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NANOCAVITY SENSOR ARRAY FOR THE ISOLATION, DETECTION AND QUANTITATION OF ENGINEERED NANOPARTICLES
Impact/Purpose:
The overall objective of this proposal is to develop nanocavity sensor arrays for the isolation, detection and quantitation of engineered nanoparticles (ENPs) and distinguish these from naturally occurring nanomaterials in complex environmental matrices. The proposed monitoring system relies on the hypothesis that one could consider the cell (bacteria cells, viral particles, spores etc) to be either a particle or an analyte with unique shapes, sizes and morphology. Since engineered nanoparticles are also distinguished by their size, shape and morphologies, these properties could be utilized for monitoring the differences in their physicochemical characteristics, chemical and biological reactivity. Other important implication of the "cell as particles" concept requires that cell viability/integrity is taken into consideration, thus presenting an underlying differences for differentiation. Hence the specific goals are to design, optimize, fabricate and field-test arrays of nanocavity capillary substrates for monitoring engineered nanoparticles (e,g Au, Ag), and naturally-occurring cell particles.
Description:
This project has led to the development of novel category 2 nanosensors and phase-inverted poly (amic) acid PAA nanofilter membranes. The membranes have been fitted onto an optical transducer that was previously developed in our lab and the possibility of ultrasensitive detection of the nanomaterials has been explored. In addition, we have tested the sensors for analysis in complex environmental samples including soil, sediments and water. Finally, we have determined the analytical performance of the nanosensor for continuous and insitu sensing. These have been compared to existing technology. During the final segment of the grant activities, we explored the use of the membranes to sense different types of engineered nanomaterials and validated the sensors at a waste water treatment plant (Figure 1). Overall, this project resulted in 15 peer-reviewed publications, two patent disclosures, 16 invited and/or keynote presentations and 21 conference abstracts. The PI also started the first Gordon Conference on Environmental Nanotechnology and held the meeting in NH from May 29-June 3, 2011 (Table 1).
The following section highlights the salient aspects of the project:
Size-exclusive Nanosensor for Quantitative Analysis of Fullerene C60: A Concept Paper: This paper presents the first development of a mass-sensitive nanosensor for the isolation and quantitative analyses of engineered fullerene (C60) nanoparticles, while excluding mixtures of structurally similar fullerenes. Amino-modified beta cyclodextrin (β-CD-NH2) was synthesized and confirmed by 1HNMR as the host molecule to isolate the desired fullerene C60. This was subsequently assembled onto the surfaces of gold-coated quartz crystal microbalance (QCM) electrodes using N-Dicyclohexylcarbodiimide/N-hydroxysuccinimide (DCC/NHS) surface immobilization chemistry to create a selective molecular configuration described as (Au)-S (CH2)2-CONH-betaCD sensor. The mass change on the sensor configuration on the QCM was monitored for selective quantitative analysis of fullerene C60 from a C60/C70 mixture and soil samples. About ~1014-1016 C60 particles/cm2 were successfully quantified by QCM measurements. Continuous spike of 200 µl of 0.14 mg C60 /ml produced changes in frequency (-∆f) that varied exponentially with concentration. FESEM and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) confirmed the validity of sensor surface chemistry before and after exposure to fullerene C60. The utility of this sensor for spiked real-world soil samples has been demonstrated. Comparable sensitivity was obtained using both the soil and purified toluene samples. This work demonstrates that the sensor has potential application in complex environmental matrices.
Catalytic Reduction of Hexavalent Chromium using Flexible Nanostructured Poly(amic acids): Conducting polymers can be tuned by manipulating the delocalized π electron system for chemical and electrocatalytic applications. We hereby describe the reduction of Cr(VI) to Cr(III) by flexible nanostructured conducting poly(amic acid) (PAA) in both solution phase and as a thin film on gold electrode. Sodium borohydride was used as a reducing agent to prepare different sizes (3-20 nm) of palladium nanoparticles (PdNPs). The effects of experimental parameters such as particle size, temperature and Cr(VI) concentration on the kinetics and efficiency of reduction process were investigated. Results show that in PAA solution, Cr(VI) was efficiently reduced by 85.9% within a concentration range of 1.0 x 10-1 1.0 x 102 mM. In the presence of PdNPs and heat (40oC), the reduction efficiency increased to 96.6% and 99.9% respectively. When employed on a solid electrode, PAA undergoes a quasi-reversible electrochemistry in acidic media with reduction efficiency for Cr(VI) at 72.84%. The method was validated using both colorimetric and Electron Paramagnetic Resonance techniques, which confirmed the formation of Cr(III) as the product of catalytic reduction. Additional characterization conducted using TEM, XRD and XPS confirmed that there was no significant change in Pd particle size and distributions after dispersion in PAA whereas its phase and oxidation state remained unchanged. Electrochemical characterization showed the reversible and recyclable features of PAA thus confirming its dual role as catalyst stabilizer and reducing agent. This approach provides a significant advantage over conventional methods such as bioremediation which typically require longer time for complete reduction.
Environmental Applications of Poly(amic acid)-based Nanomaterials: Nanoscale materials offer new possibilities for the development of novel remediation and environmental monitoring technologies. Different nanoscale materials have been exploited for preventing environmental degradation and pollutant transformation. However, the rapid self-aggregation of nanoparticles or their association with suspended solids or sediments where they could bioaccumulate supports the need for polymeric coatings to improve mobility, allows faster site cleanups and reduces remediation cost. The ideal material must be able to coordinate different nanomaterials functionalities and exhibit the potential for reusability. We hereby describe two novel environmental applications of nanostructured poly (amic acid)-based (nPAA) materials. In the first application, nPAA was used as both reductant and stabilizer during the in-situ chemical reduction of Chromium (VI) to Chromium (III). Results showed that Cr (VI) species were rapidly reduced within the concentration range of 1.0 - 10-1 x 102 mM with efficiency of 99.9% at 40ºC in water samples and 90% at 40oC in soil samples respectively. Furthermore, the presence of PdNPs on the PAA-Au electrode was found to significantly enhance the rate of reduction. In the second application, nPAA membranes were tested as filters to capture, isolate and detect nanosilver. Preliminary results demonstrate the capability of the nPAA membranes to quantitatively capture nanoparticles from suspension and quantify their abundance on the membranes. Silver nanoparticles detection at concentrations near the toxic threshold of silver was also demonstrated.
Accomplishments
- The PI started the first Gordon Conference on Environmental Nanotechnology and chaired the first meeting, which was held at the Waterville Valley Resort, Waterville, NH from May 29-June 3, 2011 (Conference program, Table 1).
- This grant has led to the development of the mass-sensitive nanosensor for the isolation and quantitative analyses of engineered fullerene (C60) nanoparticles, while excluding mixtures of structurally similar fullerenes.
- PAA membranes were successfully fabricated as flexible, free-standing membranes using phase inversion techniques. These membranes show well-defined and uniform filtration properties. The surface pore sizes were controlled by the synthesis conditions, method of desolvation and the concentrations of the polymer composition. The synthetic approach affords well controlled membranes leading to various desired sizes from less than 5nm to greater than 100nm.
- Preliminary results showed that these PAA membranes can filter quantum dots (smaller than 5nm) directly from aqueous solution at 96.78% efficiency. The standard deviation could be significantly improved at much lower concentrations of the nanoparticles (5nm).
- PAA membranes were placed on a 13mm Millipore stainless steel swinny filter holder to create a filter paper-type device. This is followed by the addition of the environmental (aqueous) samples to be filtered: Specified volume (mL) of aqueous food supplements and environmental samples containing the AgNPs or specified volume (ml) standard AgNPs stocking solutions. The AgNPs contained in the aqueous samples were trapped on the PAA membranes. The captured AgNPs were imaged and characterized by SEM and EDX techniques.
- PAA have been tested as nanofilters to isolate and remove silver nanoparticles, quantum dots and titanium dioxide particles in food supplements and environmental samples. Filtration efficiency of over 99% was recorded.
- PAA membranes were also used as a sensor for silver nanoparticles and other synthetic metal oxides. Results showed that concentration relationship in low concentration range (0.1ppm to 10ppm) with detection limit of ~50ppb.
- Filtration characteristics of the PAA membranes using the sandwich two chamber cell showed that size-dependent isolation of engineered nanoparticles of varying sizes in water and food supplements samples could be achieved based on redox current from the silver nanoparticles. The approach was tested to remove silver nanoparticles from commercial food supplements of varying particle sizes with > 99.9% removal efficiency. PAA showed excellent performance not only for isolation at sub-nanometer size range but also as a platform for detection of engineered nanoparticles.
- PAA have been tested for application in environmental matrices with significant improvements recorded over the conventional approaches for Chromium (VI), silver nanoparticles and fullerenes (Table 2).
Record Details:
Record Type:PROJECT( ABSTRACT )
Start Date:12/01/2008
Completion Date:11/30/2011
Record ID:
203143