Computational Investigation on Electronic Structures and Properties of 4,6-Bis(nitroimino)-1,3,5-triazinan-2-one: An Insensitive Munition Compound.

In order to minimize unintentional detonation, munitions researchers have focused on the development of chemical compounds that are insensitive to external stimuli while maintaining their effectiveness. Although these compounds, known as high-performance insensitive munition compounds, are promising in terms of potency and stability, their environmental impacts have either not been fully understood or are yet to be investigated. In the present research, we have performed a quantum chemical investigation on electronic structures and properties of an insensitive munition compound 4,6-bis(nitroimino)-1,3,5-triazinan-2-one (DNAM). The density functional theory using the B3LYP and M06-2X functionals and MP2 methodology were used for geometry optimization of various tautomeric forms of DNAM. The effect of bulk water solution was evaluated using the conductor-like polarizable continuum model and the density-based solvation model. Ionization potentials, electron affinities, redox properties, and p Ka values were also computed and compared with the available experimental data. These physical and chemical properties of DNAM have been discussed with regard to the varying tautomeric forms in which DNAM can exist.

Thermochemical Processes During the Degradation of Nitroguanidine in Water: A Density Functional Theory Investigation.

In the present study, thermochemical mechanisms are proposed for the decomposition of nitroguanidine (NQ) in aqueous solution. Minnesota density functional M06-2X was employed for depicting the pathways for the NQ decomposition with a conductor-like polarizable continuum model (CPCM) approach to consider the effect of bulk water solution. Followed by the formation of hydroxyguanidine and/or guanidine along with nitrite by eliminating the nitro group from NQ through photolysis, two main degradation steps through the thermochemical process were investigated. These thermochemical degradation steps include the formation of cyanamide from hydroxyguanidine and/or guanidine along with ammonia, and the formation of cyanoguanidine from the dimerization of cyanamide. Further, degradations of the fragments of cyanamide, cyanoguanidine, guanidine, and hydroxyguandine were also explored. The results show that melamine and urea may exist as degradation fragments while cyanide and nitrosoguanidine are unlikely to form through usual thermochemical processes due to the presence of high energy barriers. Water and hydroxide ions play important roles in the degradation process; in particular, hydroxide ions significantly lower the energy barriers demonstrating that the proposed pathway is energetically viable.

Macrocycle threading using solvatochromic squaraine dyes

ABSTRACTNon-covalent assembly is an attractive way to fabricate deep-red fluorescent probes for biological imaging. Four new solvatochromic squaraine dyes with unsymmetric structures are prepared and shown to exhibit macrocyclic encapsulation by tetralactam macrocycle in chloroform solvent or in water. Macrocycle threading in chloroform produces a relatively small 20 nm red-shift in absorption wavelength. In contrast, macrocycle threading in water produces ~80 nm red-shift in absorption wavelength, indicating a large change in polarity surrounding the solvatochromic squaraine as it transfers from bulk water solution to the relatively non-polar macrocycle interior. The large red-shift in absorption maxima translates into a very large 70-fold enhancement of squaraine fluorescence. Macrocycle threading in water by two homologous squaraines was studied and there was a large difference in threading kinetics. Macrocycle threading by a squaraine with an N-methyl substituent at the end of the structure was 5 million times faster than threading by a squaraine with an N-propyl substituent.

Temperature dependence of water-water and ion-water correlations in bulk water and electrolyte solutions probed by femtosecond elastic second harmonic scattering.

The temperature dependence of the femtosecond elastic second harmonic scattering (fs-ESHS) response of bulk light and heavy water and their electrolyte solutions is presented. We observe clear temperature dependent changes in the hydrogen (H)-bond network of water that show a decrease in the orientational order of water with increasing temperature. Although D2O has a more structured H-bond network (giving rise to more fs-ESHS intensity), the relative temperature dependence is larger in H2O. The changes are interpreted in terms of the symmetry of H-bonds and are indicators of nuclear quantum effects. Increasing the temperature in electrolyte solutions decreases the influence of the total electrostatic field from ions on the water-water correlations, as expected from Debye-Hückel theory, since the Debye length becomes longer. The effects are, however, 1.9 times (6.3 times) larger than those predicted for H2O (D2O). Since fs-ESHS responses can be computed from known molecular coordinates, our observations provide a unique opportunity to refine quantum mechanical models of water.

On the solvation of the phosphocholine headgroup in an aqueous propylene glycol solution.

The atomic-scale structure of the phosphocholine (PC) headgroup in 30 mol. % propylene glycol (PG) in an aqueous solution has been investigated using a combination of neutron diffraction with isotopic substitution experiments and computer simulation techniques-molecular dynamics and empirical potential structure refinement. Here, the hydration of the PC headgroup remains largely intact compared with the hydration of this group in a bilayer and in a bulk water solution, with the PG molecules showing limited interactions with the headgroup. When direct PG interactions with PC do occur, they are most likely to coordinate to the N(CH3)3+ motifs. Further, PG does not affect the bulk water structure and the addition of PC does not perturb the PG-solvent interactions. This suggests that the reason why PG is able to penetrate into membranes easily is that it does not form strong-hydrogen bonding or electrostatic interactions with the headgroup allowing it to easily move across the membrane barrier.

An integrated theoretical and experimental investigation of insensitive munition compounds adsorption on cellulose, cellulose triacetate, chitin and chitosan surfaces

This manuscript reports results of combined computational chemistry and batch adsorption investigation of insensitive munition compounds, 2,4-dinitroanisole (DNAN), triaminotrinitrobenzene (TATB), 1,1-diamino-2,2-dinitroethene (FOX-7) and nitroguanidine (NQ), and traditional munition compound 2,4,6-trinitrotoluene (TNT) on the surfaces of cellulose, cellulose triacetate, chitin and chitosan biopolymers. Cellulose, cellulose triacetate, chitin and chitosan were modeled as trimeric form of the linear chain of 4C1 chair conformation of β-d-glucopyranos, its triacetate form, β-N-acetylglucosamine and D-glucosamine, respectively, in the 1➔4 linkage. Geometries were optimized at the M062X functional level of the density functional theory (DFT) using the 6-31G(d,p) basis set in the gas phase and in the bulk water solution using the conductor-like polarizable continuum model (CPCM) approach. The nature of potential energy surfaces of the optimized geometries were ascertained through the harmonic vibrational frequency analysis. The basis set superposition error (BSSE) corrected interaction energies were obtained using the 6-311G(d,p) basis set at the same theoretical level. The computed BSSE in the gas phase was used to correct interaction energy in the bulk water solution. Computed and experimental results regarding the ability of considered surfaces in adsorbing the insensitive munitions compounds are discussed.

The Conformation of Aβ-Peptide Aggregates on 2D Surfaces is Different than in Solution: A Molecular Dynamics Study

Alzheimer's Disease (AD) is an important and increasingly prevalent neurodegenerative disease. Aggregation of Aβ-peptides is important in etiology of AD. It has been shown experimentally that Aβ-peptides self assemble to form fibrils on 2D surfaces at much faster rates than they form fibrils in the 3D environment of solutions. However, the molecular mechanism of the fibril formation and the conformation of the fibril on 2D surfaces remain unknown. We have run long molecular dynamics simulations of Aβ (1-40) monomers on Alkanethiol self-assembled monolayers (SAM) with different functional head groups and also in bulk water solution. We began with Aβ-peptides pre-adsorbed on SAMs (∼ 5A from the surface). SAM-CH3 and -COOH restricted Aβ-peptide motion, leading to inter-monomer β-strand formation within orders of 100s of nanoseconds. The same effect was not observed in bulk solution. Unlike the SAM-CH3 and -COOH surfaces, Aβ-monomer adsorption on the SAM-OH surface was weak, causing monomers to leave the surface and move into solution. These results indicate the importance of the combination of hydrophobic and electrostatic interactions for mediating Aβ self-assembly on the SAM. A simulation in which Aβ-peptides were initiated 15A above the SAM-CH3 surface further supported our result. Aβ-peptides initially showed low β-content, but once they were adsorbed (∼ 170 ns) the β-content increased to values similar to our simulations of pre-adsorbed monomers. The β-sheet formation was both inter- and intra-peptide though mostly parallel to the surface in contrast to the NMR data in bulk solution where the Aβ-monomers stacked on top of each other. The residues involved in β-sheet formation were somewhat different from those observed in the NMR data. These observations suggested that Aβ-peptides could possibly blanket the cell surface disrupting cell communication with the outside.

Computational prediction of electronic excited-state structures and properties of 2,4-dinitroanisole (DNAN)

This manuscript reports results of density functional theory (DFT) investigation on ground-state and electronic excited-state structures of 2,4-dinitroanisole (DNAN) in the bulk water solution. The cam-B3LYP functional along with 6-311G(d,p) basis set was used, and time-dependent DFT (TD-DFT) method was used for excited-state calculations. The effect of bulk water was modeled using the CPCM approach. Nature of potential energy surfaces (PESs) was ascertained through the harmonic vibrational frequency analysis; all optimized geometries were found to be minima at the respective PESs. It was predicted that singlet excited-state geometries are significantly changed compared to the ground state. Further, it was also revealed that irrespective of nature of the electronic singlet excited states, the length of C7O1 bond is increased compared to the ground state. Further, electronic structures and properties consequent to electronic excitations are also discussed.

Structure of hydrogen tetroxide in gas phase and in aqueous environments: relationship to the hydroperoxyl radical self-reaction

Hydrogen polyoxides are important species in atmospheric chemistry, advanced oxidation processes for wastewater treatment, and biological processes, among other fields. However, the electronic structure and chemical properties of the largest synthesized members of this chemical family remain poorly understood. In the present work, we have carried out a detailed theoretical study of hydrogen tetroxide (HO4H), which is a reaction interme- diate of the hydroperoxyl radical (HO2) self-reaction. We have considered the molecule in gas phase, in microhy- drated environments, in bulk water solution, and at the air- water interface. Very high level ab initio calculations have been carried out to describe the isolated molecule and the water complexes. Combined QM/MM molecular dynamics simulations have been performed to describe the system in liquid water and at the water surface. We show that the interactions with water strongly stabilize the tetraoxide adduct with respect to the (HO2)2 dimer. The chemical process leading to hydrogen tetroxide from two separated hydroperoxyl radicals is predicted to be an exothermic and exergonic reaction at 298 K in all the studied media, with the reaction free energy being slightly smaller (in absolute value) in the condensed phase with respect to the gas phase. An estimation of the pKa of hydrogen tetroxide has been reported (7.3), which suggests that this species is less acidic than previously thought.

Efficient "on-the-fly" calculation of Raman spectra from ab-initio molecular dynamics: Application to hydrophobic/hydrophilic solutes in bulk water.

We present a novel computational method to accurately calculate Raman spectra from first principles. Together with an extension of the second-generation Car-Parrinello method of Kühne et al. (Phys. Rev. Lett. 2007, 98, 066401) to propagate maximally localized Wannier functions together with the nuclei, a speed-up of one order of magnitude can be observed. This scheme thus allows to routinely calculate finite-temperature Raman spectra "on-the-fly" by means of ab-initio molecular dynamics simulations. To demonstrate the predictive power of this approach we investigate the effect of hydrophobic and hydrophilic solutes in water solution on the infrared and Raman spectra.

Selectable Surface and Bulk Fluorescence Imaging with Plasmon-Coupled Waveguides.

In this letter, we propose a new method for selective imaging of surface bound probes or simultaneous imaging of surface bound plus fluorescence from dye molecules in bulk water solution. The principle of this method relies on use of two optical modes with different mode distributions, filed decay lengths and polarization states that are sustaining in a plasmon waveguide. The two modes with different decay lengths couple with dye molecules of different regions, at different distances from the PCW-water interface. The emission from two different regions occur as two coupled emission rings with different polarizations and emitting angles in the back focal plane (BFP) images. By using an electric-driven liquid crystal in BFP imaging, we selectively imaged surface or surface plus bulk fluorescence. Accordingly two coupled emissions can be switched ON or OFF independently, that are for either surface or bulk fluorescence imaging. Our work provides a new method for fluorescence imaging or sensing just by using a planar multilayer film, which may be a useful for fluorescence-based techniques in chemistry, materials science, molecular biology, and medicine.