Sensitive Reaction Research Articles

Development and Application of RAA Nucleic Acid Test Strip Assay and Double RAA Gel Electrophoresis Detection Methods for ASFV and CSFV.

African swine fever (ASF) is an acute, severe and hemorrhagic infectious disease caused by African swine fever virus (ASFV) infecting domestic pigs and wild boars. Since the outbreak of the disease in China in 2018, it has brought a great impact on China’s pig industry. Classical swine fever (CSF) is an acute contact infectious disease of pigs caused by classical swine fever virus (CSFV) infection. Clinically, acute CSF usually shows persistent high fever, anorexia, extensive congestion and bleeding of the skin and mucosa, which are similar to ASF. It is of great significance to prevent, control and accurately detect ASF and CSF in pig farms. In this study, Recombinase aided amplification (RAA) technology combined with a nucleic acid test strip (RAA-strip) was established for simple and specific detection of ASFV/CSFV. The sensitivity and preliminary clinical application results showed that the RAA test strip established in this study could detect recombinant plasmids containing ASFV/CSFV gene fragments as low as 103 copies/µL. The minimum detection limits of virus DNA/cDNA were 10 and 12 pg respectively, and there was no cross-reaction with other porcine viruses. The specificity of the method was good. We used 37–42 clinical samples to evaluate the performance of our established method, and the positive concordance rates with conventional PCR were 94.1 and 57.1%, respectively. In addition, ASFV and CSFV double RAA agarose gel electrophoresis detection methods were established. The results showed that the method had good specificity. The detection limit of this method is 106 copies for ASFV p72 gene recombinant plasmid and 105 copies for CSFV NS5B Gene recombinant plasmid. The use of this method for clinical material detection was consistent with the PCR method. In summary, the developed method of RAA-strip assay for ASFV and CSFV realized the visual detection of pathogens, and the developed method of dual RAA agarose gel electrophoresis assay for ASFV and CSFV realized the simultaneous detection of two pathogens in one reaction, with good specificity, high sensitivity and rapid reaction rate, which was expected to be clinically feasible for the differential diagnosis of ASF and CSF provided technical support.

Thermal oxygen sensitization modification and its visible light catalytic antibacterial performance for ZIF-8

ZIF-8 has excellent antibacterial potential as an important metal organic framework (MOFs) photocatalytic material. However, ZIF-8 is greatly restricted in photocatalytic antibacterial applications due to the wide band gap and only response to ultraviolet light. In this work, the spectral response of ZIF-8 is successfully extended to the visible light region by the thermal gas sensitization treatment technology. Meanwhile, the forbidden band width of the materials is narrowed by about 47%. The results of FTIR, XPS and EDS prove that the elements and functional groups in ZIF-8 have changed, indicating the completion of the thermal gas sensitization reaction. The results of XRD and SEM show that the modification process doesn’t change the crystal structure and morphology of ZIF-8; The result of BET demonstrates that the specific surface area of ZIF-8 decreases slightly after sensitization, but it is still as high as about 1500 m²/g. Photocatalysis studies indicate that the photo-generated charge separation and transfer efficiency of ZIF-8 improve significantly and the recombination reduce substantially after thermal oxygen sensitization. Photocatalytic antibacterial performances reveal that ZIF-8 after thermo-oxygen sensitization can rapidly produce active species such as·O2- and h+ under visible light irradiation, and the bactericidal efficiency exceed 99% against Escherichia coli and Staphylococcus aureus within 20 min. This research provides scientific basis and experimental data for the application of ZIF-8 in microbial management and health protection.

Serum hepatitis B virus RNA detectability, composition and clinical significance in patients with ab initio hepatitis B e antigen negative chronic hepatitis B

BackgroundSerum hepatitis B virus (HBV) RNA is a surrogate biomarker for intrahepatic covalently closed circular DNA (cccDNA) transcriptional activity and persistence. In this retrospective study, we investigated its presence, levels and composition in ab initio Hepatitis B e antigen (HBeAg) negative chronically infected patients and examined possible associations with disease activity and the outcome of nucleos(t)ide analogue (NA) discontinuation.MethodsWe developed a sensitive real time polymerase chain reaction (RT-PCR) for the specific detection of HBV pregenomic RNA (pgRNA) and precore (preC) mRNA and analyzed 220 serum specimens, 160 under NA treatment, from 116 Greek patients initially negative for HBeAg.ResultsHBV pgRNA was detected in 31% and preC mRNA in 15% of samples, at lower levels representing a small fraction (3.4%) of total core promoter produced transcripts. In the absence of NAs, pgRNA was detected in 57% of samples with median value of 5.19 (2.61–8.35) log10 cp/mL, at lower levels than HBV DNA and correlated significantly with ALT (r = 0.764) and serum HBV DNA (r = 0.906). A wide range of HBV DNA/pgRNA ratio was observed with significant inter- and intra-patient variation. During NA treatment, pgRNA displayed low detectability (22%) and variable levels, median 3.97 (2.30– 8.13) log10 cp/mL, as well as, a significant inverse correlation with the duration of treatment (r = − 0.346, p < 0.01). In 74 events of NA discontinuation, end-of-treatment pgRNA-positive compared to pgRNA-negative cases, experienced more frequently virological (p = 0.016) and clinical (p = 0.011) relapse.ConclusionsIn genotype D ab initio HBeAg negative patients, serum HBV RNA is primarily composed of pgRNA plus a minor fraction of preC mRNA transcripts. Serum pgRNA is associated with disease activity, suggesting lysis of infected hepatocytes as a possible source of serum HBV RNA in untreated patients and in the early phase of NA treatment. During long term NA treatment, detectable serum pgRNA predicts viral rebound and clinical relapse following treatment discontinuation and may thus serve as a marker for the decision of cessation of therapy.

Laminar flame speed of ethanol/ammonia blends–An experimental and kinetic study

Blending bio-ethanol with ammonia is an interesting approach to reach carbon-neutrally combustion systems. As a fundamental parameter, laminar flame speed for different blends of ethanol/ammonia is explored using the spherical expanding flame technique under constant pressure conditions. A comparison to the few recent literature experimental results is proposed. An empirical correlation is developed to estimate the laminar flame speed of any ammonia/ethanol mixture as a function of the equivalence ratio at 1 bar and 423 K. Some simulation results are also provided to compare kinetics mechanisms accuracy to experimental data and identify the most relevant sensitive reactions. Two mechanisms are compared, one from the literature and another from the fusion of two mechanisms originally developed for pure ethanol and pure ammonia respectively. One major conclusion is that none of these mechanisms allows sufficient agreement with experimental data and more in-depth studies are still needed to provide high accurate kinetics mechanisms for ethanol/ammonia mixture. Sensitivity analysis highlights an important difference between the sensitive reactions with pure ammonia and ethanol blends. The key role of carbon reactions HCO(+M)<=>H+CO(+M) and CO+OH<=>CO2+H on the laminar flame speed is shown for blends containing more than 50% of ethanol.

Effect of NO 2 on ignition characteristics of methanol and chemical kinetics analysis

Based on the shock tube experiments, the influence of NO2 on the ignition characteristics of methanol fuel was systematically studied. The ignition delay time of the CH3OH/NO2/O2/Ar mixture with equivalence ratios of 0.5, 1, and 1.5 was measured at the reflected shock temperatures of 1100 ~ 1650 K and the reflected shock pressure of 0.20 MPa. The methanol–NO2 mechanism was newly constructed based on previously developed mechanisms for methanol and NO2 reaction pathways. The new combined reduced mechanism could well predict the ignition delay time of the CH3OH/NO2/O2/Ar mixture. Based on the newly constructed methanol–NO2 mechanism, the reaction path, sensitivity, and important elementary reactions of the stoichiometric mixture were analyzed, and the reasons why NO2 promoted the ignition of methanol fuel were found out: the increase of OH radicals generation and rapid accumulation in the early ignition stage enhanced the activity of the reaction system, interfered the ignition process of CH3OH/NO2/O2/Ar mixture in advance, and promoted the ignition of methanol fuel.

Novel Sensitizing Agent Formulation for Bulk Emulsion Explosives with Improved Energetic Parameters.

Bulk emulsion explosives, although they are very convenient and safe to use, also have disadvantages, with the main one being the relatively low power in relation to cartridged emulsion explosives or classic nitroesters (e.g., dynamites). Therefore, materials of this type currently have only limited use. In addition, these materials are characterized by the variability of blasting parameters over time from loading into the blasthole, which is closely dependent on the utilised mining method of the mine, which makes it difficult to precisely control the fragmentation. The industry is trying to respond to the demand for bulk emulsion explosives with increased energy and improved parameter stability, but so far it has not been possible to do so in a safe and effective way. Methods of improving blasting parameters mainly rely on additives to oxidant solutions during production, which creates additional risks at the production stage, as it involves handling hot and concentrated ammonium nitrate solutions, for which there are known cases of uncontrolled decomposition of such solutions, even leading to an explosion. This paper presents a method of improving the thermodynamic parameters and the stability of the sensitization reaction without the need for changes in the oxidant solution.

Oral Abundance of Actinomyces spp. in Breast Cancer Patients

Objectives: Pathophysiology of medication-related osteonecrosis of the jaw (MRONJ) is still unclear, and disease development is associated with adverse reaction of bisphosphonates and denosumab, and Actinomyces spp. as well. In this study, we evaluated the abundance of Actinomyces spp. in breast cancer patients undergoing chemotherapy compared to healthy controls. Methods: Oropharyngeal samples were collected from treatment-naive early-stage breast cancer patients, who were scheduled for standard of care therapy (eight samples throughout chemotherapy, one prior to radiotherapy and one after a year of start), as well as from healthy controls at matched timepoints. We quantified Actinomyces spp. in the samples with a highly sensitive and specific quantitative polymerase chain reaction. Results: Twenty-one patients and 16 healthy subjects were enrolled. Forty-eight percent of patients suffered from estrogen receptor-positive/progesterone receptor-positive or -negative/human epidermal growth factor receptor 2 (HER2)-negative disease, 38% were HER2-positive, and 14% were triple-negative. Comparison of Actinomyces spp. loads in cancer patients and healthy controls did not reveal significant difference. Fluctuations on bacterial quantity were observed in both groups over time. Tumor receptor status or different chemotherapy schemes of patients were not correlated with a particular pattern on abundance of Actinomyces spp. Conclusions: We suggest that Actinomyces spp. are not the initiative factors in MRONJ development. These bacteria are not altered in abundance during chemotherapy, but they behave opportunistic when there is a bone disruption in the oropharynx in the first place caused by antiresorptive drugs or dental trauma and proliferate in their new niche. Thus, Actinomyces spp. plays a latter role in MRONJ development, rather than a primary causative one.

On the issue of iodine content in drinking waters of the Mari region

When determining the iodine content in drinking water, one must first of all take into account the fact that it is impossible to use directly taken water samples not only for quantitative determinations, but even for the qualitative discovery of iodine, since the most sensitive reactions can often turn out to be completely unusable.

Untargeted and Targeted LC-MS/MS Based Metabolomics Study on In Vitro Culture of Phaeoacremonium Species.

Grapevine (Vitis vinifera L.) can be affected by many different biotic agents, including tracheomycotic fungi such as Phaeomoniella chlamydospora and Phaeoacremonium minimum, which are the main causal agent of Esca and Petri diseases. Both fungi produce phytotoxic naphthalenone polyketides, namely scytalone and isosclerone, that are related to symptom development. The main objective of this study was to investigate the secondary metabolites produced by three Phaeoacremonium species and to assess their phytotoxicity by in vitro bioassay. To this aim, untargeted and targeted LC-MS/MS-based metabolomics were performed. High resolution mass spectrometer UHPLC-Orbitrap was used for the untargeted profiling and dereplication of secondary metabolites. A sensitive multi reaction monitoring (MRM) method for the absolute quantification of scytalone and isosclerone was developed on a UPLC-QTrap. Different isolates of P. italicum, P. alvesii and P. rubrigenum were grown in vitro and the culture filtrates and organic extracts were assayed for phytotoxicity. The toxic effects varied within and among fungal isolates. Isosclerone and scytalone were dereplicated by matching retention times and HRMS and MS/MS data with pure standards. The amount of scytalone and isosclerone differed within and among fungal species. To our best knowledge, this is the first study that applies an approach of LC-MS/MS-based metabolomics to investigate differences in the metabolic composition of organic extracts of Phaeoacremonium species culture filtrates.

Safety evaluation of a food enzyme containing chymosin, pepsin and gastricsin from the abomasum of suckling goats.

The food enzyme containing chymosin (EC 3.4.23.4), pepsin (EC 3.4.23.1) and gastricsin (EC 3.4.23.3) is prepared from the abomasum of suckling goats by Consejo Regulador de la Denominación de Origen Queso Palmero and Consejo Regulador de la Denominación de Origen Queso Majorero. The food enzyme is intended to be used in milk processing for cheese production. As no concerns arise from the animal source of the food enzyme, from its manufacture, and based on the history of safe use and consumption, the Panel considered that toxicological data were not required and no exposure assessment was necessary. Similarity of the amino acid sequences of the three proteins (chymosin, pepsin and gastricsin) to those of known allergens was searched and one match was found. The Panel considered that, under the intended conditions of use, the risk of allergic sensitisation and elicitation reactions by dietary exposure cannot be excluded, but the likelihood is considered to be low. Based on the data provided, the Panel concludes that this food enzyme does not give rise to safety concerns under the intended conditions of use.

Safety evaluation of the food enzyme containing chymosin and pepsin from the abomasum of suckling lambs.

The food enzyme rennet containing chymosin (EC 3.4.23.4) and pepsin (EC 3.4.23.1) is prepared from the abomasum (stomach) of suckling lambs, by Productos Nievi, SA. The food enzyme is intended to be used in milk processing for cheese production. As no concerns arise from the animal source of the food enzyme, from its manufacture, and based on the history of safe use and consumption, the Panel considered that toxicological data were not required and no exposure assessment was necessary. On the basis of literature data, the Panel considered that, under the intended conditions of use, the risk of allergic sensitisation and elicitation reactions by dietary exposure could not be excluded, but the likelihood for this to occur was considered to be low. Based on the data provided, the Panel concludes that this food enzyme does not give rise to safety concerns under the intended conditions of use.

Safety evaluation of the food enzyme cyclomaltodextrin glucanotransferase from Anoxybacillus caldiproteolyticus strain St-88.

The food enzyme cyclomaltodextrin glucanotransferase ((1→4)‐α‐d‐glucan 4‐α‐d‐[(1→4)‐α‐d‐glucano]‐transferase (cyclising), EC 2.4.1.19) is produced with Anoxybacillus caldiproteolyticus strain St‐88 by PureCircle USA. It is intended to be used in the manufacture of glycosylated steviol glycosides. Residual amounts of total organic solids are removed by the purification steps applied during the production of the modified steviol glycosides; consequently, dietary exposure was not calculated. For the same reason, toxicological studies other than assessment of allergenicity were not considered necessary. Similarity of the amino acid sequence of the food enzyme to those of known allergens was searched and four matches were found. The Panel considered that, under the intended conditions of use, the risk of allergic sensitisation and elicitation reactions by dietary exposure cannot be excluded, but the likelihood is considered to be low. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

Response of wheat genotypes to excess boron estimated by in vitro culture

The objective of this study was to evaluate boron tolerance of wheat genotypes using mature embryo culture. The analysis involved 79 recombinant inbred lines of the International Triticeae Mapping Initiative (ITMI) population and three Serbian varieties with known boron (B) tolerance (Pobeda - sensitive S, Balerina-medium tolerant MT, and Nevesinjka - tolerant T). The evaluation was performed on a modified MS medium to which 15 mM of boric acid was added. The control medium contained no excess B. Callus fresh weight (CFW) and reduction of fresh callus weight (RFCW) were determined after one month of cultivation. ANOVA has shown highly significant effect of genotype, the media, and their interaction to callus tissue growth and also significant genotypic effect on RFCW. Majority of genotypes (39) had sensitive reaction to excess boron, twenty-three were medium tolerant, while four of them were tolerant. The obtained results can be potentially used for mapping QTLs associated with tolerance to excess B in wheat breeding program.

Topical diphenylcyclopropenone in the treatment of alopecia areata: A 10-year follow-up of 86 cases in a single center

Background: Diphenylcyclopropenone (DPCP) is a topical contact allergen used for contact immunotherapy in alopecia areata (AA). Objectives: We aimed to evaluate the treatment effectiveness and prognostic factors in Taiwanese patients with AA treated with topical DPCP. Methods: We performed a retrospective study of all consecutive patients with AA affecting more than 10% of scalp area treated with topical DPCP for more than 90 days. Results: Eighty-six patients were assessed in the study. The greatest hair regrowth percentages of 0%, 1%–25%, 26%–50%, 51%–75%, and 76%–100% were 26.7% (23/86), 7.0% (6/86), 2.3% (2/86), 10.5% (9/86), and 53.5% (46/86) of patients, respectively. 32.6% (28/86) of patients achieved near-complete remission (with or without maintenance DPCP therapy), defined as more than 90% sustainable hair regrowth. Positive prognostic factors include older age of onset, shorter duration of AA before DPCP treatment, less severity of hair loss, and no nonscalp hair loss. Multivariate logistic regression analysis showed that more than a 2-year duration of AA before DPCP treatment (P = 0.015) and more than 90% of hair loss (P = 0.032) had a poorer treatment outcome. Factors including eczematous sensitization reaction, history of atopy, adverse reactions, or concentrations of DPCP do not predict treatment effectiveness. Pigmentary change may cause cosmetic concerns in Chinese ethnicity. Conclusion: Topical DPCP is effective for AA. Various factors were associated with the clinical outcomes. Monitoring the possible adverse events is warranted.

Competition between reverse water gas shift reaction and methanol synthesis from CO2: influence of copper particle size.

Converting CO2 into value-added chemicals and fuels, such as methanol, is a promising approach to limit the environmental impact of human activities. Conventional methanol synthesis catalysts have shown limited efficiency and poor stability in a CO2/H2 mixture. To design improved catalysts, crucial for the effective utilization of CO2, an in-depth understanding of the active sites and reaction mechanism is desired. The catalytic performance of a series of carbon-supported Cu catalysts, with Cu particle sizes in the range of 5 to 20 nm, was evaluated under industrially relevant temperature and pressure, i.e. 260 °C and 40 bar(g). The CO2 hydrogenation reaction exhibited clear particle size effects up to 13 nm particles, with small nanoparticles having the lower activity, but higher methanol selectivity. MeOH and CO formation showed a different size-dependence. The TOFCO increased from 1.9 × 10-3 s-1 to 9.4 × 10-3 s-1 with Cu size increasing from 5 nm to 20 nm, while the TOFMeOH was size-independent (8.4 × 10-4 s-1 on average). The apparent activation energies for MeOH and CO formation were size-independent with values of 63 ± 7 kJ mol-1 and 118 ± 6 kJ mol-1, respectively. Hence the size dependence was ascribed to a decrease in the fraction of active sites suitable for CO formation with decreasing particle size. Theoretical models and DFT calculations showed that the origin of the particle size effect is most likely related to the differences in formate coverage for different Cu facets whose abundancy depends on particle size. Hence, the CO2 hydrogenation reaction is intrinsically sensitive to the Cu particle size.

Comparing interfacial cation hydration at catalytic active sites and spectator sites on gold electrodes: understanding structure sensitive CO2 reduction kinetics.

Hydrated cations present in the electrochemical double layer (EDL) are known to play a crucial role in electrocatalytic CO2 reduction (CO2R), and numerous studies have attempted to explain how the cation effect contributes to the complex CO2R mechanism. CO2R is a structure sensitive reaction, indicating that a small fraction of total surface sites may account for the majority of catalytic turnover. Despite intense interest in specific cation effects, probing site-specific, cation-dependent solvation structures remains a significant challenge. In this work, CO adsorbed on Au is used as a vibrational Stark reporter to indirectly probe solvation structure using vibrational sum frequency generation (VSFG) spectroscopy. Two modes corresponding to atop adsorption of CO are observed with unique frequency shifts and potential-dependent intensity profiles, corresponding to direct adsorption of CO to inactive surface sites, and in situ generated CO produced at catalytic active sites. Analysis of the cation-dependent Stark tuning slopes for each of these species provides estimates of the hydrated cation radius upon adsorption to active and inactive sites on the Au electrode. While cations are found to retain their bulk hydration shell upon adsorption at inactive sites, catalytic active sites are characterized by a single layer of water between the Au surface and the electrolyte cation. We propose that the drastic increase in catalytic performance at active sites stems from this unique solvation structure at the Au/electrolyte interface. Building on this evidence of a site-specific EDL structure will be critical to understand the connection between cation-dependent interfacial solvation and CO2R performance.

Effects of Magneto Active Compensation of Geomagnetic Field on Heart Rate Variability of Healthy Males

Geomagnetic field (GMF) is characterized by a strength of a few nT; however, during geomagnetic storms (GMSs), it can be sharply increased hundreds of times and pose a serious threat to magneto-sensitive people. A key scientific question is: How to compensate the possible negative influence of GMSs. The objective of the study was to determine the effects of magneto-active compensation (MAC) of GMF for its future use for protection from the negative influence of GMSs. The measurement of heart rate variability (HRV) on 25 healthy young male volunteers was carried out in the laboratory using the MAC at different levels of outdoor geomagnetic activity (GMA). The geomagnetic K-index was used to characterize the magnitude of GMSs; volunteers were tested during quiet magnetic days (K=1-3), during days with K=4 and during days with GMSs (K≥5). During quiet magnetic days, the comparison between HRV initial values with values measured under GMS compensation mode (CM) did not reveal any changes. On days with K=4 some HRV indices shifted from their initial values, but it was statistically not significant. However, on days with GMSs statistically significant changes in SDNN (p=0.033) and LF/HF (p=0.034) indices of HRV were observed in the GMS CM compared to their initial values. The experiments showed that GMSs cause a sensitive reaction of the heart rate regulatory mechanism, the effect of which can be cancelled in the GMS CM. The efficiency of the used MAC technology is supported by the results presented in this paper.

Development of a reduced chemical kinetic mechanism for biodiesel/natural gas mixture

Biodiesel as an alternative fuel for diesel in compression ignition engines cab be used directly to this type of engine without any significant changes in geometry. Some negative points of biodiesel in compression ignition (CI) engines such as high viscosity, injector carbonize and high NOx emissions cause to use this fuel with other fuels such as alcohol fuels and natural gas based on desired properties of second fuel. Numerical study of fuels such as biodiesel needs to have a chemical kinetic mechanism that can predict combustion characteristics and output emissions. In this study, a reduced detailed mechanism of biodiesel introduced by Zhang et al. is chosen to merged with natural gas GRI-Mech 3.0 mechanism to obtain a chemical kinetic mechanism of biodiesel/natural gas. Direct relation graph with error propagation (DRGP) method and consequently sensitivity analysis was employed to 525 reactions and 126 species that modified with highly sensitive reactions. At first, reduced mechanism of biodiesel/natural gas compared with merged mechanism of these fuels’ mixture with 0-Dimension simulation of ignition delay and 1-Dimension simulation of flame speed. Obtained results show error less than 1% for all intake temperatures and equivalence ratios. In the following, the reduced mechanism with zero percent of natural gas compared with original biodiesel mechanism. Yet again, results show errors almost near zero in lower equivalence ratio and acceptable error, in maximum condition about 10%, in moderate and high equivalence ratios (ERs) during predicting ignition delay with 0-Dimension simulation. Also, flame speed in this evaluation shows less than 2% error in 1-Dimension simulation.

Study on the laminar burning velocity of ethanol/RP-3 aviation kerosene premixed flame

Ethanol biofuel is one renewable liquid fuel which can mix with aviation kerosene and be used as the alternative fuel in aero-engine to release oil security as well as reduce CO2 emission. In the present work, experiments were carried out in a constant volume chamber to obtain the laminar burning velocity (LBV) of ethanol/RP-3 premixed flame. The effects of ethanol addition on the LBV of RP-3 were analyzed experimentally and theoretically. Experimental results show that with the increase of ethanol addition, the LBV of ethanol/RP-3 premixed flame increases. Theoretical analysis indicates that the chemical effect of ethanol addition on the LBV of ethanol/RP-3 plays a decisive role. The three effects of ethanol addition are in the order of chemical > dilution > thermal effect. Sensitivity analysis and reaction pathway analysis of ethanol/RP-3 combustion process shows that with the increase of ethanol addition, the formation of CH3, CH2O, and HCO increase due to the more active radical of OH participates in the primary reactions. In addition, the active radicals of H, O, and OH also increase because of the increase of ethanol addition, which promote the LBV of ethanol/RP-3 premixed flame.

Environmental DNA evidence of the Critically Endangered smalltooth sawfish, Pristis pectinata, in historically occupied US waters

Abstract Formerly common in tropical and subtropical waters of the Atlantic Ocean, the Critically Endangered smalltooth sawfish, Pristis pectinata, underwent severe declines over the past century, restricting population(s) to south and south‐west Florida in the US, and Bahamian waters. Anecdotal evidence (e.g. encounter reports from the public) suggests that P. pectinata have recently been observed in historically occupied US waters; however, no directed surveys have been conducted to verify their extent of occupancy. Here, environmental DNA (eDNA) surveys were used to investigate the occurrence of P. pectinata in three formerly occupied estuaries in US waters. Water samples were collected in the summer from the Indian River Lagoon and Tampa Bay, Florida, in 2018 and 2019, and from Mississippi Sound, Mississippi, in 2018, and screened for target DNA using a highly sensitive Droplet Digital™ polymerase chain reaction assay. Target DNA was detected at four sites in the Indian River Lagoon in 2018 and at one site in 2019 (average concentration: 0.086 copies μl−1; SE = 0.004), but was not detected in either year in Tampa Bay. Target DNA was also detected at three sites near Deer Island in Mississippi Sound in 2018 (average concentration: 0.090 copies μl−1; SE = 0.005). These surveys provide additional lines of evidence that P. pectinata is re‐occurring within two historically occupied estuaries in US waters. More comprehensive eDNA surveys in historically occupied regions, combined with clearly defined post‐survey management actions, can direct additional research and outreach initiatives in emerging priority areas, fostering recovery of this Critically Endangered species.