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Clay/polymer nanocomposites (CPNs) are polymers incorporating refined clay particles that are frequently functionalized with quaternary ammonium cations (QACs) as dispersion aids. There is interest in commercializing CPNs for food contact applications because they have improved strength and barrier properties, but there are few studies on the potential for QACs in CPNs to transfer to foods under conditions of intended use. In this study, we manufactured low-density poly(ethylene) (LDPE)-based CPNs and assessed whether QACs can migrate into several food simulants under accelerated storage conditions. QACs were found to migrate to a fatty food simulant (ethanol) at levels of ∼1.1 μg mg–1 CPN mass after 10 days at 40 °C, constituting about 4% total migration (proportion of the initial QAC content in the CPN that migrated to the simulant). QAC migration into ethanol was ∼16× higher from LDPE containing approximately the same concentration of QACs but no clay, suggesting that most QACs in the CPN are tightly bound to clay particles and are immobile. Negligible QACs were found to migrate into aqueous, alcoholic, or acidic simulants from CPNs, and the amount of migrated QACs was also found to scale with the temperature and the initial clay concentration. The migration data were compared to a theoretical diffusion model, and it was found that the diffusion constant for QACs in the CPN was several orders of magnitude slower than predicted, which we attributed to the potential for QACs to migrate as dimers or other aggregates rather than as individual ions. Nevertheless, the use of the migration model resulted in a conservative estimate of the mass transfer of QAC from the CPN test specimens.

Toxicological risk assessment approaches are increasingly being used in lieu of animal testing to address toxicological concerns associated with release of chemical constituents from polymeric medical device components. These approaches currently rely on in vitro extraction testing in aggressive environments to estimate patient exposure to these constituents, but the clinical relevance of the test results is often ambiguous. Physics-based mass transport models can provide a framework to interpret extraction test results to provide more clinically relevant exposure estimates. However, the models require system-specific material properties, such as diffusion (D) and partition coefficients (K), to be established a priori for the extraction conditions. Using systems comprised high-density polyethylene and 4 different additives, we demonstrate that these properties can be quantified through standard extraction testing in hexane and isopropyl alcohol. The values of D and K derived in this manner were consistent with theoretical predictions for these quantities. Based on these results, we discuss both the challenges and benefits to leveraging extraction data to parameterize physics-based exposure models. Our observations suggest that clinically relevant, yet still conservative, exposure dose estimates provided by applying this approach to a single extraction measurement can be more than 100 times lower than would be measured under typical aggressive extraction conditions. However, to apply the framework on a routine basis, limiting values of D and K must be established for device-relevant systems either through the aggregation and analysis of more extensive extraction test data and/or advancements in theoretical and computational modeling efforts to predict these quantities.

As far as chemical analysis is concerned, foods are among the most difficult matrices to work with because they are complex, heterogeneous substances with a high degree of variety. Assaying foods for trace levels of chemical and microbiological substances is a challenge that often requires the application of time-consuming, expensive analytical instrumentation in dedicated facilities populated by highly trained personnel. Therefore there is a continued demand for new analytical technologies that can detect small concentrations of chemicals or microbes in a more cost- and time-effective manner, preferably in the field, on the production line, and/or non-destructively, with little to no sample pre-treatment, and possibly by individuals with scant scientific training. In the last decade, nanotechnology - a branch of science that takes advantage of the unique chemical and physical properties of matter on the nanoscale - has created new opportunities for both qualitative and quantitative detection of vapors/gasses, small molecules, biopolymers, and even living microbes in a fraction of the time and expense of traditional analytical techniques. This article offers a focused review of recent progress in nanotechnology-enabled biosensing as applied to foods and related matrices, paying particular attention to trends in the field, recent breakthroughs, and current areas of need. Special focus is paid to two primary categories of nanobiosensors - optical and electrochemical - and the discussion includes a comparison of their various strengths and weaknesses as they pertain ensuring the safety of the food supply.

Octopolar D2-symmetric chromophores, based on the MPZnM supermolecular motif in which (porphinato)zinc(II) (PZn) and ruthenium(II) polypyridyl (M) structural units are connected via ethyne linkages, were synthesized. These structures take advantage of electron-rich meso-arylporphyrin or electron-poor meso-(perfluoroalkyl)porphyrin macrocycles, unsubstituted terpyridyl and 4′-pyrrolidinyl-2,2′;6′,2″-terpyridyl ligands, and modulation of metal(II) polypyridyl-to-(porphinato)zinc connectivity, to probe how electronic and geometric factors impact the measured hyperpolarizability. Transient absorption spectra obtained at early time delays (tdelay < 400 fs) demonstrate fast excited-state relaxation, and formation of a highly polarized T1 excited state; the T1 states of these chromophores display expansive, intense T1 → Tn absorption manifolds that dominate the 800–1200 nm region of the NIR, long (μs) triplet-state lifetimes, and unusually large NIR excited absorptive extinction coefficients [ε(T1 → Tn) ∼ 105 M–1 cm–1]. Dynamic hyperpolarizability (βλ) values were determined from hyper-Rayleigh light scattering (HRS) measurements, carried out at multiple incident irradiation wavelengths spanning the 800–1500 nm spectral domain. The measured βHRS value (4600 ± 1200 × 10–30 esu) for one of these complexes, RuPZnRu, is the largest yet reported for any chromophore at a 1500 nm irradiation wavelength, highlighting that appropriate engineering of strong electronic coupling between multiple charge-transfer oscillators provides a critical design strategy to realize octopolar NLO chromophores exhibiting large βHRS values at telecom-relevant wavelengths. Generalized Thomas–Kuhn sum (TKS) rules were utilized to compute the effective excited-state-to-excited-state transition dipole moments from experimental linear-absorption spectra; these data were then utilized to compute hyperpolarizabilities as a function of frequency, that include two- and three-state contributions for both βzzz and βxzx tensor components to the RuPZnRu hyperpolarizability spectrum. This analysis predicts that the βzzz and βxzx tensor contributions to the RuPZnRu hyperpolarizability spectrum maximize near 1550 nm, in agreement with experimental data. The TKS analysis suggests that relative to analogous dipolar chromophores, octopolar supermolecules will be likely characterized by more intricate dependences of the measured hyperpolarizability upon irradiation wavelength due to the interactions among multiple different β tensor components., Coupling of multiple charge-transfer oscillators generates D2-symmetric octopolar NLO chromophores that exhibit large βHRS values at telecom-relevant wavelengths.

Background: A flow-injection MS (FI/MS) method was evaluated for the quantitation of quaternary ammonium cations (QACs) in simple food simulants. Methods: The calibration standard was dimethyldioctadecyl ammonium ion (C18-C18), and the internal standard was benzyldimethylhexadecyl (BDMHD) ammonium ion. Calibration standards based on the C18-C18 ion were prepared in ethanol with a range of 5 to 500 ppb and contained 100 ppb BDMHD. The mobile phase was 90 + 10 (v/v) acetonitrile–5 mM aqueous ammonium acetate and flowed directly into an electrospray source of the mass spectrometer. Detection was accomplished by single ion recording (SIR) in positive mode. Results: Calibration curves were linear with coefficients of determination above 0.995, and the LOQ was 5 ppb. Recoveries of four QACs derived from Arquad 2HT-75, a commercially available surfactant, were measured in common food simulants: ethanol, water, 10% (v/v) ethanol in water, and 3% (v/v) aqueous acetic acid. A solvent exchange procedure was employed for the three aqueous solvents, which included complete evaporation of the sample followed by reconstitution in ethanol prior to injection. The solvent exchange method minimized losses because of QAC adsorption on glass surfaces. Recoveries ranged from 74.4 ± 4.0 to 106.7 ± 6.6% for the two most abundant Arquad 2HT-75 component cations, dimethyldioctadecyl ammonium and dimethyloctadecyl-hexadecyl ammonium. Conclusions: This method is suitable to quantify trace levels of QACs in food simulants as part of exposure evaluations related to their use in emerging food contact materials.

Concomitant with the development of polymer nanocomposite (PNC) technologies across numerous industries is an expanding awareness of the uncertainty with which engineered nanoparticles embedded within these materials may be released into the external environment, particularly liquid media. Recently there has been an interest in evaluating potential exposure to nanoscale fillers from PNCs, but existing studies often rely upon uncharacterized, poor quality, or proprietary materials, creating a barrier to making general mechanistic conclusions about release phenomena. In this study we employed semiconductor nanoparticles (quantum dots, QDs) as model nanofillers to quantify potential release into liquid media under specific environmental conditions. QDs of two sizes were incorporated into low-density polyethylene by melt compounding and the mixtures were extruded as free-standing fluorescent films. These films were subjected to tests under conditions intended to accelerate potential release of embedded particles or dissolved residuals into liquid environments. Using inductively-coupled plasma mass spectrometry and laser scanning confocal microscopy, it was found that the acidity of the external medium, exposure time, and small differences in particle size (on the order of a few nm) all play pivotal roles in release kinetics. Particle dissolution was found to play a major if not dominant role in the release process. This paper also presents the first evidence that internally embedded nanoparticles contribute to the mass transfer, an observation made possible via the use of a model system that was deliberately designed to probe the complex relationships between nanoparticle-enabled plastics and the environment.

This article is one of a series of 4 that report on a task of the NanoRelease Food Additive project of the Intl. Life Science Inst. Center for Risk Science Innovation and Application to identify, evaluate, and develop methods that are needed to confidently detect, characterize, and quantify intentionally produced engineered nanomaterials (ENMs) released from food along the alimentary tract. This particular article focuses on the problem of detecting ENMs that become released into food indirectly from food contact materials. In this review, an in-depth analysis of the release literature is presented and relevant release mechanisms are discussed. The literature review includes discussion of articles related to the release phenomenon in general, as experimental methods to detect ENMs migrating from plastic materials into other (nonfood) complex matrices were determined to be relevant to the focus problem of food safety. From the survey of the literature, several “control points” were identified where characterization data on ENMs and materials may be most valuable. The article concludes with a summary of findings and a discussion of potential knowledge gaps and targets for method development in this area.

Graphical abstract Nanotechnology may revolutionize the food industry by providing stronger, high-barrier packaging materials, more potent antimicrobial agents, and a host of sensors which can detect trace contaminants, gasses or microbes in packaged foods. Highlights ► Focuses on the use of nanomaterials in food packaging and sensing applications. ► Polymer nanocomposites offer high gas barriers, strength, and flame retardancy. ► Silver and metal oxide nanoparticles are potent biocides. ► Nanosensors and assays detect gasses, small molecules and microorganisms. ► Economic outlook and health and safety implications are also briefly reviewed., In this article, several applications of nanomaterials in food packaging and food safety are reviewed, including: polymer/clay nanocomposites as high barrier packaging materials, silver nanoparticles as potent antimicrobial agents, and nanosensors and nanomaterial-based assays for the detection of food-relevant analytes (gasses, small organic molecules and food-borne pathogens). In addition to covering the technical aspects of these topics, the current commercial status and understanding of health implications of these technologies are also discussed. These applications were chosen because they do not involve direct addition of nanoparticles to consumed foods, and thus are more likely to be marketed to the public in the short term.

Transient dynamical studies of bis[(5,5'-10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)palladium(II)]ethyne (PPd(2)), 5,15-bis{[(5'-10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)palladium(II)]ethynyl}(10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)palladium(II) (PPd(3)), bis[(5,5'-10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)platinum(II)]ethyne (PPt(2)), and 5,15-bis{[(5'-10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)platinum(II)]ethynyl}(10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)platinum(II) (PPt(3)) show that the electronically excited triplet states of these highly conjugated supermolecular chromophores can be produced at unit quantum yield via fast S(1) → T(1) intersystem crossing dynamics (τ(isc): 5.2-49.4 ps). These species manifest high oscillator strength T(1) → T(n) transitions over broad NIR spectral windows. The facts that (i) the electronically excited triplet lifetimes of these PPd(n) and PPt(n) chromophores are long, ranging from 5 to 50 μs, and (ii) the ground and electronically excited absorptive manifolds of these multipigment ensembles can be extensively modulated over broad spectral domains indicate that these structures define a new precedent for conjugated materials featuring low-lying π-π* electronically excited states for NIR optical limiting and related long-wavelength nonlinear optical (NLO) applications.

We report a new method to generate families of organic fluorophores with any desirable emission wavelengths based upon the controlled oxidation of the light-emitting conjugated polymer, poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV), with meta-chloroperbenzoic acid (m-CPBA). In this method, m-CPBA reacts with ethylene moieties along the MEH-PPV backbone to create conjugation breaks, which gives rise to a gradual and controllable change in the emission wavelength. By simply adjusting the reaction time, light-emitting polymers possessing emission wavelengths spanning a 470-555 nm wavelength range can be easily prepared. Significantly, fluorescence quantum yields (QYs) of the oxidized polymers were comparable to or greater than that of the pristine polymer, contrary to the products typically resulting from oxidation of MEH-PPV by dioxygen. This new method should provide a simple way to generate color-tunable organic fluorophores with high QYs in a time- and cost-effective manner.

The electron transfer (ET) dynamics of an unusually rigid pi-stacked (porphinato)zinc(II)-spacer-quinone (PZn-Q) system, [5-[8'-(4' '-[8' ''-(2' '' ',5' '' '-benzoquinonyl)-1' ''-naphthyl]-1' '-phenyl)-1'-naphthyl]-10,20-diphenylporphinato]zinc(II) (2a-Zn), in which sub-van der Waals interplanar distances separate juxtaposed porphyryl, aromatic bridge, and quinonyl components of this assembly, have been measured by ultrafast pump-probe transient absorption spectroscopy over a 80-320 K temperature range in 2-methyl tetrahydrofuran (2-MTHF) solvent. Analyses of the photoinduced charge-separation (CS) rate data are presented within the context of several different theoretical frameworks. Experiments show that at higher temperatures the initially prepared 2a-Zn vibronically excited S1 state relaxes on an ultrafast time scale, and ET is observed exclusively from the equilibrated lowest-energy S1 state (CS1). As the temperature decreases, production of the photoinduced charge-separated state directly from the vibrationally unrelaxed S1 state (CS2) becomes competitive with the vibrational relaxation time scale. At the lowest experimentally interrogated temperature ( approximately 80 K), CS2 defines the dominant ET pathway. ET from the vibrationally unrelaxed S1 state is temperature-independent and manifests a subpicosecond time constant; in contrast, the CS1 rate constant is temperature-dependent, exhibiting time constants ranging from 4x10(10) s(-1) to 4x10(11) s(-1) and is correlated strongly with the temperature-dependent solvent dielectric relaxation time scale over a significant temperature domain. Respective electronic coupling matrix elements for each of these photoinduced CS1 and CS2 pathways were determined to be approximately 50 and approximately 100 cm-1. This work not only documents a rare, if not unique, example of a system where temperature-dependent photoinduced charge-separation (CS) dynamics from vibrationally relaxed and unrelaxed S1 states can be differentiated, but also demonstrates a temperature-dependent mechanistic transition of photoinduced CS from the nonadiabatic to the solvent-controlled adiabatic regime, followed by a second temperature-dependent mechanistic evolution where CS becomes decoupled from solvent dynamics and is determined by the extent to which the vibrationally unrelaxed S1 state is populated.

The photophysics of triplet excitons in a series of electronically asymmetric “push−pull” π-conjugated meso-to-meso ethyne-bridged (porphinato)metal oligomers, along with electronically symmetric analogues, were studied by X-band electron paramagnetic resonance (EPR) spectroscopy under continuous-wave (CW) optical pumping conditions in the 4−100 K temperature range. In all of the systems studied, the spatial extent of the triplet wave function, as inferred from the |D| zero-field splitting (ZFS) parameter, never exceeds the dimensions of a single porphyryl moiety and its meso-pendant ethynyl groups. The |D| values determined for an oligomeric series of these electronically asymmetric species that span one through four porphyryl units are respectively 0.0301, 0.0303, 0.0300, and 0.0301 cm-1, indicating a common triplet wave function spatial delocalization of approximately 0.4−0.45 nm. Electron spin−spin and spin−lattice relaxation times were determined over the 4−30 K temperature range using progressive mi...

For more than a century, national and international governing bodies have had some involvement in regulating the quality and safety of food during production and delivery. Since the beginnings of this "modern" food regulation in the early 20th century, the way that food is produced, packaged and distributed has changed drastically. It is difficult to determine if technological advances in the areas of polymer science, refrigeration, and transportation have driven the globalization of the food supply or if the food industry has drawn from these technologies to satisfy consumer's desire and need. Ensuring the safety of food requires a complex and ever-changing set of interactions between producers, distributors, consumers and regulators. As advances are made in packaging and food additives, as food distributions systems evolve to meet consumer needs, or as these respond to environmental and population changes, adjustments to regulatory systems may become necessary. Analytical, environmental and materials chemistry can often play important roles in responding to these changes and in continuing to help with the improvement of food safety and security. These five co-editors bring their respective expertise to the subject of the food system and the chemical advancements behind it.

The photophysics of bis(terpyridyl)osmium-(porphinato)zinc-bis(terpyridyl)osmium (OsPZnOs), a D-π-A-π-D symmetric supermolecule, were investigated in the femtosecond and nanosecond regimes. The supermolecule exhibits a two-photon absorption (δpeak ~900 GM) in the near IR (900-1300 nm) and optical pumping by two-photon absorption leads to a broad excited state absorption (σpeak ~1.1 × 10−16 cm2) in the same near IR region. Since the excited state has a long lifetime, OsPZnOs exhibits a strong nanosecond nonlinear absorption in this region. That nonlinear absorption is substantially enhanced when OsPZnOs is incorporated into a multimode waveguide. When two-photon pumping is the dominant mechanism, an additional enhancement of up to ~100 × in the nonlinear absorption is observed in a microchannel waveguide. OsPZnOs is a promising material for photonic applications such as optical noise suppression and optical limiting in the near IR.

Formed through cooperative self-assembly of amphiphilic diblock copolymers and electronically conjugated porphyrinic near-infrared (NIR) fluorophores (NIRFs), NIR-emissive polymersomes (50 nm to 50 microm diameter polymer vesicles) define a family of organic-based, soft-matter structures that are ideally suited for deep-tissue optical imaging and sensitive diagnostic applications. Here, we describe magic angle and polarized pump-probe spectroscopic experiments that: (i) probe polymersome structure and NIRF organization and (ii) connect emitter structural properties and NIRF loading with vesicle emissive output at the nanoscale. Within polymersome membrane environments, long polymer chains constrain ethyne-bridged oligo(porphinato)zinc(II) based supermolecular fluorophore (PZn n ) conformeric populations and disperse these PZn n species within the hydrophobic bilayer. Ultrafast excited-state transient absorption and anisotropy dynamical studies of NIR-emissive polymersomes, in which the PZn n fluorophore loading per nanoscale vesicle is varied between 0.1-10 mol %, enable the exploration of concentration-dependent mechanisms for nonradiative excited-state decay. These experiments correlate fluorophore structure with its gross spatial arrangement within specific nanodomains of these nanoparticles and reveal how compartmentalization of fluorophores within reduced effective dispersion volumes impacts bulk photophysical properties. As these factors play key roles in determining the energy transfer dynamics between dispersed fluorophores, this work underscores that strategies that modulate fluorophore and polymer structure to optimize dispersion volume in bilayered nanoscale vesicular environments will further enhance the emissive properties of these sensitive nanoscale probes.