Free-Standing DNA Origami Superlattice to Facilitate Cryo-EM Visualization of Membrane Vesicles

Technological breakthroughs in cryo-electron microscopy (cryo-EM) methods open new perspectives for highly detailed structural characterizations of extracellular vesicles (EVs) and synthetic liposome-protein assemblies. Structural characterizations of these vesicles in solution under a nearly native hydrated state are of great importance to decipher cell-to-cell communication and to improve EVs' application as markers in diagnosis and as drug carriers in disease therapy. However, difficulties in preparing holey carbon cryo-EM grids with low vesicle heterogeneities, at low concentration and with kinetic control of the chemical reactions or assembly processes, have limited cryo-EM use in the EV study. We report a straightforward membrane vesicle cryo-EM sample preparation method that assists in circumventing these limitations by using a free-standing DNA-affinity superlattice for covering holey carbon cryo-EM grids. Our approach uses DNA origami to self-assemble to a solution-stable and micrometer-sized ordered molecular template in which structure and functional properties can be rationally controlled. We engineered the template with cholesterol-binding sites to specifically trap membrane vesicles. The advantages of this DNA-cholesterol-affinity lattice (DCAL) include (1) local enrichment of artificial and biological vesicles at low concentration and (2) isolation of heterogeneous cell-derived membrane vesicles (exosomes) from a prepurified pellet of cell culture conditioned medium on the grid.

Bronchial aspirate obtained during bronchoscopy yields increased fungal load compared to bronchoalveolar lavage fluid in patients at risk of invasive aspergillosis and Pneumocystis pneumonia

Bronchoalveolar lavage fluid (BALF) is a standard respiratory sample for diagnosing invasive fungal diseases like Pneumocystis pneumonia (PCP) and invasive pulmonary aspergillosis (IPA). However, procedural variations exist across medical centers and wards. This study aimed to compare the diagnostic potential of BALF and bronchial aspirate (BA) obtained during bronchoscopy in 173 patients suspected of fungal infections. A prospective observational study was conducted from April 2020 to November 2021. BALF and BA were collected during bronchoscopy and subjected to direct examination, fungal culture, Aspergillus fumigatus qPCR (AfqPCR), and Pneumocystis jirovecii qPCR (PjqPCR). Galactomannan detection was performed on BALF. Patients were classified based on established European Organization for Research and Treatment of Cancer (EORTC) criteria. Out of 173 patients, 75 tested positive for at least one test in BA or BALF. For Aspergillus, proportion of positive AfqPCR (14.5% vs. 9.2%; P < 0.0001) and fungal loads (Cq of 31.3 vs. 32.8; P = 0.0018) were significantly higher in BA compared to BALF. For Pneumocystis, fungal loads by PjqPCR was also higher in BA compared to BALF (Cq of 34.2 vs. 35.7; P = 0.003). BA only detected A. fumigatus and P. jirovecii in 12 (42.9%) and 8 (19.5%) patients, respectively. BA obtained during a BAL procedure can be a suitable sample type for increased detection of P. jirovecii and A. fumigatus by qPCR. The use of BA in diagnostic algorithms requires further investigation in prospective studies.

Mechanical DNA Origami to Investigate Biological Systems

The ability to self-assemble DNA nanodevices with programmed structural dynamics that can sense and respond to the local environment can enable transformative applications in fields including mechanobiology and nanomedicine. The responsive function of biomolecules is often driven by alterations in conformational distributions mediated by highly sensitive interactions with the local environment. In this review, the current state-of-the-art in constructing complex DNA geometries with dynamic and mechanical properties to enable a molecular scale force measurement is first summarized. Next, an overview of engineering modular DNA devices that interact with cell surfaces is highlighted detailing examples of mechanosensitive proteins and the force-induced dynamic molecular interaction on the downstream biochemical signaling. Finally, the challenges and an outlook on this promising class of DNA devices acting as nanomachines to operate at a low piconewton range suitable for a majority of biological effects or as hybrid materials to achieve higher tension exertion required for other biological investigations, are discussed.

First Patient-to-Patient Intrahospital Transmission of Clade I Candida auris in France Revealed after a Two-Month Incubation Period

Candida auris is a recently described emerging pathogen in hospital settings. Five genetic clades have been delineated, with each clade being isolated from specific geographic regions. We here describe the first transmission between 2 patients (P0 and P1) of a clade I C. auris strain imported into our burn intensive care unit from the Middle East. The strains have been investigated with whole-genome sequencing, which validated the high similarity of the genomes between isolates from P0 and P1. We repeatedly screened the two patients and contact patients (i.e., other patients present in the same hospital ward at the time of the first positive sample from P0 or P1; n = 49; 268 tests) with fungal culture and a C. auris-specific quantitative PCR assay to assess transmission patterns. We observed that P1 developed C. auris colonization between 41 and 61 days after potential exposure to P0 contamination, despite three negative screening tests as recommended by our national authorities. This study illustrates that transmission of C. auris between patients can lead to long-term incubation times before the detection of colonization. The recommended screening strategy may not be optimal and should be improved in the light of our findings. IMPORTANCE While large outbreaks of C. auris in hospital settings have been described, few clear cases of direct transmission have been documented. We here investigated the transmission of C. auris clade I between two patients with a 41- to 61-day delay between exposure and the development of colonization. This may lead to changes in the recommendations concerning treatment of C. auris cases, as an incubation period of this length is one of the first to be reported.

Investigation of CryptoPS LFA-positive sera in patients at risk of cryptococcosis

Cryptococcal antigen (CrAg) is a capsule polysaccharide antigen that can be detected in fluids of patients with cryptococcal infections. Cryptococcal Antigen Latex Agglutination System (CALAS), enzyme-linked immunosorbent assays (EIA) and lateral flow assay (LFA) are the main methods available. Two main commercial LFA kits are available: CryptoPS (Biosynex, Illkirch Graffenstaden, France) and CrAg LFA (IMMY, Inc. USA). In our lab, we prospectively used CryptoPS as a screening tool in serum for confirmed positive results with Cryptococcal Antigen Latex Agglutination System (CALAS). We investigated the rigor of the CryptoPS test in serum in a multicentric evaluation over 3 years. To improve the specificity of CryptoPS in serum, we additionally implemented and evaluated a pretreatment protocol before CryptoPS testing. A total of 43 serum samples collected from 43 patients were investigated. We found that the CryptoPS assay is hampered by a high rate of false-positive results in serum with high rate of CryptoPS-positive but CrAg LFA-negative and CALAS-negative sera in patients with no proof of Cryptococcus infection (n = 29). Using a simple pretreatment procedure (5 min incubation at 100°C and centrifugation) we were able to reverse false-positive results, suggesting that there could be interferent material present in serum. Pretreatment also impacted the CryptoPS results (negative result) in two patients with cryptococcal disease, one with isolated antigenemia and one with cryptococcal meningitis. Comparing the titers obtained with CALAS and CrAg LFA, we noticed that the titer obtained with CrAg LFA was almost 10-fold higher than those with CALAS. This study showed that Biosynex CryptoPS in serum could give false-positive results even in the absence of cryptococcal disease. These could be reduced by applying an easy pretreatment procedure to the serum before testing, with little but existing impact on the sensitivity.

Imported leishmaniasis in travelers: a 7-year retrospective from a Parisian hospital in France

BACKGROUND

Leishmaniases are regularly seen in non-endemic areas due to the increase of international travels. They include cutaneous leishmaniases (CL) and mucocutaneous (MC) caused by different Leishmania species, and visceral leishmaniases (VL) which present with non-specific symptoms.

METHODS

We reviewed all consecutive leishmaniasis cases seen between September 2012 and May 2020. The diagnostic strategy included microscopy after May-Grünwald-Giemsa staining, a diagnostic quantitative PCR (qPCR) assay, and species identification based on sequencing of the cytochrome b gene.

RESULTS

Eighty-nine patients had a definitive leishmaniasis diagnosis. Nine patients had VL with Leishmania infantum. Eighty patients had CL. Twelve patients acquired CL after trips in Latin America (7 Leishmania guyanensis, 2 Leishmania braziliensis, 2 Leishmania mexicana, and 1 Leishmania panamensis). Species could be identified in 63 of the 68 CLs mainly after travel in North Africa (59%) with Leishmania major (65%), Leishmania tropica/killicki (24%), and L. infantum (11%), or in West Sub-Saharan Africa (32%), all due to L. major. The median day between appearance of the lesions and diagnosis was 90 [range 60-127].

CONCLUSIONS

Our diagnostic strategy allows both positive diagnoses and species identifications. Travelers in West Sub-Saharan Africa and North Africa should be better aware of the risk of contracting leishmananiasis.

Melanotransferrin is efficiently sorted on the surface of exosomes secreted by melanoma cells

Cutaneous melanoma is the most lethal type of skin cancer. Early detection is crucial to improve the outcome of melanoma patients. The identification of noninvasive prognostic biomarkers for the follow-up of melanoma patients is still in demand for clinical use. We show here that exosomal melanotransferrin fulfills the biomarker characteristics required to meet this demand. Melanotransferrin is typically overexpressed in melanoma cells compared to other cell types - including cancer cells - and is efficiently sorted and secreted with nanovesicles, or so-called exosomes, due to its membrane-anchoring by a glycosylphosphatidylinositol. Melanotransferrin is exposed on the surface of exosomes and is accessible for antibody recognition. An ELISA was set up to quantify melanotransferrin after immobilization of nanovesicles through the exosomal constituent tetraspanins CD63. Melanotransferrin was detected using a low number of exosomes purified from melanoma cell line cultures, and melanotransferrin detection was abolished by phosphatidylinositol-specific phospholipase C treatment. This exosomal melanotransferrin ELISA was able to discriminate an equal number of assayed exosomes purified from two different melanoma cell lines (A-375 vs. SK-MEL-28). Moreover, plasma samples from patients with melanoma and noncancer disease were assayed using this ELISA and elevated levels of exosomal melanotransferrin were seen in the plasma of patients with melanoma. We propose that exosomal melanotransferrin should be assessed as a potential melanoma biomarker.

Increased sensitivity of a new commercial reverse transcriptase-quantitative PCR for the detection of Pneumocystis jirovecii in respiratory specimens

Optimal sensitivity to detect low Pneumocystis loads is of importance to take individual and collective measures to avoid evolution towards Pneumocystis pneumonia and outbreaks in immunocompromised patients. This study compares two qPCR procedures, a new automated RTqPCR using the GeneLEAD VIII extractor/thermocycler (GLVIII; ∼2.2 h workflow) and a previously validated in-house qPCR assays (IH; ∼5 h workflow) both targeting mtSSU and mtLSU for detecting P. jirovecii in 213 respiratory samples. GLVIII was found to be more sensitive than IH, detecting eight more specimens. Bland-Altman analysis between the two procedures showed a Cq bias of 1.17 ± 0.07 in favor of GLVIII.

LAY SUMMARY

The fungus Pneumocystis needs to be detected early in respiratory samples to prevent pneumonia in immunocompromised hosts. We evaluated a new commercial RTqPCR on 213 respiratory samples to detect Pneumocystis and found it more sensitive and faster than our routine sensitive in-house qPCR assay.

Modular Imaging Scaffold for Single-Particle Electron Microscopy

Technological breakthroughs in electron microscopy (EM) have made it possible to solve structures of biological macromolecular complexes and to raise novel challenges, specifically related to sample preparation and heterogeneous macromolecular assemblies such as DNA-protein, protein-protein, and membrane protein assemblies. Here, we built a V-shaped DNA origami as a scaffolding molecular system to template proteins at user-defined positions in space. This template positions macromolecular assemblies of various sizes, juxtaposes combinations of biomolecules into complex arrangements, isolates biomolecules in their active state, and stabilizes membrane proteins in solution. In addition, the design can be engineered to tune DNA mechanical properties by exerting a controlled piconewton (pN) force on the molecular system and thus adapted to characterize mechanosensitive proteins. The binding site can also be specifically customized to accommodate the protein of interest, either interacting spontaneously with DNA or through directed chemical conjugation, increasing the range of potential targets for single-particle EM investigation. We assessed the applicability for five different proteins. Finally, as a proof of principle, we used RNAP protein to validate the approach and to explore the compatibility of the template with cryo-EM sample preparation.

Folding of phosphodiester-linked donor–acceptor oligomers into supramolecular nanotubes in water

Water soluble foldamers, synthesized by DNA synthesis with dialkoxynaphthalene and naphthalene-tetracarboxylic diimide blocks, formed supramolecular nanotubes in water.

P4167Non-shockable rhythm related sudden cardiac arrest in the community

Introduction

A significant increase in the prevalence of sudden cardiac arrest (SCA) with non-shockable rhythm has been reported, related to asystole and pulseless electrical activity (PEA). Factors associated with non-shockable rhythm and the mode to the return of spontaneous circulation (ROSC) may help for a better understanding.

Purpose

We aimed to describe the frequency, characteristics and outcome of SCA related to non-shockable versus shockable rhythm in the community.

Methods

In this prospective ongoing, multicentre population-based registry (6.7 million inhabitants), data from all SCA over a 5-year period were analyzed. Initial rhythm was obtained from the EMS report and the initial recorded rhythm strip when available. Medical records for each SCA were reviewed by cardiologists to identify underlying aetiology and associated conditions.

Results

Among the 3,028 SCAs admitted alive out of a total of 18,622 out-of-hospital cardiac arrests from May 2011 to May 2016, 2,904 patients had available information regarding initial rhythm at the time of EMS arrival. Among them, 1,314 patients (45.3%) presented with non-shockable rhythm: 1,109 (38.2%) cases with asystole, 197 (6.8%) with PEA and 8 (0.3%) with high degree atrioventricular block.

Cases with non-shockable rhythm were older (60.6 vs. 57.4 years, P<0.001), with greater proportion of females (34.9 vs. 19.2%, P<0.001) and less proportion of family history of coronary artery disease or SCA. Proportion of warning symptoms prior to the SCA was higher among patients with non-shockable rhythm (74.3 vs. 64.9%, P<0.001) but the proportion of chest pain was lower (24.0 vs. 43.3%, P<0.001). Survival rate was much lower in non-shockable rhythm cases (7.2 vs. 42.3%, P<0.001).

Among the 1,314 non-shockable cases eventually admitted alive to hospital, 1,022 (77.8%) did not require external defibrillation prior to ROSC, and a majority (91.7%) received adrenaline during resuscitation. In this subgroup, the main identified cardiac cause was acute coronary syndrome (45.3%), followed by chronic CAD (27.1%), structural non-ischemic heart disease (22.4%), and non-structural heart disease (5.2%).

Conclusions

Initial non-shockable rhythm is encountered in almost half of SCA cases admitted alive; mostly occurs in older patients with higher proportion of females. Over three quarters of these cases did not require external defibrillation prior to ROSC.

P2823Lack of early systematic investigations among young victims of sudden cardiac arrest

Introduction

Since a large proportion of patients resuscitated from out-of-hospital sudden cardiac arrest (SCA) die in the intensive care unit (ICU), early systematic investigation towards identifying etiology may be crucial to ensure targeted therapy and appropriate future prevention among relatives, especially when the index case is young.

Purpose

We hypothesized that etiologic investigations were not initiated in a timely manner in a significant proportion of young SCA patients, alive at ICU admission, prior to death.

Methods

In this prospective, ongoing, multicenter, population-based registry (6.7 million inhabitants), data from all SCA over a 5-year period were analyzed, in collaboration with all the 48 hospitals of the area, with a specific focus on young patients (<45 year-old) alive at hospital admission and who eventually died prior to ICU discharge. Investigations performed and diagnoses arrived at were analyzed from the medical records by two cardiologists for each case.

Results

Of the 18,622 out-of-hospital cardiac arrests from May 2011 to May 2016, 3,028 were admitted alive to ICU. Among them, 2,190 (72.3%) died in ICU, including 367 (16.8%) young cases (<45 yo). Among the young patients, while 163 cases (44.4%) had a specific diagnosis established, 204 (55.6%) remained unexplained. Coronary angiograms (18.3%), CT scan (brain and chest) (24.5%), and transthoracic echocardiography (29.1%) were all underutilized. Main established SCA causes were acute coronary syndrome (44.5%), followed by structural non-ischemic heart disease (25.5%), pulmonary embolism (13.6%), chronic CAD (10%), non-structural heart disease (1.8%) and miscellaneous (4.6%). The proportion of systematic autopsy (10.9%), as well as blood sample collection for further genetic testing (1.4%) was low. Information on family screening was rarely provided in the ICU.

Conclusion

More than half of young SCA cases who died in ICU remained unexplained. There was significant underuse of core cardiac investigations. Efforts to promote prompt and systematic investigation through better collaboration between intensivist and cardiologist may improve both acute management and future targeted preventive strategies for family members.

P2827Different views of sudden cardiac arrest characteristics according to the assessed population

Background

Survival rate remains extremely low in sudden cardiac arrest (SCA) and death may occur at all stages of its management. We hypothesized that different medical care providers have different visions of the SCA population characteristics.

Purpose

To assess SCA characteristics among four groups: all-comers SCA, resuscitated SCA, SCA admitted alive to intensive care unit (ICU), and SCA admitted to cardiology.

Methods

Data was taken from the Paris Sudden Cardiac Death Expertise Center prospective registry that includes all adults presenting SCA in Paris and suburbs (6.7 millions). We compared SCA characteristics according to the management phase where the population was assessed.

Results

Of 18,622 out-of-hospital cardiac arrests occurring between 2011 and 2016, 15,207 fulfilled SCA criteria and had known resuscitation status. Among them, 9,721 SCA (63.9%) underwent resuscitation, leading to 3,349 SCA (22.0%) admitted to ICU, then 735 (4.8%) admitted to Cardiology. Mean age was highest in the global population (70.7yrs), and decreased progressively throughout the phases to 57.0yrs in cardiology (P<0.001). Ratio of male victims and rates of witnessed SCA and bystanders' cardiopulmonary resuscitation and automated external defibrillator use increased gradually (all P<0.001). No flow duration decreased by a third (9.1min overall to 3.0min in cardiology, P<0.001). The rate of shockable initial rhythm increased drastically, from 19.5% overall to 26.8% in resuscitated patients, 48.9% in ICU-admitted SCA, and 89.4% in cardiology-admitted (Table).

Sudden cardiac arrests characteristics Entire SCA population SCA with attempted resuscitation SCA admitted to ICU SCA admitted to Cardiology P value n=15,207 n=9,721 n=3349 n=735 Age (years ± SD) 70.7±16.9 65.8±16.1 59.7±15.7 57.0±14.5 <0.001 Male sex, n (%) 9,353 (61.6) 6607 (68.0) 2395 (71.5) 599 (81.5) <0.001 Home location, n (%) 12,297 (81.1) 7075 (73.0) 1906 (56.9) 269 (36.6) <0.001 Bystander, n (%) 10,546 (71.2) 7545 (78.7) 3037 (90.7) 715 (97.3) <0.001 Bystander CPR, n (%) 5,684 (39.1) 4504 (47.7) 2120 (63.5) 583 (81.2) <0.001 Public AED use, n (%) 155 (1.0) 142 (1.5) 116 (3.5) 51 (6.9) <0.001 No flow, (min ± SD) 9.1±12.5 7.5±10.4 5.3±6.6 3.0±3.8 <0.001 EMS call-to-arrival delay, (min ± SD) 10.2±5.8 10.1±5.7 10.1±6.1 9.6±6.4 0.068 Initial Shockable rhythm, n (%) 2,643 (19.5) 2529 (26.8) 1635 (48.9) 657 (89.4) <0.001 SCA: sudden cardiac arrest; AED: automated external defibrillator; CPR: cardiopulmonary resuscitation; EMS: emergency medical service; ICU: intensive care unit.

Conclusion

Characteristics of SCA change considerably according to the assessed population, leading to different views on SCA reality. Keeping in mind the SCA population considered is paramount for a non-biased view of SCA.

A 2-year multicenter, observational, prospective, cohort study on extracorporeal CO2 removal in a large metropolis area

Background

Extracorporeal carbon dioxide removal (ECCO₂R) is a promising technique for the management of acute respiratory failure, but with a limited level of evidence to support its use outside clinical trials and/or data collection initiatives. We report a collaborative initiative in a large metropolis.

Methods

To assess on a structural basis the rate of utilization as well as efficacy and safety parameters of 2 ECCO₂R devices in 10 intensive care units (ICU) during a 2-year period.

Results

Seventy patients were recruited in 10 voluntary and specifically trained centers. The median utilization rate was 0.19 patient/month/center (min 0.04; max 1.20). ECCO₂R was started under invasive mechanical ventilation (IMV) in 59 patients and non-invasive ventilation in 11 patients. The Hemolung Respiratory Assist System (Alung) was used in 53 patients and the iLA Activve iLA kit (Xenios Novalung) in 17 patients. Main indications were ultraprotective ventilation for ARDS patients (n = 24), shortening the duration of IMV in COPD patients (n = 21), preventing intubation in COPD patients (n = 9), and controlling hypercapnia and dynamic hyperinflation in mechanically ventilated patients with severe acute asthma (n = 6). A reduction in median V_T was observed in ARDS patients from 5.9 to 4.1 ml/kg (p <0.001). A reduction in PaCO₂ values was observed in AE-COPD patients from 67.5 to 51 mmHg (p< 0.001). Median duration of ECCO₂R was 5 days (IQR 3–8). Reasons for ECCO₂R discontinuation were improvement (n = 33), ECCO₂R-related complications (n = 18), limitation of life-sustaining therapies or measures decision (n = 10), and death (n = 9). Main adverse events were hemolysis (n = 21), bleeding (n = 17), and lung membrane clotting (n = 11), with different profiles between the devices. Thirty-five deaths occurred during the ICU stay, 3 of which being ECCO₂R-related.

Conclusions

Based on a registry, we report a low rate of ECCO₂R device utilization, mainly in severe COPD and ARDS patients. Physiological efficacy was confirmed in these two populations. We confirmed safety concerns such as hemolysis, bleeding, and thrombosis, with different profiles between the devices. Such results could help to design future studies aiming to enhance safety, to demonstrate a still-lacking strong clinical benefit of ECCO₂R, and to guide the choice between different devices.

Trial registration

ClinicalTrials.gov: Identifier: NCT02965079 retrospectively registered https://clinicaltrials.gov/ct2/show/NCT02965079

Impact du nombre d’interventions infirmières sur la durée d’administration des catécholamines chez les patients de réanimation : étude INTERVAL

Objectifs : Bien que quotidiennement géré par les infirmier(ière)s diplômé(e)s d’État (IDE) de réanimation, le sevrage des catécholamines a rarement été étudié. L’hypothèse de notre étude était que l’augmentation du nombre d’interventions menées sur la vitesse de perfusion des catécholamines permettait de raccourcir la durée d’administration de celles-ci.

Patients et méthodes : Il s’agissait d’une étude prospective observationnelle dans 21 réanimations. Tous les patients traités par vasopresseurs pendant la période d’étude ont été inclus. Le nombre d’interventions effectuées par l’IDE en charge du patient sur la vitesse d’administration des catécholamines était noté toutes les quatre heures. La posologie de catécholamines en cours ainsi que la pression artérielle moyenne (PAM) du patient étaient également relevées. Les facteurs influençant la rapidité du sevrage des catécholamines étaient également analysés.

Résultats : Nous avons inclus 226 patients dont l’âge moyen était de 65 ± 14 ans. La durée moyenne du traitement par catécholamines était de 71,6 (±81) heures. Le nombre d’interventions IDE par quatre heures était de 1,9 (±2,8) intervention. La durée du traitement par catécholamines était significativement moindre lorsque le nombre d’interventions augmentait (p = 0,04). L’existence d’un protocole spécifique à la gestion des catécholamines raccourcissait leur durée de sevrage. Un IGS2 élevé, une PAM élevée ainsi que la période diurne étaient associés à une augmentation du nombre des interventions IDE.

Conclusion : Le nombre d’interventions par les IDEs menées sur la perfusion de catécholamines était inversement lié à la durée du traitement par catécholamines. Des études complémentaires permettront d’évaluer l’impact de ces interventions sur le pronostic des patients.

Reversible Immobilization of Proteins in Sensors and Solid-State Nanopores

The controlled functionalization of surfaces with proteins is crucial for many analytical methods in life science research and biomedical applications. Here, a coating for silica-based surfaces is established which enables stable and selective immobilization of proteins with controlled orientation and tunable surface density. The coating is reusable, retains functionality upon long-term storage in air, and is applicable to surfaces of complex geometry. The protein anchoring method is validated on planar surfaces, and then a method is developed to measure the anchoring process in real time using silicon nitride solid-state nanopores. For surface attachment, polyhistidine tags that are site specifically introduced into recombinant proteins are exploited, and the yeast nucleoporin Nsp1 is used as model protein. Contrary to the commonly used covalent thiol chemistry, the anchoring of proteins via polyhistidine tag is reversible, permitting to take proteins off and replace them by other ones. Such switching in real time in experiments on individual nanopores is monitored using ion conductivity. Finally, it is demonstrated that silica and gold surfaces can be orthogonally functionalized to accommodate polyhistidine-tagged proteins on silica but prevent protein binding to gold, which extends the applicability of this surface functionalization method to even more complex sensor devices.

FRET enhancement close to gold nanoparticles positioned in DNA origami constructs

Here we investigate the energy transfer rates of a Förster resonance energy transfer (FRET) pair positioned in close proximity to a 5 nm gold nanoparticle (AuNP) on a DNA origami construct. We study the distance dependence of the FRET rate by varying the location of the donor molecule, D, relative to the AuNP while maintaining a fixed location of the acceptor molecule, A. The presence of the AuNP induces an alteration in the spontaneous emission of the donor (including radiative and non-radiative rates) which is strongly dependent on the distance between the donor and AuNP surface. Simultaneously, the energy transfer rates are enhanced at shorter D-A (and D-AuNP) distances. Overall, in addition to the direct influence of the acceptor and AuNP on the donor decay there is also a significant increase in decay rate not explained by the sum of the two interactions. This leads to enhanced energy transfer between donor and acceptor in the presence of a 5 nm AuNP. We also demonstrate that the transfer rate in the three "particle" geometry (D + A + AuNP) depends approximately linearly on the transfer rate in the donor-AuNP system, suggesting the possibility to control FRET process with electric field induced by 5 nm AuNPs close to the donor fluorophore. It is concluded that DNA origami is a very versatile platform for studying interactions between molecules and plasmonic nanoparticles in general and FRET enhancement in particular.

Enzyme immobilization on silane-modified surface through short linkers: fate of interfacial phases and impact on catalytic activity

We investigated the mechanism of enzyme immobilization on silanized surfaces through coupling agents (cross-linkers) in order to understand the role of these molecules on interfacial processes and their effect on catalytic activity. To this end, we used a model multimeric enzyme (G6PDH) and several cross-linking molecules with different chemical properties, including the nature of the end-group (-NCO, -NCS, -CHO), the connecting chain (aliphatic vs aromatic), and geometrical constraints (meta vs para-disubstituted aromatics). There did not seem to be radical differences in the mechanism of enzyme adsorption according to the linker used as judged from QCM-D, except that in the case of DIC (1,4-phenylene diisocyanate) the adsorption occurred more rapidly. In contrast, the nature of the cross-linker exerted a strong influence on the amount of enzyme immobilized as estimated from XPS, and more unexpectedly on the stability of the underlying silane layer. DIC, PDC (1,4-phenylene diisothiocyanate), or GA (glutaraldehyde) allowed successful enzyme immobilization. When the geometry of the linker was changed from 1,4-phenylene diisothiocyanate to 1,3-phenylene diisothiocyanate (MDC), the silane layer was subjected to degradation, upon enzyme adsorption, and the amount of immobilized molecules was significantly lowered. TE (terephtalaldehyde) and direct enzyme deposition without cross-linker were similar to MDC. The organization of immobilized enzymes also depended on the immobilization procedure, as different degrees of aggregation were observed by AFM. A correlation between the size of the aggregates and the catalytic properties of the enzyme was established, suggesting that aggregation may enhance the thermostability of the multimeric enzyme, probably through a compaction of the 3D structure.