Preparation and characterization of aptamer-polyelectrolyte films and microcapsules for biosensing and delivery applications.

"Smart" materials are polymer systems that are able to change their physical or chemical properties in response to external stimuli in their environment. By adding a specific molecular recognition probe to a polymer, hybrid materials can be developed that retain the properties of the advanced polymer and gain the ability to respond to a specific molecular target. Aptamers are single-stranded oligonucleotides that are well-suited to serve as molecular recognition probes due to the specificity and affinity of their target recognition as well as their stability and ease of synthesis and labeling. In particular, their negatively charged backbone makes for their facile incorporation into polyelectrolyte-based materials. This article will provide a brief review of the currently reported biosensor and delivery platforms that have been reported employing aptamer-polyelectrolyte materials, as well as a detailed description of the methods used to synthesize and study films and microcapsules containing small-molecule aptamer probes.

Dissolution Behavior of Silver Nanoparticles and Formation of Secondary Silver Nanoparticles in Municipal Wastewater by Single-Particle ICP-MS.

Ag nanoparticles (nAg) are used in various consumer products and a significant fraction is eventually discharged with municipal wastewater (WW). In this study we assessed the release of Ag from polyvinylpyrrolidone (PVP)- and citrate-coated 80 nm nAg in aerobic WW effluent and mixed liquor and the related changes in nAg size, using single particle ICP-MS (spICP-MS). The concentration of dissolved (nonparticulate) Ag in WW effluent was 0.89 ± 0.05 ppb at 168 h and was 71% lower than in deionized (DI) water, in batch reactors spiked with 5 × 106 PVP-nAg particles/mL (10 µg/L), an environmentally relevant concentration. Dissolved Ag in WW was partly reformed into ∼22 nm nAgxSy by inorganic sulfides and organosulfur dissolved organic carbon (DOC) after 120 h, whereas the parent nAg mean diameter decreased to 65.89 ± 0.9 nm. Reformation of nAgxSy from Ag+ also occurred in cysteine solutions but not in DI water, or humic and fulvic acid solutions. Dissolution experiments with nAg in WW mixed liquor showed qualitatively similar dissolution trends. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) analyses indicated binding of thiol- and amine-containing DOC as well as inorganic sulfides with nAg. Those WW components, as well as limited dissolved oxygen, decreased dissolution in WW.

Considerations of Environmentally Relevant Test Conditions for Improved Evaluation of Ecological Hazards of Engineered Nanomaterials.

Engineered nanomaterials (ENMs) are increasingly entering the environment with uncertain consequences including potential ecological effects. Various research communities view differently whether ecotoxicological testing of ENMs should be conducted using environmentally relevant concentrations-where observing outcomes is difficult-versus higher ENM doses, where responses are observable. What exposure conditions are typically used in assessing ENM hazards to populations? What conditions are used to test ecosystem-scale hazards? What is known regarding actual ENMs in the environment, via measurements or modeling simulations? How should exposure conditions, ENM transformation, dose, and body burden be used in interpreting biological and computational findings for assessing risks? These questions were addressed in the context of this critical review. As a result, three main recommendations emerged. First, researchers should improve ecotoxicology of ENMs by choosing test end points, duration, and study conditions-including ENM test concentrations-that align with realistic exposure scenarios. Second, testing should proceed via tiers with iterative feedback that informs experiments at other levels of biological organization. Finally, environmental realism in ENM hazard assessments should involve greater coordination among ENM quantitative analysts, exposure modelers, and ecotoxicologists, across government, industry, and academia.

Advancing Risk Analysis for Nanoscale Materials: Report from an International Workshop on the Role of Alternative Testing Strategies for Advancement.

The Society for Risk Analysis (SRA) has a history of bringing thought leadership to topics of emerging risk. In September 2014, the SRA Emerging Nanoscale Materials Specialty Group convened an international workshop to examine the use of alternative testing strategies (ATS) for manufactured nanomaterials (NM) from a risk analysis perspective. Experts in NM environmental health and safety, human health, ecotoxicology, regulatory compliance, risk analysis, and ATS evaluated and discussed the state of the science for in vitro and other alternatives to traditional toxicology testing for NM. Based on this review, experts recommended immediate and near-term actions that would advance ATS use in NM risk assessment. Three focal areas-human health, ecological health, and exposure considerations-shaped deliberations about information needs, priorities, and the next steps required to increase confidence in and use of ATS in NM risk assessment. The deliberations revealed that ATS are now being used for screening, and that, in the near term, ATS could be developed for use in read-across or categorization decision making within certain regulatory frameworks. Participants recognized that leadership is required from within the scientific community to address basic challenges, including standardizing materials, protocols, techniques and reporting, and designing experiments relevant to real-world conditions, as well as coordination and sharing of large-scale collaborations and data. Experts agreed that it will be critical to include experimental parameters that can support the development of adverse outcome pathways. Numerous other insightful ideas for investment in ATS emerged throughout the discussions and are further highlighted in this article.

Target binding influences permeability in aptamer-polyelectrolyte microcapsules.

Aptamer-polyelectrolyte microcapsules are prepared for potential use as triggered delivery vehicles and microreactors. The hollow microcapsules are prepared from the sulforhodamine B aptamer and the polyelectrolytes poly(allylamine hydrochloride) and poly(sodium 4-styrene-sulfonate), using layer-by-layer (LbL) film deposition templated on a sacrificial CaCO(3) spherical core. Scanning electron microscopy and confocal microscopy confirm the formation of spherical CaCO(3) cores and LbL-aptamer microcapsules. Colocalization studies with fluorescently-tagged aptamer and sulforhodamine B verify the ability of the aptamer to recognize its cognate target in the presence of the K(+) ions that are required for its characteristic G-quadruplex formation. Fluorescence recovery after photobleaching studies confirms a significant difference in the permeability of the aptamer-polyelectrolyte microcapsules for the sulforhodamine B dye target compared to control microcapsules prepared with a random oligonucleotide. These results suggest that aptamer-based 'smart' responsive films and microcapsules could be applied to problems of catalysis and controlled release.

Preparation of functional aptamer films using layer-by-layer self-assembly.

Advances in many aptamer-based applications will require a better understanding of how an aptamer's molecular recognition ability is affected by its incorporation into a suitable matrix. In this study, we investigated whether a model aptamer system, the sulforhodamine B aptamer, would retain its binding ability while embedded in a multilayer polyelectrolyte film. Thin films consisting of poly(diallyldimethylammonium chloride) as the polycation and both poly(sodium 4-styrene-sulfonate) and the aptamer as the polyanions were deposited by the layer-by-layer approach and were compared to films prepared using calf thymus DNA or a random single-stranded oligonucleotide. Data from UV-vis spectroscopy, quartz crystal microbalance studies, confocal microscopy, and time of flight secondary ion mass spectrometry confirm that the aptamer's recognition of its target is retained, with no loss of specificity and only a modest reduction of binding affinity, while it is incorporated within the thin film. These findings open up a raft of new opportunities for the development and application of aptamer-based functional thin films.

Target-molecule-triggered rupture of aptamer-encapsulated polyelectrolyte microcapsules.

Polyelectrolyte microcapsules have great potential for serving as carriers for the delivery of their contents when triggered by an external stimulus. Aptamers are synthetic ssDNA or RNA that can bind to specific targets with high affinity and selectivity. Aptamers may retain these superior molecular recognition properties after encapsulation within polymer microcapsules. In this work, stable polyelectrolyte microcapsules with encapsulated aptamers were obtained by the layer-by-layer (LbL) method. Polyelectrolyte films were deposited onto a CaCO3 template that had been predoped with polystyrene sulfonate (PSS) and aptamer sequences (SA) that have an affinity for the dye sulforhodamine B (SRB). The PSS and aptamers are thought to serve as an internal scaffold supporting the microcapsule walls. These microcapsules would present target-molecule-triggered rupture properties. Microcapsule collapse was triggered by the binding of SRB to the encapsulated aptamer. The specificity of microcapsule collapse was investigated using a similar dye, tetramethylrosamine (TMR), which does not have affinity for SA. A high concentration of TMR did not lead to the collapse of the microcapsules. The effect of target binding on the microcapsules was confirmed by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). These microcapsules may have potential applications in targeted delivery systems for the controlled release of drugs, pesticides, or other payloads.

Water-based oxygen-sensor films.

The luminescent cyclometalated iridium complex [Ir(fppy)(2)(t-Bu-iCN)(2)]CF(3)SO(3), 1 (fppy = 4-(2-pyridyl)benzaldehyde, and t-Bu-iCN = tert-butyl isocyanide), was synthesized and characterized by X-ray crystallography and (1)H NMR, absorption, and emission spectroscopies. Complex 1 was quantitatively bound to the water-soluble amine-functionalized polymer Silamine D208-EDA by reductive amination, to produce 2. The quantum yield of emission and excited state lifetime of 2 (varphi(em) = 0.23 and tau = 20.6 mus) are comparable to that of the model complex [Ir(tpy)(2)(t-Bu-iCN)(2)]CF(3)SO(3), 3 (tpy = 2-(p- tolyl) pyridine) with varphi(em) = 0.28 and tau = 35.6 mus. Aqueous blends of 2 with Silamine and colloidal microcrystalline cellulose (MC) were used to prepare oxygen-sensor films. Oxygen sensitivities of these films were determined as a function of Silamine:MC ratio and obeyed Stern-Volmer kinetics. The optimum oxygen-sensor film composition was 2 in 1:1 Silamine:MC, which had an oxygen sensitivity of 0.502 over an atmospheric pressure range of 0.007-45 psi. Temperature sensitivity (percentage loss of intensity per degrees C) of this film was determined to be -1.1 and -1.4% degrees C(-1) at vacuum and 1 bar atmospheric pressure, respectively. These results were compared to those of films incorporating dispersions of 1 and 3. Luminescence microscopy of 9:1, 1:1, and 1:5 Silamine:MC films of 2 show that the charged iridium complex in 2 associates with the surface of MC and lifetime measurements of these films show an increase in lifetime with increasing MC fraction. The optimum quenching sensitivity observed for the 1:1 Silamine:MC film suggests that the diffusion of oxygen must decrease with increasing fraction of MC and thereby decrease oxygen sensitivity. These novel materials offer an environmentally friendly alternative to the preparation of oxygen-sensor films.