Mercury is a highly toxic environmental pollutant with bioaccumulative properties. Therefore, new materials are required to not only detect but also effectively remove mercury from environmental sources, such as water. We herein describe a polyacrylamide hydrogel-based sensor functionalized with a thyminerich DNA that can simultaneously detect and remove mercury from water. Detection is achieved by selective binding of Hg 2+ between two thymine bases inducing a hairpin structure where upon addition of SYBR Green I dye green fluorescence is observed. In the absence of Hg 2+ , however, addition of the dye results in yellow fluorescence. Using the naked eye, the detection limit in a 50 mL water sample is 10 nM Hg 2+ . This sensor can be regenerated using a simple acid treatment and can remove Hg 2+ from water at a rate of ~1 hr -1 . This sensor was also used to detect and remove Hg 2+ from samples of Lake Ontario spiked with mercury. In addition, these hydrogel-based sensors are resistant to nuclease and can be rehydrated from dried gels for storage and DNA protection. Similar methods can be used to functionalize hydrogels with other nucleic acids, proteins, and small molecules for environmental and biomedical applications.

The presence of top predators can affect prey behaviour, morphology and life history, and thereby can produce indirect population consequences greater and further reaching than direct depredation would have alone. Raptor species in the Americas are recovering since restrictions on the use of dichlorodiphenyltrichloroethane (DDT) and the implementation of conservation measures, in effect constituting a hemisphere-wide predator-reintroduction experiment, and profound effects on populations of their prey are to be expected. Here, we document changes in the behaviour of western sandpipers (Calidris mauri ) at migratory stopover sites over two decades. Since 1985, migratory body mass and stopover durations of western sandpipers have fallen steadily at some stopovers in the Strait of Georgia, British Columbia. Comparisons between years, sites and seasons strongly implicate increasing danger from the recovery of peregrine falcons (Falco peregrinus) as a causal factor. A decade-long ongoing steep decline in sandpiper numbers censused on our study site is explained entirely by the shortening stopover duration, rather than fewer individuals using the site. Such behavioural changes are probably general among migratory shorebird species, and may be contributing to the widespread census declines reported in North America.

Background Repeat COVID-19 molecular testing can lead to positive test results after negative tests and to multiple positive test results over time. The association between positive tests and infectious virus is important to quantify. Methods A two months cohort of retrospective data and consecutively collected specimens from COVID-19 patients or patients under investigation were used to understand the correlation between prolonged viral RNA positive test results, cycle threshold (Ct) values and growth of SARS-CoV-2 in cell culture. Whole genome sequencing was used to confirm virus genotype in patients with prolonged viral RNA detection. Droplet digital PCR (ddPCR) was used to assess the rate of false negative COVID-19 diagnostic tests. Results In two months, 29,686 specimens were tested and 2,194 patients received repeated testing. Virus recovery in cell culture was noted in specimens with SARS-CoV-2 target genes’ Ct value average of 18.8 ± 3.4. Prolonged viral RNA shedding was associated with positive virus growth in culture in specimens collected up to 20 days after the first positive result but mostly in individuals symptomatic at time of sample collection. Whole genome sequencing provided evidence the same virus was carried over time. Positive tests following negative tests had Ct values higher than 29.5 and were not associated with virus culture. ddPCR was positive in 5.6% of negative specimens collected from COVID-19 confirmed or clinically suspected patients. Conclusions Low Ct values in SARS-CoV-2 diagnostic tests were associated with virus growth in cell culture. Symptomatic patients with prolonged viral RNA shedding can also be infectious.

Highly sensitive and selective DNA detection plays a central role in many fields of research and various assay platforms have been developed. Compared to homogeneous DNA detection, surface immobilized probes allow washing steps and signal amplification to give higher sensitivity. Previously research was focused on developing glass or gold based surfaces for DNA immobilization, we herein report hydrogel immobilized DNA. Specifically, acrydite-modified DNA was covalently functionalized to the polyacrylamide hydrogel during gel formation. There are several advantages of these DNAfunctionalized monolithic hydrogels. First, they can be easily handled in a way similar to that in homogeneous assays. Second, they have a low optical background where in combination with DNAfunctionalized gold nanoparticles, even ~0.1 nM target DNA can be visually detected. By using the attached gold nanoparticles to catalyze the reduction of Ag + , as low as 1 pM target DNA can be detected. The gels can be regenerated by a simple thermal treatment and the regenerated gels perform similarly compared to freshly prepared ones. The amount of gold nanoparticles adsorbed through DNA hybridization decreases with increasing gel percentage. Other parameters including DNA concentration, DNA sequence, ionic strength of the solution and temperature have also been systematically characterized in this study.

We report that a latitudinal cline in intertidal food distribution is associated with the nonbreeding distribution of the Western Sandpiper (Calidris mauri). This novel result is the first to demonstrate a clear relationship between patterns of differential nonbreeding distribution and food availability for any shorebird species. Within each age class and sex, longer-billed Western Sandpipers winter further south. Moreover, females, the longer-billed sex, tend to winter south of males. Thus, both inter- and intra-sexual clines in bill morphology result in an overall gradient of increasing bill length from north to south. Longer-billed birds are able to extract prey that are buried more deeply in the sediment; therefore, we predicted shifts in the vertical distribution of food resources to coincide with the clines in bill morphology across the nonbreeding range. We tested our prediction by measuring biofilm density and the vertical distribution of macrofaunal invertebrates at six nonbreeding sites. Although no latitudinal trend was observed for biofilm, the vertical distribution of invertebrates was consistent with our prediction and revealed that the greatest relative abundance of surface prey occurred at northern nonbreeding sites and declined with decreasing latitude. We discuss the potential implications of these findings in the context of competing evolutionary hypotheses of differential migration and bill dimorphism in shorebirds.