Quantum Dot Fluorescent Imaging: Using Atomic Structure Correlation Studies to Improve Photophysical Properties.

Efforts to study intricate, higher-order cellular functions have called for fluorescence imaging under physiologically relevant conditions such as tissue systems in simulated native buffers. This endeavor has presented novel challenges for fluorescent probes initially designed for use in simple buffers and monolayer cell culture. Among current fluorescent probes, semiconductor nanocrystals, or quantum dots (QDs), offer superior photophysical properties that are the products of their nanoscale architectures and chemical formulations. While their high brightness and photostability are ideal for these biological environments, even state of the art QDs can struggle under certain physiological conditions. A recent method correlating electron microscopy ultrastructure with single-QD fluorescence has begun to highlight subtle structural defects in QDs once believed to have no significant impact on photoluminescence (PL). Specific defects, such as exposed core facets, have been shown to quench QD PL in physiologically accurate conditions. For QD-based imaging in complex cellular systems to be fully realized, mechanistic insight and structural optimization of size and PL should be established. Insight from single QD resolution atomic structure and photophysical correlative studies provides a direct course to synthetically tune QDs to match these challenging environments.

Clostridioides difficile ferrosome organelles combat nutritional immunity.

Iron is indispensable for almost all forms of life but toxic at elevated levels1-4. To survive within their hosts, bacterial pathogens have evolved iron uptake, storage and detoxification strategies to maintain iron homeostasis1,5,6. Recent studies showed that three Gram-negative environmental anaerobes produce iron-containing ferrosome granules7,8. However, it remains unclear whether ferrosomes are generated exclusively by Gram-negative bacteria. The Gram-positive bacterium Clostridioides difficile is the leading cause of nosocomial and antibiotic-associated infections in the USA9. Here we report that C. difficile undergoes an intracellular iron biomineralization process and stores iron in membrane-bound ferrosome organelles containing non-crystalline iron phosphate biominerals. We found that a membrane protein (FezA) and a P1B6-ATPase transporter (FezB), repressed by both iron and the ferric uptake regulator Fur, are required for ferrosome formation and play an important role in iron homeostasis during transition from iron deficiency to excess. Additionally, ferrosomes are often localized adjacent to cellular membranes as shown by cryo-electron tomography. Furthermore, using two mouse models of C. difficile infection, we demonstrated that the ferrosome system is activated in the inflamed gut to combat calprotectin-mediated iron sequestration and is important for bacterial colonization and survival during C. difficile infection.

Remarkable heat conduction mediated by non-equilibrium phonon polaritons.

Surface waves can lead to intriguing transport phenomena. In particular, surface phonon polaritons (SPhPs), which result from coupling between infrared light and optical phonons, have been predicted to contribute to heat conduction along polar thin films and nanowires1. However, experimental efforts so far suggest only very limited SPhP contributions2-5. Through systematic measurements of thermal transport along the same 3C-SiC nanowires with and without a gold coating on the end(s) that serves to launch SPhPs, here we show that thermally excited SPhPs can substantially enhance the thermal conductivity of the uncoated portion of these wires. The extracted pre-decay SPhP thermal conductance is more than two orders of magnitude higher than the Landauer limit predicted on the basis of equilibrium Bose-Einstein distributions. We attribute the notable SPhP conductance to the efficient launching of non-equilibrium SPhPs from the gold-coated portion into the uncoated SiC nanowires, which is strongly supported by the observation that the SPhP-mediated thermal conductivity is proportional to the length of the gold coating(s). The reported discoveries open the door for modulating energy transport in solids by introducing SPhPs, which can effectively counteract the classical size effect in many technologically important films and improve the design of solid-state devices.

Quantitative morphological analysis of InP-based quantum dots reveals new insights into the complexity of shell growth.

The incorporation of quantum dots in display technology has fueled a renewed interest in InP-based quantum dots, but difficulty controlling the Zn chemistry during shelling has stymied thick, even ZnSe shell growth. The characteristic uneven, lobed morphology of Zn-based shells is difficult to assess qualitatively and measure through traditional methods. Here, we present a methodological study utilizing quantitative morphological analysis of InP/ZnSe quantum dots to analyze the impact of key shelling parameters on InP core passivation and shell epitaxy. We compare conventional hand-drawn measurements with an open-source semi-automated protocol to showcase the improved precision and speed of this method. Additionally, we find that quantitative morphological assessment can discern morphological trends in morphologies that qualitative methods cannot. In conjunction with ensemble fluorescence measurements, we find that changes to shelling parameters that promote even shell growth often do so at the cost of core homogeneity. These results indicate that the chemistry of passivating the core and promoting shell growth must be balanced carefully to maximize brightness while maintaining emission color-purity.

Water splitting with silicon p-i-n superlattices suspended in solution.

Photoelectrochemical (PEC) water splitting to produce hydrogen fuel was first reported 50 years ago1, yet artificial photosynthesis has not become a widespread technology. Although planar Si solar cells have become a ubiquitous electrical energy source economically competitive with fossil fuels, analogous PEC devices have not been realized, and standard Si p-type/n-type (p-n) junctions cannot be used for water splitting because the bandgap precludes the generation of the needed photovoltage. An alternative paradigm, the particle suspension reactor (PSR), forgoes the rigid design in favour of individual PEC particles suspended in solution, a potentially low-cost option compared with planar systems2,3. Here we report Si-based PSRs by synthesizing high-photovoltage multijunction Si nanowires (SiNWs) that are co-functionalized to catalytically split water. By encoding a p-type-intrinsic-n-type (p-i-n) superlattice within single SiNWs, tunable photovoltages exceeding 10 V were observed under 1 sun illumination. Spatioselective photoelectrodeposition of oxygen and hydrogen evolution co-catalysts enabled water splitting at infrared wavelengths up to approximately 1,050 nm, with the efficiency and spectral dependence of hydrogen generation dictated by the photonic characteristics of the sub-wavelength-diameter SiNWs. Although initial energy conversion efficiencies are low, multijunction SiNWs bring the photonic advantages of a tunable, mesoscale geometry and the material advantages of Si-including the small bandgap and economies of scale-to the PSR design, providing a new approach for water-splitting reactors.

A Single Source, Scalable Route for Direct Isolation of Earth-Abundant Nanometal Carbide Water-Splitting Electrocatalysts.

Single-phase MxCs (M = Fe, Co, and Ni) were prepared by solvothermal conversion of Prussian blue single source precursors. The single source precursor is prepared in water, and the conversion process is carried out in alkylamines at reaction temperatures above 200 °C. The reaction is scalable using a commercial source of Fe-PB. High-resolution transmission electron microscopy, X-ray photoelectron microscopy, and powder X-ray diffraction confirm that carbides have thin oxide termination but lack graphitic surfaces. Electrocatalytic activity reveals that Fe3C and Co2C are oxygen evolution reaction electrocatalysts, while Ni3C is a bifunctional [OER and hydrogen evolution reaction (HER)] electrocatalyst.

Ultrafast spectroscopy studies of carrier dynamics in semiconductor nanocrystals.

Semiconductor nanocrystals have become ubiquitous both in scientific research and in applied technologies related to light. When a nanocrystal absorbs a photon an electron-hole pair is created whose fate dictates whether the nanocrystal will be suitable for a particular application. Ultrafast spectroscopy provides a real-time window to monitor the evolution of the electron-hole pair. In this review, we focus on CdSe nanocrystals, the most-studied nanocrystal system to date, and also highlight ultrasmall nanocrystals, "standard nanocrystals" of different binary composition, alloyed nanocrystals, and core/shell nanocrystals and nanorods. We focus on four time-resolved spectroscopies used to interrogate nanocrystals: pump-probe, fluorescence upconversion, time-correlated single photon counting, and non-linear spectroscopies. The basics of the nanocrystals and the spectroscopies are presented, followed by a detailed synopsis of ultrafast spectroscopy studies performed on the various semiconductor nanocrystal systems.

Fluorescent Colloidal Ferroelectric Nanocrystals.

We report the appearance of ferroelectric behavior arising from a room-temperature cation exchange of cadmium-based semiconductor nanoparticles. Fluorescence retention was achieved through protective CdS shelling before cation exchange with tin(IV) by containing defects in the CdS shell rather than the fluorescent CdSe cores. Ferroelectric response, measured using a Sawyer-Tower circuit, was kept constant, while fluorescence retention increases with an increase in the number of CdS monolayers. At 8 monolayers, fluorescence retention reached 99%, allowing for the addition of ferroelectric applications to the already ever-growing list of quantum dot applications.

Bidirectional Modulation of Contact Thermal Resistance between Boron Nitride Nanotubes from a Polymer Interlayer.

Enhancing the thermal conductivity of polymer composites could improve their performance in applications requiring fast heat dissipation. While significant progress has been made, a long-standing issue is the contact thermal resistance between the nanofillers, which could play a critical role in the composite thermal properties. Through systematic studies of contact thermal resistance between individual boron nitride nanotubes (BNNTs) of different diameters, with and without a poly(vinylpyrrolidone) (PVP) interlayer, we show that the contact thermal resistance between bare BNNTs is largely determined by reflection of ballistic phonons. Interestingly, it is found that a PVP interlayer can either enhance or reduce the contact thermal resistance, as a result of converting the ballistic phonon dominated transport into diffusion through the PVP layer. These results disclose a previously unrecognized physical picture of thermal transport at the contact between BNNTs, which provides insights into the design of high thermal conductivity BNNT-polymer composites.

Harvesting Sub-Bandgap IR Photons by Photothermionic Hot Electron Transfer in a Plasmonic p-n Junction.

Plasmonic semiconductors are an emerging class of low-cost plasmonic materials, and the presence of a bandgap and band-bending in these materials offer new opportunities to overcome some of the limitations of plasmonic metals. Here, we demonstrate that in a plasmonic p-n heterojunction (Cu2-xSe-CdSe) the near-IR excitation (1.1 eV) of the hole plasmon in the p-Cu2-xSe phase results in rapid hot electron transfer to n-CdSe, with an energy 2.2 eV above the Fermi level. This hot electron generation and energy upconversion process can be well-described by a photothermionic mechanism, where the presence of a bandgap in p-Cu2-xSe facilitates the generation of energetic photothermal electrons. The lifetime of the transferred electrons in Cu2-xSe-CdSe can reach ∼130 ps, which is nearly 100× longer than that of its metal-semiconductor counterpart. This result demonstrates a novel approach for harvesting the sub-bandgap near IR photons using plasmonic p-n junctions and the potential advantages of plasmonic semiconductors for hot carrier-based devices.

Implementation, adherence, and results of systematic SARS-CoV-2 testing for asymptomatic patients treated at a tertiary care regional radiation oncology network.

BACKGROUND: Coronavirus disease 2019 (COVID-19) caused by the SARS-CoV-2 virus is a current pandemic. We initiated a program of systematic SARS-CoV-2 polymerase chain reaction (PCR) testing in all asymptomatic patients receiving radiotherapy (RT) at a large radiation oncology network in the Charlotte, NC metropolitan region and report adherence and results of the testing program. METHODS: Patients undergoing simulation for RT between May 18, 2020 and July 10, 2020 within the Levine Cancer Institute radiation oncology network who were asymptomatic for COVID-19 associated symptoms, without previous positive SARS-CoV-2 testing, and without recent high-risk contacts were included. PCR testing was performed on nasal cavity or nasopharyngeal swab samples. Testing was performed within 2 weeks of RT start (pre-RT) and at least every 4 weeks during RT for patients with prolonged RT courses (intra-RT). An automated task based process using the oncology electronic medical record (EMR) was developed specifically for this purpose. RESULTS: A total of 604 unique patients were included in the cohort. Details on testing workflow and implementation are described herein. Pre-RT PCR testing was performed in 573 (94.9%) patients, of which 4 (0.7%) were positive. The adherence rate to intra-RT testing overall was 91.6%. Four additional patients (0.7%) tested positive during their RT course, of whom 3 were tested due to symptom development and 1 was asymptomatic and identified via systematic testing. A total of 8 (1.3%) patients tested positive overall. There were no known cases of SARS-CoV-2 transmission from infected patients to clinic staff and/or other patients. CONCLUSIONS: We detailed the workflows used to implement systematic SARS-CoV-2 for asymptomatic patients at a large radiation oncology network. Adherence rates for pre-RT and intra-RT testing were high using this process. This information allowed for appropriate delay in initiating RT, minimizing the occurrence of RT treatment interruptions, and no known cases of transmission from infected patients to clinic staff and/or other patients.

Ultrafast and Long-Lived Transient Heating of Surface Adsorbates on Plasmonic Semiconductor Nanocrystals.

Plasmonic photocatalysts have demonstrated promising potential for enhancing the selectivity and efficiency of important chemical transformations. However, the relative contributions of nonphotothermal (i.e., hot carrier) and photothermal pathways remain a question of intense current debate, and the time scale and extent of surface adsorbate temperature change are still poorly understood. Using p-type Cu2-xSe nanocrystals as a semiconductor plasmonic platform and adsorbed Rhodamine B as a surface thermometer and hot carrier acceptor, we measure directly by transient absorption spectroscopy that the adsorbate temperature rises and decays with time constants of 1.4 ± 0.4 and 471 ± 126 ps, respectively, after the excitation of Cu2-xSe plasmon band at 800 nm. These time constants are similar to those for Cu2-xSe lattice temperature, suggesting that fast thermal equilibrium between the adsorbates and nanocrystal lattice is the main adsorbate heating pathway. This finding provides insights into the transient heating effect on surface adsorbates and their roles in plasmonic photocatalysis.

Magnetic properties of γ-Fe2O3nanoparticles in a porous SiO2shell for drug delivery.

A method is presented for synthesizing core-shell nanoparticles with a magnetic core and a porous shell suitable for drug delivery and other medical applications. The core contains multiple $\gamma$-Fe$_2$O$_3$ nanoparticles ($\sim$15~nm) enclosed in a SiO$_2$ ($\sim$100-200~nm) matrix using either methyl (denoted TMOS-$\gamma$-Fe$_2$O$_3$) or ethyl (TEOS-$\gamma$-Fe$_2$O$_3$) template groups. Low-temperature M{\"o}ssbauer spectroscopy showed that the magnetic nanoparticles have the maghemite structure, $\gamma$-Fe$_2$O$_3$, with all the vacancies in the octahedral sites. Saturation magnetization measurements revealed that the density of $\gamma$-Fe$_2$O$_3$ was greater in the TMOS-$\gamma$-Fe$_2$O$_3$ nanoparticles than TEOS-$\gamma$-Fe$_2$O$_3$ nanoparticles, presumably because of the smaller methyl group. Magnetization measurements showed that the blocking temperature is around room temperature for the TMOS-$\gamma$-Fe$_2$O$_3$ and around 250~K for the TEOS-$\gamma$-Fe$_2$O$_3$. Three dimensional topography analysis shows clearly that the magnetic nanoparticles are not only at the surface but have penetrated deep in the silica to form the core-shell structure.

Tuning Composition of Polymer and Porous Silicon Composite Nanoparticles for Early Endosome Escape of Anti-microRNA Peptide Nucleic Acids.

Porous silicon nanoparticles (PSNPs) offer tunable pore structure and easily modified surface chemistry, enabling high loading capacity for drugs with diverse chemicophysical properties. While PSNPs are also cytocompatible and degradable, PSNP integration into composite structures can be a useful approach to enhance carrier colloidal stability, drug-cargo loading stability, and endosome escape. Here, we explored PSNP polymer composites formed by coating of oxidized PSNPs with a series of poly[ethylene glycol-block-(dimethylaminoethyl methacrylate-co-butyl methacrylate)] (PEG-DB) diblock copolymers with varied molar ratios of dimethylaminoethyl methacrylate (D) and butyl methacrylate (B) in the random copolymer block. We screened and developed PSNP composites specifically toward intracellular delivery of microRNA inhibitory peptide nucleic acids (PNA). While a copolymer with 50 mol % B (50B) is optimal for early endosome escape in free polymer form, its pH switch was suppressed when it was formed into 50B polymer-coated PSNP composites (50BCs). We demonstrate that a lower mol % B (30BC) is the ideal PEG-DB composition for PSNP/PEG-DB nanocomposites based on having both the highest endosome disruption potential and miR-122 inhibitory activity. At a 1 mM PNA dose, 30BCs facilitated more potent inhibition of miR-122 in comparison to 40BC (p = 0.0095), 50BC (p < 0.0001), or an anti-miR-122 oligonucleotide delivered with the commercial transfection reagent Fugene 6. Using a live cell galectin 8-based endosome disruption reporter, 30BCs had greater endosomal escape than 40BCs and 50BCs within 2 h after treatment, suggesting that rapid endosome escape correlates with higher intracellular bioactivity. This study provides new insight on the polymer structure-dependent effects on stability, endosome escape, and cargo intracellular bioavailability for endosomolytic polymer-coated PSNPs.

Surface passivation extends single and biexciton lifetimes of InP quantum dots.

Indium phosphide quantum dots (InP QDs) are nontoxic nanomaterials with potential applications in photocatalytic and optoelectronic fields. Post-synthetic treatments of InP QDs are known to be essential for improving their photoluminescence quantum efficiencies (PLQEs) and device performances, but the mechanisms remain poorly understood. Herein, by applying ultrafast transient absorption and photoluminescence spectroscopies, we systematically investigate the dynamics of photogenerated carriers in InP QDs and how they are affected by two common passivation methods: HF treatment and the growth of a heterostructure shell (ZnS in this study). The HF treatment is found to improve the PLQE up to 16-20% by removing an intrinsic fast hole trapping channel (τ h,non = 3.4 ± 1 ns) in the untreated InP QDs while having little effect on the band-edge electron decay dynamics (τ e = 26-32 ns). The growth of the ZnS shell, on the other hand, is shown to improve the PLQE up to 35-40% by passivating both electron and hole traps in InP QDs, resulting in both a long-lived band-edge electron (τ e > 120 ns) and slower hole trapping lifetime (τ h,non > 45 ns). Furthermore, both the untreated and the HF-treated InP QDs have short biexciton lifetimes (τ xx ∼ 1.2 ± 0.2 ps). The growth of an ultra-thin ZnS shell (∼0.2 nm), on the other hand, can significantly extend the biexciton lifetime of InP QDs to 20 ± 2 ps, making it a passivation scheme that can improve both the single and multiple exciton lifetimes. Based on these results, we discuss the possible trap-assisted Auger processes in InP QDs, highlighting the particular importance of trap passivation for reducing the Auger recombination loss in InP QDs.

Barriers and enablers to physical activity and aerobic fitness deficits among childhood cancer survivors.

BACKGROUND: Physical activity and aerobic fitness are modifiable risk factors for cardiovascular disease (CVD) after childhood cancer. How survivors engage in physical activity remains unclear, potentially increasing CVD risk. We assessed survivors' physical activity levels, barriers and enablers, fitness, and identified predictors of fitness and physical activity stage of change. METHODS: Childhood cancer survivors (CCS; 8-18 years old) ≥1 year post-treatment were assessed for aerobic fitness (6-min walk test), used to extrapolate VO2max , and body composition (InBody 570). Survivors self-reported physical activity to determine stage of change (Patient-Centered Assessment and Counselling for Exercise). Physical activity and fitness were compared with guidelines and CVD-risk cut-points (VO2max  < 42 mL/kg/min: males; VO2max  < 35 mL/kg/min: females). Multiple regression and mediator-moderator analysis were used to identify fitness predictors and stage of change. RESULTS: One hundred two survivors (12.8 ± 3.3 years) participated (46% acute lymphoblastic leukaemia). Forty percent of males (VO2max  = 43.3 ± 6.3 mL/kg/min) and 28% of females (VO2max  = 36.5 ± 5.9 mL/kg/min) were in the CVD-risk category, while 25% met physical activity guidelines. Most prevalent physical activity barriers were fatigue (52%), preferring television instead of exercise (38%), and lacking time (34%). Predictive factors for reduced fitness included being older, female, higher waist-to-height ratio, higher screen time, and moderated by lower physical activity (r2  = 0.91, P < .001). Survivors with higher physical activity stage of change were male, lower body fat percentage, lower screen time, and lived with both parents (r = 0.42, P = .003). CONCLUSION: Aerobic fitness and physical activity of CCS is low compared with population norms, potentially increasing CVD risk. Addressing physical activity barriers and enablers, including reducing screen time, could promote regular physical activity, reducing CVD risk.

Effect of indium alloying on the charge carrier dynamics of thick-shell InP/ZnSe quantum dots.

Thick-shell InP/ZnSe III-V/II-VI quantum dots (QDs) were synthesized with two distinct interfaces between the InP core and ZnSe shell: alloy and core/shell. Despite sharing similar optical properties in the spectral domain, these two QD systems have differing amounts of indium incorporation in the shell as determined by high-resolution energy-dispersive x-ray spectroscopy scanning transmission electron microscopy. Ultrafast fluorescence upconversion spectroscopy was used to probe the charge carrier dynamics of these two systems and shows substantial charge carrier trapping in both systems that prevents radiative recombination and reduces the photoluminescence quantum yield. The alloy and core/shell QDs show slight differences in the extent of charge carrier localization with more extensive trapping observed in the alloy nanocrystals. Despite the ability to grow a thick shell, structural defects caused by III-V/II-VI charge carrier imbalances still need to be mitigated to further improve InP QDs.

Ratcheting quasi-ballistic electrons in silicon geometric diodes at room temperature.

Ratcheting effects play an important role in systems ranging from mechanical socket wrenches to biological motor proteins. The underlying principle is to convert a fluctuating, unbiased force into unidirectional motion. Here, we report the ratcheting of electrons at room temperature using a semiconductor nanowire with precisely engineered asymmetry. Modulation of the nanowire diameter creates a cylindrical sawtooth geometry with broken inversion symmetry on a nanometer-length scale. In a two-terminal device, this structure responded as a three-dimensional geometric diode that funnels electrons preferentially in one direction through specular reflection of quasi-ballistic electrons at the nanowire surface. The ratcheting effect causes charge rectification at frequencies exceeding 40 gigahertz, demonstrating the potential for applications such as high-speed data processing and long-wavelength energy harvesting.

Role of shell composition and morphology in achieving single-emitter photostability for green-emitting "giant" quantum dots.

The use of the varied chemical reactivity of precursors to drive the production of a desired nanocrystal architecture has become a common method to grow thick-shell graded alloy quantum dots (QDs) with robust optical properties. Conclusions on their behavior assume the ideal chemical gradation and uniform particle composition. Here, advanced analytical electron microscopy (high-resolution scanning transmission electron microscopy coupled with energy dispersive spectroscopy) is used to confirm the nature and extent of compositional gradation and these data are compared with performance behavior obtained from single-nanocrystal spectroscopy to elucidate structure, chemical-composition, and optical-property correlations. Specifically, the evolution of the chemical structure and single-nanocrystal luminescence was determined for a time-series of graded-alloy "CdZnSSe/ZnS" core/shell QDs prepared in a single-pot reaction. In a separate step, thick (∼6 monolayers) to giant (>14 monolayers) shells of ZnS were added to the alloyed QDs via a successive ionic layer adsorption and reaction (SILAR) process, and the impact of this shell on the optical performance was also assessed. By determining the degree of alloying for each component element on a per-particle basis, we observe that the actual product from the single-pot reaction is less "graded" in Cd and more so in Se than anticipated, with Se extending throughout the structure. The latter suggests much slower Se reaction kinetics than expected or an ability of Se to diffuse away from the initially nucleated core. It was also found that the subsequent growth of thick phase-pure ZnS shells by the SILAR method was required to significantly reduce blinking and photobleaching. However, correlated single-nanocrystal optical characterization and electron microscopy further revealed that these beneficial properties are only achieved if the thick ZnS shell is complete and without large lattice discontinuities. In this way, we identify the necessary structural design features that are required for ideal light emission properties in these green-visible emitting QDs.

Pepsin as a Marker of Reflux Aspiration in Children With Esophageal Atresia: A Pilot Study.

Background: Reflux aspiration secondary to gastroesophageal reflux disease (GERD) is one of the causes of chronic gastrointestinal and respiratory morbidity in children with esophageal atresia (EA). Currently there are no simple, validated non-invasive tests for the diagnosis of reflux aspiration in children. Objectives: The aim of this pilot study was to investigate pepsin detected in exhaled breath condensate (EBC) and saliva as a potential non-invasive marker of reflux aspiration in children with EA. Methods: EBC and saliva samples were prospectively collected from children with EA aged between 5 and 18 years attending a multidisciplinary EA Clinic. Pepsin in the samples was assayed by two methods, a commercial lateral flow device, the Peptest™ and an enzyme-linked immunosorbent assay (ELISA) and correlated with validated gastrointestinal and respiratory symptom questionnaires and objective measures of GERD and respiratory function. Results: EBC were collected from 18 children with EA, 15/18 also provided salivary samples. Pepsin was not detected in any of the EBC samples using the Peptest™ and only 1/14 (7.1%) samples by the ELISA. However, pepsin was detected in 33 and 83% of saliva samples when analyzed with Peptest™ and the ELISA respectively. Salivary pepsin levels were significantly higher in children with reflux symptoms or wheeze. Pepsin was detected by the Peptest™ in the saliva of 5/5 (100%) children with histological evidence of reflux esophagitis compared with 0/2 (0%) in children with normal histology (p = 0.048). Conclusions: Salivary pepsin was detected in a large proportion of children with EA and was significantly associated with GERD symptoms or wheeze. The role of salivary pepsin as a potential non-invasive marker of reflux aspiration in children with EA needs further validation in future studies with larger cohorts.