The relationship between body size and stridulatory sound production in loricariid catfishesa).

Sound production capabilities and characteristics in Loricariidae, the largest catfish family, have not been well examined. Sounds produced by three loricariid catfish species, Otocinclus affinis, Pterygoplichthys gibbiceps, and Pterygoplichthys pardalis, were recorded. Each of these species produces pulses via pectoral-fin spine stridulation by rubbing the ridged condyle of the dorsal process of the pectoral-fin spine base against a matching groove-like socket in the pectoral girdle. Light and scanning electron microscopy were used to examine the dorsal process of the pectoral-fin spines of these species. Mean distances between dorsal process ridges of O. affinis, P. gibbiceps, and P. pardalis were 53, 161, and 329 µm, respectively. Stridulation sounds occurred during either abduction (type A) or adduction (type B). O. affinis produced sounds through adduction only and P. pardalis through abduction only, whereas P. gibbiceps often produced pulse trains alternating between abduction and adduction. In these species, dominant frequency was an inverse function of sound duration, fish total length, and inter-ridge distance on the dorsal process of the pectoral-fin spine and sound duration increased with fish total length. While stridulation sounds are used in many behavioral contexts in catfishes, the functional significance of sound production in Loricariidae is currently unknown.

Communication via Biotremors in the Veiled Chameleon (Chamaeleo calyptratus): Part II-Social Contexts.

This study extends recent research demonstrating that the veiled chameleon (Chamaeleo calyptratus) can produce and detect biotremors. Chameleons were paired in various social contexts: dominance (male-male; female-female C. calyptratus); courtship (male-female C. calyptratus); heterospecific (C. calyptratus + C. gracilis); and inter-size class dominance (adult + juvenile C. calyptratus). Simultaneous video and accelerometer recordings were used to monitor their behavior and record a total of 398 biotremors. Chamaeleo calyptratus produced biotremors primarily in conspecific dominance and courtship contexts, accounting for 84.7% of the total biotremors recorded, with biotremor production varying greatly between individuals. Biotremors were elicited by visual contact with another conspecific or heterospecific, and trials in which chameleons exhibited visual displays and aggressive behaviors were more likely to record biotremors. Three classes of biotremor were identified-hoots, mini-hoots, and rumbles, which differed significantly in fundamental frequency, duration, and relative intensity. Biotremor frequency decreased with increasing signal duration, and frequency modulation was evident, especially in hoots. Overall, the data show that C. calyptratus utilizes substrate-borne vibrational communication during conspecific and possibly heterospecific interactions.

Communication via Biotremors in the Veiled Chameleon (Chamaeleo calyptratus): Part I- Biotremor Production and Response to Substrate-Borne Vibrations.

Biotremors are vibrations, usually surface waves along the boundary of a medium, produced by an organism. While substrate-borne vibrations are utilized by different reptile species, true conspecific communication via biotremors has not yet been demonstrated in lizards. Recent research revealed that the veiled chameleon (Chamaeleo calyptratus) produces biotremors. The prerequisites for any communication system are the ability of an organism to produce and detect a signal. We tested C. calyptratus behavioral responses to vibrations by placing them on a dowel attached to a shaker, emitting vibrations of 25, 50, 150, 300, and 600 Hz and compared their locomotory velocity before and after the stimulus. Adult chameleons exhibited a freeze response to 50 and 150 Hz, while juveniles exhibited a similar response to frequencies between 50 and 300 Hz. In a second experiment, chameleons were induced to produce biotremors via experimenter contact. These biotremors ranged in mean fundamental frequency from 106.4 to 170.3 Hz and in duration from 0.06 to 0.29 s. Overall, two classes of biotremors were identified, "hoots" and "mini-hoots," which differed significantly in mean relative signal intensity (-7.5 and -32.5 dB, respectively). Juvenile chameleons 2 months of age were able to produce biotremors, suggesting this behavior may serve a wide range of ecological functions throughout ontogeny. Overall, the data demonstrate that C. calyptratus can both produce and detect biotremors that could be used for intraspecific communication.

Integration of urban science and urban climate adaptation research: opportunities to advance climate action.

There is a growing recognition that responding to climate change necessitates urban adaptation. We sketch a transdisciplinary research effort, arguing that actionable research on urban adaptation needs to recognize the nature of cities as social networks embedded in physical space. Given the pace, scale and socioeconomic outcomes of urbanization in the Global South, the specificities and history of its cities must be central to the study of how well-known agglomeration effects can facilitate adaptation. The proposed effort calls for the co-creation of knowledge involving scientists and stakeholders, especially those historically excluded from the design and implementation of urban development policies.

Physical effects of sound exposure from underwater explosions on Pacific mackerel (Scomber japonicus): Effects on the inner ear.

Studies of the effects of sounds from underwater explosions on fishes have not included examination of potential effects on the ear. Caged Pacific mackerel (Scomber japonicus) located at seven distances (between approximately 35 and 800 m) from a single detonation of 4.5 kg of C4 explosives were exposed. After fish were recovered from the cages, the sensory epithelia of the saccular region of the inner ears were prepared and then examined microscopically. The number of hair cell (HC) ciliary bundles was counted at ten preselected 2500 µm2 regions. HCs were significantly reduced in fish exposed to the explosion as compared to the controls. The extent of these differences varied by saccular region, with damage greater in the rostral and caudal ends and minimal in the central region. The extent of effect also varied in animals at different distances from the explosion, with damage occurring in fish as far away as 400 m. While extrapolation to other species and other conditions (e.g., depth, explosive size, and distance) must be performed with extreme caution, the effects of explosive sounds should be considered when environmental impacts are estimated for marine projects.

Vaccine-associated attenuation of subjective severity among outpatients with influenza.

Influenza vaccines can mitigate illness severity, including reduced risk of ICU admission and death, in people with breakthrough infection. Less is known about vaccine attenuation of mild/moderate influenza illness. We compared subjective severity scores in vaccinated and unvaccinated persons with medically attended illness and laboratory-confirmed influenza. Participants were prospectively recruited when presenting for care at five US sites over nine seasons. Participants aged ≥ 16 years completed the EQ-5D-5L visual analog scale (VAS) at enrollment. After controlling for potential confounders in a multivariable model, including age and general health status, VAS scores were significantly higher among 2,830 vaccinated participants compared with 3,459 unvaccinated participants, indicating vaccinated participants felt better at the time of presentation for care. No differences in VAS scores were observed by the type of vaccine received among persons aged ≥ 65 years. Our findings suggest vaccine-associated attenuation of milder influenza illness is possible.

Research on the Epidemiology of SARS-CoV-2 in Essential Response Personnel (RECOVER): Protocol for a Multisite Longitudinal Cohort Study.

BACKGROUND: Workers critical to emergency response and continuity of essential services during the COVID-19 pandemic are at a disproportionally high risk of SARS-CoV-2 infection. Prospective cohort studies are needed for enhancing the understanding of the incidence of symptomatic and asymptomatic SARS-CoV-2 infections, identifying risk factors, assessing clinical outcomes, and determining the effectiveness of vaccination. OBJECTIVE: The Research on the Epidemiology of SARS-CoV-2 in Essential Response Personnel (RECOVER) prospective cohort study was designed to estimate the incidence of symptomatic and asymptomatic SARS-CoV-2 infections, examine the risk factors for infection and clinical spectrum of illness, and assess the effectiveness of vaccination among essential workers. METHODS: The RECOVER multisite network was initiated in August 2020 and aims to enroll 3000 health care personnel (HCP), first responders, and other essential and frontline workers (EFWs) at 6 US locations. Data on participant demographics, medical history, and vaccination history are collected at baseline and throughout the study. Active surveillance for the symptoms of COVID-19-like illness (CLI), access of medical care, and symptom duration is performed by text messages, emails, and direct participant or medical record reports. Participants self-collect a mid-turbinate nasal swab weekly, regardless of symptoms, and 2 additional respiratory specimens at the onset of CLI. Blood is collected upon enrollment, every 3 months, approximately 28 days after a reverse transcription polymerase chain reaction (RT-PCR)-confirmed SARS-CoV-2 infection, and 14 to 28 days after a dose of any COVID-19 vaccine. From February 2021, household members of RT-PCR-confirmed participants are self-collecting mid-turbinate nasal swabs daily for 10 days. RESULTS: The study observation period began in August 2020 and is expected to continue through spring 2022. There are 2623 actively enrolled RECOVER participants, including 280 participants who have been found to be positive for SARS-CoV-2 by RT-PCR. Enrollment is ongoing at 3 of the 6 study sites. CONCLUSIONS: Data collected through the cohort are expected to provide important public health information for essential workers at high risk for occupational exposure to SARS-CoV-2 and allow early evaluation of COVID-19 vaccine effectiveness. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/31574.

Messenger RNA Vaccine Effectiveness Against Coronavirus Disease 2019 Among Symptomatic Outpatients Aged ≥16 Years in the United States, February-May 2021.

Evaluations of vaccine effectiveness (VE) are important to monitor as coronavirus disease 2019 (COVID-19) vaccines are introduced in the general population. Research staff enrolled symptomatic participants seeking outpatient medical care for COVID-19-like illness or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing from a multisite network. VE was evaluated using the test-negative design. Among 236 SARS-CoV-2 nucleic acid amplification test-positive and 576 test-negative participants aged ≥16 years, the VE of messenger RNA vaccines against COVID-19 was 91% (95% confidence interval, 83%-95%) for full vaccination and 75% (55%-87%) for partial vaccination. Vaccination was associated with prevention of most COVID-19 cases among people seeking outpatient medical care.

A Visual Hydrogen Sensor Prototype for Monitoring Magnesium Implant Biodegradation.

Alternative metals such as magnesium (Mg) and its alloys have been recently developed for clinical applications such as temporary implants for bone and tissue repair due to their desirable mechanical properties and ability to biodegrade harmlessly in vivo by releasing Mg2+, OH-, and H2 as biodegradation products. The current methods for monitoring in vivo Mg-alloy biodegradation are either invasive and/or costly, complex, or require large equipment and specially trained personnel, thus making real-time and point-of-care monitoring of Mg-alloy implants problematic. Therefore, innovative methods are critically needed. The objective of this research was to develop a novel, thin, and wearable visual H2 sensor prototype for noninvasive monitoring of in vivo Mg-implant biodegradation in medical research and clinical settings with a fast response time. In this work, we successfully demonstrate such a prototype composed of resazurin and catalytic bimetallic gold-palladium nanoparticles (Au-Pd NPs) incorporated into a thin agarose/alginate hydrogel matrix that rapidly changes color from blue to pink upon exposure to various levels of H2 at a constant flow rate. The irreversible redox reactions occurring in the sensor involve H2, in the presence of Au-Pd NPs, converting resazurin to resorufin. To quantify the sensor color changes, ImageJ software was used to analyze photographs of the sensor taken with a smartphone during H2 exposure. The sensor concentration range was from pure H2 down to limits of detection of 6 and 8 µM H2 (defined via two methods). This range is adequate for the intended application of noninvasively monitoring in vivo Mg-alloy implant biodegradation in animals for medical research and patients in clinical settings.

Prevention and Attenuation of Covid-19 with the BNT162b2 and mRNA-1273 Vaccines.

BACKGROUND: Information is limited regarding the effectiveness of the two-dose messenger RNA (mRNA) vaccines BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) in preventing infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and in attenuating coronavirus disease 2019 (Covid-19) when administered in real-world conditions. METHODS: We conducted a prospective cohort study involving 3975 health care personnel, first responders, and other essential and frontline workers. From December 14, 2020, to April 10, 2021, the participants completed weekly SARS-CoV-2 testing by providing mid-turbinate nasal swabs for qualitative and quantitative reverse-transcriptase-polymerase-chain-reaction (RT-PCR) analysis. The formula for calculating vaccine effectiveness was 100% × (1 - hazard ratio for SARS-CoV-2 infection in vaccinated vs. unvaccinated participants), with adjustments for the propensity to be vaccinated, study site, occupation, and local viral circulation. RESULTS: SARS-CoV-2 was detected in 204 participants (5%), of whom 5 were fully vaccinated (≥14 days after dose 2), 11 partially vaccinated (≥14 days after dose 1 and <14 days after dose 2), and 156 unvaccinated; the 32 participants with indeterminate vaccination status (<14 days after dose 1) were excluded. Adjusted vaccine effectiveness was 91% (95% confidence interval [CI], 76 to 97) with full vaccination and 81% (95% CI, 64 to 90) with partial vaccination. Among participants with SARS-CoV-2 infection, the mean viral RNA load was 40% lower (95% CI, 16 to 57) in partially or fully vaccinated participants than in unvaccinated participants. In addition, the risk of febrile symptoms was 58% lower (relative risk, 0.42; 95% CI, 0.18 to 0.98) and the duration of illness was shorter, with 2.3 fewer days spent sick in bed (95% CI, 0.8 to 3.7). CONCLUSIONS: Authorized mRNA vaccines were highly effective among working-age adults in preventing SARS-CoV-2 infection when administered in real-world conditions, and the vaccines attenuated the viral RNA load, risk of febrile symptoms, and duration of illness among those who had breakthrough infection despite vaccination. (Funded by the National Center for Immunization and Respiratory Diseases and the Centers for Disease Control and Prevention.).

The persistence of ancient settlements and urban sustainability.

We propose a dedicated research effort on the determinants of settlement persistence in the ancient world, with the potential to significantly advance the scientific understanding of urban sustainability today. Settlements (cities, towns, villages) are locations with two key attributes: They frame human interactions and activities in space, and they are where people dwell or live. Sustainability, in this case, focuses on the capacity of structures and functions of a settlement system (geography, demography, institutions) to provide for continuity of safe habitation. The 7,000-y-old experience of urbanism, as revealed by archaeology and history, includes many instances of settlements and settlement systems enduring, adapting to, or generating environmental, institutional, and technological changes. The field of urban sustainability lacks a firm scientific foundation for understanding the long durée, relying instead on narratives of collapse informed by limited case studies. We argue for the development of a new interdisciplinary research effort to establish scientific understanding of settlement and settlement system persistence. Such an effort would build upon the many fields that study human settlements to develop new theories and databases from the extensive documentation of ancient and premodern urban systems. A scientific foundation will generate novel insights to advance the field of urban sustainability.

Cisplatin and phenanthriplatin modulate long-noncoding RNA expression in A549 and IMR90 cells revealing regulation of microRNAs, Wnt/ß-catenin and TGF-ß signaling.

The monofunctional platinum(II) complex, phenanthriplatin, acts by blocking transcription, but its regulatory effects on long-noncoding RNAs (lncRNAs) have not been elucidated relative to traditional platinum-based chemotherapeutics, e.g., cisplatin. Here, we treated A549 non-small cell lung cancer and IMR90 lung fibroblast cells for 24 h with either cisplatin, phenanthriplatin or a solvent control, and then performed microarray analysis to identify regulated lncRNAs. RNA22 v2 microRNA software was subsequently used to identify microRNAs (miRNAs) that might be suppressed by the most regulated lncRNAs. We found that miR-25-5p, -30a-3p, -138-5p, -149-3p, -185-5p, -378j, -608, -650, -708-5p, -1253, -1254, -4458, and -4516, were predicted to target the cisplatin upregulated lncRNAs, IMMP2L-1, CBR3-1 and ATAD2B-5, and the phenanthriplatin downregulated lncRNAs, AGO2-1, COX7A1-2 and SLC26A3-1. Then, we used qRT-PCR to measure the expression of miR-25-5p, -378j, -4516 (A549) and miR-149-3p, -608, and -4458 (IMR90) to identify distinct signaling effects associated with cisplatin and phenanthriplatin. The signaling pathways associated with these miRNAs suggests that phenanthriplatin may modulate Wnt/ß-catenin and TGF-ß signaling through the MAPK/ERK and PTEN/AKT pathways differently than cisplatin. Further, as some of these miRNAs may be subject to dissimilar lncRNA targeting in A549 and IMR90 cells, the monofunctional complex may not cause toxicity in normal lung compared to cancer cells by acting through distinct lncRNA and miRNA networks.

Interim Estimates of Vaccine Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Health Care Personnel, First Responders, and Other Essential and Frontline Workers - Eight U.S. Locations, December 2020-March 2021.

Messenger RNA (mRNA) BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) COVID-19 vaccines have been shown to be effective in preventing symptomatic COVID-19 in randomized placebo-controlled Phase III trials (1,2); however, the benefits of these vaccines for preventing asymptomatic and symptomatic SARS-CoV-2 (the virus that causes COVID-19) infection, particularly when administered in real-world conditions, is less well understood. Using prospective cohorts of health care personnel, first responders, and other essential and frontline workers* in eight U.S. locations during December 14, 2020-March 13, 2021, CDC routinely tested for SARS-CoV-2 infections every week regardless of symptom status and at the onset of symptoms consistent with COVID-19-associated illness. Among 3,950 participants with no previous laboratory documentation of SARS-CoV-2 infection, 2,479 (62.8%) received both recommended mRNA doses and 477 (12.1%) received only one dose of mRNA vaccine.† Among unvaccinated participants, 1.38 SARS-CoV-2 infections were confirmed by reverse transcription-polymerase chain reaction (RT-PCR) per 1,000 person-days.§ In contrast, among fully immunized (≥14 days after second dose) persons, 0.04 infections per 1,000 person-days were reported, and among partially immunized (≥14 days after first dose and before second dose) persons, 0.19 infections per 1,000 person-days were reported. Estimated mRNA vaccine effectiveness for prevention of infection, adjusted for study site, was 90% for full immunization and 80% for partial immunization. These findings indicate that authorized mRNA COVID-19 vaccines are effective for preventing SARS-CoV-2 infection, regardless of symptom status, among working-age adults in real-world conditions. COVID-19 vaccination is recommended for all eligible persons.

Clinical Symptoms Among Ambulatory Patients Tested for SARS-CoV-2.

We compared symptoms and characteristics of 4961 ambulatory patients with and without laboratory-confirmed severe acute respiratory syndrome coronavirus 2 infection. Findings indicate that clinical symptoms alone would be insufficient to distinguish between coronavirus disease 2019 and other respiratory infections (eg, influenza) and/or to evaluate the effects of preventive interventions (eg, vaccinations).

Effects of L-Serine Against Cisplatin-Mediated Reactive Oxygen Species Generation in Zebrafish Vestibular Tissue Culture and HEI-OC1 Auditory Hybridoma Cells.

Cisplatin is a platinum-based chemotherapy compound effective against a variety of cancers. However, it can cause increased reactive oxygen species (ROS) production in auditory and vestibular tissue leading to permanent hearing and balance loss. The amino acid, L-serine, has been shown to reduce ROS in some tissue types. In this project, we first investigated whether L-serine could reduce cisplatin-mediated ROS generation in zebrafish utricular tissue culture using spectrophotometry and the fluorescent ROS detector dye, H2DCFDA. Then, we examined whether L-serine could prevent the effect of cisplatin against cellular viability in the mouse auditory hybridoma cell line, HEI-OC1, using the spectrophotometric (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay. As a final step, we used H2DCFDA dye and flow cytometry analysis to determine if L-serine could counteract the effect of cisplatin on ROS production in this cell line. We found that cisplatin and L-serine treatment may influence ROS production in utricular tissue. Further, although L-serine did not counteract the effect of cisplatin against HEI-OC1 cellular viability, the amino acid did prevent the platinum compound's effect to increase ROS in these cells. These results suggest that L-serine may act in auditory and vestibular tissues as an effective protectant against cisplatin-mediated toxicity.

RNA-Seq Analysis of Cisplatin and the Monofunctional Platinum(II) Complex, Phenanthriplatin, in A549 Non-Small Cell Lung Cancer and IMR90 Lung Fibroblast Cell Lines.

Phenanthriplatin is a new monofunctional platinum(II) complex that binds only one strand of DNA and acts by blocking gene transcription, but its effect on gene regulation has not been characterized relative to the traditional platinum-based complex, cisplatin. A549 non-small cell lung cancer and IMR90 lung fibroblast cells were treated with cisplatin, phenanthriplatin, or a control and then their RNA transcripts were subjected to next generation sequencing analysis. DESeq2 and CuffDiff2 were used to identify up- and downregulated genes and Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases were used to identify pathways and functions. We found that phenanthriplatin may regulate the genes GPRC5a, TFF1, and TNFRSF10D, which act through p53 to control apoptosis, differently or to a greater extent than cisplatin, and that it, unlike cisplatin, could upregulate ATP5MD, a gene which signals through the Wnt/ß catenin pathway. Furthermore, phenanthriplatin caused unique or enhanced effects compared to cisplatin on genes regulating the cytoskeleton, cell migration, and proliferation, e.g., AGAP1, DIAPH2, GDF15, and THSD1 (p < 0.05; q < 0.05). Phenanthriplatin may modulate some oncogenes differently than cisplatin potentially leading to improved clinical outcome, but this monofunctional complex should be carefully matched with cancer gene data to be successfully applied in chemotherapy.

Cities: Complexity, theory and history.

In recent decades researchers in a variety of disciplines have developed a new "urban science," the central goal of which is to build general theory regarding the social processes underlying urbanization. Much work in urban science is animated by the notion that cities are complex systems. What does it mean to make this claim? Here we adopt the view that complex systems entail both variation and structure, and that their properties vary with system size and with respect to where and how they are measured. Given this, a general framework regarding the social processes behind urbanization needs to account for empirical regularities that are common to both contemporary cities and past settlements known through archaeology and history. Only by adopting an explicitly historical perspective can such fundamental structure be revealed. The identification of shared properties in past and present systems has been facilitated by research traditions that define cities (and settlements more broadly) as networks of social interaction embedded in physical space. Settlement Scaling Theory (SST) builds from these insights to generate predictions regarding how measurable properties of cities and settlements are related to their population size. Here, we focus on relationships between population and area across past settlement systems and present-day world cities. We show that both patterns and variations in these measures are explicable in terms of SST, and that the framework identifies baseline infrastructural area as an important system-level property of urban systems that warrants further study. We also show that predictive theory is helpful even in cases where the data do not conform to model predictions.

The role of hyoid muscles in biotremor production in Chamaeleo calyptratus.

The production of biotremors has been described in veiled chameleons (Chamaeleo calyptratus), but the mechanism by which they are produced is unknown. We gathered muscle activation data via electromyography (EMG), with simultaneous recordings of biotremors using an accelerometer, to test for the role of hyoid muscles in biotremor production. We recorded a mean biotremor frequency of 150.87 Hz for females and 136.01 Hz for males. The durations of activity and the latencies to onset and offset for the M. sternohyoideus profundus (SP), M. sternohyoideus superficialis (SS), Mm. mandibulohyoideus (MH) and M. levator scapulae (LS) were all significantly correlated with biotremor durations and biotremor onset and offset, respectively. Linear mixed-effect regression model comparisons of biotremor duration indicated that models containing either the MH and/or the SP and LS account for the most variation in biotremor duration. Twitch times for the SP (100 ms) and the SS (132 ms) at field active body temperature, however, were individually too slow to produce the biotremors at the observed frequency without alteration after production by other anatomical structures. These results implicate the SP, SS, MH and LS in the production of biotremors, but the exact mechanism of production requires further study.

Indicator Dyes and Catalytic Nanoparticles for Irreversible Visual Hydrogen Sensing.

Using ultraviolet-visible (UV-vis) absorption spectroscopy, we have tested the reactivity of various indicator molecules combined with catalytic bimetallic gold-palladium nanoparticles (Au-Pd NPs) in solution for an irreversible and visual response to H2. Our aim was to identify the most suitable indicator/Au-Pd NP system for the future development of a thin, wearable, and visual H2 sensor for noninvasive monitoring of in vivo Mg-implant biodegradation in research and clinical settings with fast response time. The indicators studied were bromothymol blue, methyl red, and resazurin, and the reactions of each system with H2 in the presence of Au-Pd NPs caused visual and irreversible color changes that were concluded to proceed via redox processes. The resazurin/Au-Pd NP system was deemed best-suited for our research objectives because (1) this system had the fastest color change response to H2 at levels relevant to in vivo Mg-implant biodegradation compared to the other indicator/Au-Pd NP systems tested, (2) the observed redox chemistry with H2 followed well-understood reaction pathways reported in the literature, and (3) the redox products were nontoxic and appropriate for medical applications. Studying the effects of the concentrations of H2, Au-Pd NPs, and resazurin on the color change response time within the resazurin/Au-Pd NP system revealed that the H2-sensing elements can be optimized to achieve a faster or slower color change with H2 by varying the relative amounts of resazurin and Au-Pd NPs in solution. The results from this study are significant for future optical H2 sensor design.